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1

Acquisition system for the liquid helium L5 plant  

International Nuclear Information System (INIS)

The technology of low temperature at the beginning of this century, developed for the production of oxygen nitrogen and rare gases, was the basis for setting of the cryogenic technology. Engineering and construction of cryogenic plants appear today implied in: science, research and development, space technology, nuclear power techniques. An important component in this technologies is the helium liquefier of type L5. This fully automatic cryoliquefier operates for purification, liquefaction as well as reliquefaction of helium gas evaporated in cryostat systems. A helium production plant consists mainly of cold chamber with aluminium heat exchangers, two gas-lubricated turbo-expanders, instrumentation and a programmable controller as well an oil-injected screw-compressor. Cold helium with 4.5 K is transferred through a special vacuum and super insulated line to the tank. In liquefaction mode without LN2-precooling the performance data of this plant is 5 l/hour at 4.5 K. In the paper there are presented the work of designing and developing of a performing liquid helium delivery system corresponding with the basic equipment and accessories used in a L5 type helium liquefactor. The process software of LINDE L5 installation was updated and adapted to our technical conditions from our cryogenic laboratory. Therefore the new Lab-View based programme derived from the functions command protocol, allowed a reliable control on the technological process and induced as well several determinations on the performance of the process as following: - verification of the theoretical models of the cryogenic cycle energetic dimensions; - Increasing thermodynamic performances of different components of the cryogenic cycle by remodeling the geometrical flowing zones, based on gas dynamic studies, in concordance with the thermophysical characteristics of the gas; - study of the dynamic behavior of the installation by evaluation of the transient processes. (authors)

2006-01-01

2

Effect of helium on the deformation mode for Ti-7.5Al alloy  

International Nuclear Information System (INIS)

The effect of helium on the mechanical properties of Ti-7.5Al alloy was investigated at 873 K on the specimens injected with helium to the concentration C_H_e of 5, 18 and 30 appm by using a cyclotron. Helium had a small effect on the yield stress but a large one on the elongation; the elongation decreased at first with increasing C_H_e in the region of C_H_e less than 18 appm and increased again for larger C_H_e. Correspondingly, the deformation mode changed with the helium concentration. The deformation of uninjected specimens proceeded by the dislocation slip and two twin systems, that is, (1012) and (1121). The latter twin system disappeared in the 18 appm helium-injected specimen. Both deformation twins disappeared in the 30 appm specimen, the microstructure of which exhibited the uniform cellular structure of dislocations. (orig.)

1987-01-01

3

Effects of helium on void swelling in boron doped V 5Fe alloys  

Science.gov (United States)

The effects of helium on void swelling in V-5Fe were investigated with natural boron-doping techniques during FFTF/MOTA (Fast Flux Test Facility/Materials Open Test Assembly) irradiation. Microstructural observation was carried out to understand the swelling behavior obtained from density measurements. The cavity size distribution in V-5Fe- xB ( x=0, 100, and 500 appm) irradiated at temperatures lower than 713 K indicates a suppressant effect of helium on void growth, and an enhancing effect on cavity nucleation. Since the chemical effect of boron addition is competitive with the transmutation effect, the results have been compared with that of the dual ion irradiation experiments to allow separation of the effect of helium from the effect of boron.

Iwai, Takeo; Sekimura, Naoto; Garner, F. A.

1998-10-01

4

The double ionization of helium by 1.5?7.5 MeV partially stripped fluorine ions  

International Nuclear Information System (INIS)

New measurement of the ratio of the double ionization cross section to that of the single ionization of helium induced by 1.5?7.5 MeV partially stripped Fq+ ion (q = 1,2,3,4) is presented. Combining the measured data with the Olson-Schlachter scaling, the double ionization cross section of helium by partially stripped fluorine ion is obtained. It is found that the ?/qeff dependence of the obtained double ionization cross section agrees well with the (?/qeff)-4 law

1996-05-01

5

Cryosorption pumping of 95% deuterium--5% helium on molecular sieve 5A at 4.2 K  

International Nuclear Information System (INIS)

Plasma recovery systems in fusion reactors must be capable of exhausting a mixture of deuterium, tritium, and helium from the reactor between burns (and possibly during burns) to remove leaking or diverted plasma. Concentrations of helium in these mixtures may range from 1 to 15 percent. An Excalibur CVR 1106 cryosorption pump was tested to determine pumping speeds of 95 percent deuterium--5 percent helium. Tests were run with two different cooling configurations for the inner chevron (the chevron next to the cryosorption panel): (1) liquid helium boil-off vapor was routed through the chevron prior to venting (the normal mode) and (2) 770K helium was backflushed through the chevron. Three distinct types of behavior were observed. At feed rates of -4 torr-liter sec-1 cm-2, speeds decreased slightly with loading, regardless of the temperature of the inner chevron. Speeds as high as 3.7 liters sec-1 cm-2 were observed when the inner chevron was cooled by boil-off vapor; however, speeds were lower with the 77 K chevron (approximately 2.2 liters sec-1 cm-2). At high feed rates (>1.2 x 10-4 torr-liter sec-1 cm-2), behavior was dependent on the temperature of the inner chevron. All runs began with a rapid decrease in pumping speed that resulted from the accumulation of helium in the test chamber after the frozen deuterium blocked the cryosorption surface. When the inner chevron was cooled by boil-off vapor, the pump recovered and the speed increased and remained steady near 1.9 liters sec-1 cm-2. However, if the inner chevron was held at 770K, operation had to be terminated because continuing system pressurization resulted in rapid cryogenic runaway. When the pump was cooled by liquid helium boil-off vapor, increased pressure affected the helium boil-off rate sufficiently to keep the inner chevron just cold enough to collect all (or a large fraction) of the deuterium, thus leaving the cryosoprtion panel clear to pump helium

1977-10-29

6

Helium compressors for closed-cycle, 4.5-Kelvin refrigerators  

Science.gov (United States)

An improved helium compressor for traveling-wave maser and closed-cycle refrigerator systems was developed and is currently being supplied to the DSN. This new 5-hp compressor package is designed to replace the current 3-hp DSN compressors. The new compressor package was designed to retrofit into the existing 3-hp compressor frame and reuse many of the same components, therefore saving the cost of documenting and fabricating these components when implementing a new 5-hp compressor.

Hanson, T. R.

1992-01-01

7

Commissioning report of the MuCool 5 Tesla solenoid coupled with helium refrigerator  

Energy Technology Data Exchange (ETDEWEB)

MuCool 5T solenoid was successfully cooled down and operated coupled with MTA 'Brown' refrigerator. The system performed as designed with substantial performance margin. All process alarms and interlocks, as well as ODH and fire alarms, were active and performed as designed. The cooldown of the refrigerator started from warm conditions and took 44 hours to accumulate liquid helium level and solenoid temperature below 5K. Average liquid nitrogen consumption for the refrigerator precool and solenoid shield was measured as 20 gal/hr (including boil-off). Helium losses were small (below 30 scfh). The system was stable and with sufficient margin of performance and ran stably without wet expansion engine. Quench response demonstrated proper operation of the relieving devices and pointed to necessity of improving tightness of the relieving manifolds. Boil-off test demonstrated average heat load of 3 Watts for the unpowered solenoid. The solenoid can stay up to 48 hours cold and minimally filled if the nitrogen shield is maintained. A list of improvements includes commencing into operations the second helium compressor and completion of improvements and tune-ups for system efficiency.

Geynisman, Michael; /Fermilab

2010-05-01

8

Information on the nucleon-isobar content in helium from 5 GeV pion-helium interactions  

International Nuclear Information System (INIS)

Missing mass spectra from the reactions ?p ? ?x and ?? ? ?tx have been measured and found to be significantly different. Neglecting all background processes an analysis with the impulse approximation yields a 0.24 percent presence of the isobar-triton state in helium in the triton momentum range 0.32-0.70 GeV/c and the mass range 1.30-1.86 GeV/c2. (Auth.)

1979-02-26

9

Emission spectrum of the C{sub 2} radical embedded in superfluid helium around 1.5 K  

Energy Technology Data Exchange (ETDEWEB)

The C{sub 2} d{sup 3} {pi}{sub g}-a{sup 3} {pi}{sub u} ({upsilon}' - {upsilon}'') Swan band emission spectrum induced by the laser ablation of graphite in the superfluid helium around 1.5 K, was observed. Only the vibrational progression of {delta}{upsilon} = {upsilon}' - {upsilon}'', where {delta}{upsilon} less than 0 are observed, indicating fast ({tau} < 100 ns) vibrational relaxation in superfluid helium. This result also indicates a unique characteristic of superfluid helium as a circumstance of chemical processes. (author)

Wada, Akira; Aratono, Yasuyuki [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

2003-02-01

10

Tensile properties of helium-injected V-15Cr-5Ti after irradiation in EBR-II  

International Nuclear Information System (INIS)

Miniature specimens of V-15Cr-5Ti were prepared in the annealed condition and with 10, 20, and 30% cold work. The annealed specimens were cyclotron injected with helium and irradiated in sodium in EBR-II. The cold-worked specimens were irradiated in EBR-II but not helium injected. The specimens were irradiated at 400, 525, 625, and 700"0C and received a fluence of 4.1 to 5.5 x 10"2"6 neutrons/m"2 (E > 0.1 meV). Tensile testing revealed very significant embrittlement as a result of the neutron irradiation but a much smaller change, mostly at 400"0C, resulting from helium injection. 5 references, 9 figures, 2 tables

1985-03-01

11

Pressure shift of the helium triplet line ? 706.5 nm  

International Nuclear Information System (INIS)

Measurements of the self-induced pressure shift of the helium triplet line ? 706.5 nm (1s2p 3P2,1,0-1s3s 3S1) from a gas discharge have been carried out at temperatures of 77 K and 300 K using a scanning Fabry-Perot interferometer. The shift coefficient is positive (a blue shift) and at 77 K it is consistent with the results of a theoretical calculation carried out by previous authors. At 300 K, the measured shift parameter is much greater than the theoretical value. As expected, the shifts are significantly larger in both cases than those of the corresponding singlet line, for which the broadening and shift are dominated by the resonance interaction. We have also compared our experimental results with predictions based on the Lennard-Jones potential. (author)

1993-01-28

12

Tensile and fracture properties of EBR-II-irradiated V-15Cr-5Ti containing helium  

Energy Technology Data Exchange (ETDEWEB)

The alloy V-15Cr-5Ti was cyclotron-implanted with 80 appM He and subsequently irradiated in the Experimental Breeder Reactor (EBR-II) to 30 dpa. The same alloy was also irradiated in the 10, 20, and 30% cold-worked conditions. Irradiation temperatures ranged from 400 to 700/sup 0/C. No significant effects of helium on mechanical properties were found in this temperature range although the neutron irradiation shifted the temperature of transition from cleavage to ductile fracture to about 625/sup 0/C. Ten percent cold work was found to have a beneficial effect in reducing the tendency for cleavage fracture following irradiation, but high levels (20%) were observed to reduce ductility. Still higher levels (30%) improved ductility by inducing recovery during the elevated-temperature irradiation. Swelling was found to be negligible, but precipitates - titanium oxides or carbonitrides - contained substantial cavities.

Grossbeck, M.L.; Horak, J.A.

1986-01-01

13

Helium localisation in tritides  

International Nuclear Information System (INIS)

Study of titanium and LaNi_5 type alloys tritides lattice parameters evolution revealed that helium created by tritium decay remains in interstitial sites up to a limit material dependant concentration. Beyond this one exceeding helium precipites in voids

1982-06-11

14

Floating Pressure Conversion and Equipment Upgrades of Two 3.5kw, 20k, Helium Refrigerators  

Science.gov (United States)

Two helium refrigerators, each rated for 3.5KW at 20K, are used at NASA s Johnson Space Center (JSC) in Building No. 32 to provide cryo-pumping within two large thermal-vacuum chambers. These refrigerators were originally commissioned in 1996. Equipment refurbishment and upgrades to the controls of these refrigerators were recently completed. This paper describes some of the mechanical and control issues that necessitated the equipment refurbishment and controls change-over. It will describe the modifications and the new process control which allows the refrigerators to take advantage of the Ganni Cycle "floating pressure" control technology. The upgrades -- the controls philosophy change-over to the floating pressure control technology and the newly refurbished equipment -- have greatly improved the performance, stability, and efficiency of these two refrigerators. The upgrades have also given the operators more information and details about the operational status of the main components (compressors, expanders etc.) of the refrigerators at all operating conditions (i.e.: at various loads in the vacuum chambers). Capabilities, configuration, and performance data pre, and post, upgrading will be presented.

Homan, Jonathan; Linza, Robert; Garcia, Sam; Vargas, Gerardo; Lauterbach, John; Ganni, Venkatarao (Rao); Sidi-Yekhlef, Ahmed; Creel, Jonathan; Norton, Robert; Urbin, John; Howe, Don

2008-01-01

15

Physiological responses of men working in 25.5 degrees C water, breathing air or helium tri-mix.  

Science.gov (United States)

Fourteen scuba divers in swim trunks did ergometer work while breathing air at 3 m in 25.5 degrees C water. They were stressed by work and cold. Exercise produced increases in heart rate, minute ventilation (VE), oxygen consumption (VO2), and catecholamine excretion. Cold lowered rectal temperature (Tre) despite exercise, and contributed to the increase in VO2 and catecholamine excretion. Immersion, cutaneous vasoconstriction, work, and scuba breathing contributed to a brisk diuresis, probably by centralizing blood volume and thus stimulating central vascular volume receptors. Similar exercise in 25.5 degrees C water, breathing helium tri-mix (gas density less than air), produced higher VE but lower VO2 when compared to air breathing. Tri-mix scuba breathing resulted in a smaller diuresis, perhaps because its lower density leads to lesser atrial distension during work. The fall in Tre during work in 25.5 degrees C water was identical whether air or helium tri-mix was respired, since helium does not accentuate respiratory convective heat transfer. PMID:931882

Hoar, P F; Raymond, L W; Langworthy, H C; Johnsonbaugh, R E; Sode, J

1976-04-01

16

Effect of helium on swelling and microstructural evolution in ion-irradiated V-15Cr-5Ti alloy  

Energy Technology Data Exchange (ETDEWEB)

An investigation was made on the effects of implanted helium on the swelling and microstructural evolution that results from energetic single- and dual-ion irradiation of the V-15Cr-5Ti alloy. Single-ion irradiations were utilized for a simulated production of the irradiation damage that might be expected from neutron irradiation of the alloy in a reactor with a fast neutron energy spectrum (E > 0.1 MeV). Dual-ion irradiations were utilized for a simulated production of the simultaneous creation of helium atoms and irradiation damage in the alloy in the MFR environment. Experimental results are also presented on the radiation-induced segregation of the constituent atoms in the single- and dual-ion irradiated alloy.

Loomis, B.A.; Kestel, B.J.; Gerber, S.B.; Ayrault, G.

1986-03-01

17

Effect of helium on swelling and microstructural evolution in ion-irradiated V-15Cr-5Ti alloy  

International Nuclear Information System (INIS)

An investigation was made on the effects of implanted helium on the swelling and microstructural evolution that results from energetic single- and dual-ion irradiation of the V-15Cr-5Ti alloy. Single-ion irradiations were utilized for a simulated production of the irradiation damage that might be expected from neutron irradiation of the alloy in a reactor with a fast neutron energy spectrum (E > 0.1 MeV). Dual-ion irradiations were utilized for a simulated production of the simultaneous creation of helium atoms and irradiation damage in the alloy in the MFR environment. Experimental results are also presented on the radiation-induced segregation of the constituent atoms in the single- and dual-ion irradiated alloy

1986-04-13

18

Recoil and fast-particle spectrometers for the study of 5GeV pion-helium interactions  

International Nuclear Information System (INIS)

The instrumentation of an experiment, in which the recoil as well as the fast-particle is measured, is described. The principal aim of the experiment is to search for isobar configurations in the nuclear function of helium by studying 5GeV pion-helium interactions and one pion-proton interactions. In the both first reactions the object X is a pion-nucleon system, which may have been produced on one of the bound nucleons in helium or may have existed prior to the collision. The last one gives the production amplitude from free nucleons. The final-state pions which are scattered in a narrow forward half cone, are measured in a spectrometer consisting of multiwire proportional counters (MWPC) and a magnet. The residual slow nuclei are measured and identified in a recoil spectrometer with MWPC's, solid state detectors and scintillators as the basic components. With these spectrometers the nuclear and the hadron states can be specified up to very high energies as long as the missing mass resolution is sufficient to separate the different resonances in X from each other

1977-01-01

19

Helium pumping at 4.2 K by molecular sieve 5A  

International Nuclear Information System (INIS)

Helium pumping speeds measured for the Excalibur model CVR 1106 cryosorption pump fall into two regimes depending on the feed rate. At feed rates below 6.2 x 10-6 Torr l s-1 cm-2, pumping speeds decrease with loading from 2.2 l s-1 cm-2 to 0.3 l s-1 cm-2. At feed rates higher than 6.2 x 10-6 Torr l s-1 cm-2, the speed varies periodically with loading. A typical cycle begins with pumping speeds near 1.7 l s-1 cm-2; speeds decline from this value to about 0.6 Torr l s-1 cm-2 at which time the pump goes through a rapid transition that reverts it back to its original high pumping speed. During the transition, the system reaches presures greater than 10-2 Torr, and rapid boiling occurs in the liquid helium reservoir. At the end of the transition, the system pressure decreases rapidly to the initial low operating pressure, liquid helium boil-off declines, and the pump operates normally for a definite period. The length of each cycle depends on the feed rate

1979-01-01

20

Helium energy spectra from 5 to >150 MeV/n from SOHO EPHIN  

International Nuclear Information System (INIS)

Since its launch in Dec 1995 the SOHO spacecraft is providing observations of energetic particles at the lagrangian point L1. On board is the Electron Proton Helium Instrument (EPHIN), which measures nominally electrons in the energy range from 250 keV to >10 MeV, protons from 4 MeV to >53 MeV and helium from 4 MeV/n to >53 MeV/n. The instrument is based on six semiconductor silicon detectors with an anticoincidence scintillator. The total thickness for stopping particles is 13.45mm. The well-proven De/dx-E method is used to determine energy and mass of the stopping particles. However, penetrating particles, i.e. electrons >10 MeV and nuclei >53 MeV/n, are registered in a single integral channel. In this work we make use of the dE/dx-dE/dx method and show that the energy range can successfully be extended to 150 MeV/n for helium. Energy spectra as well as their temporal evolution are presented in the investigation of the modulation of anomalous cosmic rays (ACR) and Galactic cosmic rays (GCR)

2008-03-03

 
 
 
 
21

Observation of turbulent waves in a helium plasma by optical spectroscopy, ch. 5  

International Nuclear Information System (INIS)

From the combined Stark-Zeeman pattern of helium allowed and forbidden optical lines the frequency spectrum, the field strength and the dominant polarization of microfields were determined in a turbulent plasma. Two frequent domains of oscillations were found in a turbulent heating experiment: low-frequency oscillations with dominant polarization perpendicular to the current direction and high-frequency osillations (f approximately fsub(pe)) with random polarization. The r.m.s. field strength of the oscillations is between 2 kV/cm and 10 kV/cm. The energy density of turbulent microfields amounts to 1% of the thermal energy density. (Auth.)

1975-09-29

22

Development of analytical procedure for the design of 1.5 Mwt helium gas intermediate heat exchanger  

International Nuclear Information System (INIS)

This paper reports the structural integrity study of 1.5 Mwt helium gas intermediate heat exchanger performed as a part of 'Research and Development of Direct Steel Making Technology Utilizing High Temperature Reducing Gas' which is one of the National Research and Development Programs by Agency of Industrial Science and Technology, Ministry of International Trade and Industry, Japan. The normal operation temperature of the heat exchanger exceeds 10000C which is beyond the scope covered by the existing design code, e.g. ASME Code Case 1592. Therefore, a special analytical and experimental procedure should be developed to establish design rules of unprecedented components operating at extremely high temperature. (orig.)

1979-08-21

23

ISABELLE forced circulation cooling system: proposed method of producing and distributing helium refrigerant for 4.5 K superconducting magnets  

International Nuclear Information System (INIS)

A report is given of the refrigeration system proposed for ISABELLE. The system features a single refrigerator of about 25 kW capacity. The refrigerant helium is supplied to the 960 ISABELLE Magnets at a pressure of 15 atm and a temperature of 2.8"0K. The return to the refrigerator is at 14.3 atm and a 6.2"0K. As many as 60 magnets will be cooled in series. The steady-state design temperature for the warmest magnet is 4.3"0K. This temperature will rise to 4.5"0K during the acceleration cycle

1976-01-01

24

Thermal–hydraulic system study of the HELOKA-LP helium loop using RELAP5-3D code  

International Nuclear Information System (INIS)

Highlights: • Thermal–hydraulic system study for the HELOKA-LP using RELAP5-3D. • Validation of various experiments with corresponding simulations, and good comparison between the experiments and the simulations. • Simulation of the two most heated compartments of IFMIF HFTM in the modeled helium loop and prediction of the loop dynamic. -- Abstract: The thermal–hydraulic system analyses for the HELOKA-LP (Helium Loop Karlsruhe – Low Pressure) facility are presented. Typical operation ranges for the test section are mass flow rate between 12 and 120 g/s, inlet temperature between 10 and 250 °C and pressure level between 0.3 and 0.6 MPa. An orifice is used for the loop testing, for which different experiments are validated with appropriate simulations. Afterwards instead of the orifice, two most heated compartments of IFMIF (International Fusion Materials Irradiation Facility) HFTM (high flux test module) are simulated in HELOKA-LP. Using the system code REALP5-3D components in the loop are modeled as well as the main control strategy. With this model the loop dynamics in conditions relevant for the HFTM operation are analyzed and the thermal time constant of the compartment is estimated

2013-10-01

25

?-Helium-4 scattering experiment at 5GeV/c. Data processing  

International Nuclear Information System (INIS)

The context of this work is an experiment realised at CERN, with the object to search pre-existing isobaric states in helium nucleus, by means of the study of scattering reactions of ?"- with simultaneous observation of recoil nucleus ("3He or "3H) and forward pion. In this work, only the study of recoil detectors is done. This one, described with many details consists of a set of four wire chamber planes, two planes of semiconductors and two scintillators planes. The performances of this set of detectors are presented in regard to identification of recoil particle, energy and recoil angle measurements. A 'missing mass' analysis of the events of the experiment is done. Preliminary results of elastic and inelastic scattering are given. For elastic scattering a qualitative comparison is done with the multiple scattering Glauber formalism

1978-01-01

26

Helium in the Martian atmosphere  

Science.gov (United States)

A crude estimate for the current degassing rate of He-4 on of 2.2 x 10 exp 5/sq cm/s is obtained by scaling from the amounts of helium and argon on earth. Nonthermal escape processes of helium on Mars are discussed and a nonthermal helium escape rate is calculated for each process. The helium mixing ratio in the lower Martian atmospheres and the intensity of its airglow at 584 A are calculated.

Krasnopolsky, Vladimir A.; Chakrabarti, Supriya; Gladstone, G. R.

1993-01-01

27

Metal tritides helium emission  

International Nuclear Information System (INIS)

Over the past several years, we have been measuring the release of helium from metal tritides (primarily erbium tritide). We find that qualitatively all tritides of interest to us behave the same. When they are first formed, the helium is released at a low rate that appears to be related to the amount of surface area which has access to the outside of the material (either film or bulk). For example, erbium tritide films initially release about 0.3% of the helium generated. Most tritide films emit helium at about this rate initially. At some later time, which depends upon the amount of helium generated, the parent occluding element and the degree of tritium saturation of the dihydride phase the helium emission changes to a new mode in which it is released at approximately the rate at which it is generated (for example, we measure this value to be approx. = .31 He/Er for ErT_1._9 films). If erbium ditritide is saturated beyond 1.9 T/Er, the critical helium/metal ratio decreases. For example, in bulk powders ErT_2._1_5 reaches critical release concentration at approx. = 0.03. Moderate elevation of temperature above room temperature has little impact on the helium release rate. It appears that the process may have approx. = 2 kcal/mol activation energy. The first helium formed is well bound. As the tritide ages, the helium is found in higher energy sites. Similar but less extensive measurements on scandium, titanium, and zirconium tritides are also described. Finally, the thermal desorption of erbium tritides of various ages from 50 days to 3154 days is discussed. Significant helium is desorbed along with the tritium in all but the youngest samples during thermodesorption

1980-01-01

28

Linear series of stellar models. Pt. 4. Helium-carbon stars of 3.5Msub(o) and 1Msub(o)  

International Nuclear Information System (INIS)

One linear series of models for a star of 3.5Msub(o) and two linear series of models for a star of 1Msub(o) are constructed. Models consist of helium rich envelopes (Y = 0.97, Z = 0.03) and pure carbon cores, and they have a rectangular helium profile, Y(Msub(r)). The linear series for a star of 3.5Msub(o) begins on the normal branch of the helium main sequence and terminates on the normal branch of the carbon main sequence. This series has eight turning points at which the core mass attains a local extremum. One of the two linear series for a star of 1Msub(o) begins on the normal branch of the helium main sequence, terminates on the high density branch of the helium main sequence, and has one turning point. The second linear series for a star of 1Msub(o) begins on the normal branch of the carbon main sequence, terminates on the high density branch of the carbon main sequence, and has three turning points. Two such linear series may have a common bifurcation point for a star of about 1.26Msub(o). (author)

1973-01-01

29

Chromosome aberrations induced in human lymphocytes by 8.7 MeV protons and 23.5 MeV helium-3 ions  

International Nuclear Information System (INIS)

This paper describes the irradiation of thin samples of blood with 8.7 MeV protons and 23.5 MeV helium-3 ions in the track segment mode. Chromosome aberrations in human lymphocytes have been scored. The relationship between dicentric yield and dose in Gy was Y = 0.044 D + 0.058 D"2 for protons and Y = 0.394 D for helium ions. These results are compared with data from other laboratories using protons and an attempt is made to reconcile differences. An unexpected observation was that the ratio of the linear coefficients for helium ions and protons was about 9 whereas the ratio of the l.e.t. values was 4.5. This disagrees with current theory which predicts that the linear coefficients should be proportional to l.e.t. Possible sources of error in our experiments are discussed but do not adequately account for the discrepancies. (author)

1986-01-01

30

Investigation on the dynamics of helium-4 at a temperature of 24,5K and a pressure of 85 bar by means of coherent inelastic neutron scattering  

International Nuclear Information System (INIS)

Atomic dynamics in condensed helium gas has been investigated by means of coherent inelastic neutron scattering. In this way it is possible to determine the wavevector-dependent heat- and sound 'eigen-modes' in (classical) helium and, especially, the sound dispersion ?s(k). Inquiries have also been performed into the appearance of a 'gap' in ?s(k), into the direct visibility of Brillouin lines in S(k,?)-spectra and into the effects of the coupling of modes in the anomalous sound dispersion at low k-values. The dynamic structure factor S(k,?) has been determined by experiments using inelastic neutron scattering on helium-4 on the Rotating-Crystal Spectrometer-II (RKS-II) at the Inter faculty Reactor Institute IRI Delft, Netherlands. Measurements are carried out on a helium-state that is characterized by a temperature of 24.5 K and a pressure of 89 bar. The Brillouin lines are not directly visible from the S(k,?)-spectra of the measured helium-4 state. At this state there does not appear a propagation-gap in ?s(k) and, finally, the experimentally found ?s(k) is not well described by means of the Mode-Coupling-theory. (author). 46 refs.; 22 figs.; 9 tabs

1990-01-01

31

High nuclear polarization of helium-3 at low and high pressure by metastability exchange optical pumping at 1.5 Tesla  

CERN Multimedia

We perform metastability exchange optical pumping of helium-3 in a strong magnetic field of 1.5 T. The achieved nuclear polarization, from 80% at 1.33 mbar to 25% at 67 mbar, shows a substantial improvement at high pressures with respect to standard low-field optical pumping. The specific mechanisms of metastability exchange optical pumping at high field are investigated, advantages and intrinsic limitations are discussed. From a practical point of view, our results open the way to alternative technological solutions for polarized helium-3 applications and in particular for magnetic resonance imaging of human lungs.

Abboud, M; Maitre, X; Tastevin, G; Nacher, P J; Abboud, Marie; Sinatra, Alice; Maitre, Xavier; Tastevin, Genevieve; Nacher, Pierre-Jean

2003-01-01

32

Helium cryogenics  

CERN Document Server

Twenty five years have elapsed since the original publication of Helium Cryogenics. During this time, a considerable amount of research and development involving helium fluids has been carried out culminating in several large-scale projects. Furthermore, the field has matured through these efforts so that there is now a broad engineering base to assist the development of future projects. Helium Cryogenics, 2nd edition brings these advances in helium cryogenics together in an updated form. As in the original edition, the author's approach is to survey the field of cryogenics with emphasis on helium fluids. This approach is more specialized and fundamental than that contained in other cryogenics books, which treat the associated range of cryogenic fluids. As a result, the level of treatment is more advanced and assumes a certain knowledge of fundamental engineering and physics principles, including some quantum mechanics. The goal throughout the work is to bridge the gap between the physics and engineering aspe...

Van Sciver, Steven W

2012-01-01

33

Helium retention of nickel  

International Nuclear Information System (INIS)

In a fusion reactor, in order to enhance the pumping efficiency for helium ash, the use of a metal such as nickel has been conceived because of its capability to selectively retain helium. In the present study, the nickel was irradiated by He plasma, H_2 plasma or both by H_2 and He plasmas, in the ECR plasma irradiation apparatus. The range of the helium fluence and irradiation temperature were about 4 similar 5x10"1"8 He/cm"2 and from RT to 700 C, respectively. The amount of trapped helium was examined by the thermal desorption spectroscopy (TDS) technique. The retained hydrogen rapidly decreased with the irradiation temperature, and no retention was observed for temperatures higher than 100 C. In the TDS spectrum, several helium desorption peaks appeared in the low temperature region (200 similar 700 C), and the dominant peak at high temperature was about 800 C. The total amount of helium retained as a function of irradiation temperature, had two peaks at 100 similar 200 and 500 similar 600 C. It is suggested that the optimum temperature for the selective pumping of helium thus becomes 500 similar 600 C, since the nickel may be used on the vacuum chamber where the temperature is higher than about 300 C. ((orig.))

1995-04-01

34

RELAP5 and CATHARE2 benchmarking assessment on two LOFA transients conducted in HE-FUS3 helium facility  

International Nuclear Information System (INIS)

The qualification of numerical tools for the transient and safety analysis of High Temperature Gas Reactors (HTGR) is essential to demonstrate the fulfillment of the GEN IV safety requirements. The availability of experimental data from the ENEA HE-FUS3 facility (Brasimone (Italy)) has given the opportunity to organize a benchmark exercise to assess the capability of a number of transient analysis code to describe the T/H behavior of a helium cooled loop both in steady state and transients conditions. The paper presents the results obtained in the post-test analysis of experimental LOFA transients with two of the most widely used system codes: RELAP5 Mod3.3 applied by ENEA-ANSALDO and CATHARE 2 V2.5 applied by CEA-IRSN. The analysis of these results on the basis of a code-to-data comparison and a code-to-code benchmark allows to verify that both codes are able to qualitatively reproduce the gas system thermal-hydraulics and dynamics, as well as to provide recommendations on gas cooled system modeling for the development of consistent numerical models for the HTGR accident analysis. Moreover, highlighting the weakness in some aspects of the present modeling approach, it is possible to suggest the needs of the future code developments. (authors)

2010-06-13

35

Helium cryogenics  

International Nuclear Information System (INIS)

The goal of this work is to bridge the gap between physics and engineering aspects of helium fluids to encourage their use and enhance their usefulness in low-temperature systems. Topics covered include thermodynamic laws, electrical and thermal conductivities, spin systems, virial expansion, liquid He I, transport properties, density of helium as a quantum fluid, vortices and turbulence in He II, Kapitza conductance, acoustic mismatch theory, nucleate boiling heta transfer, surface effects, general considerations of internal flow, ideal liquefaction, stirling cycle, and the helium-3 isotope

1986-01-01

36

Hot HB stars in globular clusters - Physical parameters and consequences for theory; 5, Radiative levitation versus helium mixing  

CERN Multimedia

Atmospheric parameters (effective temperature Teff, surface gravity log g), masses and helium abundances are derived for 42 hot horizontal branch (HB) stars in the globular cluster NGC 6752. For 19 stars we derive magnesium and iron abundances as well and find that iron is enriched by a factor of 50 on average with respect to the cluster abundance whereas the magnesium abundances are consistent with the cluster abundance. Radiation pressure may levitate heavy elements like iron to the surface of the star in a diffusive process. Taking into account the enrichment of heavy elements in our spectroscopic analyses we find that high iron abundances can explain part, but not all, of the problem of anomalously low gravities along the blue HB. The blue HB stars cooler than about 15,100 K and the sdB stars (Teff > 20,000 K) agree well with canonical theory when analysed with metal-rich ([M/H] = +0.5) model atmospheres, but the stars in between these two groups remain offset towards lower gravities and masses. Deep Mixi...

Möhler, S; Landsman, W B; Heber, U

2000-01-01

37

A new design code for 1,5 Mwt helium heat exchanger  

International Nuclear Information System (INIS)

There is the ASME B and PV code for design criteria of high temperature heat exchanger and these design codes cannot be applied to the 1.5 Mwt Heat Exchanger System because the codes applying range are limited up to 8150C, while the new heat exchanger system is supposed to be operated at the temperatures upto 10000C. Because this heat exchanger is a test loop for nuclear direct steal making plant, its design and construction requires as much safety assurance as the nuclear power plant. In order to satisfy safety requirement, a new design code specifying heat exchanger components operable at a maximum allowable temperature of 1,0000C was proposed. (orig.)

1979-08-21

38

Effect of dynamically charged helium on tensile properties of V-5Ti, V-4Cr-4Ti, and V-3Ti-1Si  

Energy Technology Data Exchange (ETDEWEB)

In the Dynamic Helium Charging Experiment (DHCE), helium was produced uniformly in the specimen at linear rates of {approx}0.4 to 4.2 appm He/dpa by the decay of tritium during irradiation to 18-31 dpa at 424-600{degrees}C in the lithium-filled DHCE capsules in the Fast Flux Test Facility. This report presents results of postirradiation tests of tensile properties of V-5Ti, V-4Cr-4Ti, V-3Ti-1Si. The effect of helium on tensile strength and ductility was insignificant after irradiation and testing at >420{degrees}C. Contrary to initial expectation, room temperature ductility of DHCE specimens was higher than that on non-DHCE specimens, whereas strength was lower, indicating that different types of hardening centers are produced during DHCE and non-DHCE irradiation. In strong contrast to results of tritium-trick experiments, in which dense coalescence of helium bubbles is produced on grain boundaries in the absence of displacement damage, no intergranular fracture was observed in any tensile specimens irradiated in the DHCE.

Chung, H.M.; Loomis, B.A.; Nowicki, L.; Smith, D.L. [Argonne National Laboratory, Chicago, IL (United States)

1996-04-01

39

Proposal for the award of a contract, without competitive tendering, for the upgrade of the 4.5 K helium refrigerators at LHC points 4 and 6  

CERN Document Server

This document concerns the award of a contract, without competitive tendering, for the upgrade of the 4.5 K helium refrigerators at LHC points 4 and 6. The Finance Committee is invited to agree to the negotiation of a contract, without competitive tendering, with LINDE KRYOTECHNIK (CH) for the upgrade of the 4.5 K helium refrigerators at LHC points 4 and 6 for a total amount of 1 917 600 Swiss francs, not subject to revision, with options for additional work for leak testing and leak repairs for an additional amount not exceeding 190 000 Swiss francs, not subject to revision, and for the modification of the spare turbines and related spare parts for an additional amount of 371 400 Swiss francs, not subject to revision, bringing the total maximum amount to 2 479 000 Swiss francs, not subject to revision

2004-01-01

40

Helium cooled forevacuum pump  

International Nuclear Information System (INIS)

Structure of submerged condensation-sorption forevacuum pump used together with the STG-40 or STG-25 Dewar helium vessels intended for air pumping out from atmospheric pressure to <=10"-"5 Pa is described. Effective rate of pumping out with the helium pump amounts to approximately 0.5 l/s in the pressure range from 10"-"1 to 10"-"4 Pa. At that, time of pumping out of <=10 l volumes to approximately 10"-"4 pressure turns out to be 10-40 min. Use of pumps turned out effective for pumping out of electron glass unsoldered devices of <=1 l volume

1981-01-01

 
 
 
 
41

X-ray studies of nickel, steel - Kh16N15M3B and steel -Kh20N40M5B irradiated by helium ions  

International Nuclear Information System (INIS)

The effect of helium ion irradiation to the concentrations of 0.05, 0.15, 0.50 and 1.00 at.% He (with He+ ion energy up to 3.5 MeV) on the structure of recrystallized nickel, steel-Kh16N15M3B and steel-Kh20N40M5B is studied by means of X-ray analysis. It is shown that phase composition of irradiated samples does not exhibit any changes: the initial f.c.c. structure was preserved under all irradiations. The lattice spacing of irradiated samples is found to vary nonmonotonically depending on the concentration of injected helium. Experimental data on the effect of post-irradiation annealing are indicative of nonmonotonic variation of the lattice spacing depending on the annealing temperature as well. It is concluded that changes observed in the diffraction pattern for investigated samples under He+ ion irradiation are not due to radiation damages (interstices, vacancies, dislocation loops, stacking faults, etc.) but to accumulation and evolution of helium atoms in the matrix lattice

1979-10-04

42

Dielectric loss of supercritical helium  

International Nuclear Information System (INIS)

The dielectric loss of supercritical helium has been investigated at several field strengths up to 20 MV m-1 rms at 50 Hz. Its loss tangent was observed to be extremely small when the helium was very pure. However, the loss of commercial-grade helium turned out to be a few ? rad at low field strength. The dielectric loss increased to 1 x 10-5 rad at 5 MV m-1 but did not exceed 1 x 10-5 rad even at 10 MV m-1. (author)

1980-01-01

43

Cavitation pressure in liquid helium  

CERN Multimedia

Recent experiments have suggested that, at low enough temperature, the homogeneous nucleation of bubbles occurs in liquid helium near the calculated spinodal limit. This was done in pure superfluid helium 4 and in pure normal liquid helium 3. However, in such experiments, where the negative pressure is produced by focusing an acoustic wave in the bulk liquid, the local amplitude of the instantaneous pressure or density is not directly measurable. In this article, we present a series of measurements as a function of the static pressure in the experimental cell. They allowed us to obtain an upper bound for the cavitation pressure P_cav (at low temperature, P_cav -3.0 bar in helium 3, P_cav > - 10.4 bar in helium 4). In this article we thus present quantitative evidence that cavitation occurs at low temperature near the calculated spinodal limit (-3.1 bar in helium 3 and -9.5 bar in helium 4). Further information is also obtained on the comparison between the two helium isotopes. We finally discuss the magnitud...

Caupin, F; Caupin, Frederic; Balibar, Sebastien

2001-01-01

44

Helium behaviour in nuclear glasses  

International Nuclear Information System (INIS)

The present thesis focuses on the study of helium behavior in R7T7 nuclear waste glass. Helium is generated by the minor actinides alpha decays incorporated in the glass matrix. Therefore, four types of materials were used in this work. These are non radioactive R7T7 glasses saturated with helium under pressure, glasses implanted with 3He+ ions, glasses doped with curium and glasses irradiated in nuclear reactor. The study of helium solubility in saturated R7T7 glass has shown that helium atoms are inserted in the glass free volume. The results yielded a solubility of about 1016 at. cm-3 atm.-1. The incorporation limit of helium in this type of glass has been determined; its value amounted to about 2*1021 at. cm-3, corresponding to 2.5 at.%. Diffusion studies have shown that the helium migration is controlled by the single population dissolved in the glass free volume. An ideal diffusion model was used to simulate the helium release data which allowed to determine diffusion coefficients obeying to the following Arrhenius law: D = D0exp(-Ea/kBT), where D0 = 2.2*10-2 and 5.4*10-3 cm2 s-1 and Ea = 0.61 eV for the helium saturated and the curium doped glass respectively. These results reflect a thermally activated diffusion mechanism which seems to be not influenced by the glass radiation damage and helium concentrations studied in the present work (up to 8*1019 at. g-1, corresponding to 0.1 at.%). Characterizations of the macroscopic, structural and microstructural properties of glasses irradiated in nuclear reactor did not reveal any impact associated with the presence of helium at high concentrations. The observed modifications i.e. a swelling of 0.7 %, a decrease in hardness by 38 %, an increase between 8 and 34 % of the fracture toughness and a stabilization of the glass structure under irradiation, were attributed to the glass nuclear damage induced by the irradiation in reactor. Characterizations by SEM and TEM of R7T7 glasses implanted with helium at high concentrations, doped with curium and irradiated in nuclear reactor showed a homogeneous microstructure free of helium bubbles, pores or cracking. The results of the present work were used to develop a long-term diffusion model of helium in an industrial R7T7 nuclear waste glass. The model considers the thermal history, the fracturing and the alpha activity of the glass. (author)

2011-01-01

45

Calculation of the electron-impact coherence parameters for excitation of the 31D state of helium at 26.5 eV  

International Nuclear Information System (INIS)

The 19-state and 29-state R-matrix methods of Fon et al have been extended to calculate the differential cross section (DCS) and electron-impact coherence parameters (EICP) associated with excitation of the 3 1D state of helium for an incident electron energy of 26.5 eV at electron scattering angles ranging from 0-180o. The calculated EICP values are compared with the only experimental data reported recently by McLaughlin et al. The agreement is good. (Author)

1995-07-14

46

Helium production cross section measurement by helium atoms measurement system  

International Nuclear Information System (INIS)

Proton-induced helium production cross sections for nickel at proton energies up to 16 MeV have been measured with a helium accumulation method. A sample is a nickel sheet (chemical purity 99.98%, sizes 12x9x0.119 mm3) sandwiched between two gold foils (chemical purity 99.99%, size 12x9x0.051 mm3) which are collectors for the emitted ?-particles from the nickel surfaces. Nine nickel samples were irradiated by protons ranging from 8.8 to 17.5 MeV at Kyushu University Tandem Accelerator Laboratory. The number of helium atoms produced and accumulated in the nickel foil and two gold collectors was measured using the helium atoms measurement system. (author)

1996-03-01

47

Thermal desorption of implanted helium from beryllium  

International Nuclear Information System (INIS)

Hot isostatic pressed foils of 99.5 wt.% beryllium have been implanted at room temperature with 30 keV helium to fluences ranging from 1020 to 1021 He+/m2. Linear ramp thermal desorption measurements up to 1073 K (? 0.7 Tm) were performed to study the mechanisms by which the helium is trapped. Some of the samples have been deliberately corroded to investigate the effect of the surface contamination on the helium release. (orig.)

1993-12-01

48

Test of a cryogenic helium pump  

Energy Technology Data Exchange (ETDEWEB)

The design of a cryogenic helium pump for circulating liquid helium in a magnet and the design of a test loop for measuring the pump performance in terms of mass flow vs pump head at various pump speeds are described. A commercial cryogenic helium pump was tested successfully. Despite flaws in the demountable connections, the piston pump itself has performed satisfactorily. A helium pump of this type is suitable for the use of flowing supercritical helium through Internally Cooled Superconductor (ICS) magnets. It has pumped supercritical helium up to 7.5 atm with a pump head up to 2.8 atm. The maximum mass flow rate obtained was about 16 g/s. Performance of the pump was degraded at lower pumping speeds. (LCL)

Lue, J.W.; Miller, J.R.; Walstrom, P.L.; Herz, W.

1981-01-01

49

Helium embrittlement in type 316 stainless steel  

International Nuclear Information System (INIS)

In order to study high-temperature helium embrittlement, helium was injected into type 316 stainless steel (less than 5x10"-"7 and 31x10"-"6 atom fraction) using a cyclotron. Subsequent tensile testing at 700"0C revealed a loss of ductility - as measured by total elongation at rupture. The presence of helium caused the failure mode to change from trans- to intergranular failure. The cracks begin as voids on carbide particles which act as obstacles to grain boundary sliding. In the presence of helium, bubbles attach themselves to these carbide particles and serve as void nuclei thereby accelerating the process. (author)

1975-01-01

50

Standard Guide for Simulation of Helium Effects in Irradiated Metals  

CERN Document Server

1.1 This guide provides advice for conducting experiments to investigate the effects of helium on the properties of metals where the technique for introducing the helium differs in some way from the actual mechanism of introduction of helium in service. Simulation techniques considered for introducing helium shall include charged particle implantation, exposure to ?-emitting radioisotopes, and tritium decay techniques. Procedures for the analysis of helium content and helium distribution within the specimen are also recommended. 1.2 Two other methods for introducing helium into irradiated materials are not covered in this guide. They are the enhancement of helium production in nickel-bearing alloys by spectral tailoring in mixed-spectrum fission reactors, and isotopic tailoring in both fast and mixed-spectrum fission reactors. These techniques are described in Refs (1-5). Dual ion beam techniques (6) for simultaneously implanting helium and generating displacement damage are also not included here. This lat...

American Society for Testing and Materials. Philadelphia

1996-01-01

51

Thermal desorption of helium from defects in nickel  

International Nuclear Information System (INIS)

Helium atoms, introduced into materials by helium plasma or generated by the (n, ?) nuclear reaction, have a strong tendency to accumulate at trapping sites such as vacancy clusters and dislocations. In this paper, the effects of dislocations, single vacancies and vacancy clusters on the retention and desorption of helium atoms in nickel were studied. Low energy (0.1-0.15 keV) helium atoms were implanted in nickel with vacancies or dislocations without causing any displacement damage. He atoms, interstitial-type dislocation loops, and vacancy clusters were also introduced with irradiation damage by 5.0 keV helium ions. Helium thermal desorption peaks from dislocations, helium-vacancy clusters and helium bubbles were obtained by thermal desorption spectroscopy at 940 K, in the range from 900 to 1370 K, and at 1500 K, respectively. In addition, a thermally quasi-stable state was found for helium-vacancy clusters.

2011-05-01

52

Helium release from metals with face-centered cubic structure  

International Nuclear Information System (INIS)

The helium release from gold sheets of 5 and 54 ?m of thickness and helium concentrations from 10-9 to 10-5 ap of He during the isothermal and linear annealing is studied. The helium was put in the sample through the implantation of alpha particles, with variable energy,in the cyclotron. The free diffusion of the atoms of the helium, where the diffusion coefficient follows an Arrhenius law is studied. (E.G.)

1984-12-09

53

Thermal-Hydraulic System Study of the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) for ITER Using System Code RELAP5  

Science.gov (United States)

The HCPB concept has been a European DEMO reference concept for nearly one decade. Detailed thermal-hydraulic study on the control behavior of the whole system is one of the important parts of this development. The thermal-hydraulic effect of the TBM-combined cooling circuit during a cyclic operation in ITER has been studied using the system code RELAP5. The RELAP5 is based on an one-dimensional, transient two-fluid model for the flow of a two-phase steam-water mixture that can contain noncondensable components like Helium. The RELAP5-models are modified to take the cyclic operation of the circulator, heat exchanger, bypass, valves etc in to account. A sequence of operational phases is investigated, starting from the cold state through the heating phase that brings the system to a stand-by condition, followed by typical power cycles applied in ITER. The results show that the implemented control mechanisms keep the inlet temperature to the TBM and the total mass flow rate at the required values through all phases.

Jin, Xuezhou; R, Meyder

2005-04-01

54

Positronium formation in helium  

International Nuclear Information System (INIS)

Preliminary measurements of positronium formation in helium gas have been completed. The experimental method involves the transmission of a beam of slow positrons of controllable energy through a gas cell and the detection of all those positrons which do not form positronium. The method, in principle, allows the measurement of absolute values of the positronium formation cross section. Results in the energy range from 9eV to 26.5eV show a distinct drop in the collected slow positron flux above the positronium formation threshold energy. (Auth.)

1982-04-07

55

Ionization curves of C"4"+ and N"5"+ helium-like ions in a range of O (  

International Nuclear Information System (INIS)

Ionization curves of C"4"+ and N"5"+ have been calculated in the energy range of ionizing electons Esub(e) = (0-30) keV. For this purpose the matrix element squares of dipole tr tions Msub(i)"2(C"4"+ ? C"5"+)=(24.5ansi+-6) x10sup(-)"3 and Msub(i)"2(N"5"+ ? N"6"+)=(17.0+-4) x10"-"3 have been found by means of the graphic integration method. From the data obtained it follows that the ionization cross sections of C"4"+ and N"5"+ measured earlier correspond to the points in the vicinity of sigmasub(max). In order to check completely the calculated values, the cross sections sigmasub(i) should be measured at several points by Esub(e)

1977-01-01

56

Physiological Responses of Men Working in 25.5 C Water, Breathing Air or Helium Tri-Mix.  

Science.gov (United States)

Fourteen scuba divers in swim trunks did ergometer work while breathing air at 3 m in 25.5 C water. They were stressed by work and cold. Exercise produced increases in heart rate, minute ventilation (Ve), oxygen consumption (Vo2) and catecholamine excreti...

P. F. Hoar L. W. Raymond H. C. Langworthy R. E. Johnsonbaugh J. Sode

1975-01-01

57

Stopping of 5-100 keV helium in tantalum, niobium, tungsten, and AISI 316L steel  

International Nuclear Information System (INIS)

The stopping power of Ta, Nb, W, and AISI 316L stainless steel for He ions at velocities below the Bohr velocity has been deduced by comparing the ranges of 5 to 100 keV He+-ions determined with the elastic-recoil-detection-analysis method with those obtained in molecular dynamics simulations. The nuclear slowing down was treated through the use of molecular dynamics calculations and a potential obtained from density-functional theory calculations. The comparisons showed that the electronic stopping powers given by Ziegler, Biersack and Littmark, had to be multiplied with a factor of 1.4 for Ta, 1.0 for Nb, 1.1 for W, and 1.0 for AISI 316L. The uncertainty of the factors and hence the scaled stopping power values is ±5%. The total stopping powers were obtained from molecular dynamics simulations in which the modified electronic stopping powers were used. (orig.)

1996-04-01

58

Stopping of 5-100 keV helium in tantalum, niobium, tungsten, and AISI 316L steel  

Science.gov (United States)

The stopping power of Ta, Nb, W, and AISI 316L stainless steel for He ions at velocities below the Bohr velocity has been deduced by comparing the ranges of 5 to 100 keV He +-ions determined with the elastic-recoil-detection-analysis method with those obtained in molecular dynamics simulations. The nuclear slowing down was treated through the use of molecular dynamics calculations and a potential obtained from density-functional theory calculations. The comparisons showed that the electronic stopping powers given by Ziegler, Biersack and Littmark (The Stopping Powers and Ranges of Ions in Matter (Pergamon, New York, 1985), Vol. 1 [1], had to be multiplied with a factor of 1.4 for Ta, 1.0 for Nb, 1.1 for W, and 1.0 for AISI 316L. The uncertainty of the factors and hence the scaled stopping power values is ±5%. The total stopping powers were obtained from molecular dynamics simulations in which the modified electronic stopping powers were used.

Haussalo, P.; Nordlund, K.; Keinonen, J.

59

Flow cytometric immunofluorescence and DNA analysis: Using a 1.5 mW helium-neon laser (544 nm)  

Energy Technology Data Exchange (ETDEWEB)

We evaluate a 1.5 mW HeNe laser (544 nm) for use on an EPICS{reg_sign} Elite with a 76 {mu}m Sortsense flow cell. The two applications chosen were immunofluorescence and DNA analysis. We measured the fluorescence threshhold of phycoerytherin calibration beads to be approximately 336 MESF. Cell analysis with a HeNe laser and Argon laser correlated well for the CD4{sup PE}, CD56{sup PE}, CD19{sup PE} conjugates, with correlation coefficients of 0.98, 0.99, 0.94, respectively. The % positive and mean channel fluorescence were comparable to the results obtained with a 15 mW Argon laser. In addition, a three-color configuration PE yielded excellent results. Cell analysis of CD4{sup PE}, CD3{sup ECD} and CD19{sup Cy-Chrome} with the HeNe laser and Argon laser correlated well with correlation coefficients of 0.96, 0.95, and 0.92, respectively. The histograms showed good separation between the negative cells, the dimly staining cells and the brightly staining cells. Propidium Iodide was chosen for DNA analysis. Full CV values for whole blood DNA fluorescence using the green laser were good at 2.6%. These data indicate the low power 544 nm laser is sufficient to do immunophenotyping and DNA analysis. Results may be explained by higher quantum efficiency and lower background fluorescence. The wavelength of the 544 nm laser is much closer to the excitation peaks of PI, PE, and the tandem dyes ECD and Cy-Chrome. Also, the Raman scattering of water for the 544 nm laser has a longer wavelength maximum than the emission peaks of PI, PE, and ECD. The major advantages of this laser for the research laboratory are small size, no cooling fan, low power requirements and low cost. 16 refs., 5 figs., 3 tabs.

Hudson, J.C.; Porcelli, R.T.; Russell, T.R. [Coulter Corp., Miami, FL (United States)

1995-10-01

60

Paramagnetic Attraction of Impurity-Helium Solids  

Science.gov (United States)

Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

2003-01-01

 
 
 
 
61

Helium diffusion in the sun  

Science.gov (United States)

We calculate improved standard solar models using the new Livermore (OPAL) opacity tables, an accurate (exportable) nuclear energy generation routine which takes account of recent measurements and analyses, and the recent Anders-Grevesse determination of heavy element abundances. We also evaluate directly the effect of the diffusion of helium with respect to hydrogen on the calculated neutrino fluxes, on the primordial solar helium abundance, and on the depth of the convective zone. Helium diffusion increases the predicted event rates by about 0.8 SNU, or 11 percent of the total rate, in the chlorine solar neutrino experiment, by about 3.5 SNU, or 3 percent, in the gallium solar neutrino experiments, and by about 12 percent in the Kamiokande and SNO solar neutrino experiments. The best standard solar model including helium diffusion and the most accurate nuclear parameters, element abundances, and radiative opacity predicts a value of 8.0 SNU +/- 3.0 SNU for the C1-37 experiment and 132 +21/-17 SNU for the Ga - 71 experiment, where the uncertainties include 3 sigma errors for all measured input parameters.

Bahcall, J. N.; Pinsonneault, M. H.

1992-01-01

62

The Primordial Helium Abundance  

Digital Repository Infrastructure Vision for European Research (DRIVER)

I present a brief review on the determination of the primordial helium abundance by unit mass, Yp. I discuss the importance of the primordial helium abundance in: (a) cosmology, (b) testing the standard big bang nucleosynthesis, (c) studying the physical conditions in H II regions, (d) providing the initial conditions for stellar evolution models, and (e) testing the galactic chemical evolution models.

Peimbert, Manuel

2008-01-01

63

Intense pulsed helium droplet beams  

CERN Multimedia

Pulsed (30 - 100 microseconds) nozzle beams have been used to generate helium droplets ( = 10^4-10^5). The dependence of the beam intensity and the mean droplet size on the source stagnation pressure and temperature are studied via mass spectroscopy and laser induced fluorescence of embedded phthalocyanine molecules. In comparison to a cw beam the pulsed source for the same pressure and temperature has a factor of 100 higher flux and the droplet sizes are an order of a magnitude larger.

Slipchenko, M N; Momose, T; Vilesov, A F; Slipchenko, Mikhail N.; Kuma, Susumu; Momose, Takamasa; Vilesov, Andrey F.

2002-01-01

64

Spectral measurements along the path of N ions impinged into dense helium gas (400 Torr and 5.2 K). II. Excimer reactions dependent on stopping power and large emission yields near the termination of the track  

International Nuclear Information System (INIS)

Emission spectra and their decay were measured along the path of 4 MeV/amu N ions impinged into dense helium gas near 5.2 K and 420 Torr. Specific scintillation, dL/dX, and scintillation efficiency, dL/dE, for each emission band were measured separately on total, fast initial-rise (-1 cm2: Some of the emissions increased abruptly as the stopping power exceeded this value, while the other emissions decreased or their rates of increase were suppressed. This bend point corresponds to the starting point of a rapidly decreasing yield of delta rays. The result shows that helium has a good scintillation response to high-density excitation occurring at the termination of tracks of N ions, in contrast to usual scintillators, where scintillation decreases abruptly with decreasing delta-ray yield. The large yields of emissions at high-density excitation are explained by the direct excitation, induced emission, and cyclic regeneration of excimers by bimolecular reactions between the nonradiative metastable state, a3, in addition to a very low probability of quenching in helium. Furthermore, it is shown that the present results support the tentative assignment made in part I of this report that the new triplet bands centered at 4587 A result from an excimer--dimer

1986-02-15

65

KSTAR Helium Refrigeration System Design and Manufacturing  

International Nuclear Information System (INIS)

The tokamak developed in the KSTAR (Korean Superconducting Tokamak Advanced Research) project makes intensive use of superconducting magnets operated at 4.5 K. The cold components of the KSTAR tokamak require forced flow of supercritical helium for magnets/structure, boiling liquid helium for current leads, and gaseous helium for thermal shields. The cryogenic system will provide stable operation and full automatic control. A three-pressure helium cycle composed of six turbines has been customised design for this project. The '' design '' operating mode results with a system composed of a 9 kW refrigerator (including safety margin) and using gas and liquid storages for mass balancing. During Shot/Standby mode, the heat loads are highly time-dependent. A thermal damper is used to smooth these variations and will allow stable operation. (author)

2006-09-11

66

Quantum entanglement in helium  

International Nuclear Information System (INIS)

We compute the entanglement of the ground state and several singlet and triplet excited states of the helium atom using high-quality, state-of-the-art wavefunctions. The behaviour of the entanglement of the helium eigenstates is similar to that observed in some exactly soluble two-electron systems. In particular, the amount of entanglement exhibited by the eigenstates tends to increase with energy.

2012-01-14

67

Ions at helium interfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The boundaries between different phases of condensed helium provide an interesting testing ground for studying ions in a quantum matter matrix. Here we consider the simplest positive and negative ions in helium - snowballs and electron bubbles, respectively - being trapped at the liquid-liquid interface of phaseseparated 3He-4He meixtures and at the liquid-solid interrace of 4He. A comparison of experimental results for the trapping with predictions of the snowball and the bubble models shows...

1995-01-01

68

Helium analysis of subsurface waters as a uranium exploration tool  

International Nuclear Information System (INIS)

Field studies conducted in areas of known uranium deposits are described. In Weld County, Colorado, 18 samples were collected in an 80 square kilometer area around a roll-type uranium deposit approximately 70 meters deep. Stock supply wells and domestic wells, ranging from 5 to 25 meters deep, were sampled and analyzed for helium. The wells located down the ground water gradient with respect to the ore body had helium concentrations 30 to 50 times greater than those values expected from atmospheric equilibrium. The shallow wells had less helium than the deeper domestic wells. At the Schwartzwalder mine in Jefferson County, Colorado, mine water, pond water, springs and streams were sampled and analyzed for helium. The mine water and springs had helium concentrations 5 to 15 times greater than atmospheric equilibrium, but the ponds and streams, into which the mine water drained, showed no excess helium. The equilibrium values of helium found in the ponds and streams were expected because even minor turbulence effectively removes excess helium from water. Therefore, streams and standing bodies of water are not good candidates for helium analysis. Mine water was also sampled from several uranium mines at the Ambrosia Lake deposits near Grants, New Mexico. The samples were taken at the surface discharge pipes and the helium values were 2 to 7 times that of atmospheric equilibrated waters. Because of both the short residence time of the water with the ore and the great amount of turbulence from pumping, the helium values were relatively low. The large geographic area in the vicinity of a uranium deposit in which subsurface water samples show helium anomalies indicates that helium analyses can be used as a reconnaissance exploration tool

1977-10-01

69

Mechanisms of helium embrittlement  

International Nuclear Information System (INIS)

In fusion reactor environment, transmutation reactions occur that produce helium when neutrons from the plasma strike the containment first wall. This dissolved helium in the metal together with the neutron induced damage leads to premature, intergranular failure. In an attempt to clarify the role of helium in promoting high temperature intergranular failure, in situ tensile experiments were conducted in a high voltage electron microscope (HVEM) attached to a linear ion accelerator used at 80 keV. Two types of experiments were performed on 14-MeV neutron and helium irradiated 40-?m thick foil stainless steel specimens using a heating quantitative load elongation tensile stage between 25 and 700"0C. A graph of cumulative crack length plotted against total specimen elongation exhibits a slope, S, which increases as specimen ductility (reduction of area, ROA) decreases. It was found that ROA"2 x S = 0.4 for all cases studied. High temperature helium embrittlement occurs only at slow strain rates. Dislocations dragging helium bubbles to grain boundaries is commonly thought to cause the embrittlement. Specimens tensile tested under dual tensile test temperatures exhibited integranular failure at 700"0C and after the tensile test was resumed at 550"0C charged to a transgranular failure mode

1986-01-01

70

On some helium metallization parameters  

International Nuclear Information System (INIS)

A density minimum of 5 g/cm3, at which the insulator-metal phase transition in helium can take place, has been calculated. The corresponding temperature of this transition of about 9000 K has been estimated. For this purpose, the effective pair ion-to-ion interaction and the electrical resistivity in liquid helium in a vicinity of the transition point into the metallic state are studied in the framework of a nearly free electron model. As a small parameter of the theory, the ratio between, on the one hand, the energy of interaction between conduction electrons and a singly ionized helium atom and, on the other hand, the Fermi energy of electrons was used. The interaction between electrons is taken into account in the framework of the diffraction model of metal, i.e. considering the screening of the electron-to-ion interaction. The exchange interaction and correlations between conduction electrons are taken into account in the local field approximation.

2012-01-01

71

Nucleation of helium precipitates in nickel observed by HDS  

International Nuclear Information System (INIS)

Thermal Helium Desorption Spectrometry (HDS) has been used to study the room temperature nucleation of helium precipitates at point defects in Ni, notably HeV defects at depth approx.=20 nm below the crystal surface. Helium is injected into the crystal by 50 eV He ion-irradiation which causes no atomic displacements. It has been observed that Hesub(n)V defects with occupation from n=2 He to n=4 He bind helium equally strongly, but weaker than for HeV. For n>=5 He the binding increases rapidly. The observed behaviour is attributed to helium induced trap mutation and agrees qualitatively with results of atomistic calculations in nickel for this case. Helium precipitation at near surface trapping sites is held responsible for the observed increase of helium release temperatures with helium dose when an undamaged crystal is irradiated. Preliminary TEM observations of Ni specimens irradiated with 50 times higher helium doses than the maximum dose used in the HDS experiments indicated planar clustering of the helium. (orig.)

1984-05-01

72

Closed cycle liquid helium refrigerators  

Energy Technology Data Exchange (ETDEWEB)

We have developed closed cycle liquid helium refrigerators using a Joule Thomson circuit precooled by commercially available two staged Gifford Mac Mahon cryocoolers. The Joule Thomson counterflow heat exchangers are modular and have been thermo-hydraulically characterized. Fully automatic cool down and operation are achieved by two pneumatically driven by pass and expansion valves. Several apparatus have been built or are under assembly with cooling power ranging from 100 mW up to 5 Watt, for temperature ranging from 2.8 K up to 4.5 K. A trouble free operation with several warm up and cool down cycles has been proven over 7000 hours.

Claudet, G.; Lagnier, R.; Ravex, A.

1992-11-01

73

Closed cycle liquid helium refrigerators  

International Nuclear Information System (INIS)

We have developed closed cycle liquid helium refrigerators using a Joule Thomson circuit precooled by commercially available two staged Gifford Mac Mahon cryocoolers. The Joule Thomson counterflow heat exchangers are modular and have been thermo-hydraulically characterized. Fully automatic cool down and operation are achieved by two pneumatically driven by pass and expansion valves. Several apparatus have been built or are under assembly with cooling power ranging from 100 mW up to 5 Watt, for temperature ranging from 2.8 K up to 4.5 K. A trouble free operation with several warm up and cool down cycles has been proven over 7000 hours

1992-06-08

74

H. R. 2541: This Act may be cited as the Helium Act Amendments of 1989. Introduced in the House of Representatives, One Hundredth First Congress, First Session, June 5, 1989  

Energy Technology Data Exchange (ETDEWEB)

H.R. 2541 is a bill to amend the Helium Act to authorize Federal agencies to purchase helium from the private sector, to authorize and direct the Secretary of the Treasury to cancel outstanding indebtedness related to the Helium Fund and for other purposes.

1989-01-01

75

Charged Hydrogenic, Helium and Helium-Hydrogenic Molecular Chains in a Strong Magnetic Field  

CERN Multimedia

A non-relativistic classification of charged molecular hydrogenic, helium and mixed helium-hydrogenic chains with one or two electrons which can exist in a strong magnetic field $B \\lesssim 10^{16} $G is given. It is shown that for both $1e-2e$ cases at the strongest studied magnetic fields the longest hydrogenic chain contains at most five protons indicating to the existence of the $\\rm{H}_5^{4+}$ and $\\rm{H}_5^{3+}$ ions, respectively. In the case of the helium chains the longest chains can exist at the strongest studied magnetic fields with three and four $\\al-$particles for $1e-2e$ cases, respectively. For mixed helium-hydrogenic chains the number of heavy centers can reach five for highest magnetic fields studied. In general, for a fixed magnetic field two-electron chains are more bound than one-electron ones.

Turbiner, A V; Vieyra, J C Lopez

2009-01-01

76

Helium cooled Flibe blanket  

Energy Technology Data Exchange (ETDEWEB)

The blanket design uses a pressure vessel to contain the 50 atmosphere helium gas. Helium cools the first wall and blanket internals. The internals consist of a bed of beryllium balls nominally 1 cm diameter in which neutrons are multiplied and later captured, breeding adequate (even excess) amounts of tritium and releasing energy in exothermic nuclear reactions. Tritium is bred in the molten flibe salt which flows slowly (0.1m/sec) in steel tubes. The salt is kept reducing by periodic reacting with beryllium so the tritium will be in the T/sub 2/ form, however with somewhat enhanced corrosion rate the salt could be kept oxidizing in which case the tritium would be in the TF form. To prevent the tritium from permitting too much into the helium stream, a tungsten coating on the inside of the tubes is proposed. Tritium is removed from the salt and helium by processing both. Because the solubility of tritium in Flibe is so low, there will be a strong driving force for tritium permeation and this places a great burden on a high integrity tungsten permeation barrier. The tritium in the helium is prevented from permeating excessively into the steam system by jacketing the steel steam generator tubes with a 1 mm aluminum jacket. Clearly, tritium containment and barrier development are the most important feasibility issues for this design.

Moir, R.

1984-10-01

77

Helium cooled Flibe blanket  

International Nuclear Information System (INIS)

The blanket design uses a pressure vessel to contain the 50 atmosphere helium gas. Helium cools the first wall and blanket internals. The internals consist of a bed of beryllium balls nominally 1 cm diameter in which neutrons are multiplied and later captured, breeding adequate (even excess) amounts of tritium and releasing energy in exothermic nuclear reactions. Tritium is bred in the molten flibe salt which flows slowly (0.1m/sec) in steel tubes. The salt is kept reducing by periodic reacting with beryllium so the tritium will be in the T2 form, however with somewhat enhanced corrosion rate the salt could be kept oxidizing in which case the tritium would be in the TF form. To prevent the tritium from permitting too much into the helium stream, a tungsten coating on the inside of the tubes is proposed. Tritium is removed from the salt and helium by processing both. Because the solubility of tritium in Flibe is so low, there will be a strong driving force for tritium permeation and this places a great burden on a high integrity tungsten permeation barrier. The tritium in the helium is prevented from permeating excessively into the steam system by jacketing the steel steam generator tubes with a 1 mm aluminum jacket. Clearly, tritium containment and barrier development are the most important feasibility issues for this design

1984-01-01

78

Nonlocality in (helium-helium) interatomic potentials  

International Nuclear Information System (INIS)

Assuming nothing is known about the internal structure of Helium atoms, then the interaction between two atoms is to be deduced only from the phase shifts when one atom is scattered by another. However it is known that the set of phase-shifts determine the potential uniquely only if it is assumed that the potential is local. If nonlocal momentum dependent potentials are allowed, phase shifts do not determine the potential uniquely anymore. An empirical method is given to find out if there is nonlocality in the interatomic interaction. (Auth.)

1975-12-29

79

Tritium/Helium-3 Dating  

Science.gov (United States)

First, the USGS summarizes the use of tritium and helium-3 for dating geologically young groundwater (1). Researchers can find the conditions needed to solve the helium isotope mass balance as well as equations and corrections needed to obtain the age of water. The second website, provided by the Rosenstiel School of Marine and Atmospheric Sciences, discusses the presence of tritium and helium isotopes in the oceans (2). Users can find out about the Noble Gas Isotope Lab's research projects including the _Mantle 3He Distribution and Deep Circulation in the Indian Ocean_. Next, the University of Ottawa offers equations for helium and tritium concentrations and decay (3). Visitors can also learn how solubility of noble gases is affected by temperature. Fourth, the University of Waterloo describes the characteristics of the hydrogen radioisotope, tritium (4). The website explains how tritium was discovered through the work of Lord Rutherford, Sir John, Ernest Lawrence, Luis Alvarex, Willard Libby, and others. Next, the University of T'bingen furnishes a pdf file dealing with numerous dating techniques including fission track, radio carbon, and thermoluminescence dating (5). Beginning on page nine, individuals can learn about tritium formation and decay as well as its use in dating ground water. At the sixth website, the USGS describes the characteristics of the stable isotopes of helium (6). Visitors can discover how 3He is used to date geologically young ground water, whereas 4He is used to date older ground water. The seventh website, created by SAHRA (Sustainability of semi-Arid Hydrology and Riparian Areas) at the University of Arizona, illustrates the effectiveness of isotope hydrology in "understanding fundamental physical, chemical, biological, and climate forcing processes occurring in a watershed" (7). Along with the discussion of the fundamentals of age dating and sources of isotopes, visitors can learn the advantages to using tritium for water samples collected in the field. Lastly, the Victoria University of Manchester introduces its research using noble gas isotopes to better understand earth systems (8). Visitors can discover the decay rates of tritium to 3He and the rates of accumulation of 4He in older groundwater as well as many applications of dating water.

80

Helium transfer line installation details.  

CERN Multimedia

A particularity of the 32 m long four in one helium transfer line in between the cold box in USC55 and the cavern UX5 is the fact that the transfer line passes through a hole in the crane rail support beam. In order to ensure the alignment of the suspension rail in the interconnecting tunnel with the hole in the rail support as well as the connection points at both ends required precise measurements of the given geometries as well as the installation of a temporary target for the verification of the theoretical predictions.

G. Perinic

2007-01-01

 
 
 
 
81

Helium Production and Possible Projection  

Directory of Open Access Journals (Sweden)

Full Text Available The future availability of helium has been raised as an issue in the literature. However, a disaggregated projection of helium production has not been attempted, presumably due to the difficult nature of accessing disaggregated historic production data to test the accuracy of this issue. This paper presents collated and estimated historic helium production statistics from 1921 to 2012 for each helium producing country in the world and by U.S. state. A high and regular growth projection of helium has been created. It is found that helium resources are sufficient for the near future, with the projected production plateauing in 2060–2075 and 2090–2100 for the high and regular growth scenarios, respectively. As long as natural gas deposits with helium are appropriately managed, there is little likelihood for helium shortages to occur in the short term due to geologic constraints.

Steve Mohr

2014-03-01

82

Cavitation in flowing superfluid helium  

Science.gov (United States)

Flowing superfluid helium cavitates much more readily than normal liquid helium, and there is a marked difference in the cavitation behavior of the two fluids as the lambda point is traversed. Examples of cavitation in a turbine meter and centrifugal pump are given, together with measurements of the cavitation strength of flowing superfluid helium. The unusual cavitation behavior of superfluid helium is attributed to its immense thermal conductivity .

Daney, D. E.

1988-01-01

83

An Assessment of Helium Evolution from Helium-Saturated Propellant Depressurization in Space  

Science.gov (United States)

Helium evolution from the transfer of helium-saturated propellant in space is quantified to assess its impacts from creating two-phase gas/liquid flow from the supply tank, gas injection into the receiving tank, and liquid discharge from the receiving tank. Propellant transfer takes place between two similar tanks whose maximum storage capacity is approximately 2.55 cubic meters each. The maximum on-orbit propellants transfer capability is 9000 lbm (fuel and oxidizer). The transfer line is approximately 1.27 cm in diameter and 6096 cm in length and comprised of the fluid interconnect system (FICS), the orbiter propellant transfer system (OPTS), and the International Space Station (ISS) propulsion module (ISSPM). The propellant transfer rate begins at approximately 11 liter per minute (lpm) and subsequently drops to approximately 0.5 lpm. The tank nominal operating pressure is approximately 1827 kPa (absolute). The line pressure drops for Monomethy1hydrazine (MMH) and Nitrogen tetroxide (NTO) at 11.3 lpm are approximately 202 kPa and 302 kPa, respectively. The pressure-drop results are based on a single-phase flow. The receiving tank is required to vent from approximately 1827 kPa to a lower pressure to affect propellant transfer. These pressure-drop scenarios cause the helium-saturated propellants to release excess helium. For tank ullage venting, the maximum volumes of helium evolved at tank pressure are approximately 0.5 ft3 for MMH and 2 ft3 for NTO. In microgravity environment, due to lack of body force, the helium evolution from a liquid body acts to propel it, which influences its fluid dynamics. For propellant transfer, the volume fractions of helium evolved at line pressure are 0.1% by volume for MMH and 0.6 % by volume for NTO at 11.3 lpm. The void fraction of helium evolved varies as an approximate second order power function of flow rate.

Nguyen, Bich N.; Best, Frederick; Wong, Tony; Kurwitz, Cable; McConnaughey, H. (Technical Monitor)

2001-01-01

84

Liquid helium level detector  

International Nuclear Information System (INIS)

Means generally used for liquid helium level measurement are the capacitive or superconductive probes. The signal, generally electric, is collected and treated by electronic means operating at ambiant temperature; they operate the pneumatic or electric command of a control valve; the cold active element of this valve controls the necessary alimentation flow

1984-04-01

85

Helium leak finding plant  

International Nuclear Information System (INIS)

The invention concerns a helium leak finding plant with a mass spectrometer cell on the suction side of a molecular pump and a mechanical pre-pump, where a test sample or a test sensor is connected between the two pumps. The mechanical pre-pump consists of three successive stages. (orig./HP)

1986-05-15

86

Cosmological helium production simplified  

International Nuclear Information System (INIS)

We present a simplified model of helium synthesis in the early universe. The purpose of the model is to explain clearly the physical ideas relevant to the cosmological helium synthesis, in a manner that does not overlay these ideas with complex computer calculations. The model closely follows the standard calculation, except that it neglects the small effect of Fermi-Dirac statistics for the leptons. We also neglect the temperature difference between photons and neutrinos during the period in which neutrons and protons interconvert. These approximations allow us to express the neutron-proton conversion rates in a closed form, which agrees to 10% accuracy or better with the exact rates. Using these analytic expressions for the rates, we reduce the calculation of the neutron-proton ratio as a function of temperature to a simple numerical integral. We also estimate the effect of neutron decay on the helium abundance. Our result for this quantity agrees well with precise computer calculations. We use our semi-analytic formulas to determine how the predicted helium abundance varies with such parameters as the neutron life-time, the baryon to photon ratio, the number of neutrino species, and a possible electron-neutrino chemical potential. 19 refs., 1 fig., 1 tab

1988-01-01

87

Thermal helium desorption spectrometry  

International Nuclear Information System (INIS)

The principle of the thermal helium desorption spectrometry (THDS) and the atomistic simulation technique is shortly described. It is shown by means of examples how with THDS, supported by calculations, defect chemistry can be exercised. The examples demonstrate the main motive of the THDS investigations, i.e. gaining insight in fundamental defect reactions that initiate various radiation damage mechanisms in nuclear reactor materials

1981-12-16

88

New experimental device for VHTR structural material testing and helium coolant chemistry investigation – High Temperature Helium Loop in NRI ?ež  

International Nuclear Information System (INIS)

The High Temperature Helium Loop (HTHL) is an experimental device for simulation of VHTR helium coolant conditions. The purpose of the HTHL is structural materials testing and helium coolant chemistry investigation. In the HTHL pure helium will be used as working medium and its main physical parameters are 7 MPa, max. temperature in the test section 900 °C and flow rate 37.8 kg/h. The HTHL consists of an active channel, the helium purification system, the system of impurities dosage (e.g. CO, CO2, H2, H2O, O2, N2, and CH4) and the helium chemistry monitoring system (sampling and on-line analysis and determination of impurities in the helium flow). The active channel is planned to be placed into the core of the experimental reactor LVR-15 which will serve as a neutron flux source (max. 2.5 × 1018 n/m2 s for fast neutrons). The HTHL is now under construction. Some of its main parts are finished, some are still being produced (active channel internals, etc.), some should be improved to work correctly (the helium circulatory compressor); certain sub-systems are planned to be integrated to the loop (systems for the determination of moisture and other impurities in helium, etc.). The start of the HTHL operation is expected during 2011 and the integration of the active channel into the LVR-15 core during 2012.

2012-10-01

89

Calculation of electron-helium scattering  

International Nuclear Information System (INIS)

We present the Convergent Close-Coupling (CCC) theory for the calculation of electron-helium scattering. We demonstrate its applicability at a range of projectile energies of 1.5 to 500 eV to scattering from the ground state to n ?3 states. Excellent agreement with experiment is obtained with the available differential, integrated, ionization, and total cross sections, as well as with the electron-impact coherence parameters up to and including the 33 D state excitation. Comparison with other theories demonstrates that the CCC theory is the only general reliable method for the calculation of electron helium scattering. (authors). 66 refs., 2 tabs., 24 figs

1994-01-01

90

The cryogenic helium cooling system for the Tokamak physics experiment  

International Nuclear Information System (INIS)

The Tokamak Physics Experiment (TPX) will use supercritical helium to cool all the magnets and supply helium to the Vacuum cryopumping subsystem. The heat loads will come from the standard steady state conduction and thermal radiation sources and from the pulsed loads of the nuclear and eddy currents caused by the Central Solenoid Coils and the plasma positioning coils. The operations of the TPX will begin with pulses of up to 1000 seconds in duration every 75 minutes. The helium system utilizes a pulse load leveling scheme to buffer out the effects of the pulse load and maintain a constant cryogenic plant operation. The pulse load leveling scheme utilizes the thermal mass of liquid and gaseous helium stored in a remote dewar to absorb the pulses of the tokamak loads. The mass of the stored helium will buffer out the temperature pulses allowing 5 K helium to be delivered to the magnets throughout the length of the pulse. The temperature of the dewar will remain below 5 K with all the energy of the pulse absorbed. This paper will present the details of the heat load sources, of the pulse load leveling scheme operations, a partial helium schematic, dewar temperature as a function of time, the heat load sources as a function of time and the helium temperature as a function of length along the various components that will be cooled

1995-10-04

91

A Pure Helium Model Stellar Atmosphere.  

Science.gov (United States)

A model atmosphere is calculated for a pure helium star with Teff = 18,000 K and logg = 3.5 (c.g.s.), approximating the hydrogen deficient star BD + 10 2179. The only sources of opacity included are bound-free and free-free transitions of HeI and HeII and...

K. Hunger D. Van Blerkom

1966-01-01

92

Study of the TL response of LiF:Mg,Ti to 3 and 7.5 MeV helium ions: Measurements and interpretation in terms of the track interaction model  

International Nuclear Information System (INIS)

We have measured the LiF:Mg,Ti (TLD-100) thermoluminescent response, efficiency and supralinearity, to 3 and 7.5 MeV helium ions in the fluence interval between 6x107 to 1.5x1011 cm-2. Ion irradiations were performed using a flux of elastically scattered ions from a thin gold target. The measured efficiencies with respect to 60Co ?-rays are equal to 0.074 and 0.174 at 3 and 7.5 MeV, respectively, for the response of peak 5. The supralinearity functions for peaks 4, 5, 6a, 6b, 7, 8, 9 and the total TL signal indicate that supralinearity is an increasing function of energy and that it increases with peak temperature. The data for peaks 5, 8 and 9 have been successfully described by Monte Carlo simulations of the track interaction model. The fitted parameters show that peak 5 displays a special behaviour which requires the use of a much larger effective track radius than the higher temperature peaks

2000-03-01

93

Superfluid helium tanker instrumentation  

International Nuclear Information System (INIS)

An instrumentation system for a 1992 space shuttle flight demonstration of a superfluid helium (SFHe) tanker and transfer technology is presented. This system provides measurement of helium temperatures, pressures, flow rates, mass, and the presence of liquid or vapor. The instrumentation system described consists of analog and digital portions which provide a space qualified electronics system that is fault tolerant, compact, and relatively lightweight. The data processing hardware and software are ground commandable, perform measurements asynchronously, and format telemetry for transmission to the ground. The novel heat pulse mass gaging technique is described. A new liquid/vapor sensor is presented. Flowmeters for SFHe are discussed. A SFHe fountain effect pump is described. Results of tests to date are presented

1990-01-01

94

Helium behavior in vanadium-based alloys irradiated in the dynamic helium charging experiments  

International Nuclear Information System (INIS)

Helium effect of neutron irradiated vanadium alloys, containing titanium, has been studied using Dynamic Helium Charging Experiment (DHCE) in FFTF. Cavity formation was observed only in pure vanadium irradiated at 430 to 600 C and in V-5Ti irradiated at 600 C. No apparent cavity formation was obtained in V-3Ti-1Si and V-4Cr-4Ti. The precipitation of titanium oxide in V-5Ti, V-3Ti-1Si and V-4Cr-4Ti occurred in all irradiation conditions in this study and the precipitates of Ti_5Si_3 only appeared in V-3Ti-1Si irradiated at 600 C up to 15 dpa with helium generation rate of 4 appmHe/dpa. It is suggested that titanium oxide plays an important role for suppression of cavity formation and swelling from early stage of irradiation. Detail characterization of precipitates and He effect for neutron damages in vanadium alloys are discussed here

1996-06-25

95

Helium Ion Microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Helium Ion Microcopy (HIM) based on Gas Field Ion Sources (GFIS) represents a new ultra high resolution microscopy and nano-fabrication technique. It is an enabling technology that not only provides imagery of conducting as well as uncoated insulating nano-structures but also allows to create these features. The latter can be achieved using resists or material removal due to sputtering. The close to free-form sculpting of structures over several length scales has been made p...

Hlawacek, Gregor; Veligura, Vasilisa; Gastel, Raoul; Poelsema, Bene

2013-01-01

96

Helium cooling systems for large superconducting physics detector magnets  

International Nuclear Information System (INIS)

The large superconducting detector magnets used for high energy physics experiments are virtually all indirectly cooled. In general, these detector magnets are not cryogenically stabilized. Therefore, there are a number of choices for cooling large indirectly cooled detector magnets. These choices include; 1) forced two-phase helium cooling driven by the helium refrigerator J-T circuit, 2) forced two-phase helium cooling driven by a helium pump, and 3) a perculation gravity feed cooling system which uses liquid helium from a large storage dewar. The choices for the cooling of a large detector magnet are illustrated by applying these concepts to a 4.2 meter diameter 0.5 tesla thin superconducting solenoid for an experiment at the Relativistic Heavy Ion Collider (RHIC). (Author)

1992-06-08

97

Antiprotonic helium atomcules  

Science.gov (United States)

About 3% of antiprotons (bar{p}) stopped in helium are long-lived with microsecond lifetimes, against picoseconds in all other materials. This unusual longevity has been ascribed to the trapping of bar{p} on metastable bound states in bar{p}He+ helium atom-molecules thus named atomcules. Apart from their unique dual structure investigated by laser spectroscopy - a near-circular quasi-classical Rydberg atom with l n - 1 37 or a special diatomic molecule with a negatively charged bar{p} nucleus in high rotational state with J = l - the chemical physics aspects of their interaction with other atoms or molecules constitute an interesting topic for molecular physics. While atomcules may resist to million collisions in helium, molecular contaminants such as H2 are likely to destroy them in a single one, down to very low temperatures. In the Born-Oppenheimer framework, we interpret the molecular interaction obtained by ab initio quantum chemical calculations in terms of classical reactive channels, with activation barriers accounting for the experiments carried out in He and H2. From classical trajectory Monte Carlo simulations, we show that the thermalization stage strongly quenches initial populations, thus reduced to a recovered 3 % trapping fraction. This work illustrates the pertinence of chemical physics concepts to the study of exotic processes involving antimatter. New insights into the physico-chemistry of cold interstellar radicals are anticipated.

Sauge, Sébastien

2012-10-01

98

Antiprotonic helium atomcules  

Directory of Open Access Journals (Sweden)

Full Text Available About 3% of antiprotons ( stopped in helium are long-lived with microsecond lifetimes, against picoseconds in all other materials. This unusual longevity has been ascribed to the trapping of on metastable bound states in He+ helium atom-molecules thus named atomcules. Apart from their unique dual structure investigated by laser spectroscopy – a near-circular quasi-classical Rydberg atom with l ~ n – 1 ~ 37 or a special diatomic molecule with a negatively charged nucleus in high rotational state with J = l – the chemical physics aspects of their interaction with other atoms or molecules constitute an interesting topic for molecular physics. While atomcules may resist to million collisions in helium, molecular contaminants such as H2 are likely to destroy them in a single one, down to very low temperatures. In the Born-Oppenheimer framework, we interpret the molecular interaction obtained by ab initio quantum chemical calculations in terms of classical reactive channels, with activation barriers accounting for the experiments carried out in He and H2. From classical trajectory Monte Carlo simulations, we show that the thermalization stage strongly quenches initial populations, thus reduced to a recovered 3 % trapping fraction. This work illustrates the pertinence of chemical physics concepts to the study of exotic processes involving antimatter. New insights into the physico-chemistry of cold interstellar radicals are anticipated.

Sauge Sébastien

2012-10-01

99

Thermal Conductivity of Helium  

Energy Technology Data Exchange (ETDEWEB)

This engineering note examines the thermal conductivity of helium as a function of temperature and pressure. The note attempts to determine the effect of varying pressure on the thermal conductivity of the vapor state over various temperature ranges. The plots clearly show that at temperatures above 20 degrees Kelvin. pressure does not have a significant effect on the thermal conductivity of Helium. In figures 1 and 2 the four isobaric curves are indistinguishable. This is also evident from the numeric data in table 1. Comparing the thermal conductivity of any particular row in table I, the thermal conductivity does not change by more than one percent from one column to another. Below 20K, the curves begin to diverge as they approach the saturation dome. This affect is more pronounced at pressures above the critical pressure of 0.23MPa, At which point the fluid is neither a liqUid or vapor. At pressures between atmospheriC pressure and 0.01 MPa, the thermal conductivity of Helium is independent of pressure below 20K as well as above 20K.

Clark, D.; /Fermilab

1992-08-26

100

Manufacturing cycle for pure neon-helium mixture production  

International Nuclear Information System (INIS)

The manufacturing cycle for pure neon-helium mixture production with JA-300 nitrogen air distributing device has been developed. Gas mixture containing 2-3% of neon-helium mixture (the rest is mainly nitrogen 96-97%) is selected out of the cover of the JA-300 column condensator and enters the deflegmator under the 2.3-2.5 atm. pressure. The diflegmator presents a heat exchange apparatus in which at 78 K liquid nitrogen the condensation of nitrogen from the mixture of gases entering from the JA-300 column takes place. The enriched gas mixture containing 65-70% of neon-helium mixture and 30-35% of nitrogen goes out from the deflegmator. This enriched neon-helium mixture enters the gasgoeder for impure (65-70%) neon-helium mixture. Full cleaning of-neon helium mixture of nitrogen is performed by means of an adsorber. As adsorbent an activated coal has been used. Adsorption occurs at the 78 K temperature of liquid nitrogen and pressure P=0.1 atm. As activated coal cooled down to nitrogen temperature adsorbs nitrogen better than neon and helium, the nitrogen from the mixture is completely adsorbed. Pure neon-helium mixture from the adsorber comes into a separate gasgolder. In one campaign the cycle allows obtaining 2 m3 of the mixture. The mixture contains 0.14% of nitrogen, 0.01% of oxygen and 0.06% of hydrogen

1980-01-01

 
 
 
 
101

Helium molecules within carbon nanotubes  

International Nuclear Information System (INIS)

The ground-state properties of 3He and 4He dimers and trimers in infinite carbon nanotubes are studied. The ground state eigen-functions of a helium atom in tubes of different radii are obtained numerically and then fitted by analytic expressions. Total wave function is assumed to be a product of Jastrow-Feenberg pair correlation and one particle functions. After extensive Monte Carlo (MC) calculation in two successive stages, simple variational MC and diffusion MC it is found that binding depends on the tube radius and it has the maximum for a certain tube width. This radius is between 5 and 7 Angst, and the average distance between atoms in such tubes is ranges from 5 to 10 Angst. The difference in binding between bosons and fermions disappears for R?0

2003-05-01

102

Use of helium in uranium exploration, Grants district  

International Nuclear Information System (INIS)

The continuous generation of inert helium gas from uranium and its daughter products provides a potentially useful means for remote detection of uranium deposits. The practicality of conducting helium surveys in the atmosphere, soil gas, and ground water to explore for buried uranium deposits has been tested in the Grants district and in the Powder River Basin of Wyoming. No detectable helium anomalies related to buried or surface uranium deposits were found in the atmosphere. However, reproducible helium-in-soil-gas anomalies were detected spatially related to uranium deposits buried from 50 to 800 ft deep. Diurnal and atmospheric effects can cause helium content variations (noise) in soil gas that are as great as the anomalies observed from instantaneous soil-gas samples. Cumulative soil-gas helium analyses, such as those obtained from collecting undisturbed soil samples and degassing them in the laboratory, may reveal anomalies from 5 to 100 percent above background. Ground water samples from the Grants district, New Mexico, and the Powder River Basin, Wyoming, have distinctly anomalous helium values spatially related to buried uranium deposits. In the southern Powder River Basin, helium values 20 to 200 percent above background occur 2 to 18 mile down the ground-water flow path from known uranium roll-front deposits. In the Grants district, helium contents 40 to 700 percent above background levels are present in ground waters from the host sandstone in the vicinity of uranium deposits and from aquifers up to 3,000 ft stratigraphically above the deep uranium deposits. The use of helium in soil and ground-water surveys, along with uranium and radon analyses of the same materials, is strongly recommended is expensive, deep, uranium-exploration programs such as those being conducted in the Grants district

1979-05-16

103

Helium, Carbon, and Helium Isotopes in the Northern Lau Basin  

Science.gov (United States)

Helium isotope ratios in hydrothermal fluids and volcanic rocks in the northern Lau Basin show a complex pattern reflecting influences from diverse mantle sources, including the Samoan hotspot, the Tofua Arc, and mid-ocean ridge (MOR)-type upper mantle. The Samoan Islands represent a “high 3He” hotspot with 3He/4He ratios up to 38 Ra (where Ra is the 3He/4He ratio in air, 1.39 x 10-6) [Farley et al, 1992; Jackson et al., 2007]. In contrast to the 3He-rich helium in Samoa, typical back-arc spreading centers have MOR-type helium values of 7-9 Ra, while volcanic arcs have lower ratios of 5-7 Ra. In the northwestern part of the Lau Basin, basalt samples from the Northwest Lau Spreading Center and the Rochambeau Rifts have 3He/4He varying from 11 to 28 Ra, far above typical back-arc or MOR values. These elevated 3He/4He ratios indicate that the Samoan hotspot signal has somehow penetrated southward into the northern Lau Basin, presumably through a tear in the subducting Pacific Plate. In the northeastern Lau Basin, 3He/4He ratios in hydrothermal fluids from two sites on the Northeast Lau Spreading Center have 3He/4He of 8.0 and 8.7 Ra. These are MOR-type values typical for a back-arc spreading center. At the actively erupting West Mata volcano, vent fluids have 3He/4He of 7.3 Ra, while farther east at Volcano P analysis of water-column plume samples gave a value of 6.7 Ra for the estimated end-member 3He/4He value. This decrease in 3He/4He going toward the east indicates increasing arc influence with increasing proximity to the Tofua Arc. This interpretation is supported by the C/3He ratios in the hydrothermal fluids, which average 1-3 x 109 at vent sites on the NELSC (typical MOR values) and increase to a typical arc value of 2 x 1010 at West Mata. Analyses of volcanic rocks from the eruption sites on the NELSC and West Mata are in progress and should help to further define these variations.

Lupton, J. E.; Butterfield, D. A.; Lilley, M. D.; Resing, J.; Embley, R. W.; Arculus, R. J.; Rubin, K. H.; Evans, L.; Greene, R.

2009-12-01

104

Electron collisions with metastable helium  

Energy Technology Data Exchange (ETDEWEB)

Measurements and theoretical studies of electron scattering from the metastable 2{sup 1,3}S excited states of helium are briefly reviewed. A high resolution hemispherical electron spectrometer with a position sensitive detector, developed for the study of low energy differential scattering from metastable excited states is discussed in detail. This assisted in the measurement of excitation processes characterised by extremely low count rates. The first results of angular distributions for electrons superelastically scattered from the 2{sup 1,3}S states at incident energies of 5, 10 and 30 eV are presented. They have been normalised in magnitude to the convergent close coupling calculation. Cross sections from a 29-state R-matrix calculation and the first order many body theory calculation are also included for comparison. These measurements are in excellent agreement with the convergent close coupling calculations of Bray et al. (1994). 28 refs., 4 figs.

Jacka, M.; Kelly, J.; Lohmann, B.; Buckman, S. [Australian National Univ., Canberra, ACT (Australia). Research School of Physical Sciences

1996-06-01

105

Reciprocating magnetic refrigerator for helium liquefaction  

International Nuclear Information System (INIS)

We have developed a reciprocating magnetic refigerator for liquefying helium from a temperature in the 15 K region. The working material (gadolinium-gallium-garnet (GGG) single crystal, 30 mm in diameter and 40 mm in length) is placed at the end of the piston. When GGG is placed in a high-intensity magnetic field (4.5 T), its temperature rises to 15 K. The inner surface of the cylinder is cooled by an auxiliary refrigerator; the generated heat is removed through the narrow gap between GGG and cylinder (less than 50 um in the 15 K region) filled with gaseous helium. When the magnetic field in the GGG is eliminated by moving the piston, the GGG temperature falls below 4.2 K and the refrigeration occurs by condensing the helium on the GGG surface. Technical emphasis was placed on the realization of a high heat exchange rate between GGG and gaseous helium. A sufficient heat transfer rate was achieved after several component level experiments. Sources of inefficiency to the refrigeration power has been also discussed. Finally a refrigeration power of 0.95 W at 4.2 K was achieved in 0.38 Hz operation by a reciprocating magnetic refrigerator equiped with two pistons

1986-01-01

106

Helium abundance in the Orion A source  

International Nuclear Information System (INIS)

The H, He 66? (22.4 GHz) and H, He 56? (36.5 GHz) recombination line observations were made at several positions of the central region of Orion A (R ? 3'). The observed relative helium abundance y' is found to increase with the angular distance from the nebular centre and to amount the mean value of 11.6% at the peripherycal positions. The comparison with the results of low frequency observations (H, He 109?, ? ? 5.0 GHz) shows that measurements towards the centre (y'=8-9%) is in agreement with the low frequency measurements of y', however y' at the peripherycal positions are higher than that at low frequency. The nebula model of a ''blister'' type is constructed to explain such behaviour. The conclusions are made that the actual helium abundance y in Orion A is ? 12%, the Orion Nebula expands and its radial velocity is ? 5 km/s

1986-11-01

107

Study of expansion of solid Helium-4 into vacuum  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This work gives a detailed introduction into a fully new experimental method to investigate the quantum crystal behavior of solid Helium-4. It has been found that a fascinating new effect occurs in the expansion of solid Helium-4 into a vacuum through pinhole orifices with diameters between 1 and 5 µm. It is observed that the beam flux intensity shows a periodic behavior for source conditions corresponding to the solid phase of Helium-4. The period is in the range of seconds up to minutes. I...

Ka?sz, Manuel

2006-01-01

108

Method and apparatus for direct determination of helium-3 in natural gas and helium  

Energy Technology Data Exchange (ETDEWEB)

The authors present a method for determining the helium-3({sup 3}He) content of natural gas and mixtures containing 0.5 to 100 pct helium. The helium is preconcentrated by passing samples through anhydrone, a liquid-nitrogen-cooled charcoal trap, and a titanium absorption trap. The mass spectrometer used to analyze the samples is tuned to {sup 3}He at m/e = 3.016. Hydrogen deuteride (HD{sup +}) interference is minimized by the titanium absorption trap and high instrument resolution. Sample measurements are compared with identically made measurements of a gravimetrically prepared primary standard. The method has a limit of detection of 0.15 ppb with a relative deviation of 13 pct below the 1-ppb level.

Davidson, T.A.; Emerson, D.E.

1990-01-01

109

Neon-helium refrigerator  

International Nuclear Information System (INIS)

To construct economical facilities of preliminary cooling a neon-helium refrigerator is designed and produced in Which a generator gas (helium) is successively cooled at three temperature levels - 78 K, 64 K and 28 K. The first two levels are ensUred by liquid nitrogen, and the third one by a throttle neon refrigerator of 400 W cooling capacity at the 28 K level, at the 45 m"3/h neon compressor capacity. The rig trials of the refrigerator were carried out. Its real cooling capacity was 270 W while working with a compressor at the 31 m"3/h capacity. This fact is in good agreement with the calculations taking into account that the practical neon compressor capacity is less than the calculated one. The refrigerator efficiency depending on the cooling object temperature is calculated. The optimal cooling conditions are determined from the power point of view. The dynamics of object cooling is considered. It is shown that when utilizing multi-stage cooling of cryogenic objects it is necessary to determine optimal temperatures of transition from one cooling stage to another, that permits to minimize expenditure of energy during cooling process

1980-01-01

110

Tensile behavior of helium charged V?Ti?Cr?Si type alloys  

Science.gov (United States)

Helium effect on the mechanical properties of the alloy V?5Ti?5Cr?1Si?Al,Y (nominal) was studied, adopting various helium charging methods and helium-to-dpa ratio. The first method was helium ion implantation using a cyclotron accelerator at Tohoku University, where helium and displacement levels were 50 appm and 0.02 dpa, respectively. The second, helium was charged by tritium trick technique and following neutron irradiation in FFTF/MOTA-2A, associated with about 80 appm He and 43 dpa. The third was dynamic helium charging experiment (DHCE) conducted in FFTF/MOTA-2B, where helium was generated within specimens during neutron irradiation by tritium decay, and the helium-to-dpa ratio was adjusted to simulate the fusion reactor condition, that is, 177 appm He and 24 dpa. The effect of helium on tensile properties of the V?Ti?Cr?Si?Al,Y alloy depended on the helium charging methods. The uniform elongation of the alloy was 3.2% and total elongation was 8.3% at DHCE condition, which was the most fusion relevant condition of the methods. It is important that tensile properties of the present alloy could be acceptable for fusion reactor component materials.

Satou, M.; Koide, H.; Hasegawa, A.; Abe, K.; Kayano, H.; Matsui, H.

1996-10-01

111

Quantum cavitation in liquid helium  

CERN Multimedia

Using a functional-integral approach, we have determined the temperature below which cavitation in liquid helium is driven by thermally assisted quantum tunneling. For both helium isotopes, we have obtained the crossover temperature in the whole range of allowed negative p essures. Our results are compatible with recent experimental results on 4He.

Guilleumas, M; Jezek, D M; Lombard, R J; Pi, M

1996-01-01

112

Helium transport scaling law studies.  

Science.gov (United States)

Impurity behavior within the tokamak fusion plasma will be a main concern for the future tokamak operation such as ITER. Thermalized alpha particles, i.e., helium ''ashes'' constitute a key impurity within the plasma core. The helium ash accumulation with...

J. Guo G. H. Miley

1992-01-01

113

Evaluation of helium cooling for fusion divertors  

International Nuclear Information System (INIS)

The divertors of future fusion reactors will have a power throughput of several hundred MW. The peak heat flux on the diverter surface is estimated to be 5 to 15 MW/m"2 at an average heat flux of 2 MW/m"2. The divertors have a requirement of both minimum temperature (100 degrees C) and maximum temperature. The minimum temperature is dictated by the requirement to reduce the absorption of plasma, and the maximum temperature is determined by the thermo-mechanical properties of the plasma facing materials. Coolants that have been considered for fusion reactors are water, liquid metals and helium. Helium cooling has been shown to be very attractive from safety and other considerations. Helium is chemically and neutronically inert and is suitable for power conversion. The challenges associated with helium cooling are: (1) Manifold sizes; (2) Pumping power; and (3) Leak prevention. In this paper the first two of the above design issues are addressed. A variety of heat transfer enhancement techniques are considered to demonstrate that the manifold sizes and the pumping power can be reduced to acceptable levels. A helium-cooled diverter module was designed and fabricated by GA for steady-state heat flux of 10 MW/m"2. This module was recently tested at Sandia National Laboratories. At an inlet pressure of 4 MPa, the module was tested at a steady-state heat flux of 10 MW/m"2. The pumping power required was less than 1% of the power removed. These results verified the design prediction

1993-09-13

114

Ultralow temperature helium compressor for Japan Atomic Energy Research Institute  

International Nuclear Information System (INIS)

Ishikawajima Harima Heavy Industries Co., Ltd. started the development of an ultralow temperature helium compressor for helium liquefaction in 1984 jointly with Japan Atomic Energy Research Institute, and has delivered the first practical machine to the Superconductive Magnet Laboratory of JAERI. For a large superconductive magnet to be used in the stable state for a fusion reactor, conventional superconductive materials (NbTi, NbTi3Sn, etc.) must be used, being cooled forcibly with supercritical helium. The supercritical helium which is compressed above the critical pressure of 228 kPa has a stable cooling effect since the thermal conductivity does not change due to the evaporation of liquid helium. In order to maintain the temperature of the supercritical helium below 4 K before it enters a magnet, a heat exchanger is used. The compressor that IHI has developed has the ability to reduce the vapor pressure of liquid helium from atmospheric pressure to 50.7 kPa, and can attain the temperature of 3.5 K. The specification of this single stage centrifugal compressor is: mass flow rate 25 - 64 g/s, speed 80,000 rpm, adiabatic efficiency 62 - 69 %. The structure and the performance are reported. (K.I.)

1988-01-01

115

Study on Helium Blanketing Effect of Hydrogen-Storage Alloy  

International Nuclear Information System (INIS)

The Helium blanketing effect on LaNi5-xAlx and ZrCo alloy is researched. Hydrogen absorption and desorption change due to gaseous helium has been investigated by the serial experiments under different conditions. Helium reduces hydrogen absorption and desorption rate, but it would not change the ultimate quantities of hydrogen absorption and desorption. The surface electron spectrum of LaNi5-xAlx was examined by a multi-functional spectrometer. The examination shows that inert gas would not affect the electron state of the alloy surface and also the decomposition and absorption course of hydrogen molecule on the alloy surface. The research shows that Helium blanketing course is divided into two stages of 'bulk flow' and 'diffusion flow'. After reaching the blanketing pressure the microcosmic course is molecule migration controlled by diffusion

2005-07-01

116

The Hall D solenoid helium refrigeration system at JLab  

Energy Technology Data Exchange (ETDEWEB)

Hall D, the new Jefferson Lab experimental facility built for the 12GeV upgrade, features a LASS 1.85 m bore solenoid magnet supported by a 4.5 K helium refrigerator system. This system consists of a CTI 2800 4.5 K refrigerator cold box, three 150 hp screw compressors, helium gas management and storage, and liquid helium and nitrogen storage for stand-alone operation. The magnet interfaces with the cryo refrigeration system through an LN2-shielded distribution box and transfer line system, both designed and fabricated by JLab. The distribution box uses a thermo siphon design to respectively cool four magnet coils and shields with liquid helium and nitrogen. We describe the salient design features of the cryo system and discuss our recent commissioning experience.

Laverdure, Nathaniel A. [JLAB; Creel, Jonathan D. [JLAB; Dixon, Kelly d. [JLAB; Ganni, Venkatarao [JLAB; Martin, Floyd D. [JLAB; Norton, Robert O. [JLAB; Radovic, Sasa [JLAB

2014-01-01

117

Pion productions by proton and Helium-3 on Au197 target at beam energies of 2.8, 5, 10 and 16.587 GeV/nucleon  

CERN Document Server

Based on a Relativistic Boltzmann-Uehling- Uhlenbeck transport model, proton and $^{3}$He induced reactions on $^{197}$Au target at beam energies of 2.8, 5, 10 and 16.587 GeV/nucleon are studied. It is found that compared with proton induced reaction, $^{3}$He induced reaction gives a large cross section of pion production, about 5 times larger than proton induced reaction. And more importantly, pion production from $^{3}$He induced reaction is more inclined to low-angle emission. Neutrino production via positively charged pion is also discussed accordingly.

Yong, Gao-Chan; Xu, Hu-Shan; Zuo, Wei

2011-01-01

118

The Application and Improvement of Helium Turbines in the EAST Cryogenic System  

Science.gov (United States)

The helium cryogenic system supplies supercritical helium cooling capacity at 4.5 K for the superconducting magnets in the EAST superconducting tokamak. Four low-temperature helium turbines are used in the 2 kW helium refrigeration system, and their performance and reliability are critical for the continuous operation of the tokamak. The turbines were made by the Helium Mechanics Company in Russia. The start-up process is very unstable, easily broken, and thus testing and improvements are needed. In this paper, we analyze the structure of the helium turbine, make improvements, and describe the testing process and results of the improved helium turbines. Some of the operational experiences during the start-up process and tests are also presented.

Fu, Bao; Zhang, Qiyong; Zhu, Ping; Cheng, Anyi

2014-05-01

119

CERN Technical Training 2002: Learning for the LHC! HEREF-2002 : HELIUM REFRIGERATION TECHNIQUES  

CERN Multimedia

Theory, Technology, Maintenance and Control of Helium Refrigerators HeREF-2002 is a new course, in the framework of the 2002 Technical Training Programme, that will provide a complete introduction to Helium refrigeration, with a practical approach to theory, technology, maintenance and control of Helium refrigeration installations. Theoretical aspects and equations will be limited to a minimum. HeREF-2002 targets an audience of technicians and operators of Helium refrigeration plants at CERN, as well as physicists and engineers needing an overview of current Helium refrigeration techniques. HeREF-2002 will address, among other, issues related to component technology, installation maintenance, process control and Helium purity. A commented visit to a couple of CERN Helium refrigeration or liquefaction plants will also take place. Duration: 7 half days (5 mornings and 2 afternoons), 21-25 October, 2002. Estimated cost: 300.- CHF Language: Bilingual English-French. The course support will be in English, the ...

Davide Vitè

2002-01-01

120

Phase and density dependence of the delayed annihilation of metastable antiprotonic helium atoms in gas, liquid, and solid helium  

International Nuclear Information System (INIS)

Systematic studies of the phase and density dependence of the delayed annihilation time spectra of antiprotons (DATS) in gaseous, liquid, and solid helium have been performed using the low energy antiproton ring at CERN. The results show a small but significant dependence of DATS on the phase and density of the helium medium. The average lifetime of antiprotons (Tav) in gas at 10--30 K was found to be 4.03±0.02 ?s. In liquid helium Tav decreases with density from 3.0 ?s at 1 bar to 2.5 ?s at 60 bars, while in solid helium its value is 2.14±0.03 ?s, 20% shorter than that in liquid helium of the same density. There is no change of DATS betweeen normal 1-bar liquid and superfluid helium. An isotope effect between 4He and 3He similar to the one previously observed in the gas phase has also been found for liquid helium. All the data can be fitted fairly well with a simple three-level chain decay model with describes the general structure of DATS, characterized by downaward curving behavior on a logarithmic scale at later times and by the presence of a short-lived component. No delayed annihilation was observed in lithium

1995-04-01

 
 
 
 
121

Helium atoms in interstellar and interplanetary medium  

International Nuclear Information System (INIS)

According to the data of measurements of brightness distribution in the line of atomary helium lambda 584 A made in the interplanetary space at the ''Prognoz-6'' satellite, the direction of motion of interstellar gas relatively to the Sun is determined. Coordinates of a velocity vector in projection to the nel:bular sphere equa right ascension a=77+-2 deg, declination ?=17+-2.5 deg

1984-01-01

122

Correlation of Helium Solubility in Liquid Nitrogen  

Science.gov (United States)

A correlation has been developed for the equilibrium mole fraction of soluble gaseous helium in liquid nitrogen as a function of temperature and pressure. Experimental solubility data was compiled and provided by National Institute of Standards and Technology (NIST). Data from six sources was used to develop a correlation within the range of 0.5 to 9.9 MPa and 72.0 to 119.6 K. The relative standard deviation of the correlation is 6.9 percent.

VanDresar, Neil T.; Zimmerli, Gregory A.

2012-01-01

123

Modeling Space-Time Dependent Helium Bubble Evolution in Tungsten Armor under IFE Conditions  

International Nuclear Information System (INIS)

The High Average Power Laser (HAPL) program is a coordinated effort to develop Laser Inertial Fusion Energy. The implosion of the D-T target produces a spectrum of neutrons, X-rays, and charged particles, which arrive at the first wall (FW) at different times within about 2.5 ?s at a frequency of 5 to 10 Hz. Helium is one of several high-energy charged particle constituents impinging on the candidate tungsten armored low activation ferritic steel First Wall. The spread of the implanted debris and burn helium energies results in a unique space-time dependent implantation profile that spans about 10 ?m in tungsten. Co-implantation of X-rays and other ions results in spatially dependent damage profiles and rapid space-time dependent temperature spikes and gradients. The rate of helium transport and helium bubble formation will vary significantly throughout the implanted region. Furthermore, helium will also be transported via the migration of helium bubbles and non-equilibrium helium-vacancy clusters. The HEROS code was developed at UCLA to model the spatial and time-dependent helium bubble nucleation, growth, coalescence, and migration under transient damage rates and transient temperature gradients. The HEROS code is based on kinetic rate theory, which includes clustering of helium and vacancies, helium mobility, helium-vacancy cluster stability, cavity nucleation and growth and other microstructural features such as interstitial loop evolution, grain boundaries, and precipitates. The HEROS code is based on space-time discretization of reaction-diffusion type equations to account for migration of mobile species between neighboring bins as single atoms, clusters, or bubbles. HAPL chamber FW implantation conditions are used to model helium bubble evolution in the implanted tungsten. Helium recycling rate predictions are compared with experimental results of helium ion implantation experiments. (author)

2006-09-11

124

Study on the hydrogen and helium isotope yields from Ni58, Ni64 targets at the interaction with 7.5 GeV protons  

International Nuclear Information System (INIS)

To find isotope effects studied are the yield of p,d,t, 3He and 4He secondary slow light particles from the 58Ni and 64Ni isotopes while bombarding them by protons with the 7.5 GeV energy. Proton beam intensity reached 5x209 particles in one acceleration cycle outler. The outlet temporal extending was equal to 300 ms. 58Ni and 64Ni tangets were metal foils with the width of 8 mg/cm2.; the main isotopote amount was equal to 95 and 90%, respectively. Shortly described is the block diagram of electronics operating on-line with the BESM-4 computer. Secondary particles spectra are obtained in the following ranges: protons - from 4 to 18.5 Mev, deuterons - from 4.0 to 26 MeV, tritons - from 4.0 to 28 MeV, 3He, 4He - from 11 to 58 MeV. The process the psectra the simpliest variant of the nuclear particle evaporation statistical theory is used, i.e. evaporation approximation. It is found out from the comparison with the experimental results while using bombariding proton energy of 660 MeV, that at the proton energy of 7.5 GeV relative deuteron and triton yield are approximately two times higher; for 3He they almost coincide. The differences observed in relative yields of d and t are connected perhaps with the differences in secondary particle initiation processes at the transition of bombarding particle energy from 0.66 ot 7.5 GeV. The relation between neutron exceesses of nucleus-target and nucleus-product is noted, i.e. relative proton yield form 64Ni is decreased, whereas that of tritons is increased in comparison whith 58Ni target. In energy spectra the isotope effect exhibits itself in the fact that spectra of p, d, t, 3He secondary particles are not more harder for 64Ni target

1978-01-01

125

Excitations in confined helium  

CERN Multimedia

We design models for helium in matrices like aerogel, Vycor or Geltech from a manifestly microscopic point of view. For that purpose, we calculate the dynamic structure function of 4He on Si substrates and between two Si walls as a function of energy, momentum transfer, and the scattering angle. The angle--averaged results are in good agreement with the neutron scattering data; the remaining differences can be attributed to the simplified model used here for the complex pore structure of the materials. A focus of the present work is the detailed identification of coexisting layer modes and bulk--like excitations, and, in the case of thick films, ripplon excitations. Involving essentially two--dimensional motion of atoms, the layer modes are sensitive to the scattering angle.

Apaja, V

2003-01-01

126

Photoionization of helium dimers  

International Nuclear Information System (INIS)

The helium dimer is one of the most weakly bound systems in the universe. This makes it an interesting quantum mechanical object for investigation. These Van der Waals Clusters can be produced in an expansion of a cryogenic gas jet through a small nozzle into vacuum. In the present experiment we examine the interaction of He dimers with synchrotron radiation at an energy range from 64 to 78 eV. We observed different pathways leading to single ionization of both He atoms of the dimer compound. This two close standing ions begin now to dissociate in cause of their coulomb potential. All charged fragments were detected in coincidence with a COLTRIMS system. Especially Interatomic Coulombic Decay (ICD) and the two step process (TS1) were clearly identified. Furthermore a distribution of the internuclear distance was obtained from the measured Kinetic Energy Release (KER). (orig.)

2010-01-01

127

Exotic helium molecules  

International Nuclear Information System (INIS)

We study the photo-association of an ultracold cloud of magnetically trapped helium atoms: pairs of colliding atoms interact with one or two laser fields to produce a purely long range 4He2(23S1-23P0) molecule, or a 4He2(23S1-23S1) long range molecule. Light shifts in one photon photo-association spectra are measured and studied as a function of the laser polarization and intensity, and the vibrational state of the excited molecule. They result from the light-induced coupling between the excited molecule, and bound and scattering states of the interaction between two metastable atoms. Their analysis leads to the determination of the scattering length a = (7.2 ± 0.6) ruling collisions between spin polarized atoms. The two photon photo-association spectra show evidence of the production of polarized, long-range 4He2(23S1-23S1) molecules. They are said to be exotic as they are made of two metastable atoms, each one carrying a enough energy to ionize the other. The corresponding lineshapes are calculated and decomposed in sums and products of Breit-Wigner and Fano profiles associated to one and two photon processes. The experimental spectra are fit, and an intrinsic lifetime ? = (1.4 ± 0.3) ?s is deduced. It is checked whether this lifetime could be limited by spin-dipole induced Penning autoionization. This interpretation requires that there is a quasi-bound state close to the dissociation threshold in the singlet interaction potential between metastable helium atoms for the theory to match the experiment. (author)

2007-01-01

128

Transition probabilities for the helium singly excited states 1snl/sup 1//sup ,//sup 3/L with n = 2--21 and l = 0. 5  

Energy Technology Data Exchange (ETDEWEB)

Theoretical dipole transition probabilities, oscillator strengths, lifetimes, and branching ratios are presented for all transitions between states of the He 1snl series with nless than or equal to21 for singlet and less than or equal to22 for triplet states, and lless than or equal to5. The experimental wavelengths are also tabulated. The calculations were performed by a recently developed approach which combines the traditional Coulomb approximation with the representation of the atomic core by a realistic central-field potential. copyright 1987 Academic Press, Inc.

Theodosiou, C.E.

1987-01-01

129

Effect of radiation damage in thermal desorption of helium from the ferritic-martensitic steel EP-450  

International Nuclear Information System (INIS)

The results of the study of helium thermal desorption from polycrystalline samples of steel EP-450 implanted helium ions with energy of 12 keV to doses (5 - 10 1016 cm-2 are given. The effect of precreated damage to the spectra of helium is considered. A comparison of temperature intervals of helium desorption from the ferriticmartensitic steel EP-450, nickel and iron are conducted.

2012-01-01

130

Five second helium neutral beam injection using argon-frost cryopumping techniques  

International Nuclear Information System (INIS)

High power helium neutral beams for the heating of tokamak discharges can now be provided for 5 s by using argon cryopumping (of the helium gas) in the beamlines. A system has now been installed to deposit a layer of argon frost on the DIII-D neutral beam cryopanels, between tokamak injection pulses. The layer serves to trap helium on the cryopanels providing sufficient pumping speed for 5 s helium beam extraction. The argon frosting hardware is now present on two of four DIII-D neutral beamlines, allowing injection of up to 6 MW of helium neutral beams per discharge, with pulse lengths of up to 5 s. The argon frosting system is described, along with experimental results demonstrating its effectiveness as a method of economically extending the capabilities of cryogenic pumping panels to allow multi-second helium neutral beam injection

1995-10-01

131

Electronic properties of physisorbed helium  

Energy Technology Data Exchange (ETDEWEB)

This thesis deals with electronic excitations of helium physisorbed on metal substrates. It is studied to what extent the electronic properties change compared to the gas phase due to the increased helium density and the proximity of the metal. Furthermore, the influence of different substrate materials is investigated systematically. To this end, up to two helium layers were adsorbed onto Ru (001), Pt (111), Cu (111), and Ag (111) surfaces in a custom-made cryostat. These samples were studied spectroscopically using synchrotron radiation and a time-of-flight detector. The experimental results were then analyzed in comparison with extensive theoretical model calculations.

Kossler, Sarah

2011-09-22

132

Ion implantation of helium in silicon carbide, 2  

International Nuclear Information System (INIS)

Silicon carbide was implanted at room temperature and 600 "0C with helium ions with continuous energy distribution ranging from 0.5 keV to 20 keV up to a total fluence of 1 x 10"1"9 ions/cm"2 using an ion accelerator controlled by a microcomputer. It was shown that the surface deformation depended ramarkably not only on the implantation profile, but also on irradiation modes of helium ions. Flaking was completely avoided by prebombardment of helium ions with continuous energy distribution, which deliberately produced a pathway for gas release. In order to simulate wall erosion due to helium bombardment in fusion reactors, SiC was also irradiated with Maxwellian distribution. No blistering or flaking was observed for an average energy of 3 kev. (author)

1985-01-01

133

The influence of electrostatic fields on films of liquid helium  

International Nuclear Information System (INIS)

Prompted by the recent striking experimental results reported by Babkin and Hakonen that appeared to show that liquid helium-II does not wet magnesium fluoride, the authors have examined the effects that an inhomogeneous electrostatic field has on thin films of liquid helium at temperatures below 0.5 K. Their model includes the influence of gravity, surface tension, the electric field and the van der Waals interaction between the helium and its supporting substrate. The authors show that an inhomogeneous charge on the substrate can produce effects that mimic the surface profiles between wetted and non-wetted areas. The calculations also indicate that some special precautions may be necessary when studying films of liquid or solid helium on insulators

1996-01-01

134

The influence of electrostatic fields on films of liquid helium  

Science.gov (United States)

Prompted by the recent striking experimental results reported by Babkin and Hakonen that appeared to show that liquid helium-II does not wet magnesium fluoride, we have examined the effects that an inhomogeneous electrostatic field has on thin films of liquid helium at temperatures below 0.5K. Our model includes the influence of gravity, surface tension, the electric field and the van der Waals interaction between the helium and its supporting substrate. We show that, an inhomogeneous charge on the substrate can produce effects that mimic the surface profiles between wetted and non-wetted areas. The calculations also indicate that some special precautions may be necessary when studying films of liquid or solid helium on insulators.

Williams, C. D. H.; Wyatt, A. F. G.

1996-01-01

135

Continuous-flow helium cryostat for electron irradiation  

International Nuclear Information System (INIS)

A continuous-flow/helium cryostat for the irradiation of materials with high energy electrons up to 50 ?A/cm2 beam density and subsequent annealing in the range 4.2- 500 K is described. During operation liquid helium is fed from a large storage vessel through a flexible vacuum-insulated transfer line. The cryostat design allows the storage vessel to be replaced without warming the samples. This eliminates any limitation on the length of continuous operation. In the range 150-500 K it is possible to use helium gas with either external cooling or internal heating. Helium consumption is up to 5 1/h (liquid) or 10 m3/h (gas) depending on the irradiation temperature and heat evolved in the irradiation zone. (Author)

1992-01-01

136

Thermal conductivity of the helium-argon system  

International Nuclear Information System (INIS)

A semiempirical relation for the thermal conductivity of helium--argon gas mixtures is suggested. The analyses used in support of the proposed conductivity relations are based on low-temperature (T 0C) thermal conductivity data for helium, argon and helium--argon mixtures. The report is a compilation of available data and theories, and does not contain any new experimental results. With the approach presented here, one should be able to predict thermal conductivities of helium--argon mixtures to within 5% of their true values for temperatures up to 1200 K. The recommended equations are best estimates and should be treated as such. A definite need exists for experimental data to verify or modify the recommendation

1979-01-01

137

Energy of helium dissolved in metals  

International Nuclear Information System (INIS)

An explanation for the large negative heat of solution of helium in metals, in terms of the strong repulsive helium pseudopotential interacting with the metal conduction electrons is proposed. Calculations for helium in aluminium and magnesium show that this mechanism indeed generates the expected negative heats. It is expected that the helium atoms will always seek out the site of lowest charge density. (author)

1976-01-01

138

A pool type liquid helium cryopump  

International Nuclear Information System (INIS)

Design and fabrication details of a pool type Liquid Helium Cryopump are described. It has got a liquid helium capacity of 5 litres and a/ pumping surface area of about 450 sq. cms. Three types of baffles having different geometries are used for radiation shield. Effect on pumping speed for argon, carbon dioxide and nitrogen gas using the baffles is determined at various pressures. The circular array baffle geometry provides the maximum pumping speed. Using circular array type baffle the maximum pumping speed for nitrogen, argon and carbon dioxide are 2700 1/s, 3600 1/s, 2550 1/s respectively at a pressure of 6.0 x 10"-"4 torr. The ultimate pressure obtained is 3.0 x 10"-"8 torr. (author)

1986-01-01

139

Random walk of helium bubbles in vanadium  

International Nuclear Information System (INIS)

Helium bubbles will be generated in the first wall of any fusion reactor. These bubbles will either cause swelling and embrittlement in their own right or act as precursors to a population of voids, depending on the temperature and various irradiation and material parameters. Bubbles can, in principle, grow either by the re-solution and re-precipitation of the inert gas (ripening) or by migration and coalescence. We have studied the growth of bubbles arising from the room temperature implantation of helium to a concentration of 5 x 10_2_6He/m_3 in Vanadium. We demonstrate in this paper that during isothermal annealing at 950 deg C (0.55 Tsub(m)) faceted helium bubbles undergo Brownian motion and grow only by coalescence. No bubble was observed to shrink and hence ripening can be ruled out. The rate controlling process which limits the migration and hence growth rate at this temperature could be surface diffusion or the nucleation of ledges on bubble facets. We conclude both from our hot stage electron microscope observations and from isothermal annealing of bulk specimens that ledge nucleation is rate limiting even for bubbles less than 10 nm in size. The energy of a monatomic ledge on a brace 100 brace surface in Vanadium is deduced to lie between 3 and 5 x 10"-_1_1 J/m. (author)

1981-01-01

140

Two-photon spectroscopy of antiprotonic helium  

Science.gov (United States)

The precision of laser spectroscopy of antiprotonic helium (a helium atom with one of its electrons replaced by an antiproton) has improved by almost 4 orders of magnitude over its 20 years of history. Experimental transition frequencies can be compared to 3-body QED calculations to derive the antiproton-electron mass ratio. In the latest measurements of the Asacusa experiment at CERN, two-photon transitions of antiprotonic helium were excited using two counter-propagating laser beams. This method reduces the Doppler-broadening caused by the thermal motion of the atoms, and allowed us to measure the transition frequencies with a fractional precision of 2.5-5 parts in 109. From these frequencies, we derived an antiproton-electron mass ratio of 1836.1526736(23). Our precision approaches that of the experimental value of the proton-electron mass ratio, and agrees with the latter within errors. Assuming CPT symmetry (i.e. mp=m_{overline {p}}), we further derived the electron's atomic mass as m e = 0.0005485799091(7)u from the more accurately known atomic mass of the proton.

Barna, Dániel

2014-04-01

 
 
 
 
141

Ion implantation of helium in silicon carbide, 1  

International Nuclear Information System (INIS)

The surface damage of CVD and sintered SiC induced by helium implantation at energies of 1 to 20 keV and fluence up to 10"1"9 ions/cm"2 was studied by measuring helium depth profile and gas reemission behavior. The depth profiles were determined with a depth resolution of less than 100A using a new mehtod based on a combination of ion sputtering and helium desorption. The profiles for implantation at fluence below 5 x 10"1"6 ions/cm"2 were in good agreement with theoretical predictions. Double-peaked profiles obtained at a fluence of 1 x 10"1"7 ions/cm"2 were associated with the formation of helium gas bubbles at the most probable range. The critical fluence for blister and/or flaking formation was found to lie between 2 and 4 x 10"1"7 ions/cm"2, except for implantation energy below 5 keV. The surface topographic change was shown to be correlated closely with the helium gas reemission behavior during implantation. The flaking of SiC was explained by crack propagation through the implanted layer, with gas pressure being the driving force for cracking. The effects of the grain-boudary diffusion of implanted helium on the surface damage were also described. (author)

1985-01-01

142

Measurement of helium production cross sections of iron for d-T neutrons by helium accumulation method  

Energy Technology Data Exchange (ETDEWEB)

Helium production cross sections of Iron were measured by helium accumulation method for neutron energies from 13.5 to 14.9 MeV. Iron samples were irradiated with FNS, an intense d-T neutron source of JAERI. As the neutron energy varies according to the emission angle at the neutron source, the samples were set around the neutron source and were irradiated by neutrons of different energy depending on each sample position. The amount of helium produced in a sample was measured by Helium Atoms Measurement System at Kyushu University. The results of this work are in good agreement with other experimental data in the literature and also compared with the evaluated values in JENDL-3. (author)

Takao, Yoshiyuki; Kanda, Yukinori; Nagae, Koji; Fujimoto, Toshihiro [Kyushu Univ., Fukuoka (Japan); Ikeda, Yujiro

1997-03-01

143

Operating Manual of Helium Refrigerator (Rev. 2)  

Energy Technology Data Exchange (ETDEWEB)

A helium refrigerator was installed as a supplier of 20K cold helium to the cryogenic distillation system of WTRF pilot plant. The operating procedures of the helium refrigerator, helium compressor and auxiliary apparatus are described for the safety and efficient operation in this manual. The function of the helium refrigerator is to remove the impurities from the compressed helium of about 250psig, to cool down the helium from ambient temperature to 20K through the heat exchanger and expansion engine and to transfer the cold helium to the cryogenic distillation system. For the smoothly operation of helium refrigerator, the preparation, the start-up, the cool-down and the shut-down of the helium refrigerator are described in this operating manual. (author). 3 refs., 14 tabs.

Song, K.M.; Son, S.H.; Kim, K.S.; Lee, S.K.; Kim, M.S. [Korea Electric Power Research Institute, Taejon (Korea)

2002-07-01

144

Energy Levels of Helium Nucleus  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Helium-4 nucleus is more similar to the Hydrogen atom of atomic physics. In the case of hydrogen atom, there are many energy levels which were experimentally seen and theoretically explained using non-r...

Cvavb Chandra Raju

2013-01-01

145

Helium embrittlement of iron-chromium alloys  

International Nuclear Information System (INIS)

The helium embrittlement of Fe-(0 to 15) wt%Cr alloys was examined with high temperature tensile testing. Helium injection was performed by using cyclotron and partly by thermal neutron irradiation with boron alloying. The helium embrittlement was severer in lower chromium alloys. Helium bubbles were observed in Fe but not in Fe-15Cr, both of which contained 24 atppm helium tested at 1023 K. (author)

1983-01-01

146

Helium shell flashes  

International Nuclear Information System (INIS)

Helium shell flashes are studied in models of Population I stars with a core mass of 0.8 M/sub sun/ and a total mass of 3 M/sub sun/ and 8 M/sub sun/. With the new type of initial conditions used in this study a full flash amplitude is achieved in just one or two flash cycles. Flash strength and interflash period are found to be independent of the envelope mass provided there is no overshoot at the base of the convective envelope. If convective overshoot is taken into account, then up to 50% of the intershell, carbon-enriched matter is mixed into the envelope following each flash in the 8 M/sub sun/ model. Convective overshoot is possible in stars with massive envelopes, but the efficiency of this process has to be considered a free parameter at this time. In any case, it is not likely that more than 10% of the intershell mass can be mixed into the envelope if the energetics of this process is taken into account

1977-06-15

147

Helium population model  

International Nuclear Information System (INIS)

Elementary processes in helium plasma are studied numerically within the framework of the radiation-scattering model. The energy states scheme used consists of ten states of the parahelium subsystem, six states of orthohelium, and the quasicontinuum state. The excitation and deexcitation due to electron collisions, to electron ionization and corresponding three-body recombination, to emission and absorption of photons, to photoionization and corresponding radiative recombination are taken into account. The global population coefficients and radiation-scattering velocities for the parahelium subsystem are computed using the TESLA 200 computer. The energy region studied is 1 to 10 eV. For electron energies up to 2 eV the populations are given by the electron-gas density and the excited states are underpopulated with respect to Saha equilibrium. For higher energies the influence of the ground and metastable states becomes more pronounced. For electron densities above 10_1_4 cm"-_3 the populations approach thermal equilibrium. (J.U.)

1981-10-01

148

Hydrogen Production Using the Modular Helium Reactor  

Energy Technology Data Exchange (ETDEWEB)

The high-temperature characteristics of the Modular Helium Reactor (MHR) make it a strong candidate for the production of hydrogen using either thermochemical or high-temperature electrolysis (HTE) processes. Using heat from the MHR to drive a Sulfur-Iodine (S-I) thermochemical hydrogen process has been the subject of a DOE sponsored Nuclear Engineering Research Initiative (NERI) project lead by General Atomics, with participation from the Idaho National Engineering and Environmental Laboratory (INEEL) and Texas A&M University. While the focus of much of the initial work was on the S-I thermochemical production of hydrogen, recent activities have also included development of a preconceptual design for an integral HTE hydrogen production plant driven by the process heat and electricity produced by a 600 MWt MHR. This paper describes RELAP5-3D analyses performed to evaluate alternative primary system cooling configurations for the MHR to minimize peak reactor vessel and core temperatures while achieving core helium outlet temperatures in the range of 900 oC to 1000 oC, needed for the efficient production of hydrogen using either the S-I thermochemical or HTE process. The cooling schemes investigated are intended to ensure peak fuel temperatures do not exceed specified limits under normal or transient upset conditions, and that reactor vessel temperatures do not exceed ASME code limits for steady-state or transient conditions using standard LWR vessel materials. Preconceptual designs for both an S-I thermochemical and HTE hydrogen production plant driven by a 600 MWt MHR at helium outlet temperatures in the range of 900 oC to 1000 oC are described and compared. An initial SAPHIRE model to evaluate the reliability, maintainablility, and availability of the S-I hydrogen production plant is also discussed, and plans for future assessments of conceptual designs for both a S-I thermochemical and HTE hydrogen production plant coupled to a 600 MWt modular helium reactor are described.

E. A. Harvego; S. M. Reza; M. Richards; A. Shenoy

2005-05-01

149

Development of ultrahigh pressure helium booster system  

International Nuclear Information System (INIS)

Operation principle, design principle, fabrication and cautions in operation of ultrahigh pressure He booster system are introduced, and main parts selection method and high pressure seal design of the booster system are discussed. The as-developed system can output 300 MPa helium gas with (3.5 ? 5.0) x 10-7 Pa · m3/s leak rate through manual or automatic pressure boosting and keeping. Main function parameters of the system are accessed and compared with those of three congeneric systems. The result shows that the system was rationally designed with superior performance and safety, and the system would be used to test ICF microsphere filling DT system. (authors)

2010-02-01

150

Helium in deep circulating groundwater in the Great Hungarian Plain: Flow dynamics and crustal and mantle helium fluxes  

Science.gov (United States)

Observed helium concentrations in deep circulating groundwater of the sedimentary basin of the Great Hungarian Plain (GHP), Hungary, cover a range of three orders of magnitude (?4 ·10 -8 to 4 · 10 -5 ccSTP g-1). 3He /4He ratios and noble gas concentrations are used to separate helium components originating from the atmosphere, tritium decay, crustal production, and mantle degassing. The characteristic distribution of measured helium concentrations and isotope ratios can be reproduced qualitatively by a simple two-dimensional advection/diffusion model. Other simple models isolating parts of the regional flow domain (recharge, discharge, and horizontal flow) are discussed and applied to derive quantitative information on helium fluxes due to degassing of the Earth's crust /mantle and on the dynamics of groundwater flow. The estimated helium flux of 0.7-4.5 · 10 9 atoms 4He m -2 s -1 is lower than values derived from other deep groundwater circulation systems, probably because the relatively young upper few thousand meters of the sedimentary basin (Tertiary to Quaternary age) shield the flux from the deeper crust. The high mantle helium flux of up to 4.2 · 10 8 atoms 4He m -2 s -1 is probably related to the Miocene volcanism or to continuing intrusion accompanying extension. By fitting calculated helium depth profiles to measured data in the discharge area, vertical flow velocities of the order of 1.5 mm y -1 are estimated. Assuming that a flux of 0.7-4.5 · 10 9 atoms 4He m -2 s -1 is representative for the entire basin, the turnover time of the regional groundwater flow system is estimated to be about 10 6 y.

Stute, M.; Sonntag, C.; Deák, J.; Schlosser, P.

1992-05-01

151

Five second helium neutral beam injection using argon-frost cryopumping techniques  

International Nuclear Information System (INIS)

High power helium neutral beams for the heating of tokamak discharges can now be provided for 5 s by using argon cryopumping (of the helium gas) in the beamlines. The DIII-D neutral beam system has routinely provided up to 20 MW of deuterium neutral beam heating in support of experiments on the DIII-D tokamak. Operation of neutral beams with helium has historically presented a problem in that pulse lengths have been limited to 500 ms due to reliance solely on volume pumping of the helium gas. Helium is not condensed on the cryopanels. A system has now been installed to deposit a layer of argon frost on the DIII-D neutral beam cryopanels, between tokamak injection pulses. The layer serves to trap helium on the cryopanels providing sufficient pumping speed for 5 s helium beam extraction. The argon frosting hardware is now present on two of four DIII-D neutral beamlines, allowing injection of up to 6 MW of helium neutral beams per discharge, with pulse lengths of up to 5 s. The argon frosting system is described, along with experimental results demonstrating its effectiveness as a method of economically extending the capabilities of cryogenic pumping panels to allow multi-second helium neutral beam injection

1995-10-01

152

Helium generation rates in isotopically tailored Fe-Cr-Ni alloys irradiated in FFTF/MOTA  

International Nuclear Information System (INIS)

Three Fe-Cr-Ni alloys have been doped with 0.4% "5"9Ni for side-by-side irradiations of doped and undoped materials in order to determine the effects of fusion-relevant levels of helium production on microstructural development and mechanical properties. The alloys were irradiated in three successive cycles of the Materials Open Test Assembly (MOTA) located in the Fast Flux Test Facility (FFTF). Following irradiation, helium levels were measured by isotope dilution mass spectrometry. The highest level of helium achieved in doped alloys was 172 appm at 9.1 dpa for a helium(appm)-to-dpa ratio of 18.9. The overall pattern of predicted helium generation rates in doped and undoped alloys is in good agreement with the helium measurements

1991-11-17

153

Asteroseismic estimate of helium abundance of a solar analog binary system  

CERN Multimedia

16 Cyg A and B are among the brightest stars observed by Kepler. What makes these stars more interesting is that they are solar analogs. 16 Cyg A and B exhibit solar-like oscillations. In this work we use oscillation frequencies obtained using 2.5 years of Kepler data to determine the current helium abundance of these stars. For this we use the fact that the helium ionization zone leaves a signature on the oscillation frequencies and that this signature can be calibrated to determine the helium abundance of that layer. By calibrating the signature of the helium ionization zone against models of known helium abundance, the helium abundance in the envelope of 16 Cyg A is found to lie in the range 0.231 to 0.251 and that of 16 Cyg B lies in the range 0.218 to 0.266.

Verma, Kuldeep; Antia, H M; Basu, Sarbani; Mazumdar, Anwesh; Monteiro, Mario J P F G; Appourchaux, Thierry; Chaplin, William J; Garcia, Rafael A; Metcalfe, Travis S

2014-01-01

154

The interaction potential of a symmetric helium trimer  

International Nuclear Information System (INIS)

The interaction potential of three helium atoms in symmetric linear configurations is calculated under the Born--Oppenheimer approximation using an ''exact'' Green's function quantum Monte Carlo method. The results are compared with those of ''exact'' quantum Monte Carlo calculations for the helium dimer and the Axilrod--Teller triple-dipole energy expression. For nearest neighbor separations of 5.6 bohrs, the equilibrium distance for a helium dimer, the corresponding trimer energy is -21.5±1.9 K, compared to -22.3±0.2 K, calculated for pairwise additive behavior. For all internuclear separations in the neighborhood of the van der Waals well (?5.6 bohrs), the nonadditive contribution is found to be very small

1994-06-15

155

Thermal desorption of helium from graphite irradiated by He+ ions  

International Nuclear Information System (INIS)

Thermal desorption of helium from graphite irradiated with 20 keV He+ ions and surface erosion caused by ion irradiation have been studied. After He+ ion irradiation, localized protrusions and uniform domed surface uplifting were observed on isotropic graphite irradiation doses of 5.0x1017 ions/cm2 and 5.0x1018 ions/cm2, respectively. The peak temperatures in thermal desorption curves have a tendency to rise with irradiation dose, and become constant at about 3300C for irradiation doses above 5.0x1017 ions/cm2. Thermal desorption of helium considerably depends on the structure of graphite samples studied here. Glassy carbon and graphitized paper (PAPYEX) retained only 22% and 12% of the helium retention of isotropic graphite, respectively. (orig.)

1986-01-01

156

Helium generation and release in MOX fuels  

International Nuclear Information System (INIS)

Measurement of the retained helium in MOX fuel matrices was carried out. Helium generation under irradiation was estimated by adding the released helium to the retained value. The measured helium generation agreed with the calculated one, when modified by adding ternary fission yield. Helium pressure increase in a high burn-up MOX fuel rod can reach 30% or more of the FP gas pressure. This should contribute to higher internal rod pressure. The impact of generated helium on fuel performance requires further investigation. (author)

1999-05-17

157

Performance of the Helium Circulation System on a Commercialized MEG  

International Nuclear Information System (INIS)

We report the performance of a helium circulation system (HCS) mounted on a MEG (Magnetoencephalography) at Nagoya University, Japan. This instrument is the first commercialized version of an HCS. The HCS collects warm helium gas at approximately 300 K and then cools it to approximately 40 K. The gas is returned to the neck tube of a Dewar of the MEG to keep it cold. It also collects helium gas in the region just above the liquid helium surface while it is still cold, re-liquefies the gas and returns it to the Dewar. A special transfer tube (TT) of approximately 3 m length was developed to allow for dual helium streams. This tube separates the HCS using a MEG to reduce magnetic noise. A refiner was incorporated to effectively collect contaminating gases by freezing them. The refiner was equipped with an electric heater to remove the frozen contaminants as gases into the air. A gas flow controller was also developed, which automatically controlled the heater and electric valves to clean up contamination. The developed TT exhibited a very low heat inflow of less than 0.1 W/m to the liquid helium, ensuring efficient operation. The insert tube diameter, which was 1.5 in. was reduced to a standard 0.5 in. size. This dimensional change enabled the HCS to mount onto any commercialized MEG without any modifications to the MEG. The HCS can increase liquid helium in the Dewar by at least 3 liters/Day using two GM cryocoolers (SRDK-415D, Sumitomo Heavy Industries, Ltd.). The noise levels were virtually the same as before this installation.

2012-12-17

158

Effects of implanted helium on void nucleation during hvem irradiation of stainless steel containing silicon  

Science.gov (United States)

The combined effects of both silicon and helium on void nucleation in a high purity stainless steel have been studied during electron irradiation in a high voltage electron microscope in the temperature range 400-750°C. The nucleation of voids was not affected by silicon up to 0.5wt%, either with or without 10ppm helium. At higher silicon levels continuous nucleation occurred with a reduced maximum void density. The void density was increased by helium in all case.s and up to 0.5% silicon showed a characteristic two stage temperature dependence, with activation energies of 0.5 and 1.0eV, in contrast to the single stage in alloys without helium and in >0.5% silicon materials with helium. The results are discussed in terms of two mechanisms; the binding of gas to silicon atom clusters and the segregation of silicon to void nuclei.

Singh, B. N.; Leffers, T.; Makin, M. J.; Walters, G. P.; Foreman, A. J. E.

159

Helium behavior in vanadium-based alloys irradiated in the dynamic helium charging experiments  

Energy Technology Data Exchange (ETDEWEB)

Helium effect of neutron irradiated vanadium alloys, containing titanium, has been studied using Dynamic Helium Charging Experiment (DHCE) in FFTF. Cavity formation was observed only in pure vanadium irradiated at 430 to 600 C and in V-5Ti irradiated at 600 C. No apparent cavity formation was obtained in V-3Ti-1Si and V-4Cr-4Ti. The precipitation of titanium oxide in V-5Ti, V-3Ti-1Si and V-4Cr-4Ti occurred in all irradiation conditions in this study and the precipitates of Ti{sub 5}Si{sub 3} only appeared in V-3Ti-1Si irradiated at 600 C up to 15 dpa with helium generation rate of 4 appmHe/dpa. It is suggested that titanium oxide plays an important role for suppression of cavity formation and swelling from early stage of irradiation. Detail characterization of precipitates and He effect for neutron damages in vanadium alloys are discussed here.

Fukumoto, K.; Matsui, H. [Tohoku Univ., Sendai (Japan). Inst. for Materials Research; Chung, H.M.; Gazda, J.; Smith, D.L. [Argonne National Lab., IL (United States)

1996-12-31

160

Solubility of helium in water  

International Nuclear Information System (INIS)

The problem of solubility of various gases in water during the operation of nuclear power plants (NPP) assumed practical importance in recent years. This is due to the fact that gaseous volume compensators are used in NPP's. Water radiolysis occurs during the operation of a reactor plant. Introduction of helium or some other gas in the reactor loop contributes to boiling suppression and reduction of coolant radiolysis. In the gas-cooled reactors planned in the USSR and abroad (VGR-300, VG-400, HTGR), helium can enter the water because of leakages when the pressure is larger in the first loop than in the second, for instance, in steam superheaters. The aim was to calculate, and compose tables of, the solubility of helium in water for the parameters characterizing the operating conditions of various NPP's

1989-11-01

 
 
 
 
161

Thermophysical properties of helium using molecular dynamics simulations  

International Nuclear Information System (INIS)

The equation of state, melting line and metallization of helium have been studied by using quantum and classical molecular dynamics simulations. The melting line has been obtained by analyzing the radial distribution function and the diffusion parameter which is close to the experimental values. Equations of state when the temperature is less than 4.5 eV and the density is between 0.3 g/cm3 and 5.0 g/cm3 are also studied. Finally, it is found that the temperature can reduce the metallization density and metallization pressure of helium. (authors)

2011-06-01

162

Cavity morphology in a Ni based superalloy under heavy ion irradiation with hot pre-injected helium. II  

Science.gov (United States)

In the current investigation, TEM in-situ heavy ion (1 MeV Kr2+) irradiation with helium pre-injected at elevated temperature (400 °C) was conducted to simulate in-reactor neutron irradiation induced damage in CANDU spacer material Inconel X-750, in an effort to understand the effects of helium on irradiation induced cavity microstructures. Three different quantities of helium, 400 appm, 1000 appm, and 5000 appm, were pre-injected directly into TEM foils at 400 °C. The samples containing helium were then irradiated in-situ with 1 MeV Kr2+ at 400 °C to a final dose of 5.4 dpa (displacement per atom). Cavities were formed from the helium injection solely and the cavity density and size increased with increasing helium dosage. In contrast to previous heavy ion irradiations with cold pre-injected helium, heterogeneous nucleation of cavities was observed. During the ensuing heavy ion irradiation, dynamical observation showed noticeable size increase in cavities which nucleated close to the grain boundaries. A "bubble-void" transformation was observed after Kr2+ irradiation to high dose (5.4 dpa) in samples containing 1000 appm and 5000 appm helium. Cavity distribution was found to be consistent with in-reactor neutron irradiation induced cavity microstructures. This implies that the distribution of helium is greatly dependent on the injection temperature, and helium pre-injection at high temperature is preferred for simulating the migration of the transmutation produced helium.

Zhang, He; Yao, Zhongwen; Daymond, Mark R.; Kirk, Marquis A.

2014-03-01

163

Diffusion and retention of helium in titanium carbide  

Science.gov (United States)

The knowledge of helium migration in TiC is an important issue due to its possible use as fuel coating in fission reactors and as first wall material coating in fusion reactors. Helium release measurements and diffusion coefficient calculations of helium in polycrystalline TiC have been carried out in the temperature range (1000-1600 °C) for the time period of 2 h. Polished bars of TiC were implanted with 3 MeV 3He+ ions in normal incidence at a dose of 5 × 1020 at./m2 at room temperature. Helium depth profile was measured at each step using the 3He(d, p0)4He nuclear reaction by varying the incident deuteron energy from 900 to 1800 keV. Effective diffusion coefficients vary from 4.20 × 10-18 to 2.59 × 10-17 m2 s-1 and activation energy values obtained are in the range 0.8-2.5 eV. Due to scarce availability of stoichiometric TiC, challenges in this study came from native vacancies present in the samples. The helium distribution and its release were affected by the presence of grain boundaries. He is considered to undergo two distinct populations into the sample and different values of diffusion coefficient have been determined for each population.

Agarwal, S.; Trocellier, P.; Vaubaillon, S.; Miro, S.

2014-05-01

164

Energy Levels of Helium Nucleus  

Directory of Open Access Journals (Sweden)

Full Text Available The Helium-4 nucleus is more similar to the Hydrogen atom of atomic physics. In the case of hydrogen atom, there are many energy levels which were experimentally seen and theoretically explained using non-relativistic quantum mechanics. In this note, we use a central potential to derive the energy levels of Helium-4 nucleus. The ground state and the first few energy levels agree pretty well with experiment. The same potential can be used with nuclei like Oxygen-17 and many more nuclei.

Cvavb Chandra Raju

2013-04-01

165

Pulsed helium ionization detection system  

Energy Technology Data Exchange (ETDEWEB)

A helium ionization detection system is provided which produces stable operation of a conventional helium ionization detector while providing improved sensitivity and linearity. Stability is improved by applying pulsed dc supply voltage across the ionization detector, thereby modifying the sampling of the detectors output current. A unique pulse generator is used to supply pulsed dc to the detector which has variable width and interval adjust features that allows up to 500 V to be applied in pulse widths ranging from about 150 nsec to about dc conditions.

Ramsey, Roswitha S. (Knoxville, TN); Todd, Richard A. (Knoxville, TN)

1987-01-01

166

Helium-selenium lasers (Review)  

Energy Technology Data Exchange (ETDEWEB)

Results of recent studies of the spectral characteristics of helium-selenium lasers are reviewed. A correlation is established between the spectral and lasing characteristics. In particular, it is found that the current and temperature dependences are described by stepped curves due to the competition between a series of lasing lines. A spectroscopic method is proposed for estimating the gain coefficients of the corresponding lasing lines, and the dependence of the gain coefficient at different points of the capillary is investigated using this method. Possible ways of smoothing the gain coefficient and increasing the life of helium-selenium lasers are discussed. 30 refs.

Dovgii, IA.O.; Zamorskii, M.K.; Kityk, I.V.; Koltun, V.L. (L' vovskii Gosudarstvennyi Universitet, Lvov (USSR))

1990-01-01

167

Lamb shift in muonic helium ion  

CERN Document Server

The Lamb shift (2P_{1/2}-2S_{1/2}) in the muonic helium ion (mu ^4_2He)^+ is calculated with the account of contributions of orders alpha^3, alpha^4, alpha^5 and alpha^6. Special attention is given to corrections of the electron vacuum polarization, the nuclear structure and recoil effects. The obtained numerical value of the Lamb shift 1381.716 meV can be considered as a reliable estimate for the comparison with experimental data.

Martynenko, A P

2006-01-01

168

Linde standard helium plant of medium capacity  

Energy Technology Data Exchange (ETDEWEB)

The unit is designed to deliver up to 70 l/h of liquid helium (LHe) without precooling by liquid nitrogen (LN{sub 2}), up to 105 l/h with LN{sub 2} precooling, or up to 210 W cryo-refrigeration output at 4.5 K. Its principal components are an oil-flooded screw compressor, gas-bearing expansion turbines, vacuum-brazed aluminium plate-fin heat exchangers, an automatic feed gas purifier, and a process control system. Descriptions are given of the process layout, the main system components, and operation of the unit. (orig.).

Patzelt, A.; Stephan, A.; Nienaber, U.; Weber, J.

1991-01-01

169

Linde standard helium plant of medium capacity  

International Nuclear Information System (INIS)

The unit is designed to deliver up to 70 l/h of liquid helium (LHe) without precooling by liquid nitrogen (LN2), up to 105 l/h with LN2 precooling, or up to 210 W cryo-refrigeration output at 4.5 K. Its principal components are an oil-flooded screw compressor, gas-bearing expansion turbines, vacuum-brazed aluminium plate-fin heat exchangers, an automatic feed gas purifier, and a process control system. Descriptions are given of the process layout, the main system components, and operation of the unit. (orig.)

1991-01-01

170

Helium bubble growth in nickel at temperatures below vacancy migration  

International Nuclear Information System (INIS)

It is shown that bubble growth in nickel during 5 keV He+-implantation in the temperature range 200 K-600 K and dose range 5x1020 He+/m2-1022 He+/m2 can fairly well be described by a loop-punching mechanism. The results indicate that not all helium that remains in the matrix has precipitated into visible bubbles. With increasing dose, however, the percentage of helium in the bubbles increases. It is also shown that at 2x1021 He+/m2 the helium bubble distribution changes from a random distribution to a partially ordered distribution. The bubbles are ordered in some planes of the fcc nickel matrix, but ordering is lacking in other planes. (orig.)

1983-02-01

171

Helium retention properties of plasma facing materials  

Science.gov (United States)

In a fusion reactor, the continuous removal of helium from the core plasma is needed in order to sustain the ignition condition. For this purpose, it has been proposed to place helium selective pumping metals, which can trap more helium than hydrogen, in the vicinity of the divertor. In this study, the helium and hydrogen trapping properties of nickel, tungsten, molybdenum, SS 304 and Inconel 625 were examined. Namely, the dependencies of irradiation temperature on the amount of trapped helium and hydrogen were obtained by thermal desorption spectroscopy (TDS), after helium or hydrogen plasma irradiation. In those metals, nickel showed the most suitable selective pumping capability. Nickel had the helium selective pumping property above 100°C. The maximum amount of trapped helium was (2-3) × 10 16He/ cm2 at an irradiation temperature of 200°C and 600°C. The optimum temperature becomes about 600°C when nickel is used for a selective pumping material.

Yanagihara, H.; Yamauchi, Y.; Hino, T.; Hirohata, Y.; Yamashina, T.

1997-02-01

172

The effect of primordial hydrogen/helium fractionation on the solar neutrino flux  

Science.gov (United States)

If hydrogen and helium are immiscible below some critical temperature, gravitational separation could occur in the proto-sun, resulting in a nearly pure helium core and a nearly pure hydrogen shell. We have constructed solar models according to this scenario and find the neutrino flux reduced to 1.5-3 SNU.

Wheeler, J. C.; Cameron, A. G. W.

1975-01-01

173

Modification of the grain boundary microstructure of the austenitic PCA stainless steel to improve helium embrittlement resistance. [14Cr-16Ni-2. 5Mo-. 25Ti-. 4Si-. 05C  

Energy Technology Data Exchange (ETDEWEB)

Grain boundary MC precipitation was produced by a modified thermal-mechanical pretreatment in 25% cold worked (CW) austenitic prime candidate alloy (PCA) stainless steel prior to HFIR irradiation. Postirradiation tensile results and fracture analysis showed that the modified material (B3) resisted helium embrittlement better than either solution annealed (SA) or 25% CW PCA irradiated at 500 to 600/sup 0/C to approx.21 dpa and 1370 at. ppM He. PCA SA and 25% CW were not embrittled at 300 to 400/sup 0/C. Grain boundary MC survives in PCA-B3 during HFIR irradiation at 500/sup 0/C but dissolves at 600/sup 0/C; it does not form in either SA or 25% CW PCA during similar irradiation. The grain boundary MC appears to play an important role in the helium embrittlement resistance of PCA-B3.

Maziasz, P.J.; Braski, D.N.

1986-01-01

174

Study of the hadron-helium and helium-helium scattering at high energy  

International Nuclear Information System (INIS)

Multiple scattering Glauber's theory is used to calculate the hadron-helium and helium-helium elastic differential cross-section. The theory is very sensitive to the 4He wave functions. We use better 4He wave functions than experimental ones. These wave functions have correct asymptotic shape. In some calculations, we take into account the spin effects and the 4He, S, S' and D states contribution. At high energy, we use inelastic corrections, to complete the differential cross-section. A study of the diffractive and coherent p-4He ? 4He-X dissociation is developed. We use Humble's amplitudes with a peripherical character and an helicity structure. The agreement with experimental results is good for 24 to 400 GeV

1985-01-01

175

Helium pipe diffusion along dislocations in molybdenum observed with thermal helium desorption spectrometry  

International Nuclear Information System (INIS)

Experiments were carried out to reveal the binding of helium to dislocations in molybdenum. After a subthreshold helium ion implantation in a cold-worked molybdenum single crystal, no thermal helium desorption from dislocations was observed with Thermal Helium Desorption Spectrometry (THDS). The results suggested that helium, trapped at dislocations, drained to the nearest surface by a rapid pipe diffusion process at room temperature. Subsequently accurate experiments were done, with substitutional argon implants as a probe, to detect the influence of dislocations on the diffusion of helium. The results confirmed the hypothesis of helium drain by pipe diffusion along dislocations. (orig.)

1986-01-01

176

Helium distribution functions in tokamak plasmas  

International Nuclear Information System (INIS)

Two different methods are used to obtain information on the helium distribution. The first method is a machine that measures the velocity distribution of neutral helium particles escaping from the plasma (NPA). The second method is charge exchange spectroscopy that measures the helium density and temperature as a function of time and place from the Doppler broadened intensity of He lines. (orig./HP)

1995-01-01

177

Multielectron Bubbles in Liquid Helium  

Science.gov (United States)

When a film of electrons on a flat helium surface reaches a critical density, the helium surface becomes unstable and multielectron bubbles (MEBs) form (A. P. Volodin et al., JETP Lett. 26, 543 (1977)). These MEBs are spherical cavities in the helium liquid, containing from a few to several tens of millions of electrons. The radius of the bubble is 1 micron for N=10^4 electrons and increases proportional to N^2/3. The electrons inside the bubble form a nanometer thin spherical layer anchored to the surface of the helium. The electron surface density in the spherical 2D electron gas formed in the bubble is experimentally tunable over an extremely large range (10^9-10^13 cm-2) by controlling the pressure and the number of electrons in the bubble. Therefore it is expected that several interesting regimes of the electron gas (such as quantum melting) can be observed in these MEBs. In this contribution, we give an overview of the theoretical work performed recently on the properties of the spherical electron gas in the bubble and on the surface excitations (spherical ripplons) of the MEB. The ripplon frequencies and plasmon frequencies are calculated as a function of pressure and number of electrons. We show that a small negative pressure can stabilize the MEB against fissioning into smaller parts, whereas increasing positive pressure can drive the deformational modes unstable one by one.

Tempere, J.; Silvera, Isaac F.; Devreese, J. T.

2002-03-01

178

Electron excitation rates for helium  

International Nuclear Information System (INIS)

Electron excitation cross-sections between 1"1s, 2"3s, 2"1s, 2"3p and 2"1p states of helium have been calculated recently using the R-matrix method. These cross-sections have been integrated over a Maxwellian distribution to give electron excitation rates. (author)

1982-01-01

179

UCN production in superfluid helium  

International Nuclear Information System (INIS)

Ultra-cold neutrons (UCN) are produced in superfluid helium by single- and multi-phonon excitation. The UCN production rate density RII via multiphonons can be larger than that by one-phonon excitation RI being due to the dependence of the incident neutron spectral flux density d?/d? on the wavelength ?. (orig.)

2003-04-01

180

Helium line detections from ELDWIM at 1.4 GHz  

CERN Multimedia

Helium line observations towards 11 Galactic positions using Westerbork Synthesis Radio Telescope(WSRT) have been reported. These observations were made towards nearby positions where already hydrogen lines were detected at sufficiently high intensity($\\geq$50mK) at 1.4 GHz. This approach gave a fair chance for the detection of helium line as well, keeping in mind the relative abundance(10%) of helium with respect to hydrogen. Care was also taken to avoid the presence of HII regions along the line of sight so that the line emission originates from the extended diffuse low density ionized component, ELDWIM of the Galaxy. The observations have resulted in the detection of helium line towards 5 positions out of 11 with signal to noise ratio(snr) $>$ 4$\\sigma$. An attempt has been made to associate detection/non-detection of helium line to the presence of surrounding HII regions. A weighting scheme that accounts for nearby($<$ 500pc) HII regions, their distances and other factors produces favourable results. I...

Baddi, Raju

2012-01-01

 
 
 
 
181

Detection and Imaging of He_2 Molecules in Superfluid Helium  

CERN Document Server

We present data supporting our previous proposal [1] for using cycling transitions to detect and image metastable He_2 triplet molecules in superfluid helium. We demonstrate that limitations on the cycling efficiency due to the vibrational structure of the molecule can be mitigated by the use of repumping lasers. Images of the molecules obtained using the method are also shown. This technique gives rise to a new kind of ionizing radiation detector. The use of He_2 triplet molecules as tracer particles in the superfluid promises to be a powerful tool for visualization of both quantum [2-4] and classical [5] turbulence in liquid helium.

Rellergert, W G; Garvan, A; Hanson, J C; Lippincott, W H; Nikkel, J A; McKinsey, D N

2007-01-01

182

Helium Detection in IRTF Spectra of SN 2011dh  

Science.gov (United States)

We observed SN 2011dh with the IRTF 3.5m and the SpeX instrument on June 8, 12, & 16. No helium was detected on June 8. Weak evidence for helium was present on June 12 and He I is unambiguously detected from the 1.0830 & 2.0581 micron lines in the spectrum obtained June 16. The He I velocities on June 16 are about 8000 km/s while H velocities remain above 11000 km/s. O I & Fe II are also clearly detected.

Marion, G. H.; Kirshner, R.; Wheeler, J. C.; Vinko, J.; Chornock, R.; Foley, R. J.; Challis, P.; Friedman, A.; Garnavich, P.; Krisciunas, K.

2011-06-01

183

Helium measurements for the MFE-4 spectral tailoring experiment  

International Nuclear Information System (INIS)

Measurements of helium concentration have been made on Fe-15.1Cr-34.5Ni specimens irradiated at 330, 400, 500 and 600 degree C after irradiation in ORR to displacement levels ranging from 12.6 to 13.8 dpa. The measurements compare well to previously calculated values, being 4 to 8% lower. Minor differences in helium content were also observed between specimens from capsules that were assumed to have possessed identical spectral environments. 6 refs., 1 fig., 2 tabs

1990-01-01

184

Features of wide-aperture glow discharge in helium  

International Nuclear Information System (INIS)

The characteristics of wide-aperture discharge in helium have been studied for a cathode diameter of 19.5 cm and a cathode - grid anode distance of 3 cm. It is established that the properties of discharge in this system are substantially different from those of an abnormal discharge. The difference is manifested in the bending of current-voltage characteristics, their pronounced dependence on the helium pressure, a nonmonotonic dependence of the electron beam generation efficiency ? on the discharge voltage U, and an anomalously high efficiency (? ? 100%) in the range of U ? 350...1000 V

2007-10-12

185

White Dwarfs in NGC 6791: Avoiding the Helium Flash  

CERN Document Server

We propose that the anomalously bright white dwarf luminosity function observed in NGC 6791 (Bedin et al 2005) is the consequence of the formation of 0.5 Msun white dwarfs with Helium cores instead of Carbon cores. This may happen if mass loss during the ascent of the Red Giant Branch is strong enough to prevent a star from reaching the Helium flash. Such a model can explain the slower white dwarf cooling (relative to standard models) and fits naturally with scenarios advanced to explain Extreme Horizontal Branch stars, a population of which are also found in this cluster.

Hansen, B

2005-01-01

186

A compact quadrupole ion filter for helium detection  

International Nuclear Information System (INIS)

A compact quadrupole ion filter was conceived and constructed for optimum performance at the mass four region of the mass spectra. It was primarely designed for geological applications in the measurements of helium of soil-gases. The whole ion filter structure is 15 cm long by 3.5 cm diameter, including ion source and collecting plate. The sensitivity to helium is of the order of 10-2 A.torr-1 measured at a total pressure of 6x10-6 torr and resolution 6. The system can be easily adapted to work as a dynamic residual gas analyser for other purposes. (Author)

1981-01-01

187

Effect of helium on tensile properties of vanadium alloys  

Energy Technology Data Exchange (ETDEWEB)

Tensile properties of V-4Cr-4Ti (Heat BL-47), 3Ti-1Si (BL-45), and V-5Ti (BL-46) alloys after irradiation in a conventional irradiation experiment and in the Dynamic Helium Charging Experiment (DHCE) were reported previously. This paper presents revised tensile properties of these alloys, with a focus on the effects of dynamically generated helium of ductility and work-hardening capability at <500{degrees}C. After conventional irradiation (negligible helium generation) at {approx}427{degrees}C, a 30-kg heat of V-4Cr-4Ti (BL-47) exhibited very low uniform elongation, manifesting a strong susceptibility to loss of work-hardening capability. In contrast, a 15-kg heat of V-3Ti-1Si (BL -45) exhibited relatively high uniform elongation ({approx}4%) during conventional irradiation at {approx}427{degrees}C, showing that the heat is resistant to loss of work-hardening capability.

Chung, H.M.; Billone, M.C.; Smith, D.L. [Argonne National Lab., IL (United States)

1997-08-01

188

Helium refrigeration system for BNL colliding beam accelerator  

International Nuclear Information System (INIS)

A Helium Refrigeration System which will supply the cooling required for the Colliding Beam Accelerator at Brookhaven National Laboratory is under construction. Testing of the compressor system is scheduled for late 1983 and will be followed by refrigerator acceptance tests in 1984. The refrigerator has a design capacity of 24.8 kW at a temperature level near 4K while simultaneously producing 55 kW for heat shield loads at 55K. When completed, the helium refrigerator will be the world's largest. Twenty-five oil-injected screw compressors with an installed total of 23,250 horsepower will supply the gas required. One of the unique features of the cycle is the application of three centrifugal compressors used at liquid helium temperature to produce the low temperatures (2.5K) and high flow rates (4154 g/s) required for this service

1983-08-01

189

Helium behavior in UO{sub 2} polycrystalline disks  

Energy Technology Data Exchange (ETDEWEB)

The behavior of helium implanted in sintered uranium dioxide disks has been investigated as a function of annealing temperature. UO{sub 2} disks have been implanted with 1 MeV {sup 3}He at a nominal fluence of 5 x 10{sup 16} {sup 3}He cm{sup -2} using a Van de Graaff accelerator. The {sup 3}He(d,{alpha}){sup 1}H nuclear reaction analysis method was used to determine the helium depth profile in the UO{sub 2} disks. Partial flaking was observed after annealing at 500 deg. C for local He concentration of 1 at.%. After annealing at 600 deg. C flaking has affected the whole surface. The formation of helium bubbles is discussed.

Guilbert, S. E-mail: severine.guilbert@irsn.fr; Sauvage, T.; Erramli, H.; Barthe, M.-F.; Desgardin, P.; Blondiaux, G.; Corbel, C.; Piron, J.P

2003-09-15

190

Mott and helium polarimetry of a spin polarized electron source  

International Nuclear Information System (INIS)

An absolute determination of the electron spin polarization of a GaAs photoemission source was made using the method of helium polarimetry. Measurements of the source polarization were also made using a Mott spin polarization analyser. We report an electron beam polarization of (25.5±1)% and an effective Sherman function of 0.26±0.01 for the Mott detector at 31.8±0.6 keV incident electron energy. The Sherman function is also presented for a number of incident energies between 10 keV and 37 keV. A complete set of Stoke's parameters is reported for the 33P-23S (3889 A) helium line. The characteristics of the source, Mott detector and helium polarimeter are discussed in detail. (author)

1992-09-01

191

Controlled Chemistry Helium High Temperature Materials Test Loop  

Energy Technology Data Exchange (ETDEWEB)

A system to test aging and environmental effects in flowing helium with impurity content representative of the Next Generation Nuclear Plant (NGNP) has been designed and assembled. The system will be used to expose microstructure analysis coupons and mechanical test specimens for up to 5,000 hours in helium containing potentially oxidizing or carburizing impurities controlled to parts per million levels. Impurity levels in the flowing helium are controlled through a feedback mechanism based on gas chromatography measurements of the gas chemistry at the inlet and exit from a high temperature retort containing the test materials. Initial testing will focus on determining the nature and extent of combined aging and environmental effects on microstructure and elevated temperature mechanical properties of alloys proposed for structural applications in the NGNP, including Inconel 617 and Haynes 230.

Richard N. WRight

2005-08-01

192

Trapping and release of helium in tungsten  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The behavior of tungsten under irradiation and helium implantation is a major stake of the materialrelated issues of fusion reactors. In this perspective the fate of helium in tungsten was studied by mean of several characterization techniques. The aim of this study is to highlight the trapping mechanisms of helium in tungsten and their correlation with implantation-induced defects. Helium was implanted into tungsten at two different energies, 0.32 and 60 keV. The helium was studied as a func...

Lhuillier, Pierre-emile; Belhabib, Taieb; Desgardin, Pierre; Courtois, Blandine; Sauvage, Thierry; Barthe, Marie-france; Thomann, Anne-lise; Brault, Pascal; Tessier, Yves

2011-01-01

193

Chromatographic method of measurement of helium concentration in underground waters for dating in hydrological questions  

International Nuclear Information System (INIS)

Research methods which use natural environmental indicators are widely applied in hydrology. Different concentrations of indicators and their isotopic components in ground waters allow to determine the genesis of waters and are valuable source of information about the water flow dynamics. One of the significant indicator is helium. The concentration of 4He (helium) in ground water is a fine indicator in water dating in a range from a hundreds to millions of years (Aeschbach-Hertig i in., 1999; Andrews i in., 1989; Castro i in., 2000; Zuber i in., 2007). 4He is also used for dating young waters of age about 10 years (Solomon i in., 1996). Thesis consist the description of elaborated in IFJ PAN in Krakow chromatographic measurement method of helium concentration in ground waters in aim of dating. Chapter 1 contain short introduction about ground water dating and chapter 2 description of helium property and chosen applications of helium for example in technology and earthquake predictions. Helium sources in ground waters are described in chapter 3. Helium concentration in water after infiltration (originated from atmosphere) to the ground water system depends mainly on the helium concentration coming from the equilibration with the atmosphere increased by additional concentration from '' excess air ''. With the increasing resistance time of ground water during the flow, radiogenic, non-atmospheric component of helium dissolves also in water. In chapter 4 two measurement methods of helium concentration in ground waters were introduced: mass spectrometric and gas chromatographic method. Detailed description of elaborated chromatographic measurement method of helium concentration in ground water contain chapter 5. To verify developed method the concentration of helium in ground waters from the regions of Krakow and Busko Zdroj were measured. For this waters the concentrations of helium are known from the earlier mass spectrometric measurements. The results of verification are introduced in chapter 6. Described in chapter 5 chromatographic method was applied to measurements of helium concentration in ground waters from the regions of Zakopane, Raciborz and Torun. Obtained results of this measurements are shown in chapter 7. Appendixes A and B contain explanation of chromatographic system calibration and head-space method respectively. Detailed description of calculation of helium concentration in ground water using elaborated method and measurement deviations are introduced in Appendixes C and D. (author)

2008-01-01

194

Helium production in natural gas reservoirs  

International Nuclear Information System (INIS)

About 11,000 published natural gas analyses of helium are used in the estimation of the average global scale accumulation and concentration of radiogenic helium in sediments. Simple lognormal statistics is employed to derive a net accumulation rate between 1dagger105 to 6.7dagger105 helium atoms per cubic meter of reservoir rock per second. This acccumulation rate permitted to infer an average helium concentration of nonreservoir sediments of about 67 ppm. By assuming a simple closed system model it is shown that deep seated sources of helium are not necessary to explain the present regime of helium in sediments on a global scale. Helium accumulation rates and concentrations obtained by this method are in close agreement with existing fundamental geochemical estimates of uranium and thorium in rather average type sediments

1982-01-01

195

HeREF-2003: Helium Refrigeration Techniques  

CERN Multimedia

CERN Technical Training 2003: Learning for the LHC ! Theory, Technology, Maintenance and Control of Helium Refrigerators HeREF-2003 is a course in the framework of the 2002 Technical Training Programme, that will provide a complete introduction to Helium refrigeration, with a practical approach to theory, technology, maintenance and control of Helium refrigeration installations. Theoretical aspects and equations will be limited to a minimum. HeREF-2003 targets an audience of technicians and operators of Helium refrigeration plants at CERN, as well as physicists and engineers needing an overview of current Helium refrigeration techniques. HeREF-2003 will address, among other, issues related to component technology, installation maintenance, process control and Helium purity. A commented visit to a couple of CERN Helium refrigeration or liquefaction plants will also take place. Duration: 7 half days (4 mornings and 3 afternoons), 6-10 October, 2003 Cost per participant: 500.- CHF Language: Bilingual English...

2003-01-01

196

Helium solubility in imperfect ionic crystals  

International Nuclear Information System (INIS)

In the context of the intended use of helium as a coolant in high temperature gas cooled reactors a study is undertaken into helium interaction with crystals at the stage preceding the process of helium clusters formation. Experimental and theoretical investigations of helium solubility in imperfect ionic crystals CaF2, SrF2, KBr are carried out along with the degassing kinetics in the temperature range of 500-1200 K. An analysis is made for possible mechanisms of the occurrence of observed oscillations in helium solubility at temperature variations. The solution heat for helium atoms in cation vacancies and the energy of impurity-vacancy cluster dissociation are calculated. The reason for a catastrophic increase of dissolved helium concentration with saturation pressure is discussed

2000-09-11

197

Mixed helium-3 - helium-4 calorimeter. Very low temperature calorimetry  

International Nuclear Information System (INIS)

A description is given of a double-racket calorimeter using helium-4 and helium-3 as the cryogenic fluids and making it possible to vary the temperature continuously from 0.35 K to 4.2 K. By using an electric thermal regulator together with liquid hydrogen it is possible to extend this range up to about 30 K. In the second part, a review is made of the various, methods available for measuring specific heats. The method actually used in the apparatus previously described is described in detail. The difficulties arising from the use of an exchange gas for the thermal contact have been solved by the use of adsorption pumps. (author)

1966-01-01

198

Supercritical turbo-alternator valve for the liquefaction of helium  

Energy Technology Data Exchange (ETDEWEB)

A description is given of the construction and initial results of a helium turbo-alternator valve which is used entirely as a replacement valve for a Joule-Thomson valve on a refrigerator of 400 W at a nominal temperature of 4.4 K. The isentropic yield was 37% while the refrigerator's net gain performance was 23%. 5 figures.

Dauvergne, J.P.

1982-05-11

199

Applicability of Henry's Law to helium solubility in olivine  

Science.gov (United States)

Applicability of Henry's Law to helium solubility in olivine We have experimentally determined helium solubility in San Carlos olivine across a range of helium partial pressures (PHe) with the goal of quantifying how noble gases behave during partial melting of peridotite. Helium solubility in olivine correlates linearly with PHe between 55 and 1680 bar. This linear relationship suggests Henry's Law is applicable to helium dissolution into olivine up to 1680 bar PHe, providing a basis for extrapolation of solubility relationships determined at high PHe to natural systems. This is the first demonstration of Henry's Law for helium dissolution into olivine. Averaging all the data of the PHe series yields a Henry's coefficient of 3.8(×3.1)×10-12 mol g-1 bar-1. However, the population of Henry's coefficients shows a positive skew (skewness = 1.17), i.e. the data are skewed to higher values. This skew is reflected in the large standard deviation of the population of Henry's coefficients. Averaging the median values from each experiment yields a lower Henry's coefficient and standard deviation: 3.2(× 2.3)×10-12 mol g-1 bar-1. Combining the presently determined helium Henry's coefficient for olivine with previous determinations of helium Henry's coefficients for basaltic melts (e.g. 1) yields a partition coefficient of ~10-4. This value is similar to previous determinations obtained at higher PHe (2). The applicability of Henry's Law here suggests helium is incorporated onto relatively abundant sites within olivine that are not saturated by 1680 bar PHe or ~5×10-9 mol g-1. Large radius vacancies, i.e. oxygen vacancies, are energetically favorable sites for noble gas dissolution (3). However, oxygen vacancies are not abundant enough in San Carlos olivine to account for this solubility (e.g. 4), suggesting the 3x10-12 mol g-1 bar-1 Henry's coefficient is associated with interstitial dissolution of helium. Helium was dissolved into olivine using an externally heated pressure vessel (Brown University). The starting materials were prepared by cutting gem-quality San Carlos olivine (~Fo90) into small blocks (~4×2×1 mm) using a diamond wafering blade saw and polishing with alumina slurries and colloidal silica. Analysis was completed by laser ablation-mass spectrometry using a 193 nm excimer laser and a MAP 215-50 specifically tuned for He (Open University, UK). Laser ablation pit depth varied from 2 to 40 ?m, and no correlation between pit depth and [He] is observed after accounting for variations PHe across the different experiments. This lack of correlation indicates a close approach to equilibrium was achieved over the experimental durations. Two analyses yielded spuriously high [He] (>3 std. dev. from the population mean, n = 85), and these analyses were not used to calculate Henry's coefficients. The two spuriously high analyses, in combination with the right skew of Henry's coefficients calculated from individual data points, suggests gem-quality San Carlos olivine contains volumes with anomalously high helium solubility. The nature of these volumes is currently under investigation. However, despite their presence, helium is still highly incompatible in olivine during partial melting. [1] Lux GCA 1987 [2] Heber et al. GCA 2007 [3] Shcheka & Keppler Nature 2012 [4] Walker et al. PEPI 2009

Jackson, C.; Parman, S. W.; Kelley, S. P.; Cooper, R. F.

2013-12-01

200

Helium-4 and helium-3/helium-4 mixture films on Nuclepore and hydrogen  

Science.gov (United States)

This work extends the study of helium films with the description of two experiments performed on different substrates. The primary experiment involves 4He and 3He-4He mixture films on a solid H2 substrate. The secondary experiment is concerned with the behavior of mixture films on Nuclepore. The substrate for the helium-on-hydrogen experiment was chosen for the weak binding potential for helium on hydrogen. Unlike most substrates, H 2 will support a superfluid 4He film less dense than a single bulk-density atomic layer. In recent years, interesting effects have been observed for helium-on-hydrogen systems. The H2 experiment is presented with the results of quartz crystal microbalance measurements and attempted third sound measurements. The quartz crystal microbalance technique measures mass coupling and reveals several interesting features in monolayer and submonolayer helium films on H2. Submonolayer superfluidity and possible phase separation of two-dimensional submonolayer 4He films on solid H2 is reported. 3He--4He mixture films on the H2 substrate reveal novel dependence of the Kosterlitz-Thouless transition temperature on 3He coverage and an unexpected feature at lower temperature. Third sound resonance and NMR measurements are reported for the Nuclepore experiment. The Nuclepore experiment is the continuation of a long-term study of multilayer 3He-4He mixture films. NMR relaxation times, magnetization, and spin diffusion measurements are discussed over a range of temperatures and mixture film coverages. Third sound measurements taken at the same mixture film coverages reveal interesting structure as a function of temperature. Third sound frequency data at temperatures near 150 mK and at 3He coverages greater than one atomic layer exhibit a local maximum that responds to changes in both 3He and 4He coverage.

Finley, Paul T.

 
 
 
 
201

Relaxation oscillations of a helium-burning star - Helium shell flashes not triggered by the accumulation of a critical mass  

Science.gov (United States)

Following the exhaustion of helium at its center, the compact remnant of an intermediate-mass star in a close binary experiences thermal pulses that are different in character from those experienced by a single asymptotic giant branch star. In this particular study, the mass of the main-sequence progenitor of the remnant is 3 Msun, and mass loss by Roche-lobe overflow begins just prior to the ignition of helium at the center and ends when ˜3.5 x to 10-3 Msun of hydrogen remains near the surface; the mass of the remnant is 0.378 Msun, and the mass of the helium zone is 0.18 Msun at the onset of the pulses. The amount of fresh helium that is produced by hydrogen burning between pulses is ˜100 times smaller than the amount of helium consumed during a pulse (1.5 × 10-3 Msun); thus it is not the accumulation of a critical mass of helium that is responsible for triggering pulses. Instead, the star behaves as a classic self-excited relaxation oscillator. It contracts and heats following each pulse, the matter near the base of the helium-containing region entering of its own accord into a domain of thermal instability in the density-temperature plane. Most of the energy released in the ensuing short burst of nuclear burning goes directly into the work necessary to expand matter in the large convective shell formed in consequence of the high fluxes produced in the burst. Matter in the degenerate core and in the radiative envelope expands adiabatically. The thermal instability is quenched because of the expansion of the core, and, in further contrast to the situation in asymptotic giant branch stars, a subsequent long phase of quiescent helium burning does not occur. The energy converted into gravitational potential energy during the pulse is released slowly during the interpulse phase in the form of escaping photons. Thus, during most of the oscillation cycle, the star contracts and shines because of the release of gravitational potential energy which has been built up at the expense of nuclear energy released over only a very brief portion of the cycle. The oscillations continue with steadily decreasing amplitude for ˜30 cycles. Eventually, the domain of instability is avoided and nonoscillatory shell helium burning continues for a time comparable to the time spent in the thermally pulsing stage (˜5 × 107 yr). After two final hydrogen shell flashes, which consume most of the hydrogen remaining near the surface, the remnant settles onto a normal cooling sequence for a low-mass DA white dwarf. The lifetimes of both the core helium-burning phase and the shell helium-burning phase are large enough that real counterparts may lose all of their surface hydrogen through stellar winds during these phases. We explore the possibility that a substantial fraction of all sdO and sdB stars are in one of the two helium-burning phases of a binary component whose companion has already become a cool white dwarf.

Iben, I., Jr.; Fujimoto, M. Y.; Sugimoto, D.; Miyaji, S.

1986-05-01

202

Rapidly pulsed helium droplet source  

Energy Technology Data Exchange (ETDEWEB)

A pulsed valve connected to a closed-cycle cryostat was optimized for producing helium droplets. The pulsed droplet beam appeared with a bimodal size distribution. The leading part of the pulse consists of droplets suitable for doping with molecules. The average size of this part can be varied between 10{sup 4} and 10{sup 6} helium atoms, and the width of the distribution is smaller as compared to a continuous-flow droplet source. The system has been tested in a single pulse mode and at repetition rates of up to 500 Hz with almost constant intensity. The droplet density was found to be increased by more than an order of magnitude as compared to a continuous-flow droplet source.

Pentlehner, Dominik; Riechers, Ricarda; Dick, Bernhard; Slenczka, Alkwin [Institute for Physical and Theoretical Chemistry, University of Regensburg, 93053 Regensburg (Germany); Even, Uzi; Lavie, Nachum; Brown, Raviv; Luria, Kfir [Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv (Israel)

2009-04-15

203

Muon transfer from deuterium to helium  

CERN Multimedia

We report on an experiment at the Paul Scherrer Institute, Villigen, Switzerland measuring x rays from muon transfer from deuterium to helium. Both the ground state transfer via the exotic dmu3,4He* molecules and the excited state transfer from mud* were measured. The use of CCD detectors allowed x rays from 1.5 keV to 11 keV to be detected with sufficient energy resolution to separate the transitions to different final states in both deuterium and helium. The x-ray peaks of the dmu3He* and dmu4He* molecules were measured with good statistics. For the D2+3He mixture, the peak has its maximum at E_dmu3He = 6768 +- 12 eV with FWHM Gamma_dmu3He = 863 +- 10 eV. Furthermore the radiative branching ratio was found to be kappa_dmu3He = 0.301 +- 0.061. For the D_2+4He mixture, the maximum of the peak lies at E_dmu4He = 6831 +- 8 eV and the FWHM is Gamma_dmu4He = 856 +- 10 eV. The radiative branching ratio is kappa_dmu4He = 0.636 +- 0.097. The excited state transfer is limited by the probability to reach the deuterium...

Augsburger, M A; Breunlich, W H; Cargnelli, M; Chatellard, D; Egger, J P; Gartner, B; Hartmann, F J; Huot, O; Jacot-Guillarmod, R; Kammel, P; King, R; Knowles, P; Kosak, A; Lauss, B; Marton, J; Mühlbauer, M; Mulhauser, F; Petitjean, C; Prymas, W; Schaller, L A; Schellenberg, L; Schneuwly, H; Tresch, S; Von Egidy, T; Zmeskal, J

2003-01-01

204

Detecting scintillations in liquid helium  

International Nuclear Information System (INIS)

We review our work in developing a tetraphenyl butadiene (TPB)-based detection system for a measurement of the neutron lifetime using magnetically confined ultracold neutrons (UCN). As part of the development of the detection system for this experiment, we studied the scintillation properties of liquid helium itself, characterized the fluorescent efficiencies of different fluors, and built and tested three detector geometries. We provide an overview of the results from these studies as well as references for additional information

2013-09-01

205

Superfluid Helium Tanker (SFHT) study  

Science.gov (United States)

Replenishment of superfluid helium (SFHe) offers the potential of extending the on-orbit life of observatories, satellite instruments, sensors and laboratories which operate in the 2 K temperature regime. A reference set of resupply customers was identified as representing realistic helium servicing requirements and interfaces for the first 10 years of superfluid helium tanker (SFHT) operations. These included the Space Infrared Telescope Facility (SIRTF), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (Astromag), and the Microgravity and Materials Processing Sciences Facility (MMPS)/Critical Point Phenomena Facility (CPPF). A mixed-fleet approach to SFHT utilization was considered. The tanker permits servicing from the Shuttle cargo bay, in situ when attached to the OMV and carried to the user spacecraft, and as a depot at the Space Station. A SFHT Dewar ground servicing concept was developed which uses a dedicated ground cooling heat exchanger to convert all the liquid, after initial fill as normal fluid, to superfluid for launch. This concept permits the tanker to be filled to a near full condition, and then cooled without any loss of fluid. The final load condition can be saturated superfluid with any desired ullage volume, or the tank can be totally filed and pressurized. The SFHT Dewar and helium plumbing system design has sufficient component redundancy to meet fail-operational, fail-safe requirements, and is designed structurally to meet a 50 mission life usage requirement. Technology development recommendations were made for the selected SFHT concept, and a Program Plan and cost estimate prepared for a phase C/D program spanning 72 months from initiation through first launch in 1997.

Eberhardt, Ralph N.; Dominick, Sam M.; Anderson, John E.; Gille, John P.; Martin, Tim A.; Marino, John S.; Paynter, Howard L.; Traill, R. Eric; Herzl, Alfred; Gotlib, Sam

1988-01-01

206

Commissioning result of the KSTAR helium refrigeration system  

International Nuclear Information System (INIS)

To keep the SuperConducting (SC) magnet coils of KSTAR at proper operating conditions, not only the coils but also other cold components, such as Thermal Shields (TS), magnet structures, SC Bus-Lines (BL), and Current Leads (CL) must be maintained at their respective cryogenic temperatures. A Helium Refrigeration System (HRS) with an exergetic equivalent cooling power of 9 kW at 4.5 K without Liquid Nitrogen (LN2) pre-cooling has been manufactured and installed. The main components of the KSTAR Helium Refrigeration System (HRS) can be classified into the Warm Compression System (WCS) and the cryogenic devices according to the operating temperature levels. The process helium is compressed from 1 bar to 22 bar passing through the WCS and is supplied to cryogenic devices. The main components of cryogenic devices are consist of Cold Box (C/B) and Distribution Box (D/B). The C/B cool-down and make the various cryogenic helium for the KSTAR Tokamak and the various cryogenic helium is distributed by the D/B as per the KSTAR requirement. In this proceeding, we will present the commissioning results of the KSTAR HRS. Circuits which can simulate the thermal loads and pressure drops corresponding to the cooling channels of each cold component of KSTAR have been integrated into the helium distribution system of the HRS. Using those circuits, the performance and the capability of the HRS, to fulfill the mission of establishing the appropriate operating condition for the KSTAR SC magnet coils, have been successfully demonstrated

2008-10-01

207

Contribution to the experimental study of the polarized liquid helium-3; Contributions a l'etude experimentale de l'helium-3 liquide polarise  

Energy Technology Data Exchange (ETDEWEB)

Spin-polarized liquid helium-3 is prepared by laser optical pumping in low magnetic field and at room temperature, prior to fast liquefaction of the polarized sample. The use of a new helium-3 cryostat enabled us to obtain liquid helium-3 with polarization rates up to 25 % at well-stabilized temperatures (around 0.5 K). We could thereby study the effect of nuclear polarization on liquid-vapour equilibrium, and particularly on the saturated vapour pressure. Very sensitive capacitive gauges were developed. We estimated (to first order in M{sup 2}) the expected effects when the polarization M is suddenly destroyed. These effects were experimentally observed in helium-3/helium-4 mixtures, in pure helium-3, only a transient increase in pressure has been recorded. We then describe in a third part a preliminary experiment which aimed at determining the longitudinal relaxation time T1 in mixtures. Relaxation on the walls is efficiently reduced by a cesium coating and T1s of order 20 minutes were observed. A careful determination of the helium-3 concentration in the liquid phase was made. Finally we studied the effects of dipolar field on transverse polarisation decay in our strongly polarized samples. We observed the free precession of polarization after a NMR pulse, and analysed in detail its decay time constant as a function of different parameters. This time constant drastically varied with the tipping angle, an effect which could be linked to NMR dynamical instabilities. (author)

Villard, B

1999-07-15

208

Diffuse Helium Emission as a Precursory Sign of Volcanic Unrest  

Science.gov (United States)

Since July 16, 2011, an anomalous seismicity at El Hierro island, the youngest and smallest of the Canary Islands, was recorded by IGN seismic network. After the occurrence of more than 10,000 seismic events, volcanic tremor was recorded since 05:15 of the October 10, by all of the seismic stations on the island, with highest amplitudes recorded in the southernmost station. During the afternoon of October 12 a large light-green coloured area was observed in the sea to the souht of La Restinga village (at the southernmost part of El Hierro island), suggesting the existence of a submarine eruption. Since October 12, frequent episodes of, turbulent gas emission and foaming, and the appearance of steamy lava fragments has been observed on the sea surface. As part of the volcanic surveillance of the island, the Instituto Volcanologico de Canarias (INVOLCAN) geochemical monitoring program is carrying out diffuse helium surveys on the surface environment of El Hierro (soil atmosphere). This nobel gas has been investigated because it has been considered an almost ideal geochemical indicator because it is chemically inert, physically stable, nonbiogenic, sparingly soluble in water under ambient conditions and almost non-adsorbable. At each survey, 600 sampling sites covering the whole island and following an homogeneous distribution are selected for helium measurements in the soil gases, The helium concentration gradients with respect to its value on air (5.24 ppm) allow us to estimate a pure diffusive emission rate of helium throughout the island. The first survey was carried out on the summer of 2003, when the island was on a quiescence period. At this survey, the amount of helium released by the volcanic system of El Hierro was estimated in 6 kg/d. Since the beginning of the seismic unrest, 13 helium emission surveys have been carried out. The helium emission rate has shown an excellent agreement with the evolution of the volcanic crisis of the island, reaching 30 kg/d on November 6, several days before the occurrence of the submarine eruption. A significant decrease to 13 kg/d was estimated almost 10 days after the beginning of the eruption, followed by a sudden increase to 38 kg/d several days before the largest seismic event of the volcanic crisis (M = 4.6) occurred on November 11. High volcanic-gas pressure in a magma surrounded by a less deformed and fractured crust could be responsible for the high magmatic-helium emission rate and eventual submarine eruption during the first segment of activity, whereas the second segment causing extensive crustal deformation and fracturing resulted in a low gas pressure on the magma and relatively low magmatic-helium diffuse emission rates. The energy loss in the system from the release of volcanic gases might be responsible for the observed decrease in the seismic energy released and the absence of a second volcanic eruption. The system continued to degas for one month, producing a gradual decrease in the helium emission rate. Helium emission data shown in this report demonstrate that diffuse helium surveys is a powerful tool for volcano monitoring. The geochemical parameters presented here are extremely important for forecasting the onset of volcanic unrest and subsequent volcanic eruptions, mainly when magma migrates aseismically, i.e., silently, toward the surface.

Padron, E.; Perez, N.; Hernandez Perez, P. A.; Sumino, H.; Melian Rodriguez, G.; Barrancos, J.; Nolasco, D.; Padilla, G.; Dionis, S.; Rodriguez, F.; Hernandez, I.; Calvo, D.; Peraza, M.; Nagao, K.

2012-12-01

209

Development of a Mass Flowmeter based on the Coriolis Acceleration for Liquid, Supercritical and Superfluid Helium  

CERN Document Server

Beginning in the 1980's, Coriolis meters have gained generalised acceptance in liquid applications with a worldwide installed base of over 300,000 units. To meet the demands of cryogenic applications below 20 K, off-the-shelf Coriolis meters have been used, with minor design modifications and operational changes. The meters were originally calibrated on water and tested on liquid helium at 4.5 K, supercritical helium around 5 K and superfluid helium below 2 K. The meters maintain their intrinsic robustness and accuracy of better than 1% of measured value; accuracy is independent of density and temperature.

De Jonge, T; Rivetti, A; Serio, L

2002-01-01

210

Cryostat for neutron studies of superfluid helium under a pressure up to 25 atm  

International Nuclear Information System (INIS)

The design of a cryostat enabling superfluid helium to be investigated under a pressure up to 2.5 atm by neutron methods is presented. The cryostat design is simple and reliable The accuracy of maintaining the sample temperature makes up +-0.01 K that of maintaining the pressure is +- 0.05 atm. The flow of rate liquid nitrogen is 0.5 l/h, that of liquid helium is 0.35 l/h. The volume of the liquid helium sample equals 2.6 l

1983-01-01

211

Critical Landau velocity in helium nanodroplets.  

Science.gov (United States)

The best-known property of superfluid helium is the vanishing viscosity that objects experience while moving through the liquid with speeds below the so-called critical Landau velocity. This critical velocity is generally considered a macroscopic property as it is related to the collective excitations of the helium atoms in the liquid. In the present work we determine to what extent this concept can still be applied to nanometer-scale, finite size helium systems. To this end, atoms and molecules embedded in helium nanodroplets of various sizes are accelerated out of the droplets by means of optical excitation, and the speed distributions of the ejected particles are determined. The measurements reveal the existence of a critical velocity in these systems, even for nanodroplets consisting of only a thousand helium atoms. Accompanying theoretical simulations based on a time-dependent density functional description of the helium confirm and further elucidate this experimental finding. PMID:24160595

Brauer, Nils B; Smolarek, Szymon; Loginov, Evgeniy; Mateo, David; Hernando, Alberto; Pi, Marti; Barranco, Manuel; Buma, Wybren J; Drabbels, Marcel

2013-10-11

212

Helium damage in metal-tritium systems  

Energy Technology Data Exchange (ETDEWEB)

The time evolution of Debye-Scherrer lines was investigated in metal-tritium-helium systems by neutron-scattering techniques. Polycrystalline samples of TaT{sub {ital x}}, YT{sub {ital x}}, and ScT{sub {ital x}} were measured over a period of three years. The results show that helium damage is governed by the behavior of self-interstitial atoms and dislocation loops created by helium clustering and bubble formation. The self-interstitials and loops induce a lattice expansion in the early stages of helium formation. For higher helium concentrations the self-interstitials and loops produced are completely incorporated into an evolving dislocation network. In hexagonal rare-earth systems a preferential condensation of loops into a dislocation network lying in basal planes is observed. Additional small-angle-scattering experiments show that platelike helium cavities are formed in the hexagonal systems.

Blaschko, O.; Pleschiutschnig, J.; Glas, R.; Weinzierl, P. (Institut fuer Experimentalphysik, Universitaet Wien, Strudlhofgasse 4, A-1090 Wien (Austria))

1991-11-01

213

Double-electron capture from helium by ions of helium, lithium, carbon, and oxygen  

International Nuclear Information System (INIS)

Cross sections for double-electron capture from helium atoms by fully stripped ions of lithium, carbon, and oxygen are calculated in the framework of the continuum distorted-wave (CDW) and continuum intermediate-state (CIS) approximations in the energy range of 0.125--2.5 MeV/amu. Cross sections are also calculated for ? particles as the projectile in the CIS approximation. The results are compared with existing experimental findings. The present calculated results for symmetric and near-symmetric cases show good agreement with the experimental findings. The discrepancies between the calculated and observed values for the asymmetric cases are discussed

1987-06-15

214

Device for controlling flow rate of helium  

International Nuclear Information System (INIS)

The equipment is proposed for helium flow control during leak testing of negative pressure or overpressure systems, mainly in nuclear technology. The container inside the helium space contains a silicate glass diffusion insert in the form of a bulbous vessel with one opening which is removably connected to the discharge tube. A varied helium flow rate may be obtained by combining a number of diffusion inserts of different surface sizes and using silicate glasses of different compositions. (F.M.)

1974-01-01

215

Critical Landau velocity in helium nanodroplets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The best-known property of superfluid helium is the vanishing viscosity that objects experience while moving through the liquid with speeds below the so-called critical Landau velocity. This critical velocity is generally considered a macroscopic property as it is related to the collective excitations of the helium atoms in the liquid. In the present work we determine to what extent this concept can still be applied to nanometer-scale, finite size helium systems. To this end, atoms and molecu...

Brauer, Nils Benedict; Smolarek, Szymon; Loginov, Evgeniy; Mate?o, David; Hernando Castro, Alberto; Pi, Marti; Barranco, Manuel; Buma, Wybren Jan; Drabbels, Marcel

2013-01-01

216

Silicon Detectors For Helium Liquid And Vapor  

Science.gov (United States)

Simple electrical-resistance devices made of silicon indicate whether helium liquid or helium vapor present. Devices designed primarily for use in outer space, were tested and found to operate in normal Earth gravity. Silicon cubes supported by stainless-steel wires and strips. Voltage across each cube at fixed current indicates whether immersed in helium liquid or vapor. Liquid cools more than vapor does, resulting in greater electrical resistance. Such helium-liquid/vapor detectors incorporated into ducts or containers of laboratory equipment, and used to infer locations of liquid/vapor interfaces in order to measure quantities of liquid and vapor or to control refill operations.

Di Pirro, M. J.; Serlemitsos, A. T.

1990-01-01

217

Exposure of Pershore CR39 and Kodak LR115 films to helium ions  

International Nuclear Information System (INIS)

Alpha particle plastic track detectors of the type Kodak LR115-II and Pershore CR39 have been exposed to helium ions of energies in the interval 1.3 to 5.5 MeV and of angle of incidence between 0 and 85 degrees. The helium ions were obtained from the 3UDH Pelletron tandem accelerator in Lund. Results of the angular and energy response of the detectors are presented and the consequences for radon detection are discussed. (author)

1991-01-01

218

Electron impact ionization of helium isoelectronic systems  

Science.gov (United States)

The electron impact single ionization cross sections, on the helium isoelectronic He, Li1+, B3+, C4+, N5+, O6+, Ne8+, Na9+, Ar+16, Fe24+, Mo41+, Ag45+, and U90+ targets, are calculated modifying the simplified Bell (SBELL) model [Eur. Phys. J. D 46, 281 (2008)]. The results of the present analysis are compared with the available experimental and theoretical data. The modified SBELL (MSBELL) model, incorporating the ionic correction factor in it, produces excellent agreement with the experimental data and theoretical calculations for all the two-electron systems, neutral or ions. This model may be a prudent choice in plasma modeling due to its simple inherent structure.

Talukder, M. R.

2008-09-01

219

Pulsation of high luminosity helium stars  

International Nuclear Information System (INIS)

Preliminary calculations are made on a systematic restudy of the linear and nonlinear pulsations of helium stars allowing for more recent and higher estimates of the effective temperature and for the high carbon abundance. Linear and nonlinear models are used. Results show qualitative agreement with earlier ones, models with sufficiently large L/M have a very hot blue edge for their instability strip, very large L/M values lead to dynamically unstable models which would appear to eject mass and therefore may not be realistic models for the pulsating RCrB stars, for the sequence studied a reasonable mass could be greater than or equal to 1.5 Msub solar. 12 references

1979-03-16

220

Interaction of Helium Rydberg State Atoms with Superfluid Helium  

Science.gov (United States)

The pair potentials between ground state helium and Rydberg He atoms are calculated by the full configuration interaction electronic structure method for both the electronic singlet and the triplet manifolds. The obtained pair potentials are validated against existing experimental molecular and atomic data. Most states show remarkable energy barriers at long distances ( Å), which can effectively stabilize He against the formation of He at low nuclear kinetic energies. Bosonic density functional theory calculations, based on the calculated pair potential data, indicate that the triplet ground state He reside in spherical bubbles in superfluid helium with a barycenter radius of 6.1 Å at the liquid saturated vapor pressure. The pressure dependency of the relative He absorption line blue shift in the liquid was obtained through both the statistical line broadening theory as well as the dynamic adiabatic following method. The pronounced difference between the results from the static and dynamic models is attributed to the dynamic Jahn-Teller effect that takes places in the electronically excited state within the dephasing time of 150 fs. Transient non-thermalized liquid surroundings near He may contribute to an artificial reduction in the absorption line blue shift by up to 30 cm.

Fiedler, Steven L.; Eloranta, Jussi

2014-03-01

 
 
 
 
221

Helium stratification in HD 145792: a new Helium strong star  

CERN Document Server

In this paper we report on the real nature of the star HD 145792, classified as He weak in {\\it ``The General Catalogue of Ap and Am stars''}. By means of FEROS@ESO1.52m high resolution spectroscopic data, we refined the atmospheric parameters of the star, obtaining: T$_{\\rm eff}$ = 14400 $\\pm$ 400 K, $\\log g$ = 4.06 $\\pm$ 0.08 and $\\xi$ = 0 $^{+0.6}$ km s$^{-1}$. These values resulted always lower than those derived by different authors with pure photometric approaches. Using our values we undertook an abundance analysis with the aim to derive, for the first time, the chemical pattern of the star's atmosphere. For metals a pure LTE synthesis (ATLAS9 and SYNTHE) has been used, while for helium a hybrid approach has been preferred (ATLAS9 and SYNSPEC). The principal result of our study is that HD 145792 belongs to He strong class contrary to the previous classification. Moreover, helium seems to be vertically stratified in the atmosphere, decreasing toward deepest layers. For what that concerns metals abundanc...

Catanzaro, G

2007-01-01

222

Experimental and theoretical studies of the neutralization of low energy helium ions scattered from tungsten  

International Nuclear Information System (INIS)

A combination of experimental and theoretical methods were used to study neutralization phenomena in low energy scattering of helium ions from tungsten. The ion yields of helium-3 and helium-4 scattered at 138 from tungsten were measured as a function of the incident ion energy (300-2600eV). The physical scattering process in the helium on tungsten system was simulated using the ARGUS model. The neutralization process was studied by quantum calculations. Variations in the scattered yields obtained from experiment and from simulation indicate that an additional neutralization process occurs for ions which scatter from subsurface atoms as compared to ions that scatter from the surface. The presence of only the elastic scattering peak in low energy helium ion yield spectra from tungsten is due to the preferential neutralization of subsurface scattered ions. The results of the experimental and simulation studies also indicated that the lower bound on the ion survival probability for surface scattered ions is about 0.5%. The results of the quantum calculations show that resonance tunneling neutralization, a process previously thought not to occur in the helium on tungsten system, is responsible for the initial neutralization of practically all of the incident ions en route to the surface before Auger neutralization can take place. The relatively large ion survival probability of 0.5% thus suggests that a re-ionization process is present in the helium on tungsten system

1983-01-01

223

Experimental and theoretical studies of the neutralization of low energy helium ions scattered from tungsten  

Energy Technology Data Exchange (ETDEWEB)

A combination of experimental and theoretical methods were used to study neutralization phenomena in low energy scattering of helium ions from tungsten. The ion yields of helium-3 and helium-4 scattered at 138 from tungsten were measured as a function of the incident ion energy (300-2600eV). The physical scattering process in the helium on tungsten system was simulated using the ARGUS model. The neutralization process was studied by quantum calculations. Variations in the scattered yields obtained from experiment and from simulation indicate that an additional neutralization process occurs for ions which scatter from subsurface atoms as compared to ions that scatter from the surface. The presence of only the elastic scattering peak in low energy helium ion yield spectra from tungsten is due to the preferential neutralization of subsurface scattered ions. The results of the experimental and simulation studies also indicated that the lower bound on the ion survival probability for surface scattered ions is about 0.5%. The results of the quantum calculations show that resonance tunneling neutralization, a process previously thought not to occur in the helium on tungsten system, is responsible for the initial neutralization of practically all of the incident ions en route to the surface before Auger neutralization can take place. The relatively large ion survival probability of 0.5% thus suggests that a re-ionization process is present in the helium on tungsten system.

Orvek, K.J.

1983-01-01

224

Detector for metastable helium ions  

International Nuclear Information System (INIS)

We describe a sensitive detector for metastable (2S1/2)helium ions. The detector operates in a magnetic field of 4-16 kG and has on overall efficiency of about 1%. Metastable He+ ions are quenched in an electric field causing them to decay to the ground state (1S1/2) with emission of 304 A radiation. The radiation is detected in a cylindrical photodiode whose active surfaces are made of copper foils coated with MgF2. Multiple photocathodes are used in an arrangement which maximizes the overall efficiency. (orig.)

1987-10-15

225

Helium irradiation of alkali halides  

International Nuclear Information System (INIS)

An investigation has been made of radiation damage in alkali halide crystals induced by heavy bombardment of 1 MeV helium ions. The channeling technique has been employed and three processes have been monitored simultaneously to explain the apparent reduction of damage at high doses. It is shown that the initial rise and fall of the back-scattered yield from different alkali halides can be related to the Pooley mechanism coupled with the aggregation of interstitials to form dislocation loops through the intermediate stage of clusters

1979-01-01

226

Reaction kinetics of a high pressure helium fast discharge afterglow  

International Nuclear Information System (INIS)

This work reports the study of elementary processes which govern the relaxation of the afterglow of a 3 kA 7 ns duration discharge in helium at atmospheric pressure. Populations of the dominant energy storing species were monitored as functions of time through measurements of the emission asnd absorption of radiation from the plasma. The atomic helium spectral lines, radiated during the discharge pulse, were found to rapidly transform into molecular helium bands in the visible and far ultraviolet (600--1000 A) regions during the afterglow. The observed features of this He_2 radiation were consistent with a collisional-radiative scheme of electronic recombination of molecular He_2"+ ions, the concentration of which was inferred from H/sub ?/ line broadening. A significant fraction of the He"+_2 recombination events were found to result in helium atoms in the metastable 2 "3S state, and the time dependence of this dissociation process correlated with that of He_2 populations characterized by quantum number n = 4. The concentration of 2 "3S atoms was comparable to the electron density, ranging from 10"1"4 to 10"1"5 cm"-"3. The concentration of molecular a "3?"+/sub u/ metastables was found to be one order of magnitude lower, suggesting a collisional coupling to the radiating A "1?"+/sub u/ state. From the data rate coefficients have been extracted for the processes of electron--ion recombination, ionizing collisions between atomic metastables, and superelastic electron--metastable collisions

1982-04-15

227

A precision measurement of the hyperfine structure of antiprotonic helium  

International Nuclear Information System (INIS)

Full text: Antiprotonic helium (pHe) is a neutral three body system consisting of one electron, one helium nucleus, and one antiproton (He++ e- + p). When an antiproton approaches a helium atom, at an energy of the order of the helium ionization energy, it can, simultaneously, eject one of the two ground state electrons and become captured. 97 % of the captured antiprotons annihilate within nanoseconds with one of the nucleons in the nucleus but 3 % occupy metastable states with lifetimes of the order of ? 3 %. Due to its long life time this unique particle provides an ideal subject to test three-body Quantum Electrodynamic (QED) calculations. A hyperfine structure (HFS) is caused by the coupling of the electron spin with the antiproton orbital angular momentum. This HFS can be measured using a laser-microwave- laser resonance technique, where a population asymmetry is induced through laser depopulation of one of the HF substates. A population transfer between the substates is induced with a microwave resonant pulse. Then a second laser is used to measure the transferred population. A comparison between the measured transition frequencies and three-body QED calculations can be used to determine the spin magnetic moment of the antiproton. Such a matter anti-matter comparison yields a test of CPT invariance. Over the last couple of years a factor of 5 improvement to the precision has been achieved. This talk shall describe the experiment and preliminary experimental data from the 2008 beam time. (author)

2008-09-22

228

Off-diagonal long-range order (ODLRO) and ground state properties of liquid helium  

Energy Technology Data Exchange (ETDEWEB)

An independent calculation of the condensate fraction and the ground state energy of liquid helium is given. The Froehlich ansatz for the second reduced density matrix in conjunction with the ODLORO hypothesis for liquid helium below the critical temperature is used. Froehlich's ansatz is shown to be consistent with numerical calculations of the ground state properties of liquid helium. The ground state energy was -5.10/sup 0/K, close to the experimental value. The condensate fraction turned out to be about 10% which is within the margin of error of recent neutron scattering experiments and agrees with other theoretical calculations.

Rodriguez-Gomez, J.R.

1983-01-01

229

Ultra-cold neutron production with superfluid helium and spallation neutrons  

CERN Document Server

Ultra-cold neutrons (UCN) production in superfluid helium with spallation neutrons is discussed. A source is described, where superfluid helium is located in a cold moderator of deuterium at 20 K surrounded by a thermal moderator of heavy water at 300 K. A lead target is installed in the thermal moderator for neutron production via a medium energy proton induced spallation reaction. A Monte Carlo simulation showed that a UCN density of the order of 10 sup 5 n/cm sup 3 is achievable with an acceptable heat load for the helium cryostat.

Masuda, Y

2000-01-01

230

Ultra-cold neutron production with superfluid helium and spallation neutrons  

Energy Technology Data Exchange (ETDEWEB)

Ultra-cold neutrons (UCN) production in superfluid helium with spallation neutrons is discussed. A source is described, where superfluid helium is located in a cold moderator of deuterium at 20 K surrounded by a thermal moderator of heavy water at 300 K. A lead target is installed in the thermal moderator for neutron production via a medium energy proton induced spallation reaction. A Monte Carlo simulation showed that a UCN density of the order of 10{sup 5} n/cm{sup 3} is achievable with an acceptable heat load for the helium cryostat.

Masuda, Yasuhiro

2000-02-11

231

Helium refrigerator maintenance and reliability at the OPAL cold neutron source  

Science.gov (United States)

Australia's first Cold Neutron Source (CNS) is a major asset to its nuclear research program. The CNS, and associated helium refrigerator, was commissioned in 2006 and is operated at the Open Pool Light Water nuclear Reactor (OPAL). The OPAL CNS operates a 20K, 5 kW Brayton cycle helium refrigerator. In this paper relevant experiences from helium refrigerator operation, maintenance and repair are presented along with the lessons learnt from a series of technical investigations. Turbine failure, due to volatile organic species, is discussed along with the related compressor oil degradation and oil separation efficiency.

Thiering, Russell; Taylor, David; Lu, Weijian

2012-06-01

232

Ultra-cold neutron production with superfluid helium and spallation neutrons  

Science.gov (United States)

Ultra-cold neutrons (UCN) production in superfluid helium with spallation neutrons is discussed. A source is described, where superfluid helium is located in a cold moderator of deuterium at 20 K surrounded by a thermal moderator of heavy water at 300 K. A lead target is installed in the thermal moderator for neutron production via a medium energy proton induced spallation reaction. A Monte Carlo simulation showed that a UCN density of the order of 10 5 n/cm 3 is achievable with an acceptable heat load for the helium cryostat.

Masuda, Yasuhiro

2000-02-01

233

Design of subcooled helium II refrigerator with helium-3 cold compressor  

International Nuclear Information System (INIS)

This paper will study the possibility of a He II refrigerator made up of three cold compressors by making use of helium-3 characteristics. This system is compact enough to fit inside a small cold box, so it can be easily connected with an existing helium-4 refrigerator. The authors designed the compressors, calculated the He II cooling capacity, 4.4 K refrigeration load, required inventory of helium-3, and Carnot efficiency. Though helium-3 is expensive, the required inventory of helium-3 to be filled inside this He II refrigerator was calculated to be small enough to prove practicality of constructing this refrigerator

1993-07-12

234

Helium-heated steam reformer  

International Nuclear Information System (INIS)

Catalyst action and the supply of high-temperature heat generating energy cause a steam reforming reaction on light hydrocarbons, which produces the reducing gas. The reactor, which permits this reaction to take place, is a steam reformer, the conventional type of which is a flame heating furnace. A heat-exchanger type steam reformer was newly developed for the National Research and Development Programme nuclear steel making project. Unlike conventional ones, this reactor is heated by high-temperature helium. A steam reforming process test plant was planned to test the performance and characteristics of this new steam reformer. Construction of the test plant was begun in 1975. It was completed at the end of May 1978. Subsequently, research and development passed on to the operating phase. The test plant has a nominal raw material treatment capacity of 100 kg/hr. The nominal quantity of heat exchanged is 310,000 Kcal/hr. The paper on the helium-heated steam reformer of this test plant is presented

1980-10-01

235

Advances in Liquid-Helium-Bath Cryopumps.  

Science.gov (United States)

The design, operation, and performance of liquid-helium-bath cryopumps which incorporate improvements that prolong the self-sufficiency of pumping in helium and nitrogen and that make possible the pumping of H sub 2 and N sub 2 at 4.2 exp 0 K are discusse...

J. J. Thibault J. C. Boissin J. Carle

1980-01-01

236

Nuclear fusion and the helium supply problem  

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? Fusion power plants will require helium as cryogenic medium and as coolant. ? High losses are expected: for a power plant like DEMO ? 2 t p.a. ? The same power plant is expected to produce only ?0.6 t p.a. ? Global helium resources are finite: fusion will therefore exacerbate an already difficult situation. ? The “back-stop” technology will be the extraction helium of helium from the atmosphere. -- Abstract: The natural resources required for the operation of fusion power plants are – with the possible exception of the neutron multiplier beryllium – readily available. On the other hand, the supply of helium, which is required as cryogenic medium and coolant, may be a problem due to losses during operation and decommissioning. Helium is a rare element obtained as a by-product in the extraction of natural gas. The danger exists that the natural gas will be used up without the helium being conserved. We estimate the helium demand for a global 30% base-load contribution of fusion to electricity supply and also calculate the amount produced by the power plants themselves.

Bradshaw, A.M., E-mail: alex.bradshaw@ipp.mpg.de [Max Planck Institute for Plasma Physics, Association IPP-Euratom, Boltzmannstr. 2, 85741 Garching (Germany); Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany); Hamacher, T. [Institute for Energy Economy and Application Technology, Technical University of Munich, Arcisstrasse 21, 80333 München (Germany)

2013-10-15

237

Helium-cooled high temperature reactors  

Energy Technology Data Exchange (ETDEWEB)

Experience with several helium cooled reactors has been favorable, and two commercial plants are now operating. Both of these units are of the High Temperature Graphite Gas Cooled concept, one in the United States and the other in the Federal Republic of Germany. The initial helium charge for a reactor of the 1000 MW(e) size is modest, approx.15,000 kg.

Trauger, D.B.

1985-01-01

238

LOX Tank Helium Removal for Propellant Scavenging  

Science.gov (United States)

System studies have shown a significant advantage to reusing the hydrogen and oxygen left in these tanks after landing on the Moon in fuel cells to generate power and water for surface systems. However in the current lander concepts, the helium used to pressurize the oxygen tank can substantially degrade fuel cell power and water output by covering the reacting surface with inert gas. This presentation documents an experimental investigation of methods to remove the helium pressurant while minimizing the amount of the oxygen lost. This investigation demonstrated that significant quantities of Helium (greater than 90% mole fraction) remain in the tank after draining. Although a single vent cycle reduced the helium quantity, large amounts of helium remained. Cyclic venting appeared to be more effective. Three vent cycles were sufficient to reduce the helium to small (less than 0.2%) quantities. Two vent cycles may be sufficient since once the tank has been brought up to pressure after the second vent cycle the helium concentration has been reduced to the less than 0.2% level. The re-pressurization process seemed to contribute to diluting helium. This is as expected since in order to raise the pressure liquid oxygen must be evaporated. Estimated liquid oxygen loss is on the order of 82 pounds (assuming the third vent cycle is not required).

Chato, David J.

2009-01-01

239

Helium abundances and the helium isotope anomaly of sdB stars  

CERN Multimedia

Helium abundances and atmospheric parameters have been determined from high resolution spectra for a new sample of 46 bright hot subdwarf B (sdB) stars. The helium abundances have been measured with high accuracy. We confirm the correlation of helium abundance with temperature and the existence of two distinct sequences in helium abundance found previously. We focused on isotopic shifts of helium lines and found helium-3 to be strongly enriched in 8 of our programme stars. Most of these stars cluster in a small temperature range between 27000 K and 31000 K very similar to the known helium-3-rich main sequence B stars, which cluster at somewhat lower temperatures. This phenomenon is most probably related to diffusion processes in the atmosphere, but poses a challenge to diffusion models.

Geier, S; Edelmann, H; Morales-Rueda, L; Kilkenny, D; O'Donoghue, D; Marsh, T R; Copperwheat, C

2011-01-01

240

Helium-cooled lithiuim compound suspension blanket concept for ITER  

International Nuclear Information System (INIS)

This blanket concept uses a dilute suspension of fine solid breeder particles (Li2O, LiAlO2, or Li4SiO4) in a carrier gas (He) as the coolant and the tritium breeding stream. A small fraction of this stream is processed outside the reactor for tritium recovery. The blanket consists of a beryllium multiplier and carbon/steel reflector. A steel clad is used for all materials. A carbon reflector is employed to reduce the beryllium thickness used in the blanket for a specific tritium breeding ratio. The breeder particle size has to exceed few microns (?2 microns) to avoid sticking problems on the cold surfaces of the heat exchanger. The helium gas pressure is in the range of 2 to 3 MPa to carry the blanket and the heat exchanger loop. The solid breeder concentration in the helium stream is 1 to 5 volume percent. A high lithium-6 enrichment is used to produce a high tritium breeding ratio and to reduce the breeder concentration in the helium gas. At a lithium-6 enrichment of 90%, the local tritium breeding ratio is 2.03 based on a one-dimensional poloidal model. The total thickness of the helium stream is only 4 cm out of the 50 cm total blanket thickness. The blanket uses a 35 cm of beryllium for neutron multiplication. A simple multi-layer design is employed where the blanket sector has the helium coolant flowing in the poloidal direction. The blanket concept has several unique advantages which are very beneficial for fusion reactors including ITER. 10 refs., 2 tabs

1988-10-09

 
 
 
 
241

ACOUSTIC SIGNATURES OF THE HELIUM CORE FLASH  

Energy Technology Data Exchange (ETDEWEB)

All evolved stars with masses M {approx}< 2 M{sub Sun} undergo an initiating off-center helium core flash in their M{sub c} Almost-Equal-To 0.48 M{sub Sun} He core as they ascend the red giant branch (RGB). This off-center flash is the first of a few successive helium shell subflashes that remove the core electron degeneracy over 2 Myr, converting the object into a He-burning star. Though characterized by Thomas over 40 years ago, this core flash phase has yet to be observationally probed. Using the Modules for Experiments in Stellar Astrophysics (MESA) code, we show that red giant asteroseismology enabled by space-based photometry (i.e., Kepler and CoRoT) can probe these stars during the flash. The rapid ({approx}< 10{sup 5} yr) contraction of the red giant envelope after the initiating flash dramatically improves the coupling of the p-modes to the core g-modes, making the detection of l = 1 mixed modes possible for these 2 Myr. This duration implies that 1 in 35 stars near the red clump in the H-R diagram will be in their core flash phase. During this time, the star has a g-mode period spacing of {Delta}P{sub g} Almost-Equal-To 70-100 s, lower than the {Delta}P{sub g} Almost-Equal-To 250 s of He-burning stars in the red clump, but higher than the RGB stars at the same luminosity. This places them in an underpopulated part of the large frequency spacing ({Delta}{nu}) versus {Delta}P{sub g} diagram that should ease their identification among the thousands of observed red giants.

Bildsten, Lars; Paxton, Bill; Moore, Kevin; Macias, Phillip J. [Kavli Institute for Theoretical Physics and Department of Physics Kohn Hall, University of California, Santa Barbara, CA 93106 (United States)

2012-01-15

242

Nonequilibrium magnesium complexes formed in helium nanodroplets  

International Nuclear Information System (INIS)

Doping helium droplets with alkaline earth atoms is an interesting tool to investigate the interaction with the superfluid helium. Magnesium is a corner case regarding the degree of solvation in helium, which may enable the detection of quantized vortices in helium droplets. In this contribution we add another facet to the discussion. The absorption of helium droplets doped with magnesium atoms is measured with resonant two-photon ionization at different combinations of droplet size and the number of doped Mg atoms. This enables the unambiguous identification of the absorption of an isolated atom inside the droplet centered around 279 nm. When increasing the Mg content of the droplet we find evidence for the formation of metastable, weakly bound Mg complexes. After excitation of such a complex it collapses to a Mg cluster on a timescale of 20 ps

2008-03-10

243

Nonequilibrium magnesium complexes formed in helium nanodroplets  

Energy Technology Data Exchange (ETDEWEB)

Doping helium droplets with alkaline earth atoms is an interesting tool to investigate the interaction with the superfluid helium. Magnesium is a corner case regarding the degree of solvation in helium, which may enable the detection of quantized vortices in helium droplets. In this contribution we add another facet to the discussion. The absorption of helium droplets doped with magnesium atoms is measured with resonant two-photon ionization at different combinations of droplet size and the number of doped Mg atoms. This enables the unambiguous identification of the absorption of an isolated atom inside the droplet centered around 279 nm. When increasing the Mg content of the droplet we find evidence for the formation of metastable, weakly bound Mg complexes. After excitation of such a complex it collapses to a Mg cluster on a timescale of 20 ps.

Przystawik, Andreas; Goede, Sebastian; Tiggesbaeumker, Josef; Meiwes-Broer, Karl-Heinz [Institut fuer Physik, Universitaet Rostock, Universitaetsplatz 3, 18051 Rostock (Germany)

2008-07-01

244

Improvement of helium sampling system in HTTR  

International Nuclear Information System (INIS)

Graphite structures are used as the HTTR core internals. Graphite structures have high heat resistant property but strength degrades easily by oxidization. To prevent the oxidization of graphite structures, impurity concentrations in the helium coolant are controlled strictly. The helium sampling system is installed to measure the impurity concentrations in the helium coolant. Seal-oil leakage occurred at the rod seal mechanism of gas compressor in helium sampling system. The reasons are degradation of the seal material and contaminant abrasion powder of the grand-packing. Thus, the material of the seal material was changed and contaminant was decreased. A long term operation became possible by these countermeasures. Moreover, reliable data can be obtained and efficient impurity control is enabled due to renewal of data acquisition control computer of gas chromatograph mass spectrometer and improvement of liquid nitrogen trap. This report describes the improvement items of the helium sampling system. (author)

2008-01-01

245

Photochemistry inside superfluid helium nano droplets  

Energy Technology Data Exchange (ETDEWEB)

Superfluid helium nano droplets serve as the most gentle cyrogenic matrix for creating isolated and cold molecules. High resolution electronic spectroscopy is sensitive for the investigation of the very weak perturbation of the helium droplet on the embedded molecule. Fluorescence excitation spectra, dispersed emission spectra and pump--probe-spectra show details of the salvation of molecules in helium droplets which were attributed to relaxation processes of the first solvation layer around the dopant. Photochemistry such as ESIPT, tautomerization by proton transfer and charge transfer are highly sensitive on intermolecular perturbations. We have studies such processes in superfluid helium droplets. The comparison with the respective gas phase experiments and quantum chemical calculations reveals further details on the photochemistry as well as on the perturbation by the superfluid helium droplet.

Slenczka, Alkwin; Vdovin, Alexander; Dick, Bernhard [Inst. fuer Physikalische und Theoretische Chemie, Univ. Regensburg (Germany)

2007-07-01

246

Photochemistry inside superfluid helium nano droplets  

International Nuclear Information System (INIS)

Superfluid helium nano droplets serve as the most gentle cyrogenic matrix for creating isolated and cold molecules. High resolution electronic spectroscopy is sensitive for the investigation of the very weak perturbation of the helium droplet on the embedded molecule. Fluorescence excitation spectra, dispersed emission spectra and pump--probe-spectra show details of the salvation of molecules in helium droplets which were attributed to relaxation processes of the first solvation layer around the dopant. Photochemistry such as ESIPT, tautomerization by proton transfer and charge transfer are highly sensitive on intermolecular perturbations. We have studies such processes in superfluid helium droplets. The comparison with the respective gas phase experiments and quantum chemical calculations reveals further details on the photochemistry as well as on the perturbation by the superfluid helium droplet

2007-03-19

247

Characteristics of a helium field ion gun  

International Nuclear Information System (INIS)

A helium field ion gun for a focused ion beam system was designed and constructed. The main feature of the ion gun structure is the use of a gas jet nozzle with a tungsten field emitter tip near the nozzle end. Since the helium gas jet is collimated towards the emitter tip, the local pressure in the vicinity of the tip is kept 110 times higher than the value for the location of the ion gauge which is about 20 cm away from the helium jet ion gun. Using this ion gun, current density of 1 ?A/sr was obtained although the helium gas flow rate ejected from the nozzle is as small as 1.6 x 10-3 Torr l/s. This result indicates high efficiency of the helium gas supply to the emitter tip surface

1988-01-01

248

Solubility of helium in metallic hydrogen  

International Nuclear Information System (INIS)

In the low-pressure limit, a helium atom embedded in the electron gas appropriate to metallic hydrogen is only weakly perturbed from its free space structure, and its interaction with the electron gas can be represented by an energy-dependent pseudopotential. A calculation is made for the Gibbs energy of mixing for H-He, using an Austin pseudopotential and a fluid state model based on hard-sphere structure factors. A large orthogonalisation hole is predicted, which may crudely represent the gradual transition from a helium atom to a screened ?-particle as the electron density increases. The helium solubility is predominantly determined by the structure-independent interaction of the electron gas with the repulsive pseudopotential, and is probably least at the lowest pressures. In the hydrogen-helium planets (Jupiter, Saturn) the helium concentration may be at or close to saturation at the molecular-metallic hydrogen transition. (author)

1979-01-01

249

Spectrographic detection of nitrogen impurity in helium  

International Nuclear Information System (INIS)

A device to observe very small amount of nitrogen impurity in helium gas was developed for a liquefaction system of helium. The principle of detection is based on the optical spectroscopy of the discharge arc in the helium gas. The new detector uses 427.8 nm spectral line as the detection light source while the previous works in this type of detectors used 391.4 nm spectral line. The advantage of newly introduced spectral line is that there is no strong helium spectral line in the neighbor of the observed line. As a result, it became possible to build a simple and reliable impurity detector which can continuously observe very small amount of nitrogen in helium. (author)

1987-01-01

250

Effects of helium on separation characteristics of cryogenic distillation column cascade for fusion reactor  

International Nuclear Information System (INIS)

By choosing the cryogenic distillation column cascade developed at Los Alamos National Laboratory, the effects of helium on separation characteristics of the columns are analyzed in a probable case of input and output specifications. Column (2) is mainly affected by the presence of helium. If the helium percentage in the raw fuel input is 1%, the column performance can be assured by increasing the condenser load. No special helium separator may be needed, but a larger inner diameter of the column, larger flow rate of the refrigerant gas, and larger heat transfer area at the condenser should be considered in the design stage. If the percentage is 5%, both the column pressure and condenser load must be doubled in the steady-state operation. The control operation for the tritium level in the top gas is unavoidably accompanied by a remarkable decrease in the condenser temperature; thus, the controls of the pressure and liquid level in the reboiler are greatly vitiated. If the percentage is 10%, the column must be operated at about4 atm, and even the steady state requires a three times heavier condenser load and an about 25% increase in the packed height. Considering the remarkable effects of helium on the control operation for column (2), the helium removal should be completed before feeding hydrogen isotopes to the column cascade if the helium percentage has a significant value

1984-01-01

251

The Effects of Curvature and Expansion on Helium Detonations on White Dwarf Surfaces  

CERN Multimedia

Accreted helium layers on white dwarfs have been highlighted for many decades as a possible site for a detonation triggered by a thermonuclear runaway. In this paper, we find the minimum helium layer thickness that will sustain a steady laterally propagating detonation and show that it depends on the density and composition of the helium layer, specifically C12 and O16. Detonations in these thin helium layers have speeds slower than the Chapman-Jouget (CJ) speed from complete helium burning, v_cj=1.5e9 cm/s. Though gravitationally unbound, the ashes still have unburned helium (~ 80% in the thinnest cases) and only reach up to heavy elements such as Ca40, Ti44, Cr48, and Fe52. It is rare for these thin shells to generate large amounts of Ni56. We also find a new set of solutions that can propagate in even thinner helium layers when O16 is present at a minimum mass fraction of ~0.07. Driven by energy release from alpha captures on O16 and subsequent elements, these slow detonations only create ashes up to Si28 ...

Moore, Kevin; Bildsten, Lars

2013-01-01

252

Properties of vanadium-base alloys irradiated in the dynamic helium charging experiment  

International Nuclear Information System (INIS)

One property of vanadium-base alloys that is not well understood in terms of their potential use as fusion reactor structural materials is the effect of simultaneous generation of helium and neutron damage. In the present Dynamic Helium Charging Experiment (DHCE), helium was produced uniformly in the specimen at linear rates of ? 0.4 to 4.2 appm helium/dpa by the decay of tritium during irradiation to 18--31 dpa at 425--600 C in Li-filled capsules in a sodium-cooled fast reactor. This paper presents results of postirradiation examination and tests of microstructure and mechanical properties of V-5Ti, V-3Ti-1Si, V-8Cr-6Ti, and V-4Cr-4Ti (the latter alloy has been identified as the most promising candidate vanadium alloy). Effects of helium on tensile strength and ductility were insignificant after irradiation and testing at > 420 C. However, postirradiation ductilities at -150 C in DHCE specimens. Predominantly brittle-cleavage fracture morphologies were observed only at -196 C in some specimens that were irradiated to 31 dpa at 425 C during the DHCE. For the helium generation rates in this experiment (? 0.4--4.2 appm He/dpa), grain-boundary coalescence of helium microcavities was negligible and intergranular fracture was not observed

1995-09-25

253

Exotic helium molecules; Molecules exotiques d'helium  

Energy Technology Data Exchange (ETDEWEB)

We study the photo-association of an ultracold cloud of magnetically trapped helium atoms: pairs of colliding atoms interact with one or two laser fields to produce a purely long range {sup 4}He{sub 2}(2{sup 3}S{sub 1}-2{sup 3}P{sub 0}) molecule, or a {sup 4}He{sub 2}(2{sup 3}S{sub 1}-2{sup 3}S{sub 1}) long range molecule. Light shifts in one photon photo-association spectra are measured and studied as a function of the laser polarization and intensity, and the vibrational state of the excited molecule. They result from the light-induced coupling between the excited molecule, and bound and scattering states of the interaction between two metastable atoms. Their analysis leads to the determination of the scattering length a = (7.2 {+-} 0.6) ruling collisions between spin polarized atoms. The two photon photo-association spectra show evidence of the production of polarized, long-range {sup 4}He{sub 2}(2{sup 3}S{sub 1}-2{sup 3}S{sub 1}) molecules. They are said to be exotic as they are made of two metastable atoms, each one carrying a enough energy to ionize the other. The corresponding lineshapes are calculated and decomposed in sums and products of Breit-Wigner and Fano profiles associated to one and two photon processes. The experimental spectra are fit, and an intrinsic lifetime {tau} = (1.4 {+-} 0.3) {mu}s is deduced. It is checked whether this lifetime could be limited by spin-dipole induced Penning autoionization. This interpretation requires that there is a quasi-bound state close to the dissociation threshold in the singlet interaction potential between metastable helium atoms for the theory to match the experiment. (author)

Portier, M

2007-12-15

254

Determination of helium in beryl minerals  

International Nuclear Information System (INIS)

In order to obtain the diffusion coefficients of helium in beryl and phenacite samples at various temperatures, helium leak rates were measured in these minerals at these temperatures. Mass spectrometry (MS) was used to obtain helium leak rates and the gas flow was plotted against time. The gas quantity determined by MS was first obtained at various temperatures until no helium leak rate was detected. After that, these samples were irradiated with fast neutrons to produce helium which was measured again. This procedure was used to estimate the experimental error. The quantity of helium produced by interaction of gamma radiation with beryl minerals was theoretically calculated from the amount of thorium-232 at the neighbourhood of the samples. The quantity of helium produced in the minerals due to uranium and thorium decay was calculated using the amount of these heavy elements, and the results were compared with the amounts determined by MS. The amount of potassium-40 was determined in order to derive the quantity of argonium-40, since some workers found argonium in excess in these minerals. The quantity of helium in the beryl samples (s) was determined in the center and in the surface of the samples in order to obtain informations about the effectiveness of the Be(?, ?) He reaction. Beryl and phenacite minerals were choosen in this research since they are opposite each other with respect to the helium contents. Both have beryllium in their compositon but beryl hold a large amount of helium while phenacite, in spite of having about three times more beryllium than beryl, do not hold the gas. (author)

1985-01-01

255

Low-energy electron-impact ionization of helium  

Science.gov (United States)

Normalized doubly differential cross sections for the electron-impact ionization of helium at low energies are presented. The data are taken at the incident electron energies of 26.3, 28.3, 30.3, 32.5, 34.3, 36.5, and 40.7eV and for scattering angles of 10°-130°. The measurements involve the use of the moveable target method developed at California State University Fullerton to accurately determine the continuum background in the energy-loss spectra. Normalization of experimental data is made on a relative scale to well-established experimental differential cross sections for excitation of the n=2 manifold of helium and then on an absolute scale to the well-established total ionization cross sections of Shah [J. Phys. B 21, 2751 (1988)]. Comparisons are made with available experimental data and the results of the convergent close-coupling theory.

Schow, E.; Hazlett, K.; Childers, J. G.; Medina, C.; Vitug, G.; Bray, I.; Fursa, D. V.; Khakoo, M. A.

2005-12-01

256

A GM cryocooler with cold helium circulation for remote cooling  

Science.gov (United States)

A GM cryocooler with new cold helium circulation system has been developed at Cryomech. A set of check valves connects to the cold heat exchanger to convert a small portion of AC oscillating flow in the cold head to a DC gas flow for circulating cold helium in the remote loop. A cold finger, which is used for remote cooling, is connected to the check valves through a pair of 5 m long vacuum insulated flexible lines. The GM cryocooler, Cryomech model AL125 having 120 W at 80 K, is employed in the testing. The cold finger can provide 50 W at 81 K for the power input of 4.1 kW and 70.5 W at 81.8 K for the power input of 6 kW. This simple and low cost design is very attractive for some applications in the near future.

Wang, Chao; Brown, Ethan

2014-01-01

257

High temperature mechanical properties of nickel with helium introduced by method of tritium trick  

International Nuclear Information System (INIS)

Mechanical properties of commerical nickel with 10-5-10-4 at. % helium, introduced by the tritium trick method, are studied at 600-800 deg C. It is shown that the given helium concentrations in nickel neither affect the nickel strenght nor cause elasticity drop in the 600-800 deg C temperature range, wherein the effect of high-temperature radiation embrittlement of nickel and stainless steels, and alloys with f.c.c. lattice following a reactor irradiation is observed

1983-01-01

258

Formation of nanostructured tungsten with arborescent shape due to helium plasma irradiation  

International Nuclear Information System (INIS)

Deeply nanostructured tungsten with an arborescent shape was found for the first time to be formed on tungsten-coated graphite by a high-flux helium plasma irradiation at surface temperatures of 1250 and 1600 K, an incident ion energy of 12 eV (well below the physical sputtering threshold) and a helium ion fluence of 3.5 x 1027 m-2. (author)

2006-10-01

259

Study on performances of a small cell drift chamber filled with helium-methane gas mixture  

International Nuclear Information System (INIS)

Preliminary results of study on a 1 m long small cell drift chamber filled with helium-methane gas mixture for low momentum high precision measurement of charged particles are reported. The measured performances of chamber show a good photoelectron peak of 55Fe, 5.9 keV X-ray in helium, uniformities of output signals along the wire and in different drift distance and average space resolution of 155 ?m by the method of three cells using cosmic rays

2001-11-01

260

The Hottest Horizontal-Branch Stars in Omega Centauri: Late Hot Flasher vs. Helium Enrichment  

Science.gov (United States)

UV observations of some massive globular clusters uncovered a significant population of very hot stars below the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario here stars experience the helium flash while on the white dwarf cooling curve or by the helium-rich sub-population recently postulated to exist in some clusters. Spectroscopic analyses of blue hook stars in omega Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C, N enrichment could not be verified from existing data. We want to determine effective temperatures, surface gravities and abundances of He, C, N in blue hook and canonical extreme horizontal branch (EHB) star candidates. Moderately high resolution spectra of stars at the hot end of the blue horizontal branch in the globular cluster omega Cen were analysed for atmospheric parameters (T(sub eff), log g) and abundances using LTE and Non-LTE model atmospheres. In the temperature range 30,000 K to 50,000 K we find that 37% of our stars are helium-poor (log nHe/nH less than -2), 49% have solar helium abundance within a factor of 3 (-1.5 less than or equal to log nHe/nH less than or equal to -0.5) and 14% are helium rich (log nHe/nH greater than -0.4). We also find carbon enrichment in step with helium enrichment, with a maximum carbon enrichment of 3% by mass. At least 30% of the hottest HB stars in omega Centauri show helium abundances well above the predictions from the helium enrichment scenario (Y = 0.42 corresponding to log nHe/nH approximately equal to -0.74). In addition the most helium-rich stars show strong carbon enrichment as predicted by the late hot flasher scenario. We conclude that the helium-rich HB stars in omega Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

Moehler, S.; Dreizler, S.; Lanz, T.; Bono, G.; Sweigart, A V.; Calamida, A.; Monelli, M.; Nonino, M.

2007-01-01

 
 
 
 
261

Helium gas bubble trapped in liquid helium in high magnetic field  

Science.gov (United States)

High magnetic field magnets are used widely in the area of the condensed matter physics, material science, chemistry, geochemistry, and biology at the National High Magnetic Field Laboratory. New high field magnets of state-of-the-art are being pursued and developed at the lab, such as the current developing 32 T, 32 mm bore fully superconducting magnet. Liquid Helium (LHe) is used as the coolant for superconducting magnets or samples tested in a high magnetic field. When the magnetic field reaches a relatively high value the boil-off helium gas bubble generated by heat losses in the cryostat can be trapped in the LHe bath in the region where BzdBz/dz is less than negative 2100 T2/m, instead of floating up to the top of LHe. Then the magnet or sample in the trapped bubble region may lose efficient cooling. In the development of the 32 T magnet, a prototype Yttrium Barium Copper Oxide coil of 6 double pancakes with an inner diameter of 40 mm and an outer diameter of 140 mm was fabricated and tested in a resistive magnet providing a background field of 15 T. The trapped gas bubble was observed in the tests when the prototype coil was ramped up to 7.5 T at a current of 200 A. This letter reports the test results on the trapped gas bubble and the comparison with the analytical results which shows they are in a good agreement.

Bai, H.; Hannahs, S. T.; Markiewicz, W. D.; Weijers, H. W.

2014-03-01

262

Helium hammer in superfluid transfer  

Science.gov (United States)

Large transient pressure pulses, referred to as a helium hammer, which occurred in the transfer line of the main cryogenic tank during the development tests of the Infrared Astronomical Satellite, launched on January 25, 1983, are analyzed, and the measures taken to prevent a failure described. The modifications include an installation of a 2.3-liter surge tank upstream, and a back-up relief valve downstream, of a burst disk. The surge tank is designed to attenuate a 0.33-MPa pressure pulse at the inlet down to 0.092 MPa at the outlet. A mechanism of the pulse generation is suggested, which involves flashing and rapid recondensation of the small amount of liquid entering the warm section of a transition to room temperature.

Tward, E.; Mason, P. V.

1984-01-01

263

Group representations and superfluid helium  

International Nuclear Information System (INIS)

The spectrum of states of superfluid helium-4 is described by the representation theory of groups. Starting from the symmetry group, describing the fluctuations of Bose-Einstein condensed states of zero momentum, the excited states by non-compact groups are described. This contains complete information about the system including degeneracy, energy levels etc. This leads to the possibility of classifying all realistic interactions. As this formalism is equivalent to the Hamiltonian formalism, this description restricts the ambiguous framework of the quantum-mechanical description where interaction or parameters can be varied arbitrarily. With all possible groups and representations, all the excited states can, in principle, be described. The paper is mainly concerned with the phonon spectrum and the roton-like and vortex excitations are also taken into consideration. (author)

1979-01-01

264

Helium Saturation of Liquid Propellants  

Science.gov (United States)

The research is in three areas which are: (1) techniques were devised for achieving the required levels of helium (He) saturation in liquid propellants (limited to monomethylhydrazine (MMH) and nitrogen tetroxide (NTO)); (2) the values were evaluated for equilibrium solubilities of He in liquid propellants as currently used in the industry; and (3) the He dissolved in liquid propellants were accurately measured. Conclusions drawn from these studies include: (1) Techniques for dissolving He in liquid propellants depending upon the capabilities of the testing facility (Verification of the quantity of gas dissolved is essential); (2) Until greater accuracy is obtained, the equilibrium solubility values of He in MMH and NTO as cited in the Air Force Propellant Handbooks should be accepted as standard (There are still enough uncertainties in the He saturation values to warrant further basic experimental studies); and (3) The manometric measurement of gas volume from a frozen sample of propellant should be the accepted method for gas analysis.

Yavrouian, A. H.; Moran, Clifford M.

1990-01-01

265

Helium two-phase instabilities  

International Nuclear Information System (INIS)

Instabilities encountered in helium two-phase flow during the cool down of superconducting magnets and transmission lines have been experimentally investigated in 1000 mm long vertical tubes of sizes 6.35 and 2.73 mm. Density wave oscillations were measured and recorded in both adiabatic and diabatic flow conditions. Pressure drop oscillations across the test section were observed with the aid of a sensitive differential pressure transducer. The average density at the exit of the experimental test section was a function of the dielectric constant measured by a capacitance probe. The period of the observed density wave sustained oscillations (0.2 to 3 seconds) were found to be of the same order of magnitude of the fluid particles residence time in the heated section. An empirical threshold criteria for the inception of these oscillations has been developed from similarity analysis. (author)

1979-01-01

266

Helium transport and behavior of ELMy H-mode plasmas on JT-60U  

International Nuclear Information System (INIS)

Helium (He) transport and behavior have been investigated during ELMy (edge-localized mode) H-mode using a helium beam in JT-60U. Helium transport coefficients in the ELMy H-mode plasmas (H=1.5) are found to be DA=1-2 m2/s and CV=1.0-1.5 when a neutral beam of 60 keV helium atoms is used for a source of central fuelling, and DA=1 m2/s and CV=1.0-1.5 when a short pulse He gas puff is used as peripheral fuelling. No helium accumulation is observed during ELMy H-mode. The behavior of helium in the divertor region has been studied with divertor spectroscopic measurement and compared with that in the main plasma. The He recycling flux in the divertor during ELMy H-mode is about one order of magnitude less than during L-mode with the same level of He gas fuelling. ((orig.))

1995-04-01

267

Monte Carlo simulations of neon versus helium ion beam induced deposition, sputtering and etching  

Science.gov (United States)

The ion beam induced nanoscale synthesis of PtCx (where x ˜ 5) using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPt^IVMe3) precursor is investigated by performing Monte Carlo simulations of helium and neon ions. The helium beam leads to more lateral growth relative to the neon beam because of its larger interaction volume. The lateral growth of the nanopillars is dominated by molecules deposited via secondary electrons in the both simulations. Notably, the helium pillars are dominated by SE-I electrons whereas the neon pillars by SE-II electrons. Using a low precursor residence time of 70?s resulting in an equilibrium coverage of ˜ 4%, the neon simulation has a lower deposition efficiency (3.5%) compared to that of the helium simulation (6.5%). At larger residence time (10ms) and consequently larger equilibrium coverage (85%) the deposition efficiencies of helium and neon increased to 49% and 21%, respectively; which is dominated by increased lateral growth rates leading to broader pillars. The nanoscale growth is further studied by varying the ion beam diameter at 10 ms precursor residence time. The study shows that total SE yield decreases with increasing beam diameters for the both ion types. However, the helium has the larger SE yield as compared to that of neon in the both low and high precursor residence time, and thus pillars are wider in all the simulations studied.

Timilsina, Rajendra; Smith, Daryl; Rack, Philip

2013-03-01

268

A comparison of neon versus helium ion beam induced deposition via Monte Carlo simulations  

Science.gov (United States)

The ion beam induced nanoscale synthesis of PtCx (where x ˜ 5) using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPtIVMe3) precursor is investigated by performing Monte Carlo simulations of helium and neon ions. The helium beam leads to more lateral growth relative to the neon beam because of its larger interaction volume. The lateral growth of the nanopillars is dominated by molecules deposited via secondary electrons in both the simulations. Notably, the helium pillars are dominated by SE-I electrons whereas the neon pillars are dominated by SE-II electrons. Using a low precursor residence time of 70 ?s, resulting in an equilibrium coverage of ˜4%, the neon simulation has a lower deposition efficiency (3.5%) compared to that of the helium simulation (6.5%). At larger residence time (10 ms) and consequently larger equilibrium coverage (85%) the deposition efficiencies of helium and neon increased to 49% and 21%, respectively; which is dominated by increased lateral growth rates leading to broader pillars. The nanoscale growth is further studied by varying the ion beam diameter at 10 ms precursor residence time. The study shows that total SE yield decreases with increasing beam diameters for both the ion types. However, helium has the larger SE yield as compared to that of neon in both the low and high precursor residence time, and thus pillars are wider in all the simulations studied.

Timilsina, Rajendra; Smith, Daryl A.; Rack, Philip D.

2013-03-01

269

A comparison of neon versus helium ion beam induced deposition via Monte Carlo simulations  

International Nuclear Information System (INIS)

The ion beam induced nanoscale synthesis of PtCx (where x ? 5) using the trimethyl (methylcyclopentadienyl)platinum(IV) (MeCpPtIVMe3) precursor is investigated by performing Monte Carlo simulations of helium and neon ions. The helium beam leads to more lateral growth relative to the neon beam because of its larger interaction volume. The lateral growth of the nanopillars is dominated by molecules deposited via secondary electrons in both the simulations. Notably, the helium pillars are dominated by SE-I electrons whereas the neon pillars are dominated by SE-II electrons. Using a low precursor residence time of 70 ?s, resulting in an equilibrium coverage of ?4%, the neon simulation has a lower deposition efficiency (3.5%) compared to that of the helium simulation (6.5%). At larger residence time (10 ms) and consequently larger equilibrium coverage (85%) the deposition efficiencies of helium and neon increased to 49% and 21%, respectively; which is dominated by increased lateral growth rates leading to broader pillars. The nanoscale growth is further studied by varying the ion beam diameter at 10 ms precursor residence time. The study shows that total SE yield decreases with increasing beam diameters for both the ion types. However, helium has the larger SE yield as compared to that of neon in both the low and high precursor residence time, and thus pillars are wider in all the simulations studied. (paper)

2013-03-22

270

Helium refrigeration system for the KSTAR  

International Nuclear Information System (INIS)

The KSTAR, a tokamak with fully superconducting (SC) magnets, is under construction in the National Fusion Research Center (NFRC). For the proper operation of the KSTAR, the superconducting magnets have to be maintained below the critical temperature of the SC components while charged at their corresponding operation current values. In this paper, a large scale helium refrigeration system (HRS) which has been designed and developed to fulfill such a mission is presented. The cold components of the KSTAR are kept at their operating temperatures thanks to various kinds of cryogenic helium which are produced in the cold box (C/B) of the HRS in combination with the supercritical helium (SHe) cryogenic circulators and a liquid helium (LHe) thermal damper (TD) located in the primary helium distribution box (D/B no. 1). The relative distribution of the cryogenic helium among the cooling channels of each cold component of the KSTAR is performed by the secondary helium distribution system which consists of the secondary distribution box (D/B no. 2) and the cryogenic transfer lines (CTL's)

2006-11-01

271

Helium migration in alpha-irradiated beryllium  

International Nuclear Information System (INIS)

Mass-spectrometric investigation of the kinetics of helium emission from beryllium specimens has been carried on. Helium was introduced by means of specimen irradiation with alpha particles at the Van de Graaff accelerator. An equation of gaseous diffusion to vacuum from a plate with a limited and localized quantity of diffusing substance has been solved. It is shown by means of a model calculation using an electronic computer that the whole gas emission occurs practically through a surface which are the nearest to a saturation layer. Parameters o a temperature dependence of helium diffusion in beryllium in a wide temperature range (650-1150 deg) have been calculated from kicetic curves. It is concluded on the basis of a low value of helium diffusion activation energy in beryllium at annealing temperatures below 900 deg C that there is helium migration over interstitials or in the form of helium atom complexes with vacancies. Considerable increase of helium yield at temperatures above 900 deg C is attributed to increase in the yield surface and reduction of a diffusion path at the expense of ''irreversible'' structural changes in beryllium

1981-01-01

272

Helium desorption from a (110) Mo crystal  

International Nuclear Information System (INIS)

Helium desorption measurements with a Mo-crystal show that during stage III annealing vacancies are removed but that vacancies containing helium (HeV), which are immobile, are not affected. Since interstitials injected at room temperature do recombine with HeV's, it seems that, in stage III, vacancies become mobile and interstitials remain trapped (in e.g. clusters). These observations are supported by atomistic calculations. Measured desorption energies of helium from vacancies in Mo show good agreement with the calculated energies. (author)

1976-10-16

273

The ion implantation of helium into gold  

International Nuclear Information System (INIS)

Two methods are used to investigate the very near surface (0 to 10 nm) effect of 3 keV helium implantation into evaporated gold films. X-ray reflection spectroscopy is used to determine the change in density of the implanted layer and Rutherford backscattering to determine helium concentrations; a maximum of 3.3 He atoms per metal vacancy is reported for a fluence of 4.0 x 1016 atoms cm-2. The data support the proposition that for implant conditions below those required for exfoliation, there are helium pressures well in excess of 100 kbar within implantation induced voids. (author)

1986-05-16

274

Adiabatic hyperspherical study of the helium trimer  

Energy Technology Data Exchange (ETDEWEB)

The adiabatic hyperspherical method is used to investigate the spectrum of the helium trimer and to explore effects on the spectrum of varying the helium masses as well as the interaction strength. When a realistic helium dimer potential is adopted, only two isotopic combinations are observed to have three-body bound states: {sup 4}He{sub 3} and {sup 4}He{sub 2}{sup 3}He. By artificially adjusting the dimer potential, we also determine the range of interaction strengths for which halo states can result. The existence of Efimov states for both physical and unphysical systems is also examined. {copyright} {ital 1996 American Institute of Physics.}

Esry, B.D.; Lin, C.D.; Greene, C.H. [Department of Physics and JILA,University of Colorado, Boulder, Colorado 80309-0440 (United States)

1996-07-01

275

Helium thermodesorption mechanism from irradiated boron carbide  

International Nuclear Information System (INIS)

The boron carbide powder, the particle size whereof constitutes about 10 ?m, is used as the WWER-1000 reactor absorption core. The model of the helium atoms activation yield from the accumulation centers and their diffusion to the surface of the boron carbide powder spherical particle is proposed. The evaluation of the helium yield from the material in the process of annealing is obtained. The effect of the powder grains size and change in the material temperature velocity on the helium thermodesorption from the irradiated boron carbide is evaluated

2005-03-01

276

Simulation study on retention and reflection from tungsten carbide under high fluence of helium ions  

International Nuclear Information System (INIS)

We have studied, by a Monte Carlo simulation code ACAT-DIFFUSE, the fluence-dependence of the amount of retained helium atoms in tungsten carbide at room temperature under helium ion bombardment. The retention behavior may be understood qualitatively in terms of irradiation-dependent diffusion coefficient assumed and range. The emission processes from tungsten carbide under helium ion irradiation derived were compared with each other. We have discussed the retention curves for incident energy of 5 keV at incident angles of 0deg and 80deg and of 500 eV at 0deg. The energy spectra of helium atoms reflected from tungsten carbide for incident energy of 500 eV at 0deg and 80deg were compared with those from graphite and tungsten. (author)

2000-01-01

277

Characteristics of an activated carbon monolith for a helium adsorption compressor  

Energy Technology Data Exchange (ETDEWEB)

An activated carbon monolith (ACM) with a high helium adsorption/desorption capacity, high density, low pressure drop, low thermal expansion and good mechanical properties was prepared and applied successfully in a helium adsorption compressor as a part of a 4.5 K sorption cooler. The activated carbon (AC) used in the monolith preparation was selected from a series of ACs prepared from an anthracite and bituminous coals activated using KOH, NaOH and CO{sub 2}, and having a variety of surface areas, micropore size distributions and packing densities. The selected AC was combined with a binder to prepare an ACM with suitable mechanical properties for machining. The results of this study, related to an helium sorption compressor includes: packing density, mechanical properties (compression strength, vibration tests), thermal expansion, pressure-drop measurements and also helium adsorption isotherms measured at high pressure (up to 35 bar) and low temperatures (from 20 K up to 150 K).

Lozano-Castello, D.; Jorda-Beneyto, M.; Cazorla-Amoros, D.; Linares-Solano, A.; Burger, J.F.; ter Brake, H.J.M.; Holland, H.J. [University of Alicante, Alicante (Spain)

2010-01-15

278

The effect of helium accumulation and radiation damage on the weldability of 316-type steel  

International Nuclear Information System (INIS)

The embrittlement simulated by helium accumulation, with the ITER components repaired by welding during maintenance, is one of the factors limiting the materials lifetime. This work presents the results of the investigations into the effect of neutron produced helium, 0.1 dpa Tirr - 80 C, (at a low He/dpa) and cyclotron introduced helium, 5-430 appm He (at high He/dpa) on the quality and mechanical properties of the type 316 steel welds. The samples, both irradiated and controls, were welded by e-beam welding (cyclotron injection) or on the automatic argon-arc welding device in the hot cell SRIIAr (neutron irradiation). Low-cycle fatigue (LCF) testing in bending was used to assess impact of helium on the degradation of welded joint properties. (orig.)

1998-10-01

279

Simulation study on retention and reflection from tungsten carbide under high fluence of helium ions  

Energy Technology Data Exchange (ETDEWEB)

We have studied, by a Monte Carlo simulation code ACAT-DIFFUSE, the fluence-dependence of the amount of retained helium atoms in tungsten carbide at room temperature under helium ion bombardment. The retention behavior may be understood qualitatively in terms of irradiation-dependent diffusion coefficient assumed and range. The emission processes from tungsten carbide under helium ion irradiation derived were compared with each other. We have discussed the retention curves for incident energy of 5 keV at incident angles of 0deg and 80deg and of 500 eV at 0deg. The energy spectra of helium atoms reflected from tungsten carbide for incident energy of 500 eV at 0deg and 80deg were compared with those from graphite and tungsten. (author)

Ono, T.; Yamamura, Y. [Okayama University of Science, Okayama (Japan); Kawamura, T. [Chubu University, Kasugai, Aichi (Japan); Kenmotsu, T. [National Inst. for Fusion Science, Toki, Gifu (Japan)

2000-08-01

280

Effects of dislocations on thermal helium desorption from nickel and iron  

International Nuclear Information System (INIS)

Helium atoms in metals have a strong tendency to accumulate at defects. Unfortunately, the experimental identification of the trapping sites of helium atoms is difficult. In this paper, the effects of dislocations on the trapping and desorption of helium atoms in nickel and iron were studied by thermal desorption spectroscopy. Defects were introduced in well-annealed high-purity metals by cold rolling. Positron annihilation spectroscopy was carried out to identify defects by measuring the positron lifetime before annihilation with various defects. The trapping and desorption of helium atoms at dislocations were investigated by implantation with low-energy He+ ions, both without irradiation damage (0.1 keV or 0.15 keV) and with irradiation damage (5.0 keV).

2011-10-01

 
 
 
 
281

Implementation of two-phase tritium models for helium bubbles in HCLL breeding blanket modules  

Science.gov (United States)

Tritium self-sufficiency requirement of future DT fusion reactors involves large helium production rates in the breeding blankets; this might impact on the conceptual design of diverse fusion power reactor units, such as Liquid Metal (LM) blankets. Low solubility, long residence-times and high production rates create the conditions for Helium nucleation, which could mean effective T sinks in LM channels. A model for helium nano-bubble formation and tritium conjugate transport phenomena in liquid Pb17.5Li and EUROFER is proposed. In a first approximation, it has been considered that He bubbles can be represented as a passive scalar. The nucleation model is based on the classical theory and includes a simplified bubble growth model. The model captures the interaction of tritium with bubbles and tritium diffusion through walls. Results show the influence of helium cavitation on tritium inventory and the importance of simulating the system walls instead of imposing fixed boundary conditions.

Fradera, J.; Sedano, L.; Mas de les Valls, E.; Batet, L.

2011-10-01

282

Neovascular glaucoma after helium ion irradiation for uveal melanoma  

International Nuclear Information System (INIS)

Neovascular glaucoma developed in 22 of 169 uveal melanoma patients treated with helium ion irradiation. Most patients had large melanomas; no eyes containing small melanomas developed anterior segment neovascularization. The mean onset of glaucoma was 14.1 months (range, 7-31 months). The incidence of anterior segment neovascularization increased with radiation dosage; there was an approximately three-fold increase at 80 GyE versus 60 GyE of helium ion radiation (23% vs. 8.5%) (P less than 0.05). Neovascular glaucoma occurred more commonly in larger tumors; the incidence was not affected by tumor location, presence of subretinal fluid, nor rate of tumor regression. Fifty-three percent of patients had some response with intraocular pressures of 21 mmHg or less to a combination of antiglaucoma treatments

1986-01-01

283

Failure of choroidal melanoma to respond to helium ion therapy  

International Nuclear Information System (INIS)

Helium ion irradiation is a promising alternative therapy for choroidal melanoma. In short-term follow-up (less than 5 years), more than 90% (18/19) of treated patients demonstrated tumor regression. Researchers had to enucleate five eyes after helium ion therapy either because of continued tumor growth (four patients) or other complications (one patient). Two melanomas continued to grow and seemed to be radioresistant. In two other tumors it retrospectively seemed that the entire lesion was not inside the radiation field. In one patient total retinal detachment and glaucoma developed; enucleation was performed because of a painful eye. Metastatic disease developed in no patients. The treatment failures emphasize that there are a number of unresolved issues regarding the use of charged-particle irradiation in the treatment of melanoma. Further studies must be performed to answer these questions and better delineate the use of these newer forms of therapy

1983-01-01

284

Helium magnetic refrigerator. II. Liquefaction process and efficiency  

International Nuclear Information System (INIS)

Magnetic refrigeration techniques are based on the utilization of the magnetocaloric effect. A change in entropy occurring as a result of a change in magnetization leads to heat-transfer processes. The magnetic refrigerator consists of two parts, including the magnetic materials and the heat-exchange system. Advantages of this type of refrigerator compared to the gas refrigerator are related to high efficiency, compactness, and high reliability. The present investigation is concerned with a new Carnot type refrigeration system which liquefies helium with the aid of Gd3Ga5O12 (GGG) as a refrigerant. Attention is given to the heat transfer between GGG and helium gas, the experimental apparatus, and the obtained experimental results. 7 references

1984-01-01

285

Genetic changes in Mammalian cells transformed by helium cells  

International Nuclear Information System (INIS)

Midterm Syrian Hamster embryo (SHE) cells were employed to study high LET-radiation induced tumorigenesis. Normal SHE cells (secondary passage) were irradiated with accelerated helium ions at an incident energy of 22 MeV/u (9--10 keV/?m). Transformed clones were isolated after growth in soft agar of cells obtained from the foci of the initial monolayer plated postirradiation. To study the progression process of malignant transformation, the transformed clones were followed by monolayer subculturing for prolonged periods of time. Subsequently, neoplasia tests in nude mice were done. In this work, however, we have focused on karyotypic changes in the banding patterns of the chromosomes during the early part of the progressive process of cell transformation for helium ion-induced transformed cells. 26 refs., 5 figs., 2 tabs

1990-07-06

286

Thermal desorption of helium from homogeneously implanted graphite  

Science.gov (United States)

Super-fine grain graphite (FGG) and pyrolytic carbon (PYC) of thicknesses around 200 ?m were homogeneously implanted at room temperature with ?-particles (0.5 MeV ? E? ? 22 MeV). Thermal helium desorption spectrometry in the temperature range from 400 to 1900 K can be described by diffusion kinetics with an activation energy of 1.1 eV in FGG and about 0.75 eV in PYC. Desorption during temperature ramping at a constant rate of 0.83 K/s also shows significant differences of the two graphite species. It is found that in FGG and especially in PYC a considerable fraction of the implanted helium is retained even beyond 1000 K. This is in contrast to results reported after low energy implantations to high doses for various graphite species.

Jung, P.; Schroeder, H.

1991-11-01

287

Thermal desorption of helium from homogeneously implanted graphite  

Energy Technology Data Exchange (ETDEWEB)

Super-fine grain graphite (FGG) and pyrolytic carbon (PYC) of thicknesses around 200 {mu}m were homogeneously implanted at room temperature with {alpha}-particles (0.5 MeV {<=} E{sub {alpha}} {<=} 22 MeV). Thermal helium desorption spectrometry in the temperature range from 400 to 1900 K can be described by diffusion kinetics with an activation energy of 1.1 eV in FGG and about 0.75 eV in PYC. Desorption during temperature ramping at a constant rate of 0.83 K/s also shows significant differences of the two graphite species. It is found that in FGG and especially in PYC a considerable fraction of the implanted helium is retained even beyond 1000 K. This is in contrast to results reported after low energy implantations to high doses for various graphite species. (orig.).

Jung, P.; Schroeder, H. (Inst. fuer Festkoerperforschung, Forschungszentrum Juelich, Association Euratom-KFA (Germany))

1991-11-01

288

Singly charged energetic helium emitted in solar flares  

International Nuclear Information System (INIS)

First direct charge state measurements of 0.41--1.05 MeV per nucleon helium accelerated at the Sun reveal surprisingly large abundances of singly ionized helium, with typical He"+/He"+"+ ratios between 0.04 and 0.21. This unexpected overabundance of He"+ was observed in each of the three large solar-flare particle events which occurred between 1978 August and 1979 October. The data were obtained with the Max-Planck-Institut/University of Maryland Experiment on board the ISEE-3 spacecraft. Our observations suggest either strong coronal temperature inhomogeneities including cool regions approx.10"5 K or injection of ''cold'' chromospheric/photospheric material into the flare acceleration region

1981-06-01

289

Singly charged energetic helium emitted in solar flares  

Energy Technology Data Exchange (ETDEWEB)

First direct charge state measurements of 0.41--1.05 MeV per nucleon helium accelerated at the Sun reveal surprisingly large abundances of singly ionized helium, with typical He/sup +//He/sup + +/ ratios between 0.04 and 0.21. This unexpected overabundance of He/sup +/ was observed in each of the three large solar-flare particle events which occurred between 1978 August and 1979 October. The data were obtained with the Max-Planck-Institut/University of Maryland Experiment on board the ISEE-3 spacecraft. Our observations suggest either strong coronal temperature inhomogeneities including cool regions approx.10/sup 5/ K or injection of ''cold'' chromospheric/photospheric material into the flare acceleration region.

Hovestadt, D.; Gloeckler, G.; Hoefner, H.; Klecker, B.; Ipavich, F.M.; Fan, C.Y.; Fisk, L.A.; O' Gallagher, J.J.; Scholer, M.

1981-06-01

290

Electrical heater for very-low pressure helium gas  

CERN Multimedia

Testing superconducting magnets for the Large Hadron Collider (LHC) in superfluid helium requires large-capacity refrigeration at 1.8K. At CERN, this is provided by a combination of a cold compressor and a set of warm vacuum pumps capable of handling up to 18g/s at 1 kPa suction pressure. The cold helium vapour, after the cold compressor, is warmed up from about 5K to ambient temperature in a 32 kW electrical heater. The device is designed to operate reliably at flow rates varying from 1 to 18g/s, inlet pressure of 1 kPa to 3 kPa, with pressure drop 100 Pa. Design and construction of the heater, completely realised at CERN, are presented, as well as measured performance. Some technological problems are discussed.

Benda, V; Vuillierme, B

1996-01-01

291

Failure of choroidal melanoma to respond to helium ion therapy  

Energy Technology Data Exchange (ETDEWEB)

Helium ion irradiation is a promising alternative therapy for choroidal melanoma. In short-term follow-up (less than 5 years), more than 90% (18/19) of treated patients demonstrated tumor regression. Researchers had to enucleate five eyes after helium ion therapy either because of continued tumor growth (four patients) or other complications (one patient). Two melanomas continued to grow and seemed to be radioresistant. In two other tumors it retrospectively seemed that the entire lesion was not inside the radiation field. In one patient total retinal detachment and glaucoma developed; enucleation was performed because of a painful eye. Metastatic disease developed in no patients. The treatment failures emphasize that there are a number of unresolved issues regarding the use of charged-particle irradiation in the treatment of melanoma. Further studies must be performed to answer these questions and better delineate the use of these newer forms of therapy.

Char, D.H.; Crawford, J.B.; Castro, J.R.; Woodruff, K.H.

1983-02-01

292

Neovascular glaucoma after helium ion irradiation for uveal melanoma  

Energy Technology Data Exchange (ETDEWEB)

Neovascular glaucoma developed in 22 of 169 uveal melanoma patients treated with helium ion irradiation. Most patients had large melanomas; no eyes containing small melanomas developed anterior segment neovascularization. The mean onset of glaucoma was 14.1 months (range, 7-31 months). The incidence of anterior segment neovascularization increased with radiation dosage; there was an approximately three-fold increase at 80 GyE versus 60 GyE of helium ion radiation (23% vs. 8.5%) (P less than 0.05). Neovascular glaucoma occurred more commonly in larger tumors; the incidence was not affected by tumor location, presence of subretinal fluid, nor rate of tumor regression. Fifty-three percent of patients had some response with intraocular pressures of 21 mmHg or less to a combination of antiglaucoma treatments.

Kim, M.K.; Char, D.H.; Castro, J.L.; Saunders, W.M.; Chen, G.T.; Stone, R.D.

1986-02-01

293

Two-electron ejection from helium by Compton scattering  

International Nuclear Information System (INIS)

Double ionization of the ground state of helium by Compton scattering is investigated using many-body perturbation theory. Representative calculations of cross sections differential in the scattered photon energy and angle are given to illustrate the nature of the process. Total cross sections for single ionization and double ionization of helium and the ratio of these cross sections are presented for energies from 2.5 to 20 keV. Current experimental data for the ratio due to both Compton scattering and photoionization are in reasonable agreement with the corresponding calculations presented here. However, comparisons of the present results with other calculations reveal substantial discrepancies. Possible reasons for these differences at finite energies are proposed. Our results for double ionization by Compton scattering have not reached an asymptotic limit

1995-04-01

294

Solar models with helium and heavy element diffusion  

CERN Document Server

Heavy element and helium diffusion are both included for the first time in this series of papers on precise solar models, along with improvements in the input data for nuclear reaction rates, the solar luminosity, the solar age, heavy element abundances, radiative opacities, helium and metal diffusion rates, and neutrino interaction cross sections. The calculated neutrino event rates, including all of the improvements, are 9.3_{-1.4}^{+1.2} SNU for the \\hbox{^{37}Cl} experimentand 137_{-7}^{+8} SNU for the \\hbox{^{71}Ga} experiments. The calculated flux of \\hbox{^{7}Be} neutrinos is 5.1(1.00_{-0.07}^{+0.06}) \\times 10^{9}~{\\rm cm^{-2}s^{-1}} and the flux of {\\rm ^8B} neutrinos is 6.5 (1.00_{-0.17}^{+0.14})\\times 10^{6}~{\\rm cm^{-2}s^{-1}}. The present-day surface helium abundance of the model is Y_s = 0.247, in agreement with the helioseismological measurement of Y_s = 0.242 \\pm 0.003 determined by Hernandez and Christensen-Dalsgaar d (1994). The computed depth of the convective zone is \\hbox{R = 0.712~ R_{\\o...

Bahcall, J N; Bahcall, John N

1995-01-01

295

LOCA analysis for Korean helium cooled solid breeder TBM  

International Nuclear Information System (INIS)

One of the major ITER goals is test blanket module (TBM) program which is for the demonstration of the breeding capability that would lead to tritium self-sufficiency in a reactor and the extraction of high-grade heat suitable for electricity generation under the ITER fusion environment. While the engineering design of Korean helium cooled solid breeder (HCSB) TBM and its ancillary systems has been performed, a safety assessment on different possible accident scenarios should be carried out for the purpose of licensing. In this paper, accident analyses for several loss of coolant accident (LOCA) cases were performed in order to assess safety aspects of the TBM design using RELAP5/MOD3.2. Since the TBM forms a loop with helium cooling system (HCS) which is one of ancillary systems required for removing heat deposited in the TBM by neutron wall loading and surface heat flux from plasma, it is necessary to model the complete loop for accident analysis. In this study, the helium passage including the TBM and HCS was nodalized for each accident scenario. The TBM and HCS components were modeled as the associated heat structures provided by RELAP5 to include heat transfer across solid boundaries. Based on computational results it was found that current design of the TBM is robust from the safety point of view.

2009-06-01

296

The growth of helium bubbles in stainless steel at high temperatures  

International Nuclear Information System (INIS)

The influence of annealing time (1 to 1000 hours), applied tensile stress (0 to 130 MPa), temperature (973 to 1073 K) and helium content (10 to 300 a.p.p.m.) on the size distribution and density of helium bubbles within the grains of AISI type 316 stainless steel has been studied by TEM of ?-implanted foil specimens. The results are compared with theoretical predictions assuming different growth mechanisms. The experimental data are best described by assuming that (1) the bubble coarsening is due to Ostwald ripening and (2) the helium in the bubbles obeys a highly non-ideal equation of state. From such a comparison an activation energy for helium permeation through the lattice of 3.5 eV can be deduced, which is comparable with theoretical estimates. It was further observed that tensile stresses can lead to bimodal size distributions, which are attributed to the presence of two mobile and supersaturated components (helium and vacancies) during the nucleation stage. The subsequent growth of matrix bubbles seems to be rather insensitive to stress, in contrast to the behaviour of grain boundary bubbles. Finally it could be shown that, within the covered parameter range, the implanted helium is entirely precipitated into bubbles with diameters > approx. 1.5 nm that are detectable by TEM. (author)

1983-01-01

297

Trace Detection of Metastable Helium Molecules in Superfluid Helium by Laser-Induced Fluorescence  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We describe an approach to detecting ionizing radiation that combines the special properties of superfluid helium with the sensitivity of quantum optics techniques. Ionization in liquid helium results in the copious production of metastable helium molecules, which can be detected by laser-induced fluorescence. Each molecule can be probed many times using a cycling transition, resulting in the detection of individual molecules with high signal to noise. This technique could b...

Mckinsey, D. N.; Lippincott, W. H.; Nikkel, J.; Rellergert, W.

2005-01-01

298

Behavior of the helium in metals and the problem of helium induced brittleness in stainless steels  

International Nuclear Information System (INIS)

The representative works from an extensive literature on the helium in metals are reviewed. The status of researches in this field is summarized with an emphasis on the states of helium atoms in metals, their microscopical distribution and migration, and also their macroscoptical effects. The problem of the helium induced brittleness in stainless steels is particularly discussed. Some relevant experimental results obtained by authors are also included as examples

1989-01-01

299

Diffusion of helium and nucleation-growth of helium-bubbles in metallic materials  

International Nuclear Information System (INIS)

Studies of diffusion and aggregation behaviour of helium in metallic materials are very important to solve the problem of helium embrittlement in structural materials used in the environment of nuclear power. Experimental studies on helium diffusion and aggregation in austenitic stainless steels in a wide temperature range have been performed in authors' research group and the main results obtained are briefly summarized. The mechanism of nucleation-growth of helium-bubbles has been discussed and some problems to be solved are also given

2001-03-01

300

Helium migration in alkali germanate glasses  

International Nuclear Information System (INIS)

Helium permeability, diffusivity, and solubility have been measured for sodium, potassium, rubidium, and cesium germanate glasses, and for one series of sodium-potassium germanate glasses. In each case, the helium permeability and diffusivity exhibit minima in the property-composition curves. These minima shift to greater alkali oxide content and increase in magnitude in the order Cs, Rb, K, Na-K, Na. These minima result from corresponding maxima in activation energy for helium migration. Helium solubilities do not exhibit similar minima, but rather decrease monotonically with increasing alkali oxide content. These results appear to be related to free-volume changes in the glasses as a function of composition. The inability of the current structural model for these glasses to explain the results of the present study raises questions regarding the validity of that model

1979-01-01

 
 
 
 
301

Helium cosmic ray flux measurements at Mars  

International Nuclear Information System (INIS)

The helium energy spectrum in Martian orbit has been observed by the MARIE charged particle spectrometer aboard the 2001 Mars Odyssey spacecraft. The orbital data were taken from March 13, 2002 to October 28, 2003, at which time a very intense Solar Particle Event caused a loss of communication between the instrument and the spacecraft. The silicon detector stack in MARIE is optimized for the detection of protons and helium in the energy range below 100MeV/n, which typically includes almost all of the flux during SPEs. This also makes MARIE an efficient detector for GCR helium in the energy range of 50-150MeV/n. We will present the first fully normalized flux results from MARIE, using helium ions in this energy range

2006-01-01

302

Helium cosmic ray flux measurements at Mars  

Energy Technology Data Exchange (ETDEWEB)

The helium energy spectrum in Martian orbit has been observed by the MARIE charged particle spectrometer aboard the 2001 Mars Odyssey spacecraft. The orbital data were taken from March 13, 2002 to October 28, 2003, at which time a very intense Solar Particle Event caused a loss of communication between the instrument and the spacecraft. The silicon detector stack in MARIE is optimized for the detection of protons and helium in the energy range below 100MeV/n, which typically includes almost all of the flux during SPEs. This also makes MARIE an efficient detector for GCR helium in the energy range of 50-150MeV/n. We will present the first fully normalized flux results from MARIE, using helium ions in this energy range.

Lee, Kerry [University of Houston, 4800 Calhoun Rd. Houston, TX 77204 (United States)]. E-mail: ktlee@ems.jsc.nasa.gov; Pinsky, Lawrence [University of Houston, 4800 Calhoun Rd. Houston, TX 77204 (United States); Andersen, Vic [University of Houston, 4800 Calhoun Rd. Houston, TX 77204 (United States); Zeitlin, Cary [National Space Biomedical Research Institute, Baylor College of Medicine, Houston, TX (United States); Cleghorn, Tim [NASA Johnson Space Center, 2101 NASA Road 1, Houston, TX 77058 (United States); Cucinotta, Frank [NASA Johnson Space Center, 2101 NASA Road 1, Houston, TX 77058 (United States); Saganti, Premkumar [Prairie View A and M University, P.O. Box 519, Prairie View, TX 77446-0519 (United States); Atwell, William [The Boeing Company, Houston, TX (United States); Turner, Ron [Advancing National Strategies and Enabling Results (ANSER), Arlington, Virginia (United States)

2006-10-15

303

Intrinsic Critical Velocities in Superfluid Helium.  

Science.gov (United States)

The occurrence of superflow, that is, persistent, non-dissipative current, is undoubtedly the most dramatic feature of the superfluid phase of liquid helium. Yet, a really complete understanding of the stability of superflow has been very elusive. It has ...

J. S. Langer J. D. Reppy

1970-01-01

304

Development of charcoal sorbents for helium cryopumping  

Energy Technology Data Exchange (ETDEWEB)

Testing of the cryogenically cooled charcoal using fusion-compatible binders for pumping helium has shown promising results. The program demonstrated comparable or improved performance with these binders compared to the charcoal (type and size) using an epoxy binder.

Sedgley, D.W.; Tobin, A.G.

1984-01-01

305

Development of charcoal sorbents for helium cryopumping  

International Nuclear Information System (INIS)

Testing of the cryogenically cooled charcoal using fusion-compatible binders for pumping helium has shown promising results. The program demonstrated comparable or improved performance with these binders compared to the charcoal (type and size) using an epoxy binder

1984-01-01

306

On the helium gas leak test  

International Nuclear Information System (INIS)

The helium gas leak test (Helium mass spectrometer testing) has a leak detection capacity of the highest level in practical leak tests and is going to be widely applied to high pressure vessels, atomic and vacuum equipments that require high tightness. To establish a standard test procedure several series of experiments were conducted and the results were investigated. The conclusions are summarized as follows: (1) The hood method is quantitatively the most reliable method. The leak rate obtained by tests using 100% helium concentration should be the basis of the other method of test. (2) The integrating method, bell jar method, and vacuum spray method can be considered quantitative when particular conditions are satisfied. (3) The sniffer method is not to be considered quantitive. (4) The leak rate of the hood, integrating, and bell jar methods is approximately proportional to the square of the helium partial pressure. (auth.)

1975-01-01

307

Gas turbine modeling for NPP with helium cooled reactor  

International Nuclear Information System (INIS)

The performance analyzes of closed helium cycle for NPPs with high-temperature gas-cooled reactors was carried out. Air-turbine units and helium-turbine units were compared. Helium turbine features were particularized in comparison with conventional air turbines. Simulation results of gas turbine setting with helium as a working medium were presented. Problems concerning high economic efficiency advance of helium turbines were discussed

2010-01-01

308

Primordial helium abundance determination from metal-poor galaxies  

International Nuclear Information System (INIS)

The advantages of measuring the helium abundance in metal-poor emission-line galaxies are emphasized. Recent results are reviewed and seem to converge to a primordial helium abundance Yp = 0.24 + or - 0.01. There is little evidence so far for a relation between the helium abundance and the oxygen abundance whereas nitrogen seems to correlate better with the observed helium. Uncertainties are discussed as well as prospects for future improvements in the helium abundance determination. 20 references

1986-01-01

309

The helium spectrum in erupting solar prominences  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Even quiescent solar prominences may become active and sometimes erupt. These events are occasionally linked to coronal mass ejections. However we know very little about the plasma properties during the activation and eruption processes. We present new computations of the helium line profiles emitted by an eruptive prominence. The prominence is modelled as a plane-parallel slab standing vertically above the solar surface and moving upward as a solid body. The helium spectrum is computed with ...

Labrosse, N.; Vial, J. -c; Gouttebroze, P.

2006-01-01

310

Helium burning in moderate-mass stars  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The evolution of low- and intermediate mass stars at the onset and during core helium burning is reviewed. Particular emphasis is laid on structural differences, which may allow to identify a star's nature and evolutionary phase in spite of the fact that it is found in a region of the Hertzsprung-Russell-Diagram objects from both mass ranges may populate. Seismic diagnostics which are sensitive to the temperature and density profile at the border of the helium core and outsi...

Weiss, Achim

2011-01-01

311

Helium-propane as drift chamber gas  

International Nuclear Information System (INIS)

A light gas mixture, consisting of helium and propane (0.938 : 0.062) at atmospheric pressure has been tested in a large single-volume drift chamber. Contrary to the general belief that helium cannot be used as a drift gas due to its high ionisation potential, the above mixture was found to have stable operation with spatial resolution of 260+-40 ?m. (orig.)

1985-01-01

312

Effects of helium impurities on superalloys  

International Nuclear Information System (INIS)

A review of the literature on the effects of helium impurities on superalloys at elevated temperatures was undertaken. The actual effects of these impurities vary depending on the alloy, composition of the gas atmosphere, and temperature. In general, exposure in helium produces significant but not catastrophic changes in the structure and properties of the alloys. The effects of these treatments on the structure, creep, fatigue, and mechanical properties of the various alloys are reviewed and discussed. Suggestions for future work are presented

1977-01-01

313

Calculation of the resonant ionization of helium  

International Nuclear Information System (INIS)

Autoionizing resonances in the compound system of an electron and a helium ion are observed in kinematically-complete ionization experiments for electrons on helium atoms. The differential cross section is calculated for comparison with these experiments in an equivalent-local form of the distorted-wave impulse approximation. Resonant scattering amplitudes are calculated by a six-state momentum-space coupled-channels method. 10 refs., 1 tab., 2 figs

1993-01-01

314

Helium embrittlement tests on ferritic steels  

International Nuclear Information System (INIS)

Tensile tests at 700"0C on nickel-doped 9 Cr-1 MoVNb and 12 Cr-1 MoVW steels that were irradiated at 55"0C in HFIR to produce up to about 50 at. ppM He indicated that there was no helium embrittlement. These results contrast with literature data showing that very small amounts of helium can cause a large decrease in ductility for many alloys when tested under equivalent conditions

1982-09-01

315

Helium leak detector of high sensitivity  

International Nuclear Information System (INIS)

A sensitive mass spectrometer helium leak detector using stigmatic focussing conditions for ion optical geometry has been designed. The minimum detectable leak rate is found to be 2 x 10-11 std cc/sec for helium (8 x 10-12 std cc/sec for air) with a system response of less than 1 second. In this paper we present briefly its design features and performance data. (author). 4 refs., 4 figs

1995-02-02

316

Primary neutral helium in the heliosphere  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Two years of neutral measurements by IBEX-Lo have yielded several direct observations of interstellar neutral helium and oxygen during preferred viewing seasons. Besides the interstellar signal, there are indications of the presence of secondary neutral helium and oxygen created in the heliosphere. Detailed modeling of these particle species is necessary to connect the measured fluxes to the pristine local interstellar medium while accounting for loss and production of neutr...

Mueller, Hans-reinhard; Cohen, Jill H.

2012-01-01

317

Lattice thermal conductivity of solid helium crystals  

International Nuclear Information System (INIS)

Vacancy like excitations are suggested for solid helium which can be scattered due to the vacancy-phonon interaction processes. The phonon conductivity of solid helium is analysed by modifying Callaway's expression for high frequency phonons and for Poiseuille's flow of phonons. An excellent agreement between theory and experiment is obtained when the combination of static and dynamic dislocation scattering processes is considered as an effective dislocation scattering of phonons. (author)

1987-04-01

318

Sonic helium detectors in the Fermilab Tevatron  

Energy Technology Data Exchange (ETDEWEB)

In the Fermilab Tevatron cryogenic system there are many remotely located low-pressure plate relief valves that must vent large volumes of cold helium gas when magnet quenches occur. These valves can occasionally stick open or not reseat completely, resulting in a large helium loss. As such, the need exists for a detector to monitor the relief valve's discharge area for the presence of helium. Due to the quantity needed, cost is an important factor. A unit has been developed and built for this purpose that is quite inexpensive. Its operating principle is based on the speed of sound, where two closely matched tubes operate at their acoustic resonant frequency. When helium is introduced into one of these tubes, the resulting difference in acoustic time of flight is used to trigger an alarm. At present, there are 39 of these units installed and operating in the Tevatron. They have detected many minor and major helium leaks, and have also been found useful in detecting a rise in the helium background in the enclosed refrigerator buildings. This paper covers the construction, usage and operational experience gained with these units over the last several years.

Bossert, R.J.; /Fermilab

2006-01-01

319

Tritium-helium effects in metals  

Energy Technology Data Exchange (ETDEWEB)

Investigations of helium effects in metals at the Savannah River Laboratory have been carried out by introducing helium by radioactive decay of tritium. This process does not create concurrent radiation damage, such as accompanies ion implantation and (n,..cap alpha..) reactions. The process has its own peculiarities, however, which partially mask and interact with the helium effect of interest. The distribution and local concentration of helium and tritium, which are responsible for changes in mechanical properties and fracture mode, are controlled by the large difference in solubility and diffusivity between the two atoms and by their differing interaction energies with lattice defects, impurities, and internal boundaries. Furthermore, in all investigations with helium generated from tritium decay, some tritium and deuterium are always present. Consequently, property changes include tritium-helium interaction effects to some extent. Results of investigations with several austenitic stainless steels, Armco iron, and niobium single crystals illustrate the variety of phenomena and some of the complex interactions that can be encountered.

Caskey, G.R. Jr.

1985-01-01

320

Equation of state of metallic helium  

Energy Technology Data Exchange (ETDEWEB)

The effective ion-ion interaction, free energy, pressure, and electric resistance of metallic liquid helium have been calculated in wide density and temperature ranges using perturbation theory in the electron-ion interaction potential. In the case of conduction electrons, the exchange interaction has been taken into account in the random-phase approximation and correlations have been taken into account in the local-field approximation. The solid-sphere model has been used for the nuclear subsystem. The diameter of these spheres is the only parameter of this theory. The diameter and density of the system at which the transition of helium from the singly ionized to doubly ionized state occurs have been estimated by analyzing the pair effective interaction between helium atoms. The case of doubly ionized helium atoms has been considered. Terms up to the third order of perturbation theory have been taken into account in the numerical calculations. The contribution of the third-order term is significant in all cases. The electric resistance and its temperature dependence for metallic helium are characteristic of simple divalent metals in the liquid state. The thermodynamic parameters-temperature and pressure densities-are within the ranges characteristic of the central regions of giant planets. This makes it possible to assume the existence of helium in the metallic state within the solar system.

Shvets, V. T., E-mail: tarval@breezein.net [Odessa State Academy of Refrigeration (Ukraine)

2013-01-15

 
 
 
 
321

The role of helium gas in medicine  

Science.gov (United States)

The noble gas helium has many applications owing to its distinct physical and chemical characteristics, namely: its low density, low solubility, and high thermal conductivity. Chiefly, the abundance of studies in medicine relating to helium are concentrated in its possibility of being used as an adjunct therapy in a number of respiratory ailments such as asthma exacerbation, COPD, ARDS, croup, and bronchiolitis. Helium gas, once believed to be biologically inert, has been recently shown to be beneficial in protecting the myocardium from ischemia by various mechanisms. Though neuroprotection of brain tissue has been documented, the mechanism by which it does so has yet to be made clear. Surgeons are exploring using helium instead of carbon dioxide to insufflate the abdomen of patients undergoing laparoscopic abdominal procedures due to its superiority in preventing respiratory acidosis in patients with comorbid conditions that cause carbon dioxide retention. Newly discovered applications in Pulmonary MRI radiology and imaging of organs in very fine detail using Helium Ion Microscopy has opened exciting new possibilities for the use of helium gas in technologically advanced fields of medicine.

2013-01-01

322

Advances in helium ion microscopy  

International Nuclear Information System (INIS)

With the advent of a reliable high brightness ion source, utilizing helium (He) as the ion species, a new branch of microscopy has emerged. The promise of sub-nm focused probe sizes coupled with the unique He beam/sample interactions has led to a range of both high resolution imaging and high fidelity material modification applications. However, realizing the full potential of the He ion source is not without its challenges. Some of the difficulties are presented, along with a discussion of a systematic effort to overcome these issues. This work has resulted in the ability to routinely take images with an edge resolution of 0.35 nm or better. The nature of the He ion beam interaction with the sample makes possible numerous diverse applications, beyond the high resolution imaging already mentioned. A few of these will be highlighted, including imaging insulating samples, scanning transmission He ion microscopy, and material modification. Finally an extension of the high source brightness technology to utilizing neon (Ne) as the ion species is described. The source properties are given, along with a calculation of the expected probe size from such a Ne ion source and column.

2011-07-21

323

Helium-cooled nuclear reactor  

International Nuclear Information System (INIS)

In helium cooled HTR's there is a by-pass circuit for cleaning purposes in addition to the main cooling circuit. This is to remove such impurities as hydrogen, methane, carbon monoxide and water from the coolant. In this system, part of the coolant successively flows first through an oxidation bed of copper oxide and an absorption bed of silica gel, then through activated charcoal or a molecular sieve. The hydrogen and carbon monoxide impurities are absorbed and the dry gas is returned to the main cooling circuit. To lower the hydrogen/water ratio without increasing the hydrogen fraction in the main cooling circuit, some of the hydrogen fraction converted into water is added to the cooling circuit. This is done, inter alia, by bypassing the water produced in the oxidation bed before it enters the absorption bed. The rest of the by-pass circuit, however, also includes an absorption bed with a molecular sieve. This absorbs the oxidized carbon monoxide fraction. In this way, such side effects as the formation of additional methane, carburization of the materials of the by-pass circuit or loss of graphite are avoided. (DG/RF)

1975-01-01

324

Study of helium diffusion, implanted at a cyclotron, in face-centered cubic metals: Au, Ag and Al  

International Nuclear Information System (INIS)

Helium in metals is produced by nuclear reactions of energetic particles. In nuclear technology the interest on helium in metals is import, due to its production by (n, ?) reaction. Because helium has extremely low solubility in metals, the precipitation in the form of filled bubbles at elevated temperatures occurs, which have detrimental effects on mechanical properties and may limit the lifetime of structural components. One typical example is the high temperature embrittlement. The nucleation and growth of the bubbles strongly depends on the mobility of the helium. This work presents the study of helium diffusion in Au, Ag and Al at temperatures above room temperature. The helium created by (n, ?) reactions has been simulated by homogeneous alpha particles implantation in cyclotron, at room temperature, in specimens of thicknesses between 5 and 50 ?m and helium concentration between 10-3 to 10 ppm. After implantation, the specimens were dropped in a furnace in a UHV-chamber and the diffusion was measured by observing the He-release during linear and isothermal annealings. The occurence of free diffusion was comparing the dependence of release kinetics on helium concentration, sample thickness, time and heating rate to diffusion theory and is clearly separeted from agglomeration process. The diffusion constants of helium in Au, Ag and Al follow an Arrhenius behavior, with: Au:Do=10-1.0 cm2/s ?H=1.70eV Ag:D0=10-1.2cm2/s ?H=1.51eV Al:Do=10+0.5cm2/s ?H=1.40eV. The results are compared to self-diffusion and to the diffusion of other gases in these metals. Comparison with theoretical estimates favours the vacancy mechanism for helium diffusion in Au, Ag and Al. (author)

1985-01-01

325

Lung Function Measurement with Multiple-Breath-Helium Washout System  

CERN Document Server

Multiple-breath-washout (MBW) measurements are regarded as a sensitive technique which can reflect the ventilation inhomogeneity of respiratory airways. Typically nitrogen is used as the tracer gas and is washed out by pure oxygen in multi-breath-nitrogen (MBNW) washout tests. In this work, instead of using nitrogen, helium is used as the tracer gas and a multiple-helium-breath-washout (MBHW) system has been developed for the lung function study. A commercial quartz tuning fork with a resonance frequency of 32768 Hz has been used for detecting the change of the respiratory gas density. The resonance frequency of the tuning fork decreases linearly with increasing density of the surrounding gas. Knowing the CO2 concentration from the infrared carbon dioxide detector, the helium concentration can be determined. Results from 12 volunteers (3 mild asthmatics, 2 smokers, 1 with asthma history, 1 with COPD history, 5 normal) have shown that mild asthmatics have higher ventilation inhomogeneity in either conducting o...

Wang, Jau-Yi; Owers-Bradley, John; Mellor, Chris

2011-01-01

326

Hydrogen and helium in the spectra of Type Ia supernovae  

CERN Document Server

We present predictions for hydrogen and helium emission line luminosities from circumstellar matter around Type Ia supernovae (SNe Ia) using time dependent photoionization modeling. ESO/VLT optical echelle spectra of the SN Ia 2000cx were taken before and up to 70 days after maximum. We detect no hydrogen and helium lines, and place an upper limit on the mass loss rate for the putative wind of less than 1.3EE{-5} solar masses per year, assuming a speed of 10 km/s and solar abundances for the wind. In a helium-enriched case, the best line to constrain the mass loss would be He I 10,830 A. We confirm the details of interstellar Na I and Ca II absorption towards SN 2000cx as discussed by Patat et al., but also find evidence for 6613.56 A Diffuse Interstellar Band (DIB) absorption in the Milky Way. We discuss measurements of the X-ray emission from the interaction between the supernova ejecta and the wind and we re-evaluate observations of SN 1992A obtained 16 days after maximum by Schlegel & Petre. We find a...

Lundqvist, Peter; Sollerman, Jesper; Kozma, Cecilia; Baron, E; Cox, Nick L J; Fransson, Claes; Leibundgut, Bruno; Spyromilio, Jason

2013-01-01

327

Helium irradiation effects on deuterium retention in tungsten  

Energy Technology Data Exchange (ETDEWEB)

To investigate effects of helium irradiation on deuterium retention properties in tungsten, thermal desorption spectroscopy of deuterium from a specimen irradiated with a sequential irradiation of 3 keV helium and 1.5 keV deuterium ions at room temperature was measured and the related microstructure was observed by transmission electron microscopy. It was found that pre-irradiation of 3 keV He{sup +} ions to fluences of 1.0 × 10{sup 21}–1.0 × 10{sup 22} He{sup +}/m{sup 2} increased, while the retention of deuterium drastically decreased above the fluences of 1.0 × 10{sup 23} He{sup +}/m{sup 2}. A similar reduction of deuterium retention was also observed by the pre-exposure of the specimen to a very low energy (?10 eV) and high fluence helium plasma. The reduction effects on deuterium retention are discussed in terms of the formation of linked or interconnected structure of bubbles, which could create an easy release and diffusion path for deuterium desorption.

Sakoi, Yuki [Department of Material Science, Shimane University, Matsue, Shimane 690-8504 (Japan); Miyamoto, Mitsutaka, E-mail: miyamoto@riko.shimane-u.ac.jp [Department of Material Science, Shimane University, Matsue, Shimane 690-8504 (Japan); Ono, Kotaro [Department of Material Science, Shimane University, Matsue, Shimane 690-8504 (Japan); Sakamoto, Mizuki [Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan)

2013-11-15

328

Cryosorption of helium on argon frost in Tokamak Fusion Test Reactor neutral beamlines  

International Nuclear Information System (INIS)

Helium pumping on argon frost has been investigated on Tokamak Fusion Test Reactor (TFTR) neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are ?25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, >20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a twofold increase in adsorption capacity as the cryopanel temperature is reduced from 4.3 K to 3.7 K. Pumping speed was found to be independent of cryopanel temperature over the temperature range studied. After pumping a total of 2000 Torr l of helium, the beamline base pressure rose to 2x10-5 Torr from an initial value of 10-8 Torr. Accompanying this three order of magnitude increase in pressure was a modest 40% decrease in pumping speed. The introduction of 168 Torr l of deuterium prior to helium injection reduced the pumping speed by a factor of two with no decrease in adsorption capacity

1990-01-01

329

Cryosorption of helium on argon frost TFTR [Tokamak Fusion Test Reactor] neutral beamlines  

International Nuclear Information System (INIS)

Helium pumping on argon frost has been investigated on TFTR neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are ? 25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, > 20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a two-fold increase in adsorption capacity as the cryopanel temperature is reduced from 4.3 K to 3.7 K. Pumping speed was found to be independent of cryopanel temperature over the temperature range studied. After pumping a total of 2000 torr-l of helium, the beamline base pressure rose to 2x10"-"5 torr from an initial value of 10"-"8 torr. Accompanying this three order of magnitude increase in pressure was a modest 40% decrease in pumping speed. The introduction of 168 torr-l of deuterium prior to helium injection reduced the pumping speed by a factor of two with no decrease in adsorption capacity. 29 refs., 7 figs

1989-01-01

330

Helium-Shell Nucleosynthesis and Extinct Radioactivities  

Science.gov (United States)

Although the exact site for the origin of the r-process isotopes remains mysterious, most thinking has centered on matter ejected from the cores of massive stars in core-collapse supernovae [13]. In the 1970's and 1980's, however, difficulties in understanding the yields from such models led workers to consider the possibility of r-process nucleosynthesis farther out in the exploding star, in particular, in the helium burning shell [4,5]. The essential idea was that shock passage through this shell would heat and compress this material to the point that the reactions 13C(alpha; n)16O and, especially, 22Ne(alpha; n)25Mg would generate enough neutrons to capture on preexisting seed nuclei and drive an "n process" [6], which could reproduce the r-process abundances. Subsequent work showed that the required 13C and 22Ne abundances were too large compared to the amounts available in realistic models [7] and recent thinking has returned to supernova core material or matter ejected from neutron star-neutron star collisions as the more likely r-process sites.

Meyer, B. S.; The, L.-S.; Clayton, D. D.; ElEid, M. F.

2004-01-01

331

Dilution refrigerator with no liquid helium supply  

International Nuclear Information System (INIS)

We have designed and constructed a "3He-"4He dilution refrigerator which does not require the use of liquid nitrogen or liquid helium dewars. The "3He-"4He mixture, compressed to 10"5Pa, is first precooled to near 12K in a closed-cycle regenerative refrigerator (AIR PRODUCTS DE202) then cooled to near 4.2K by a separate "4He compression stage. The mixture then undergoes a series of expansions and coolings in a heat exchanger which takes the temperature to below 0.1K. The limiting steady state temperature is 70mK and the total cool down time is 20 hours. This system is a test prototype which has enabled a number of problems to be analysed. It is equipped with a very basic dilution stage operating at 70mK. The chief aim was to verify the good working order of the ensemble. A new apparatus is being constructed which will reach near 20mK in less than 12 hours

1989-07-24

332

Tritium and helium behavior in irradiated beryllium  

International Nuclear Information System (INIS)

Large quantities of Be (> 100 metric tons) are planned for use in the ITER blanket design to enhance tritium breeding and to act as a thermal barrier between coolant and breeder. Tritium retention/release and He-induced swelling are important issues in blanket design. The data base on tritium and helium behavior in Be is reviewed. New data on tritium retention/release and He bubble growth are presented for Be irradiated to 5 x 1022 n(E > 1 MeV)/cm2 at ?75 degree C and postirradiation-annealed for 700 hours at 500 degree C. A model (diffusion/desorption) is proposed and tested against the data base to determine tritium diffusivity and the desorption rate constant. Similarly a model for He-induced swelling is developed and tested against the data base. The dependence of tritium retention and release on He content and impurities (e.g. BeO) is also explored. 11 refs., 6 figs

1990-10-07

333

Stark shifts of ionized helium lines  

International Nuclear Information System (INIS)

The shifts of the ionized helium lines lambda4686A (n = 4 ? 3) and lambda3203A (n = 5 ? 3) were measured relative to the centers of gravity of the fine structures of these lines. A capillary tube, through which condensed discharge was passed, was used as a plasma light source. Side-on observation enabled one to obtain optically thin plasma. In each case the center of gravity of the fine structure lines excited by a liquid-nitrogen-cooled hollow cathode discharge was assumed to be the unperturbed position. The measured red shifts of the He II lines lambda4686A and lambda3203A are -0.041 +- 0.023 cm-1 and -1.3 +- 0.3 cm-1 respectively, under the plasma condition of Nsub(e) = (1.6 +- 0.4) x 1016cm-3, Tsub(e) = (2.2 +- 0.3) x 104 K, and Nsub(e) = (1.2 +- 0.3) x 1016cm-3, Tsub(e) = (1.3 +- 0.3) x 104 K respectively. The present results are consistent with those of Murakawa but not with those of Pittman et al. (author)

1982-01-01

334

Stark shifts of ionized helium lines  

Energy Technology Data Exchange (ETDEWEB)

The shifts of the ionized helium lines lambda4686A (n = 4 ..-->.. 3) and lambda3203A (n = 5 ..-->.. 3) were measured relative to the centers of gravity of the fine structures of these lines. A capillary tube, through which condensed discharge was passed, was used as a plasma light source. Side-on observation enabled one to obtain optically thin plasma. In each case the center of gravity of the fine structure lines excited by a liquid-nitrogen-cooled hollow cathode discharge was assumed to be the unperturbed position. The measured red shifts of the He II lines lambda4686A and lambda3203A are -0.041 +- 0.023 cm/sup -1/ and -1.3 +- 0.3 cm/sup -1/ respectively, under the plasma condition of Nsub(e) = (1.6 +- 0.4) x 10/sup 16/cm/sup -3/, Tsub(e) = (2.2 +- 0.3) x 10/sup 4/ K, and Nsub(e) = (1.2 +- 0.3) x 10/sup 16/cm/sup -3/, Tsub(e) = (1.3 +- 0.3) x 10/sup 4/ K respectively. The present results are consistent with those of Murakawa but not with those of Pittman et al.

Hashimoto, Shizuyo (Tokai Univ., Hiratsuka, Kanagawa (Japan). Dept. of Physics)

1982-05-01

335

Cosmic-Ray Proton and Helium Spectra from the First CREAM Flight  

CERN Document Server

Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of ~38.5 km with an average atmospheric overburden of ~3.9 g cm$^{-2}$. Individual elements are clearly separated with a charge resolution of ~0.15 e (in charge units) and ~0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of -2.66 $\\pm$ 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 $\\pm$ 0.02 for helium nuclei from 630 GeV/nucleon to 63 TeV/nucleon. They are harder than previous measurements at a few tens of GeV/nucleon. The helium flux is higher than that expected from the extrapolation of the power law fitted to the lower-energy data. The relative abundance of protons to helium nuclei is 9.1 $\\pm$ 0.5 for the range from 2.5 TeV/nucleon to 63 TeV/...

Yoon, Y S; Allison, P S; Bagliesi, M G; Beatty, J J; Bigongiari, G; Boyle, P J; Childers, J T; Conklin, N B; Coutu, S; DuVernois, M A; Ganel, O; Han, J H; Jeon, J A; Kim, K C; Lee, M H; Lutz, L; Maestro, P; Malinine, A; Marrocchesi, P S; Minnick, S A; Mognet, S I; Nam, S; Nutter, S; Park, I H; Park, N H; Seo, E S; Sina, R; Swordy, S; Wakely, S P; Wu, J; Yang, J; Zei, R; Zinn, S Y; 10.1088/0004-637X/728/2/122

2011-01-01

336

COSMIC-RAY PROTON AND HELIUM SPECTRA FROM THE FIRST CREAM FLIGHT  

International Nuclear Information System (INIS)

Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of ?38.5 km with an average atmospheric overburden of ?3.9 g cm-2. Individual elements are clearly separated with a charge resolution of ?0.15 e (in charge units) and ?0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of -2.66 ± 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 ± 0.02 for helium nuclei from 630 GeV nucleon-1 to 63 TeV nucleon-1. They are harder than previous measurements at a few tens of GeV nucleon-1. The helium flux is higher than that expected from the extrapolation of the power law fitted to the lower-energy data. The relative abundance of protons to helium nuclei is 9.1 ± 0.5 for the range from 2.5 TeV nucleon-1 to 63 TeV nucleon-1. This ratio is considerably smaller than the previous measurements at a few tens of GeV nucleon-1.

2011-02-20

337

Helium isotope ratios in Japan sea water. Nihonkai kaisuichu no helium doitai hi  

Energy Technology Data Exchange (ETDEWEB)

The three straits, Soya, Tsugaru and Tsushima connecting the Japan Sea and the Pacific Ocean are all shallow and the water in the deep part of the Pacific Ocean cannot come directly into the Japan Sea. It is considered that the deep part of the Japan Sea is occupied by an uniform water mass and altenation of this water and the surface water is done in a short time. On the other hand, helium is the only component established to be originated in the mantle in the deep part of the earth among various geochemical parameters. In this article, in order to measure precisely the isotopic ratio of helium, the existing system was modified for conducting basic experiments and the measured results of the isotopic ratio of helium as well as the helium/neon ratio of the distilled water agreed well with documented values. Then helium concentrations, helium isotopic ratios and helium/neon ratios in the sea water taken from respective predetermined depths of the eastern edge of the Japan Sea were measured and with regard to concentration, changes were observed between those above and below 1,500m through 2,000m in depth. Also concerning the bottom layer water, discharge of mantle helium from the bottom of the Japan Sea is suggested. 21 refs, 3 figs, 2 tabs.

Sano, Yuji; Wakita, Hiroshi; Ishibashi, Juneichiro; Gamo, Toshitaka; Sakai, Hitoshi (The Univ. of Tokyo, Faculty of Science, Tokyo (Japan) Ocean Research Inst., The Univ. of Tokyo, Tokyo (Japan))

1989-12-30

338

Quantum statistics and liquid helium 3 - helum 4 mixtures  

International Nuclear Information System (INIS)

The behaviour of liquid helium 3-helium 4 mixtures is considered from the point of view of manifestation of quantum statistics effects in macrophysics. The Boze=Einstein statistics is shown to be of great importance for understanding superfluid helium-4 properties whereas the Fermi-Dirac statistics is of importance for understanding helium-3 properties. Without taking into consideration the interaction between the helium atoms it is impossible to understand the basic properties of liquid helium 33 - helium 4 mixtures at constant pressure. Proposed is a simple model of the liquid helium 3-helium 4 mixture, namely the binary mixture consisting of solid spheres of two types subjecting to the Fermi-Dirac and Bose-Einstein statistics relatively. This model predicts correctly the most surprising peculiarities of phase diagrams of concentration dependence on temperature for helium solutions. In particular, the helium 4 Bose-Einstein statistics is responsible for the phase lamination of helium solutions at low temperatures. It starts in the peculiar critical point. The helium 4 Fermi-Dirac statistics results in incomplete phase lamination close to the absolute zero temperatures, that permits operation of a powerful cooling facility, namely refrigerating machine on helium solution

1979-09-01

339

Effects of tungsten on thermal desorption of helium from Fe-9Cr-2W ferritic alloy irradiated with low energy helium ions  

International Nuclear Information System (INIS)

Thermal desorption of helium gas atoms from Fe-9Cr-2W ferritic alloy which was irradiated with 5 keV He+ ions has been studied, particularly to extract tungsten effects, by Thermal Desorption Spectroscopy (TDS) at temperatures from room temperature to 1370 K. Three small peaks (peaks I, II, III) and three large peaks (peaks IV, V, VI) appeared, and dependence of these peaks on the irradiation temperature and fluence has been demonstrated. The small peaks I, II and III have been related to the release of helium atoms by shrinkage or glide of different size dislocation loops. The large peaks have been attributed to release of helium gas atoms by migration of different size bubbles to the specimen surface. In comparison with TDS spectra in Fe-9Cr, these large peaks have been found to shift to higher temperatures. The present results suggest that tungsten atoms precipitated on the bubble surface could retard the bubble migration.

2011-10-01

340

Helium Exhaust Studies in H-Mode Discharges in the DIII-D Tokamak Using an Argon-Frosted Divertor Cryopump  

International Nuclear Information System (INIS)

The first experiments demonstrating exhaust of thermal helium in a diverted, H-mode deuterium plasma have been performed on the DIII-D tokamak. The helium, introduced via gas puffing, is observed to reach the plasma core, and then is readily removed from the plasma with a time constant of ?10--20 energy-confinement times by an in-vessel cryopump conditioned with argon frosting. Detailed analysis of the helium profile evolution suggests that the exhaust rate is limited by the exhaust efficiency of the pump (?5%) and not by the intrinsic helium-transport properties of the plasma

1995-04-03

 
 
 
 
341

Special operations in the helium system, III-4  

International Nuclear Information System (INIS)

Special operations in the helium system are: pouring helium form the low pressure reservoir to the high pressure reservoir by compressor with membrane, measuring the percent of hydrogen-oxygen gas and percent of free deuterium by manual gas analyzer, measurement of deuterium content, adding helium into the cover gas system, adding oxygen into the helium system, control of hydrogen-oxygen gas increase rate bypassing the contact device, activating the automated analyzer of percent of hydrogen-oxygen gas in helium and activating the automated analyzer of percent of air in helium

1989-01-01

342

Hydrodynamic simulations of the core helium flash  

CERN Multimedia

We describe and discuss hydrodynamic simulations of the core helium flash using an initial model of a 1.25 M_sol star with a metallicity of 0.02 near at its peak. Past research concerned with the dynamics of the core helium flash is inconclusive. Its results range from a confirmation of the standard picture, where the star remains in hydrostatic equilibrium during the flash (Deupree 1996), to a disruption or a significant mass loss of the star (Edwards 1969; Cole & Deupree 1980). However, the most recent multidimensional hydrodynamic study (Dearborn 2006) suggests a quiescent behavior of the core helium flash and seems to rule out an explosive scenario. Here we present partial results of a new comprehensive study of the core helium flash, which seem to confirm this qualitative behavior and give a better insight into operation of the convection zone powered by helium burning during the flash. The hydrodynamic evolution is followed on a computational grid in spherical coordinates using our new version of th...

Mocak, M; Weiss, A; Kifonidis, K; 10.1017/S1743921308022813

2009-01-01

343

Helium release from radioisotope heat sources  

Energy Technology Data Exchange (ETDEWEB)

Diffusion of helium in /sup 238/PuO/sub 2/ fuel was characterized as a function of the heating rate and the fuel microstructure. The samples were thermally ramped in an induction furnace and the helium release rates measured with an automated mass spectrometer. The diffusion constants and activation energies were obtained from the data using a simple diffusion model. The release rates of helium were correlated with the fuel microstructure by metallographic examination of fuel samples. The release mechanism consists of four regimes, which are dependent upon the temperature. Initially, the release is controlled by movement of point defects combined with trapping along grain boundaries. This regime is followed by a process dominated by formation and growth of helium bubbles along grain boundaries. The third regime involves volume diffusion controlled by movement of oxygen vacancies. Finally, the release at the highest temperatures follows the diffusion rate of intragranular bubbles. The tendency for helium to be trapped within the grain boundaries diminishes with small grain sizes, slow thermal pulses, and older fuel.

Peterson, D.E.; Early, J.W.; Starzynski, J.S.; Land, C.C.

1984-05-01

344

Helium release from radioisotope heat sources  

International Nuclear Information System (INIS)

Diffusion of helium in 238PuO2 fuel was characterized as a function of the heating rate and the fuel microstructure. The samples were thermally ramped in an induction furnace and the helium release rates measured with an automated mass spectrometer. The diffusion constants and activation energies were obtained from the data using a simple diffusion model. The release rates of helium were correlated with the fuel microstructure by metallographic examination of fuel samples. The release mechanism consists of four regimes, which are dependent upon the temperature. Initially, the release is controlled by movement of point defects combined with trapping along grain boundaries. This regime is followed by a process dominated by formation and growth of helium bubbles along grain boundaries. The third regime involves volume diffusion controlled by movement of oxygen vacancies. Finally, the release at the highest temperatures follows the diffusion rate of intragranular bubbles. The tendency for helium to be trapped within the grain boundaries diminishes with small grain sizes, slow thermal pulses, and older fuel

1984-01-01

345

Tritium control in helium-cooled blankets  

International Nuclear Information System (INIS)

As a part of the Blanket Comparison and Selection Study (BCSS), GA Technologies was responsible for the design of helium-cooled, solid- and liquid-metal breeder blankets. Conceptual blanket designs were developed, including the consideration of the generation, transport, and extraction of tritium. Evaluations were made of the inventory and leakage of tritium for helium-cooled Li_2O and LiAlO_2 and liquid lithium breeder blankets for tokamak and tandem mirror reactors. To facilitate the evaluation, a solid breeder tritium code TRIT4 was developed. The results from this study indicate that tritium inventories and leakages are acceptable for the proposed helium-cooled blankets. An assumption made in the tritium leakage calculations was that tritium is released to the helium purge and coolant streams as T_2 and remains in that form. If oxidation to T_2O is possible, significant reduction in the tritium leakage will be possible. We conclude that more experimental data on breeder material properties and tritium permeation behavior are needed. However, we are certain that an adequate number of different techniques are available to control the breeder tritium inventory and leakage to an acceptable level in helium-cooled solid- and lithium-breeder blankets

1985-05-02

346

Commissioning of a new helium pipeline  

Science.gov (United States)

At the commissioning of a new high-pressure helium pipeline at Kennedy Space Center, participants watch as helium-filled balloons take to the sky after their lines were cut. From left, they are Center Director Roy Bridges; Michael Butchko, president, SGS; Pierre Dufour, president and CEO, Air Liquide America Corporation; David Herst, director, Delta IV Launch Sites; Pamela Gillespie, executive administrator, office of Congressman Dave Weldon; and Col. Samuel Dick, representative of the 45th Space Wing. The nine-mile-long buried pipeline will service launch needs at the new Delta IV Complex 37 at Cape Canaveral Air Force Station. It will also serve as a backup helium resource for Shuttle launches. Nearly one launch's worth of helium will be available in the pipeline to support a Shuttle pad in an emergency. The line originates at the Helium Facility on KSC and terminates in a meter station at the perimeter of the Delta IV launch pad. Others at the ceremony were Jerry Jorgensen, pipeline project manager, Space Gateway Support (SGS), and Ramon Lugo, acting executive director, JPMO.

2000-01-01

347

Development of helium-heated steam reformers  

International Nuclear Information System (INIS)

A review of the different applications of steam reformers heated by helium from high-temperature reactors is first given. The requirements for the reformer gas are dependent on the secondary process. The thermodynamic behaviour of the compact reformer bundle in helium (heat transfer, pressure drop, heat flux) is explained in more detail. Further, an outlook on the mechanical design is given, especially concerning questions of corrosion of metallic materials in helium with impurities and hydrogen- and tritium-permeation. The design possibilities of steam reformers connected to a nuclear reactor (type of tubes, gas ducting in the bundle) are discussed in detail. A description of two typical steam reformer designs is given. The status of development of helium-heated steam reformers is reviewed. Starting with the main results of the operation of the EVA-plant, a description of the SUPEREVA is given. SUPEREVA is a reformer tube bundle of 30 tubes, which is heated by helium and connected with a methanation plant to recycle the methane. (author)

1975-10-17

348

Thermal analysis of a coaxial helium panel of a cryogenic vacuum pump for advanced divertor of DIII-D tokamak  

International Nuclear Information System (INIS)

It is planned to install a 50,000 1/s cryogenic pump for particle removal in the D3-D tokamak. A critical component of this cryogenic pump will be a helium panel which has to be maintained at a liquid helium temperature. The outer surface area of the helium panel has an area of 1 m2 and consists of a 2.5 cm diameter, 10 m long tube. From design considerations, a coaxial geometry is preferable since it requires a minimum number of welds. However, the coaxial geometry also results in a counter flow heat exchanger arrangement, where the outgoing warm fluid will exchange heat with incoming cold fluid. This is of concern since the helium panel must be cooled from liquid nitrogen temperature to liquid helium temperature in less than 5 minutes for successful operation of the cryogenic pump. In order to analyze the thermal performance of the coaxial helium panel, a finite difference computer model of the geometry was prepared. The governing equations took into account axial as well as radial conduction through the tube walls. The variation of thermal properties was modeled. The results of the analysis showed that although the coaxial geometry behaves like a counter flow heat exchanger, within the operating range of the cryogenic pump a rapid cooldown of the helium panel from liquid nitrogen temperature to the operating temperature is feasible. A prototypical experiment was also performed at General Atomics (GA) which verified the concept and the analysis. 4 refs., 8 figs

1991-06-11

349

Helium-filled proportional counter for low-temperature operation (4.2--300 K) and its application to cryogenic resonance-electron Moessbauer spectroscopy  

International Nuclear Information System (INIS)

The operation of a proportional counter filled with helium gas has been investigated at low temperatures down to 5 K. It has been found for the first time that a helium-filled counter cooled at temperatures below 30 K works well in the proportional region, but with low gas gains (? 100). The operation at low temperatures (? 30 K) is attributed to the complete removal of impurities from helium gas as well as the extreme depression of the reaction frequency of metastable heliums. The absence of impurities results in eliminating the Penning effect, i.e., an ionization process of impurity atoms or molecules by collisions with metastable helium, which spreads electron avalanches in both space and time if helium gas contains a slight amount of impurities (1--103 ppm). Continuous discharges caused by the photoeffect of ultraviolet photons, which are mostly produced in decay channels of metastable helium, are thermally quenched at low temperatures below 30 K. The helium-filled counter provides us with a new method to detect nuclear radiations at very low temperatures. The present counter technique has been successfully applied to the resonance-electron Moessbauer spectroscopy near liquid-helium temperature (--5 K)

1987-01-01

350

Curious Fluid Flows: From Complex Fluid Breakup to Helium Wetting  

Science.gov (United States)

This work encompasses three projects; pinch-off dynamics in non-Newtonian fluids; helium wetting on alkali metals; and the investigation of quartz tuning forks as cryogenic pressure transducers. Chapter 1 discusses the breakup of a non-Newtonian yield stress fluid bridge. We measured the minimum neck radius, hmin, as a function of time and fit it to a power law with exponent n 1. We then compare n1 to exponent n2, obtained from a rotational rheometer using a Herschel-Bulkley model. We confirm n1=n2 for the widest variety of non-Newtonian fluids to date. When these fluids are diluted with a Newtonian fluid n1 does not equal n2. No current models predict that behavior, identifying a new class of fluid breakup. Chapter 2 presents the first chemical potential-temperature phase diagram of helium on lithium, sodium and gold, using a novel pressure measurement system. The growth and superfluid transition of a helium film on these substrates is measured via an oscillator for isotherms (fixed temperature, varying amount of helium gas), and quenches (fixed amount of helium gas, varying temperature). The chemical potential-temperature plot is similar for gold, lithium and sodium despite the large difference in the substrate binding energies. No signs of a 2-D liquid-vapor transition were seen. Chapter 3 discusses the creation of a 32.768 kHz quartz tuning fork in situ pressure transducer. Tuning forks are used to measure pressure at room temperature, but no work addresses their potential as cryogenic pressure transducers. We mapped out the behavior of a tuning fork as a function of pressure at 298, 7.0, 2.5, 1.6, 1.0 and 0.7 K by measuring the quality factor. The fork is sensitive to pressures above 0.1 mTorr, limiting its use as a pressure gauge at 0.6 K and below. The experimental curves were compared to a theoretical Q(P, T) function that was refined using the 298 K data. At cryogenic temperatures the formula breaks down in the viscous region and becomes inaccurate. The qualitative shape of the theory, but not its quantitative values, matches the data. The discrepancy between the experimental and theoretical Q values appears to be due to unaccounted for dissipation.

Huisman, Fawn Mitsu

351

Auxiliary cooling systems for helium cryogenic facilities  

Energy Technology Data Exchange (ETDEWEB)

In helium cryogenic facilities auxiliary cooling systems are used for heat removal. There is a growing demand for these cryogenic facilities in the research, development and industrial sectors, especially for facilities operating around the helium boiling point of 4.2 K. The helium facilities work on the Claude principle with expansion machine and Joule-Thomson stage. Cooling circuits are used for heat removal, especially from the compressors. A combination of cooling by air, fresh water and chilled water connected to an intermediate water circuit has proved to be advantageous. The utilization of waste heat as well as safety measures to be taken in order to protect the environment are discussed and proposals made for solving the problems arising.

Leuchtmann, D.; Spath, F.K.

1988-01-01

352

Extended quintessence and the primordial helium abundance  

Energy Technology Data Exchange (ETDEWEB)

In extended quintessence models, a scalar field which couples to the curvature scalar R provides most of the energy density of the universe. We point out that such models can also lead naturally to a decrease in the primordial abundance of helium-4, relieving the tension which currently exists between the primordial helium-4 abundance inferred from observations and the amount predicted by standard big bang nucleosynthesis corresponding to the observed deuterium abundance. Using negative power-law potentials for the quintessence field, we determine the range of model parameters which can lead to an interesting reduction in the helium-4 abundance, and we show that it overlaps with the region allowed by other constraints on extended quintessence models.

Chen, Xuelei; Scherrer, Robert J.; Steigman, Gary

2001-06-15

353

Electron Diffraction of Superfluid Helium Droplets  

Science.gov (United States)

We present experimental results of electron diffraction of superfluid helium droplets and droplets doped with phthalocyanine gallium chloride and discuss the possibility of performing the same experiment with a laser aligned sample. The diffraction profile of pure droplets demonstrates dependence on the nozzle temperature, that is, on the average size of the droplets. Larger clusters demonstrate faster decay with increasing momentum transfer, whereas smaller clusters converge to isolated gas phase molecules at source temperatures of 18 K and higher. Electron diffraction of doped droplets shows similar modified molecular scattering intensity as that of the corresponding gas phase molecules. On the basis of fittings of the scattering profile, the number of remaining helium atoms of the doped droplets is estimated to be on the order of hundreds. This result offers guidance in assessing the possibility of electron diffraction from laser aligned molecules doped in superfluid helium droplets.

2014-01-01

354

Primary neutral helium in the heliosphere  

CERN Document Server

Two years of neutral measurements by IBEX-Lo have yielded several direct observations of interstellar neutral helium and oxygen during preferred viewing seasons. Besides the interstellar signal, there are indications of the presence of secondary neutral helium and oxygen created in the heliosphere. Detailed modeling of these particle species is necessary to connect the measured fluxes to the pristine local interstellar medium while accounting for loss and production of neutral particles during their path through the heliosphere. In this contribution, global heliosphere models are coupled to analytic calculations of neutral trajectories to obtain detailed estimates of the neutral distribution function of primary interstellar helium atoms in the heliosphere, in particular in the inner heliosphere.

Mueller, Hans-Reinhard

2012-01-01

355

Experience of operation of a set of fuel assemblies with helium pressurized elements at the WWER-440  

International Nuclear Information System (INIS)

The results of tests of fuel assemblies with fuel elements having the increased initial pressure of helium under the cladding are presented. The purpose of the tests is verification of assemblies' workability with fuel elements having an increased initial helium pressure. The tast results are positive. Fuel assemblies with fuel elements having a helium initial pressure of 0.5-0.7 MPa are advisable to be introduced at WWER-440 with a three-year fuel cycle, as well as to continue an experimental and commercial operation in the four-year fuel cycle at WWER-440 reactors. 3 figs.; 9 tabs

1989-01-01

356

The multiple ionization of helium induced by partially stripped carbon ions  

International Nuclear Information System (INIS)

The ratios of the double to single ionization cross sections of helium impacted by partially stripped Cq+ ions (q = 1,2,3,4) in energy range of 1.5-7.5 MeV were measured by using the time of flight procedure. The n-body classical trajectory Monte Carlo calculation was carried out to get the Olson-Schlachter scaling. The single and double ionization cross sections of helium were obtained by comparing the cross section ratios of the present work with the Olson-Schlachter scaling

1996-01-01

357

Helium accreting CO white dwarfs with rotation: Helium novae instead of double detonation  

Science.gov (United States)

We present evolutionary models of helium-accreting carbon-oxygen white dwarfs in which we include the effects of the spin-up of the accreting star induced by angular momentum accretion, rotationally induced chemical mixing and rotational energy dissipation. Initial masses of 0.6 M? and 0.8 M&odot and constant accretion rates of a few times 10-8 M?/yr of helium-rich matter have been considered, which is typical for the sub-Chandrasekhar mass progenitor scenario for Type Ia supernovae. It is found that the helium envelope in an accreting white dwarf is heated efficiently by friction in the differentially rotating spun-up layers. As a result, helium ignites much earlier and under much less degenerate conditions compared to the corresponding non-rotating case. Consequently, a helium detonation may be avoided, which questions the sub-Chandrasekhar mass progenitor scenario for Type Ia supernovae. We discuss implications of our results for the evolution of helium star plus white dwarf binary systems as possible progenitors of recurrent helium novae.

Yoon, S.-C.; Langer, N.

2004-05-01

358

Comparison of the yields in kaonic helium-3 and helium-4  

International Nuclear Information System (INIS)

Full text: Kaonic helium is an exotic atom where a kaon replaces a shell electron, well suited for the study of the strong interaction at low energies. The strong interaction between the kaon and the nucleus affects the low-lying atomic states in the kaonic helium atom by causing a shift compared to its purely electromagnetic value. This shift can be measured with spectroscopic tools, which was recently performed by the SIDDHARTA experiment. Via a measurement of the X-ray transitions to the 2p level, the X-ray transitions in kaonic helium-3 and helium-4 (at different densities) were measured with a complex SDD detector system. With the data set of these measurements, the X-ray yields (i.e. the net production of characteristic X-rays) of the kaonic helium gases have been determined for the rst time. The absolute yields were obtained with inputs from a Monte Carlo simulation. Since the previous measurements on the kaonic helium X-ray transitions solely used liquid helium targets, these results give crucial information on theoretical calculations of the density dependence of the yields. The evaluation procedure and the results are going to be presented in detail. (author)

2012-09-18

359

Effects of helium and 40% O2 on graded exercise with self-contained breathing apparatus.  

Science.gov (United States)

Maximal exercise performance is decreased when breathing from a self-contained breathing apparatus (SCBA), owing to a ventilatory limitation imposed by the increased expiratory resistance. To test the hypothesis that decreasing the density of the breathing gas would improve maximal exercise performance, we studied 15 men during four graded exercise tests with the SCBA. Participants breathed a different gas mixture during each test: normoxia (NOX; 21% O2, 79% N2), hyperoxia (HOX; 40% O2, 60% N2), normoxic helium (HE-OX; 21% O2, 79% He), and hyperoxic helium (HE-HOX; 40% O2, 60% He). Compared to NOX, power output at the ventilatory threshold and at maximal exercise significantly increased with both hyperoxic mixtures. Minute ventilation was increased at peak exercise with both helium mixtures, and maximal aerobic power (VO2max) was significantly increased by 12.9 +/- 5.6%, 10.2 +/- 6.3%, and 21.8 +/- 5.6% with HOX, HE-OX, and HE-HOX, respectively. At peak exercise, the expired breathing resistance imposed by the SCBA was significantly decreased with both helium mixtures, and perceived respiratory distress was lower with HE-HOX. The results show that HE-OX improved maximal exercise performance by minimizing the ventilation limitation. The performance-enhancing effect of HOX may be explained by increased arterial oxygen content. Moreover, HE-HOX appeared to combine the effects of helium and hyperoxia on VO2max. PMID:14992128

Eves, Neil D; Petersen, Stewart R; Jones, Richard L

2003-12-01

360

Defects of ultrathin Cu films on Mo(1 1 0) studied by thermal helium desorption spectrometry  

International Nuclear Information System (INIS)

Defects of ultrathin Cu films (3-200 A) deposited on Mo(1 1 0) at room temperature by e-beam evaporation in ultra-high vacuum are investigated using thermal helium desorption spectrometry. The samples are analysed with both 75 and 1000 eV He+ implantation. Cu films transform into islands on annealing and the temperature of this transformation is strongly thickness dependent. Helium release from defects close to the surface of the Cu films (?450 K), from monovacancies in as-deposited Cu film (50-200 A), and from defects close to the interface (800-1050 K) are identified. Annealing of monovacancies is mainly responsible for reduction in helium trapping in a 20 A Cu film prior to film islanding. There is an indication of retrapping of helium released from the first 5 A layer of the film in the defects located in the overlayers (5-95 A). Helium in the Cu films survives until the desorption temperature of the film (1200-1300 K).

2009-08-21

 
 
 
 
361

Hydrodynamic simulations of the core helium flash  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We describe and discuss hydrodynamic simulations of the core helium flash using an initial model of a 1.25 M_sol star with a metallicity of 0.02 near at its peak. Past research concerned with the dynamics of the core helium flash is inconclusive. Its results range from a confirmation of the standard picture, where the star remains in hydrostatic equilibrium during the flash (Deupree 1996), to a disruption or a significant mass loss of the star (Edwards 1969; Cole & Deupree 1...

Mocak, M.; Mueller, E.; Weiss, A.; Kifonidis, K.

2009-01-01

362

In Beam Tests of Implanted Helium Targets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Targets consisting of 3,4He implanted into thin aluminum foils (approximately 100, 200 or 600 ug/cm^2) were prepared using intense (a few uA) helium beams at low energy (approximately 20, 40 or 100 keV). Uniformity of the implantation was achieved by a beam raster across a 12 mm diameter tantalum collimator at the rates of 0.1 Hz in the vertical direction and 1 Hz in the horizontal direction. Helium implantation into the very thin (approximately 80-100 ug/cm^2) aluminum foils failed to produc...

2006-01-01

363

Tritium control in helium-cooled blankets  

International Nuclear Information System (INIS)

As a part of the Blanket Comparison and Selection Study (BCSS), GA Technologies was responsible for the design of helium-cooled, solidand liquid-metal breeder blankets. Conceptual blanket designs were developed, including the consideration of the generation, transport, and extraction of tritium. Evaluations were made of the inventory and leakage of tritium for helium-cooled Li_2O and LiA10_2 and liquid lithium breeder blankets for tokamak and tandem mirror reactors. To facilitate the evaluation, a solid breeder tritium code TRIT4 was developed

1985-09-01

364

Detection of solar neutrinos in superfluid helium  

International Nuclear Information System (INIS)

A new method for detecting solar neutrinos and other weakly interacting particles is proposed and described. The detector consists of a large mass of superfluid helium at low temperatures (20 mK). When a neutrino is scattered off an electron, the recoil energy of the electron (10/sup -6/ to 10/sup -7/ erg) is deposited in the helium. This small amount of energy can be detected because of the unusual kinetics of rotons at low temperatures. It should be possible to construct a detector of sufficiently low background and large size to measure solar neutrino spectra

1987-06-08

365

Helium mobility in advanced nuclear ceramics  

Science.gov (United States)

The techniques of ion implantation and nuclear reaction depth profiling are used to measure helium migration parameters under thermal ageing in advanced nuclear ceramics such as TiC, ZrC and TiN. Helium release measurements and activation energy calculations have been carried out in the temperature range of 1000–1600 °C for time periods of 2 h. Activation energy values are obtained in the range 0.7–1.2 eV. Due to rare availability of stoichiometric samples, the trapping of He in native vacancies seems to affect the mobility of He. Blisters are observed only at the surface of ZrC on thermal annealing.

Agarwal, S.; Trocellier, P.; Serruys, Y.; Vaubaillon, S.; Miro, S.

2014-05-01

366

Rotary magnetic refrigerator for superfluid helium production  

International Nuclear Information System (INIS)

A new rotary-magnetic refrigerator designed to obtain superfluid helium temperatures by executing a magnetic Carnot cycle is developed. A rotor containing 12 magnetic refrigerants (gadolinium-gallium-garnet) is immersed in liquid helium at 4.2 K and rotated at constant speed in a steady magnetic field distribution. Performance tests demonstrate that the new rotary refrigerator is capable of obtaining a temperature of 1.48 K. The maximum useful cooling power obtained at 1.8 K is 1.81 W which corresponds to a refrigeration efficiency of 34%

1986-11-01

367

Properties of hydrogen/helium accretion plasmas  

Energy Technology Data Exchange (ETDEWEB)

We study the properties of impulsively-heated plasmas initially composed of hydrogen and helium. We follow the time-dependent behavior of the ion and electron temperatures, the pair density, and the densities of hydrogen, helium, and nuclei formed in fusion and breakup reactions. We also consider neutron production and escape, and calculate the 0.431 and 0.478 MeV line luminosities from ..cap alpha..-..cap alpha.. fusion reactions, and the 2.22 MeV line luminosity from neutron capture on protons. 13 refs., 3 figs., 1 tab.

Guessoum, N.; Dermer, C.D.

1988-02-01

368

Helium damage in austenitic stainless steels  

International Nuclear Information System (INIS)

Helium produced by tritium decay was first shown to embrittle austenitic stainless steel at ambient temperature in tensile specimens of Nitronic-40 steel (Armco, Inc.). A long-term study was initiated to study this form of helium damage in five austenitic alloys. Results from this study have been analyzed by the J-integral technique and show a decrease in ductile fracture toughness with increasing He-3 concentration. Sustained-load cracking tests indicate that the stress intensity required to initiate and propagate a crack also decreases with increasing He-3 concentration. 9 figures, 3 tables

1983-03-06

369

Excited state positronium collisions with helium  

Energy Technology Data Exchange (ETDEWEB)

Calculations of the discrete positronium (Ps) transition Ps(2s) {yields} Ps(2p) in collisions with ground state helium are reported. Results are presented at total and single differential levels. Calculations are made within the first born approximation (FBA). The Hartley-Walters approximation is used to sum over all possible final excited atom states. In addition, impulse approximation (IA) calculations are reported for Ps(2s) and Ps(2p) fragmentation collisions with ground state helium, where the atom does not change state. Again, the FBA with the HWA is used to account for collisions in which the atom is excited or ionized.

Starrett, C. [Department of Applied Mathematics and Theoretical Physics, Queen' s University, Belfast BT7 1NN (United Kingdom)], E-mail: c.starrett@qub.ac.uk; Walters, H.R.J. [Department of Applied Mathematics and Theoretical Physics, Queen' s University, Belfast BT7 1NN (United Kingdom); McAlinden, Mary T. [School of Computing and Mathematical Sciences, Oxford Brookes University, Wheatley Campus, Oxford OX33 1HX (United Kingdom)

2008-02-15

370

Excited state positronium collisions with helium  

International Nuclear Information System (INIS)

Calculations of the discrete positronium (Ps) transition Ps(2s) ? Ps(2p) in collisions with ground state helium are reported. Results are presented at total and single differential levels. Calculations are made within the first born approximation (FBA). The Hartley-Walters approximation is used to sum over all possible final excited atom states. In addition, impulse approximation (IA) calculations are reported for Ps(2s) and Ps(2p) fragmentation collisions with ground state helium, where the atom does not change state. Again, the FBA with the HWA is used to account for collisions in which the atom is excited or ionized

2008-02-01

371

Settling of helium and the ages of the globular clusters  

Energy Technology Data Exchange (ETDEWEB)

Model low-mass globular-cluster stars were evolved with their helium allowed to diffuse under the influence of gravity, thermal diffusion, and concentration gradient. The evolution tended to speed up. Also, the turnoff point moved toward lower luminosity and slightly lower surface temperature. If the luminosity at turnoff is used as the sole criterion for determining the age of a globular cluster, the inferred ages of such clusters are reduced by about 22% from starting values in the vicinity of 1.5 x 10/sup 10/ yr.

Noerdlinger, P.D.; Arigo, R.J.

1980-04-01

372

Penning collisions of laser-cooled metastable helium atoms  

International Nuclear Information System (INIS)

We present experimental results on the two-body loss rates in a magneto-optical trap of metastable helium atoms. Absolute rates are measured in a systematic way for several laser detunings ranging from -5 to -30 MHz and at different intensities, by monitoring the decay of the trap fluorescence. The dependence of the two-body loss rate coefficient ? on the excited state (23P2) and metastable state (23S1) populations is also investigated. From these results we infer a rather uniform rate constant Ksp = (1±0.4) x 10-7 cm3/s. (orig.)

2001-04-01

373

Negative ions at an interface between liquid helium mixtures  

International Nuclear Information System (INIS)

The properties of electron bubbles electrostatically forced against an interface between liquid 3He and saturated 4He-3He mixture were determined at low temperatures. The equilibrium state of such objects is characterized by the binding energy of 6.5 K and oscillatory spectrum of first excitations with a frequency of 0.6 · 1010 s-1. The shifting electric field E=100 V/cm at the temperature T=0.2 K leads to decaying the bound bubble state with the lifetime ? approx 1s. The experimental study of bubble electron states can appear to be useful for determining properties of an interface between liquid helium mixtures.

2011-01-01

374

''Il Mantello'' - A helium cooled solid breeder blanket for NET  

International Nuclear Information System (INIS)

''Il Mantello'' is an engineering design study of a helium cooled blanket using solid, ceramic breeder materials, and solid, metallic neutron multipliers. This study was initiated in October 1983 and has now entered phase II. Results of the phase I work can be found in the Proc. of 13th Soft (Varese, 1984). This paper is concerned with phase II results. The design application for the blanket is the Next European Torus. However, the utility of the blanket design must extrapolate to a full-size power producing reactor. (author). 5 figs, 2 tabs

1986-06-06

375

Accuracy of helium accumulation fluence monitor for fast reactor dosimetry  

Energy Technology Data Exchange (ETDEWEB)

A helium (He) accumulation fluence monitor (HAFM) has been developed for fast reactor dosimetry. In order to evaluate the measurement accuracy of neutron fluence by the HAFM method, the HAFMs of enriched boron (B) and beryllium (Be) were irradiated in the Fast Neutron Source Reactor `YAYOI`. The number of He atoms produced in the HAFMs were measured and compared with the calculated values. As a result of this study, it was confirmed that the neutron fluence could be measured within 5 % by the HAFM method, and that met the required accuracy for fast reactor dosimetry. (author)

Ito, Chikara; Aoyama, Takafumi [Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center

1998-03-01

376

Superfluidity of Grain Boundaries in Solid Helium-4  

CERN Document Server

By large-scale quantum Monte Carlo simulations we show that grain boundaries in Helium-4 crystals are generically superfluid at low temperature, with a transition temperature of the order of ~0.5K at the melting pressure; insulating grain boundaries are found only for special orientations of the grains. We also find that close vicinity to the melting line is not a necessary condition for superfluid grain boundaries, and a grain boundary in direct contact with the superfluid liquid at the melting curve is found to be mechanically stable and the grain boundary superfluidity observed by Sasaki et al. [Science 313, 1098 (2006)] is not just a crack filled with superfluid.

Pollet, L; Kuklov, A B; Prokofiev, N V; Svistunov, B V; Troyer, M

2007-01-01

377

Thermal-accommodation measurement of helium on a suspended water droplet  

International Nuclear Information System (INIS)

An innovative method for determining the thermal-accommodation coefficients of gases by means of monitoring the Mie scattering from a single suspended water droplet is described. The heat exchange between the gas molecules and the suspended droplet is analyzed by considering the simultaneous mass- and heat-transfer processes during droplet growth by condensation in a gas--water-vapor environment. Measurements have been carried out for helium with water-vapor-to-helium ratios in the range of 1:0.5 to 1:2.5. The thermal conductivity of this mixture is found to be best represented by its reciprocal average. The thermal-accommodation coefficient of helium on water surfaces is determined to be 0.65 +- 0.05, as compared to unity for water vapor on water surfaces

1988-04-01

378

Improvement in schemes of cryogenic helium systems for cryostating of superconducting devices  

International Nuclear Information System (INIS)

An examination is made of the characteristics of a two-loop CHS (Cryogenic Helium System) in which, to prepare liquid helium, there is used a CHU constructed in accordance with a high-efficiency cycle; and, to cool the CSMS (circulating superconducting magnetic system) a cryogenic refrigerator is used which is made by a simple throttling cycle or a cycle with a final expander with excess backstream. This CHS construction makes it possible to prepare liquid helium with the least expenditure of power and with the aid of a refrigerator cycle with excess backflow, to use it rather effectively in cryostating a CSMS at a temperature level of 4.5/degree/K or less under conditions of appreciably varying thermal loads. 5 refs

1980-01-01

379

Density decrease in vanadium-base alloys irradiated in the dynamic helium charging experiment  

Energy Technology Data Exchange (ETDEWEB)

Combined effects of dynamically charged helium and neutron damage on density decrease (swelling) of V-4Cr-4Ti, V-5Ti, V-3Ti-1Si, and V-8Cr-6Ti alloys have been determined after irradiation to 18-31 dpa at 425-600{degrees}C in the Dynamic helium Charging Experiment (DHCE). To ensure better accuracy in density measurement, broken pieces of tensile specimens {approx} 10 times heavier than a transmission electron microscopy (TEM) disk were used. Density increases of the four alloys irradiated in the DHCE were <0.5%. This small change seems to be consistent with the negligible number density of microcavities characterized by TEM. Most of the dynamically produced helium atoms seem to have been trapped in the grain matrix without significant cavity nucleation or growth.

Chung, H.M.; Galvin, T.M.; Smith, D.L. [Argonne National Laboratory, Chicago, IL (United States)

1996-04-01

380

Trace Detection of Metastable Helium Molecules in Superfluid Helium by Laser-Induced Fluorescence  

CERN Multimedia

We describe an approach to detecting ionizing radiation that combines the special properties of superfluid helium with the sensitivity of quantum optics techniques. Ionization in liquid helium results in the copious production of metastable helium molecules, which can be detected by laser-induced fluorescence. Each molecule can be probed many times using a cycling transition, resulting in the detection of individual molecules with high signal to noise. This technique could be used to detect neutrinos, weakly interacting massive particles, and ultracold neutrons, and to image superfluid flow in liquid He-4.

McKinsey, D N; Nikkel, J A; Rellergert, W

2005-01-01

 
 
 
 
381

Molecular Dynamics Simulations of Helium Behaviour in Titanium Crystals  

International Nuclear Information System (INIS)

Molecular dynamics simulations are performed to investigate the behaviour of helium atoms in titanium at a temperature of 300K. The nucleation and growth of helium bubble has been simulated up to 50 helium atoms. The approach to simulate the bubble growth is to add helium atoms one by one to the bubble and let the system evolve. The titanium cohesion is based on the tight binding scheme derived from the embedded atom method, and the helium–titanium interaction is characterized by fitted potential in the form of a Lennard-Jones function. The pressure in small helium bubbles is approximately calculated. The simulation results show that the pressure will decrease with the increasing bubble size, while increase with the increasing helium atoms. An analytic function about the quantitative relationship of the pressure with the bubble size and number of helium atoms is also fitted. (condensed matter: structure, mechanical and thermal properties)

2008-05-01

382

Evaluation of the Gas Turbine Modular Helium Reactor.  

Science.gov (United States)

Recent advances in gas-turbine and heat exchanger technology have enhanced the potential for a Modular Helium Reactor (MHR) incorporating a direct gas turbine (Brayton) cycle for power conversion. The resulting Gas Turbine Modular Helium Reactor (GT-MHR) ...

1994-01-01

383

The Measurement of Absolute Helium Ion Density Profiles on the Diii-D Tokamak Using Charge Exchange Recombination Spectroscopy  

Science.gov (United States)

In future burning fusion devices, helium will be an unavoidable impurity component of the plasma. The overall performance of such devices is critically dependent on the helium transport properties of the confined plasma. Poor helium transport in reactors could lead to a buildup of fusion ash, causing fuel dilution and increased radiation that will result in degraded fusion power and possibly quench ignition altogether. As a result, it is essential to investigate the helium transport and exhaust properties of tokamak plasmas in order to design an optimized helium removal system for future reactors. These studies require accurate spatial and temporal measurements of the helium density profiles in tokamak plasmas. The purpose of this work has been to instrument and calibrate the existing charge-exchange recombination (CER) spectroscopy diagnostic used to measure the ion temperature and plasma rotation speeds on the DIII-D tokamak for the simultaneous measurement of absolute helium density profiles as well. This has involved (1) absolutely calibrating the CER system using standard calibration lamps and two novel techniques involving neutral beam injection into a gas filled torus and a pure He plasma, (2) developing and testing a neutral beam attenuation code to calculate the local neutral beam density at each viewing location, (3) assembling a database of accurate atomic data, (4) analyzing the measured CER spectra with a multi-Gaussian fitting procedure, and (5) developing and testing a modeling code that distinguishes unwanted signal contributions from drifting hydrogen-like helium ions (the 'plume effect'). Absolute helium density profiles have been measured for a variety of tokamak operating conditions, including low confinement (L-mode) and high confinement (H-mode) discharges. Helium transport behavior has been observed by injecting helium gas puffs into DIII-D plasmas and measuring the He density profile evolution. The measured profiles are found to have a similar shape as the measured electron density profiles, thereby disputing the unfavorable prediction by neo-classical transport theory that there is preferential accumulation of helium in the plasma center. The effective use of edge-localized modes (ELMs) to purge helium from H-mode discharges has also been observed.

Finkenthal, Daniel Franklin

384

Helium isotopic textures in Earth's upper mantle  

Science.gov (United States)

report 3He/4He for 150 mid-ocean ridge basalt (MORB) glasses from the Southeast Indian Ridge (SEIR). Between 81°E and 101°E 3He/4He varies from 7.5 to 10.2 RA, encompassing more than half the MORB range away from ocean island hot spots. Abrupt transitions are present and in one case the full range occurs over ˜10 km. Melting of lithologically heterogeneous mantle containing a few percent garnet pyroxenite or eclogite leads to lower 3He/4He, while 3He/4He above ˜9 RA likely indicates melting of pyroxenite-free or eclogite-free mantle. Patterns in the length scales of variability represent a description of helium isotopic texture. We utilize four complementary methods of spectral analysis to evaluate this texture, including periodogram, redfit, multitaper method, and continuous wavelet transform. Long-wavelength lobes with prominent power at 1000 and 500 km are present in all treatments, similar to hot spot-type spectra in Atlantic periodograms. The densely sampled region of the SEIR considered separately shows significant power at ˜100 and ˜30-40 km, the latter scale resembling heterogeneity in the bimodal distribution of Hf and Pb isotopes in the same sample suite. Wavelet transform coherence reveals that 3He/4He varies in-phase with axial depth along the SEIR at ˜1000 km length scale, suggesting a coupling between melt production, 3He/4He and regional variations in mantle temperature. Collectively, our results show that the length scales of MORB 3He/4He variability are dominantly controlled by folding and stretching of heterogeneities during regional (˜1000 km) and mesoscale (˜100 km) mantle flow, and by sampling during the partial melting process (˜30 km).

Graham, David W.; Hanan, Barry B.; Hémond, Christophe; Blichert-Toft, Janne; Albarède, Francis

2014-05-01

385

Helium exhaust and forced flow effects with both-leg pumping in W-shaped divertor of JT-60U  

International Nuclear Information System (INIS)

The W-shaped divertor of JT-60U was modified from inner-leg pumping to both-leg pumping. After the modification, the pumping rate was improved from 3% with inner-leg pumping to 5% with both-leg pumping in a divertor-closure configuration, which means both separatrixes close to the divertor slots. Efficient helium exhaust was realized in the divertor-closure configuration with both-leg pumping. A global particle confinement time of ?*He=0.4s and ?*He/?E=3 was achieved in attached ELMy H-mode plasmas. The helium exhaust efficiency with both-leg pumping was extended by 45% as compared with inner-leg pumping. By using central helium fueling with He-beam injection, the helium removal from the core plasma inside the internal transport barrier (ITB) in reversed shear plasmas in the divertor-closure configuration was investigated for the first time. The helium density profiles inside the ITB were peaked as compared with those in ELMy H-mode plasmas. In the case of low recycling divertor, it was difficult to achieve good helium exhaust capability in reversed shear plasmas with ITB. However, the helium exhaust efficiency was improved with high recycling divertor. Carbon impurity reduction was observed by the forced flow with gas puff and effective divertor pumping. (author)

2001-05-01

386

Gearbox Scheme in High Temperature Reactor Helium Gas Turbine System  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Helium Turbine is used in High Temperature Reactor Helium Gas Turbine (HTR-GT) system, by which the direct helium circulation between the reactor and turbine generator system will come true. Between helium turbine and generator, there is gearbox device which reduces the turbine rotation speed to normal speed required by the generator. Three optional gearbox schemes are discussed. The first is single reduction cylindrical gearbox, which consists of one high speed gear and one low speed gear. I...

2012-01-01

387

Atomic level population densities in decaying overcooled helium plasmas  

International Nuclear Information System (INIS)

Qualitative features of helium atomic level population in plasmas far from equilibrium are discussed. The excited level population densities of helium atoms are calculated in 'stationary flow' approximation for electron temperatures 0.1-0.4 eV and electron densities 1014-1016cm-3, assuming the ionization degree more than 0.001. The conditions of inverse population are investigated both for pure helium plasmas and for mixtures of helium with other gases. (Auth.)

1975-08-18

388

Helium Nanodroplets: spectroscopy and density-functional calculations  

Science.gov (United States)

Helium nanodroplet spectroscopy has shown to be an excellent tool for studying superfluid helium in nano-scale geometries. Experimental signatures of superfluidity are the free rotation of many molecules in helium nanodroplets, and the droplet phonon spectra observed in electronic transitions of molecular dopants. We present new results and interpretations from a study of helium nanodroplets using time- dependent density-functional theory and its normal-mode analysis.

Schmied, Roman; Lehmann, Kevin K.

2006-03-01

389

Adsorption of krypton from helium by low temperature charcoal  

International Nuclear Information System (INIS)

Adsorption of krypton from helium by charcoal at temperatures from -1000C to -1400C was experimentally investigated to verify adsorption system design methods and to determine effects of regeneration for the Gas Purification System of the Liquid-Metal Fast Breeder Reactor. Helium with two krypton concentrations, traced by krypton-85 at 0.0044 ?Ci/cm3, was passed through a 1/2-inch diameter, three-inch long trap packed with coconut charcoal. Breakthrough curves were measured by continuously recording the activity of the effluent gas using a sampler with a krypton-85 detection limit of about 5 x 10-7 ?Ci/cm3. Experimental breakthrough curves with continuous feed for both concentrations and for superficial gas velocities of 5 to 28 cm/sec were closely fitted when the pore diffusion term was omitted from the Anzelius linear equilibrium adsorption model indicating that the adsorption process for this system was controlled by gas phase mass transport kinetics. Adsorption capacities determined in these experiments at -1400C agreed closely with published data. A discontinuity, however, was observed in the krypton adsorption coefficient between -100 and -1200C. This discontinuity may be caused by capillary condensation of krypton in the charcoal pores. Breakthrough times for pulse experiments at 400 ppM (vol.) krypton concentration were several times greater than breakthrough for continuous feed experiments at equivalent conditions. The differences in breakthrough times indicate that the adsorption isotherms are non-linear in this concentration range. Regeneration experiments showed that purging with helium at room temperature for 16 hours was inadequate, since lower breakthrough times were obtained after this treatment. Regeneration under vacuum at 1000C or 2000C for 16 hours resulted in satisfactory regeneration (i.e., no reduction in breakthrough times occurred in subsequent runs). (U.S.)

1975-03-01

390

Ionization dynamics in a pulse disturbed magnetically confined helium plasma  

International Nuclear Information System (INIS)

The equilibrium of a magnetized Helium plasma is disturbed by a pulsed Trivelpiece-Gould-wave. The electrons obtain the energy by linear collisionless wave absorption. The relaxation phenomena of density and energy are explained in terms of two relaxation times tausub(E), tau1 and a quantity giving the additional ionization. These quantities are derived from a small signal fluid model based upon energy and particle balance equations. In the experiment they are taken from the transient curves of Langmuir-probe current, optical line radiation and the noise power at the electron cyclotron frequency. The experimental conditions are: Helium-gas, p = 1 ... 5 Pa, Tsub(e) = 4 eV, n = 1 ... 5 x 1010 cm-3, B = 6.5 x 10-2 T, 27 MHz rf plasma source, low frequency fluctuation level 1 is related to the instantaneous ionization frequency during the transient state. It shows a high value at the very beginning of the pulse which must be explained by a tail formation in the distribution function and enhanced radial losses becoming Bohm-like in the transition phase. (author)

1982-01-01

391

Defects and morphological changes in nanothin Cu films on polycrystalline Mo analyzed by thermal helium desorption spectrometry:  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Thermal helium desorption spectrometry (THDS) has been used for the investigation of defects and thermal stability of thin Cu films (5–200?Å) deposited on a polycrystalline Mo substrate in ultrahigh vacuum. These films are metastable at room temperature. On heating, the films transform into islands, giving rise to a relatively broad peak in the helium desorption spectra. The temperature of this island formation is dependent on film thickness, being 417?K for 10?Å and 1100?K for a ...

Venugopal, V.; Seijbel, L. J.; Thijsse, B. J.

2005-01-01

392

Thermalization of magnetically trapped metastable helium  

CERN Document Server

We have observed thermalization by elastic collisions of magnetically trapped metastable helium atoms. Our method directly samples the reconstruction of a thermal energy distribution after the application of an RF knife. The relaxation time of our sample towards equilibrium gives an elastic collision rate constant close to the unitarity limit.

Browaeys, A; Sirjean, O; Poupard, J; Nowak, S; Boiron, D; Westbrook, C I; Aspect, Alain

2001-01-01

393

Forbidden transitions in the helium atom  

CERN Document Server

Nonrelativistically forbidden, single-photon transition rates between low lying states of the helium atom are rigorously derived within quantum electrodynamics theory. Equivalence of velocity and length gauges, including relativistic corrections is explicitly demonstrated. Numerical calculations of matrix elements are performed with the use of high precision variational wave functions and compared to former results.

Lach, G; Lach, Grzegorz; Pachucki, Krzysztof

2001-01-01

394

Development of helium isotopic database in Japan  

International Nuclear Information System (INIS)

We constructed “Helium Isotopic Database in Japan”, which includes isotope ratios of noble gases and chemical compositions of gas samples collected from hot springs and drinking water wells. The helium isotopes are excellent natural tracers for indicating the presence of mantle derived volatiles, because they are chemically inert and thus conserved in crustal rock-water systems. It is common knowledge that mantle degassing does not occur homogeneously over the Earth's surface. The 3He/4He ratios higher than the typical crustal values are interpreted to indicate that transfer of mantle volatiles into the crust by processes or mechanisms such as magmatic intrusion, faulting. In particular the spatial variation of helium isotope ratios could provide a valuable information to identify volcanic regions and tectonically active areas. The database was compiled geochemical data of hot spring gas etc. from 108 published papers. As a result of the data compiling, the database has 1728 helium isotopic data. A CD-ROM is attached as an appendix. (author)

2012-01-01

395

Electron scattering in a helium Debye plasma  

Energy Technology Data Exchange (ETDEWEB)

Graphical abstract: We present our results of the total ionization cross sections for the helium ground state. We see agreement between experiment and the no screening calculations for all projectile energies considered. To date there is no other ab initio theory that is able to achieve such agreement over the entire energy range. The D = 100 results are barely distinguishable from the no screening ones. The D = 10 results are visibly different at the lower energies, but still converge to the other two calculations at the higher energies. Highlights: Black-Right-Pointing-Pointer Cross sections for electron scattering off helium in a Debye plasma are presented for excitation and ionization from the ground state. Black-Right-Pointing-Pointer The Debye-Huckel potential substantially effects all levels of the helium atom except the ground state. Black-Right-Pointing-Pointer Generally, a rather weak dependence of the presented cross sections was found for D = 10. - Abstract: The immense progress in the field of electron-atom scattering, where pure Coulomb potentials are involved, has been translated to collision processes in Debye plasmas. The Debye-Hueckel potential is used to describe plasma Coulomb screening effects depending on the temperature and density of the plasma. We provide benchmark results of electron-helium scattering for momentum transfer cross sections, discrete excitation and ionization over a broad range of incident energies and Debye radii.

Zammit, M.C., E-mail: mark.zammit@student.curtin.edu.au [ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, WA 6845 (Australia); Fursa, D.V.; Bray, I. [ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, WA 6845 (Australia)

2012-04-04

396

Neutrino-helium ionizing collisions: Electromagnetic contribution  

Science.gov (United States)

In terrestrial experiments searching for neutrino magnetic moments one investigates the ionization channel in the neutrino-atom scattering. We present numerical calculations that disprove the recent theoretical claim about large enhancement of the electromagnetic-interaction contribution to the neutrino impact ionization of helium relative to the case of the neutrino scattering on free electrons.

Kouzakov, Konstantin A.; Rodina, Yulia A.; Studenikin, Alexander I.

2014-04-01

397

Messer to provide helium for LHC project  

CERN Document Server

Over the course of the next few years, industrial gas specialist The Messer Group, through its Swiss subsidiary Messer Schweiz AG, is to provide a 160,000kg supply of helium to the European Organisation for Nuclear Research (CERN) for the operation of the world's largest particle accelerator.

2008-01-01

398

Messer to provide helium for LHC  

CERN Multimedia

Over the course of the next few years, industrial gas specialist The Messer Group, through its Swiss subsidiary Messer Schweiz AG, is to provide a 160,000kg supply of helium to the European Organisation for Nuclear Research (CERN) for the operation of the world's largest particle accelerator.

2008-01-01

399

On the Atmospheres of Helium Stars.  

Science.gov (United States)

The appearance of the spectra of helium stars as a function of hydrogen abundance is investigated theoretically for dwarfs and giants with effective temperatures Teff = 7350, 9900, and 12900 degrees K. For normal C, N, and O abundances, the He- and the He...

E. Bohm-Vitense

1967-01-01

400

An asteroseismic signature of helium ionization  

CERN Document Server

We investigate the influence of the ionization of helium on the low-degree acoustic oscillation frequencies in model solar-type stars. The signature in the oscillation frequencies characterizing the ionization-induced depression of the first adiabatic exponent $\\gamma$ is a superposition of two decaying periodic functions of frequency $\

Houdek, G

2006-01-01

 
 
 
 
401

Helium Pumping with Liquid Ring Vacuum Pump.  

Science.gov (United States)

At first the main principles for operation and building of liquid ring pumps are remembered and an experiment is described which allowed to assess the performance data of such pumps when used to pump helium gas with oil. Although they have been designed t...

C. Mathy B. Gravil G. Sauvigne J. Verdier

1983-01-01

402

Development of a helium cryostat for laser spectroscopy of atoms with unstable nuclei in superfluid helium  

Science.gov (United States)

We are developing a new nuclear laser spectroscopic technique for the study of nuclear structure that can be applied to short-lived low-yield atoms with unstable nuclei. The method utilizes superfluid helium (He II) as a trapping medium for high-energy ion beams. A liquid helium cryostat with optical windows is a key apparatus for this type of experiment. We describe the design and the performance of the cryostat which is developed for the present project.

Imamura, Kei; Furukawa, Takeshi; Wakui, Takashi; Yang, Xiaofei; Yamaguchi, Yasuhiro; Tetsuka, Hiroki; Mitsuya, Yosuke; Tsutsui, Yoshiki; Fujita, Tomomi; Ebara, Yuta; Hayasaka, Miki; Arai, Shino; Muramoto, Sosuke; Ichikawa, Yuichi; Ishibashi, Yoko; Yoshida, Naoki; Shirai, Hazuki; Hatakeyama, Atsushi; Wada, Michiharu; Sonoda, Tetsu; Ito, Yuta; Odashima, Hitoshi; Kobayashi, Tohru; Ueno, Hideki; Shimoda, Tadashi; Asahi, Koichiro; Matsuo, Yukari

2013-12-01

403

Femtosecond spectroscopy on alkali-doped helium nanodroplets; Femtosekundenspektroskopie an alkalidotierten Helium-Nanotroepfchen  

Energy Technology Data Exchange (ETDEWEB)

In the present thesis first studies on the short-time dynamics in alkali dimers and microclusters, which were bound on the surface of superfluid helium droplets, were presented. The experiments comprehended pump-probe measurements on the fs scale on the vibration dynamics on the dimers and on the fragmentation dynamics on the clusters. Generally by the studies it was shown that such extremely short slopes can also be observed on helium droplets by means of the femtosecond spectroscopy.

Claas, P.

2006-01-15

404

Thirty years of screw compressors for helium; Dreissig Jahre Schraubenkompressoren fuer Helium  

Energy Technology Data Exchange (ETDEWEB)

KAESER helium compressors, as well as their other industrial compressors, will be further developed with the intention to improve the availability and reliability of helium liquefaction systems. Further improvement of compressor and control system efficiency will ensure a low and sustainable operating cost. Fast supply of replacement parts with several years of warranty is ensured by a world-wide distribution system and is also worked on continuously. (orig.)

Wahl, H. [Kaeser Kompressoren GmbH, Coburg (Germany). Technisches Buero/Auftragskonstruktion

2007-07-01

405

Research and development of groundwater dating (Part 3). A proposal of determination method for diffusion coefficients of dissolved helium in rock and applicability of estimation of diffusion coefficients using anions  

International Nuclear Information System (INIS)

Dissolved helium in groundwater is one of the most suitable tracers for the groundwater dating. The diffusion coefficients in aquitard and aquifer were important to estimate an accumulation of the helium in groundwater. However, few papers have been reported about the diffusion of helium in rocks. In this study, effective diffusion coefficients of the helium in sandstones and mudstone were determined using a through-diffusion method. The effective diffusion coefficients of helium were in the range of 1.5 x 10-10 to 1.1 x 10-9 m2s-1 and larger than those of Br- ions. Geometrical factors for the diffusion of helium were also larger than those for the diffusion of Br- ions. This fact suggests that diffusion path of helium in the rocks is not more restricted than that of Br- ions. The diffusion coefficients of helium were also estimated using the diffusion coefficient of helium in bulk water and formation factors for diffusion of Br- ions. The estimated diffusion coefficients of helium were larger than the effective diffusion coefficients. It is clarified that the effective diffusion coefficients of helium are underestimated by the estimation method using anions. (author)

2006-08-01

406

Modification of the Helium Supply System with a PCHE type reciprocator  

International Nuclear Information System (INIS)

In the HCCR TBM, high pressure (8 MPa) and high temperature (300-500 .deg. C) helium gas is considered as a coolant, and therefore a helium cooling system (HCS), one of the essential auxiliary systems of the KO HCCR TBM, has been designed. The scaled-down helium supply system (HeSS, Ref. 5) was constructed in early 2012 to validate the HCS design and system design code, GAMMA. However, more than 2 MW of heating power was required to heat up a 1.5 kg/s mass flow of helium gas (for full scale HeSS) from room temperature to 300 .deg. C. In the present study, a recuperator is considered for the HeSS facility to solve the heating issues and the HeSS facility is modified. A 1/3 scaled-down helium supply system was constructed at KAERI for the development of manufacturing techniques and operational experience of the HCS of the HCCR TBM. The PCHE type recuperator was added in the HeSS to dramatically improve the energy efficiency and reduce the required electrical power of the helium pre-heater. The modified HeSS was linked with KoHLT-EB to supply high heat flux (?0.5 MW/m2) to validate the design and manufacturing techniques for the first wall of the HCCR TBM and obtain thermal-hydraulic experimental data for verification and validation of the GAMMA code. The experiment and code validation are scheduled to start in mid-2013 with the first wall mock-up under normal ITER operation condition

2013-05-01

407

Design, fabrication, and testing of helium cooled high heat flux module  

Energy Technology Data Exchange (ETDEWEB)

General Atomics (GA) has considerable expertise in use of helium cooling due to its high temperature gas cooled reactor experience. In order to prove the feasibility of helium cooling at high heat flux levels of above 5 MW/m{sup 2}, GA designed, fabricated, and tested a helium cooled module. The module was sized to have a heat flux surface of 25 mm wide and 80 mm long due to test setup limitations on maximum deposited power. The module was made from dispersion strengthened copper. The fabricated geometry was slightly different than the optimized design due to constraints of machining. The fabrication was done by electro discharge matching. The testing was carried out at the electron beam test facility of Sandia National Laboratory, Albuquerque (SNLA). It was necessary to reduce the area of heat flux deposition at higher heat flux due to limitations in the power capability of the electron beam. It is estimated that a heat transfer coefficient of about 40,000 W/m{sup 2}-C was achieved during these tests. The pumping power calculated from flow rate and pressure drop measurement was about 160 W for the test with 9 MW/m{sup 2} surface heat flux, which was less than 1% of the 18 kW power removed. As a result of this effort the authors conclude that, helium cooling of high heat flux components is feasible without requiring a very large helium pressure or a large pumping power.

Baxi, C.B.; Redler, K.M.; Smith, J.P. [General Atomics, San Diego, CA (United States)

1996-12-31

408

Design, fabrication, and testing of helium cooled high heat flux module  

International Nuclear Information System (INIS)

General Atomics (GA) has considerable expertise in use of helium cooling due to its high temperature gas cooled reactor experience. In order to prove the feasibility of helium cooling at high heat flux levels of above 5 MW/m2, GA designed, fabricated, and tested a helium cooled module. The module was sized to have a heat flux surface of 25 mm wide and 80 mm long due to test setup limitations on maximum deposited power. The module was made from dispersion strengthened copper. The fabricated geometry was slightly different than the optimized design due to constraints of machining. The fabrication was done by electro discharge matching. The testing was carried out at the electron beam test facility of Sandia National Laboratory, Albuquerque (SNLA). It was necessary to reduce the area of heat flux deposition at higher heat flux due to limitations in the power capability of the electron beam. It is estimated that a heat transfer coefficient of about 40,000 W/m2-C was achieved during these tests. The pumping power calculated from flow rate and pressure drop measurement was about 160 W for the test with 9 MW/m2 surface heat flux, which was less than 1% of the 18 kW power removed. As a result of this effort the authors conclude that, helium cooling of high heat flux components is feasible without requiring a very large helium pressure or a large pumping power

1996-08-04

409

Collisional excitation of hydrogen and the determination of the primordial helium abundance from H II regions  

CERN Multimedia

This paper investigates the effect of collisional enhancement of the hydrogen lines on the derivation of the helium abundances in low metallicity H II regions. For this, we have constructed a grid of photoionization models relevant for the analysis of giant \\hii regions in blue compact galaxies. We show that the effect of collisional excitation on the Halpha/Hbeta ratio can be quite important (up to 8% or more). The impact of this effect on the determination of the helium mass fraction has been tracked on four low-metallicity blue compact galaxies for which Keck spectra are available and which are among the best objects for the quest of the pregalactic helium abundance. We find that taking into account the effects of collisional excitation of hydrogen results in an upward correction of the helium mass fraction Y by up to 5%. However, combining with other systematic effects usually not considered in the determination of the helium abundance in low-metallicity galaxies, the resulting uncertainty should be much ...

Stasinska, G

2001-01-01

410

Helium release from neutron-irradiated Li 2O single crystals  

Science.gov (United States)

Lithium oxide (Li 2O) single crystals with various sizes (0.15-5 mm) were used as specimens. After the irradiation in JRR-4 and JRR-2 (thermal neutron fluence: 2 × 10 17-2 × 10 19 n/cm 2), and fast neutrons in FFTF (fast neutron fluence: 4 × 10 22 n/cm 2), helium release from the Li 2O specimens during the heating at a constant heating rate was continuously measured with a quadrupole mass spectrometer. The helium release curves from JRR-4 and JRR-2 specimens have only one broad peak each. From the dependence of the peak temperature on the neutron fluence and the crystal diameter, and the comparison with the results of sintered pellets, it is concluded that the helium generated in the crystal is released through the processes of bulk diffusion with trapping by irradiation defects such as some defect clusters. For the helium release from FFTF specimens, two broad peaks were observed in the release curves. It is considered that two different migration paths exist for helium migration in the specimen, that is, bulk diffusion and diffusion through the micro-cracks formed due to the heavy irradiation.

Yamaki, Daiju; Tanifuji, Takaaki; Noda, Kenji

1998-10-01

411

Engineering Sensitivity Improvement of Helium Mass Spectrometer Leak Detection System by Means Global Hard Vacuum Test  

International Nuclear Information System (INIS)

The engineering sensitivity improvement of Helium mass spectrometer leak detection using global hard vacuum test configuration has been done. The purpose of this work is to enhance the sensitivity of the current leak detection of pressurized method (sniffer method) with the sensitivity of 10-3 ? 10-5 std cm3/s, to the global hard vacuum test configuration method which can be achieved of up to 10-8 std cm3/s. The goal of this research and development is to obtain a Helium leak test configuration which is suitable and can be used as routine bases in the quality control tests of FPM capsule and AgInCd safety control rod products. The result is an additional instrumented vacuum tube connected with conventional Helium mass spectrometer. The pressure and temperature of the test object during the leak measurement are simulated by means of a 4.1 kW capacity heater and Helium injection to test object, respectively. The addition of auxiliary mechanical vacuum pump of 2.4 l/s pumping speed which is directly connected to the vacuum tube, will reduce 86 % of evacuation time. The reduction of the measured sensitivity due to the auxiliary mechanical vacuum pump can be overcome by shutting off the pump soon after Helium mass spectrometer reaches its operating pressure condition. (author)

2006-05-01

412

Helium accreting CO white dwarfs with rotation: helium novae instead of double detonation  

CERN Document Server

We present evolutionary models of helium accreting carbon-oxygen white dwarfs in which we include the effects of the spin-up of the accreting star induced by angular momentum accretion, rotationally induced chemical mixing and rotational energy dissipation. Initial masses of 0.6 Msun and 0.8 Msun and constant accretion rates of a few times 10^{-8} Msun/yr of helium rich matter have been considered, which is typical for the sub-Chandrasekhar mass progenitor scenario for Type Ia supernovae. It is found that the helium envelope in an accreting white dwarf is heated efficiently by friction in the differentially rotating spun-up layers. As a result, helium ignites much earlier and under much less degenerate conditions compared to the corresponding non-rotating case. Consequently, a helium detonation may be avoided, which questions the sub-Chandrasekhar mass progenitor scenario for Type Ia supernovae. We discuss implications of our results for the evolution of helium star plus white dwarf binary systems as possible...

Yoon, S C

2004-01-01

413

Helium physisorption on internal surfaces of radiation-induced cavities in aluminum: a positron annihilation study  

International Nuclear Information System (INIS)

Positron lifetime spectra have been measured as a function of temperature in the range 10-295 K for aluminum single crystals irradiated with 0-40 MeV ? particles to a total dose of ? 5x1017 cm-2. We present results for the temperature dependence of the lifetime component representing annihilations of the positrons trapped in helium-filled cavities. We discuss these results in terms of positron diffusion and helium physisorption on the internal surfaces of the irradiation-induced cavities. (orig.)

1991-05-01

414

Helium physisorption on internal surfaces of radiation-induced cavities in aluminum: a positron annihilation study  

Energy Technology Data Exchange (ETDEWEB)

Positron lifetime spectra have been measured as a function of temperature in the range 10-295 K for aluminum single crystals irradiated with 0-40 MeV {alpha} particles to a total dose of {approx equal} 5x10{sup 17} cm{sup -2}. We present results for the temperature dependence of the lifetime component representing annihilations of the positrons trapped in helium-filled cavities. We discuss these results in terms of positron diffusion and helium physisorption on the internal surfaces of the irradiation-induced cavities. (orig.).

Hozhabri, N.; Ma, J.; Naidu, S.V.; Eom, C.I.; Sharma, S.C. (Dept. of Physics, Univ. of Texas at Arlington (USA)); Nambissan, P.M.G.; Sen, P. (Saha Inst. of Nuclear Physics, Calcutta (India))

1991-05-01

415

Measurements of cascade times of antiprotons in molecular hydrogen and helium  

CERN Document Server

The OBELIX experiment at CERN collected samples of antiproton annihilations at rest in different gaseous targets, such as hydrogen, deuterium and helium. We analyze a set of the Obelix data using a new technique for measuring, for the first time, the cascade times independent of the capture energy and of the antiproton stopping power. We report on measurements of the cascade times for hydrogen at 3.4, 5.8, 9.8 and 150 mbar and for helium at 8.2, 50 and 150 mbar pressure. An estimate of the antiproton capture energy in hydrogen is also presented. (12 refs).

Bianconi, A; Corradini, M; Donzella, A; Gómez, G; Lodi-Rizzini, E; Venturelli, L; Vilar, R; Zenoni, A; Bertin, A; Bruschi, M; Capponi, M; De Castro, S; Donà, R; Galli, D; Giacobbe, B; Marconi, U; Massa, I; Piccinini, M; Semprini-Cesari, N; Spighi, R; Vagnoni, V M; Vecchi, S; Villa, M; Vitale, A; Zoccoli, A; Cicalò, C; De Falco, A; Masoni, A; Puddu, G; Serci, S; Usai, G L; Gorchakov, O E; Prakhov, S N; Rozhdestvensky, A M; Tretyak, V I; Poli, M; Gianotti, P; Guaraldo, C; Lanaro, A; Lucherini, V; Petrascu, C; Ableev, V G; Ricci, R A; Vannucci, Luigi; Filippini, V; Fontana, A; Montagna, P; Rotondi, A; Salvini, P; Mirfakhraee, N; Bussa, M P; Busso, L; Cerello, P G; Denisov, O Yu; Ferrero, L; Garfagnini, R; Grasso, A; Maggiora, A; Panzarasa, A; Panzieri, D; Tosello, F; Botta, E; Bressani, Tullio; Calvo, D; Costa, S; D'Isep, F; Feliciello, A; Filippi, A; Marcello, S; Agnello, M; Iazzi, F; Minetti, B; Tessaro, S; Santi, L

2000-01-01

416

Control of two-photon double ionization of helium with intense chirped attosecond laser pulses  

Science.gov (United States)

We study the two-photon double-ionization process of the helium atom by solving numerically the nonrelativistic, time-dependent Schrödinger equation in its full dimensionality. We investigate with intense chirped attosecond laser pulses of 23.5-nm wavelength the two-photon absorption near and above the sequential threshold. We show how it is possible by adjusting the chirp parameter to control the electronic transitions inside the atom, thereby reinforcing or weakening the ionization process. Attosecond chirped laser pulses offer a promising way to probe and control the two-photon double ionization of helium when compared with attosecond transform-limited pulses.

Barmaki, S.; Lanteigne, P.; Laulan, S.

2014-06-01

417

An experimental study simulating the helium liquefaction process in a reciprocating magnetic refrigerator  

International Nuclear Information System (INIS)

We have constructed a special one-shot test apparatus to investigate the properties of a reciprocating magnetic refrigerator for helium liquefaction. The liquefaction efficiency for one-shot demagnetization was only about 40% with an initial temperature of 5 K, and higher initial temperatures gave lower liquefaction efficiencies. Losses in the experiment can be classified into four causes: the thermal resistance of the film condensation heat transfer, friction, the heat flow from the holders to the refrigerant and cooling of gaseous helium above 4.2 K to 4.2 K. The last cause was the most dominant

1986-01-01

418

An efficient cooling loop for connecting cryocooler to a helium reservoir  

International Nuclear Information System (INIS)

The magnet system of the VENUS ECR Ion Source at LBNL has two 1.5-watt cryocoolers suspended in the cryostat vacuum. Helium vapor from the liquid reservoir is admitted to a finned condenser bolted to the cryocooler 2nd stage and returns as liquid via gravity. Small-diameter flexible tubes allow the cryocoolers to be located remotely from the reservoir. With 3.1 watts load, the helium reservoir is maintained at 4.35 K, 0.05K above the cryocooler temperature. Design, analysis, and performance are presented

2003-09-22

419

An efficient cooling loop for connecting cryocooler to a helium reservoir  

Energy Technology Data Exchange (ETDEWEB)

The magnet system of the VENUS ECR Ion Source at LBNL has two 1.5-watt cryocoolers suspended in the cryostat vacuum. Helium vapor from the liquid reservoir is admitted to a finned condenser bolted to the cryocooler 2nd stage and returns as liquid via gravity. Small-diameter flexible tubes allow the cryocoolers to be located remotely from the reservoir. With 3.1 watts load, the helium reservoir is maintained at 4.35 K, 0.05K above the cryocooler temperature. Design, analysis, and performance are presented.

Taylor, C.E.; Abbott, C.S.R.; Leitner, D.; Leitner, M.; Lyneis, C.M.

2003-09-21

420

Development of a zero boil-off helium cryostat for superconducting magnets  

Science.gov (United States)

This paper describes a horizontal type cryostat of a superconducting magnet with a 300mm room temperature bore. The magnet, with the diameter of 400mm and length of 815mm, is immersed in 30 liter liquid helium. Design consideration, including thermal staging of the silver/Bisco current leads, low thermal conduction mechanical support structure, and the theoretical calculation of heat load to the cryostat are discussed. And only a helium recondensing G-M cooler(40W at 50K, 1.5W at 4.2K) is used to achieve zero boil-off.

Wang, Meifen; Yang, Huan; Ning, Feipeng; Zhu, Zian

2012-12-01

 
 
 
 
421

Application of laser resonance fluorescence for investigations of helium in a near-wall plasma  

International Nuclear Information System (INIS)

Use of laser resonance fluorescence (LRF) method for solution of problems related to the presence of helium in plasma is considered. Investigations were carried on at T-10 tokamak. General principles of measurements consist in optical pumping of one of transitions in HeI with the subsequent observation of responses in different lines. In optical pumping of the 2"3P ? D"3D transition 3"3P ? 2"3S(?=388.9 nm) and 3"3S ? 2"3P(?=706.5 nm) lines were observed. Observed evaluations of elementary process rates in helium atom agree well with theoretical evaluations

1986-11-01

422

Application of JLab 12GeV helium refrigeration system for the FRIB accelerator at MSU  

Energy Technology Data Exchange (ETDEWEB)

The planned approach to have a turnkey helium refrigeration system for the MSU-FRIB accelerator system, encompassing the design, fabrication, installation and commissioning of the 4.5-K refrigerator cold box(es), cold compression system, warm compression system, gas management, oil removal and utility/ancillary systems, was found to be cost prohibitive. Following JLab’s suggestion, MSU-FRIB accelerator management made a formal request to evaluate the applicability of the recently designed 12GeV JLab cryogenic system for this application. The following paper will outline the findings and the planned approach for the FRIB helium refrigeration system.

Ganni, Venkatarao [JLAB; Knudsen, Peter N. [JLAB; Arenius, Dana M. [JLAB; Casagrande, Fabio [Michigan State University

2014-01-01

423

Development of a zero boil-off helium cryostat for superconducting magnets  

International Nuclear Information System (INIS)

This paper describes a horizontal type cryostat of a superconducting magnet with a 300mm room temperature bore. The magnet, with the diameter of 400mm and length of 815mm, is immersed in 30 liter liquid helium. Design consideration, including thermal staging of the silver/Bisco current leads, low thermal conduction mechanical support structure, and the theoretical calculation of heat load to the cryostat are discussed. And only a helium recondensing G-M cooler(40W at 50K, 1.5W at 4.2K) is used to achieve zero boil-off.

2012-12-17

424

Measurements of cascade times of anti-protons in molecular hydrogen and helium.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Obelix experiment at CERN collected samples of antiproton annihilations at rest in different gaseous targets, such as hydrogen, deuterium and helium. We analyze a set of the Obelix data using a new technique for measuring, for the first time, the cascade times independent of the capture energy and of the antiproton stopping power. We report on measurements of the cascade times for hydrogen at 3.4, 5.8, 9.8 and 150 mbar and for helium at 8.2, 50 and 150 mbar pressure. An estimate of the an...

Bressani, Tullio; Busso, Luigi; Garfagnini, Raffaello; Ferrero, Livio; Costa, Sergio; Grasso, Antonino; Botta, Elena; Marcello, Simonetta; Bussa, Maria Pia; Panzieri, Daniele

2000-01-01

425

Design, commissioning and operating experience of the PSI KA-IV multipurpose helium refrigerator  

Science.gov (United States)

Early in 1991 the Paul Scherrer Institute (PSI), Villigen, Switzerland commissioned its fourth helium liquefier/refrigerator. The facility is used for cooling superconducting magnets, purification and liquefaction of helium. It provides 4000 W of refrigeration at ca. 60 K and 900 W at 4.5 K without nitrogen precooling. Its main features are: Reciprocating compressor with labyrinth pistons, three expansion turbines with dynamic gas bearings, fully automatic operation based on a programmable logic controller and graphic process visualization. The paper describes the operating requirements, the refrigerator, the control concept designed to optimize the performance, and finally the operating experience gained during start up and half a year of operation.

Amstutz, Markus; Baumann, Hans U.; Clerc, Roger; Gloor, Walter; Kurtcuoglu, Kirkor; Löhlein, Karl; Schulze, Reinhard M.; Zichy, János A.; Ziegler, Bruno

426

Energies and Relativistic Corrections for the Metastable States of Antiprotonic Helium Atoms  

International Nuclear Information System (INIS)

We present accurate results for the energy levels of antiprotonic helium atoms with the relativistic and QED corrections of order ?4mc2 taken into account. These results reduce the discrepancy between theory and experiment to about 5 endash 10ppm and rigorously confirm Condo close-quote s model of metastability for the long-lived fraction of antiprotonic helium. The present level of precision enables the unambiguous ascription of quantum numbers to all of the transition lines observed so far. copyright 1997 The American Physical Society

1997-11-01

427

Energies and Relativistic Corrections for the Metastable States of Antiprotonic Helium Atoms  

Energy Technology Data Exchange (ETDEWEB)

We present accurate results for the energy levels of antiprotonic helium atoms with the relativistic and QED corrections of order {alpha}{sup 4}mc{sup 2} taken into account. These results reduce the discrepancy between theory and experiment to about 5{endash}10ppm and rigorously confirm Condo{close_quote}s model of metastability for the long-lived fraction of antiprotonic helium. The present level of precision enables the unambiguous ascription of quantum numbers to all of the transition lines observed so far. {copyright} {ital 1997} {ital The American Physical Society}

Korobov, V.I. [Joint Institute for Nuclear Research, 141980, Dubna (Russia); Bakalov, D.D. [Institute for Nuclear Research and Nuclear Energy, Tsarigradsko chaussee 72, Sofia 1784 (Bulgaria)

1997-11-01

428

Direct detection of vacuum ultraviolet scintillations in liquid helium using germanium photodiodes  

International Nuclear Information System (INIS)

Direct detection of vacuum ultraviolet scintillations in liquid helium produced by 5.3 MeV ? particles has been accomplished using a high-purity germanium photodiode. The diode was immersed in the liquid helium and operated in the side-entry mode with a senstive area of 0.3 x 1.0 cm. Scintillation from each ? particle was detected as a single pulse. A signal rise time or approx. =1200 V cm"-"1. The quantum efficiency of the photodiode was estimated to be approx.4

1982-08-15

429

Scintillation and charge extraction from the tracks of energetic electrons in superfluid helium-4  

CERN Document Server

An energetic electron passing through liquid helium causes ionization along its track. The ionized electrons quickly recombine with the resulting positive ions, which leads to the production of prompt scintillation light. By applying appropriate electric fields, some of the ionized electrons can be separated from their parent ions. The fraction of the ionized electrons extracted in a given applied field depends on the separation distance between the electrons and the ions. We report the determination of the mean electron-ion separation distance for charge pairs produced along the tracks of beta particles in superfluid helium at 1.5 K by studying the quenching of the scintillation light under applied electric fields. Knowledge of this mean separation parameter will aid in the design of particle detectors that use superfluid helium as a target material.

Guo, W; Cahn, S B; Nikkel, J A; Shin, Y; McKinsey, D N

2011-01-01

430

Scintillation and charge yield from the tracks of energetic electrons in superfluid helium-4  

International Nuclear Information System (INIS)

An energetic electron passing through liquid helium causes ionization along its track. The ionized electrons quickly recombine with the resulting positive ions, which leads to the production of prompt scintillation light. By applying appropriate electric fields, some of the ionized electrons can be separated from their parent ions. The fraction of the ionized electrons extracted in a given applied field depends on the separation distance between the electrons and the ions. We report the determination of the mean electron-ion separation distance for charge pairs produced along the tracks of beta particles in superfluid helium at 1.5 K by studying the quenching of the scintillation light under applied electric fields. Knowledge of this mean separation parameter will aid in the design of particle detectors that use superfluid helium as a target material.

2012-01-01

431

Collision-induced polarized and depolarized Raman spectra of helium and the diatom polarizability  

International Nuclear Information System (INIS)

The spectral distributions and absolute intensities of collision-induced Raman spectra of helium are obtained at 30 amagat, with incident beam polarizations parallel and perpendicular to the observation. These spectra can readily be separated into the polarized and the depolarized Raman continuum of the helium diatom. For comparison, spectra are also computed from wave mechanics, on the basis of Placzeck's polarizability theory. Accurate, semiempirical interaction potentials are used as input, together with ab initio computations of the helium diatom polarizability tensor components. The computed spectra of selected trace and anisotropy functions agree with the observed polarized and depolarized continua. Anisotropy functions consistent with the depolarized spectrum differ by less than 5% from the classical dipole-induced dipole (DID) values at 2.685 A separation

1980-01-15

432

Effect of implanted helium on tensile properties and hardness of 9% Cr martensitic stainless steels  

International Nuclear Information System (INIS)

Hundred micrometer thick specimens of 9% Cr martensitic steels EM10 and T91 were homogeneously implanted with He4 to concentrations up to 0.5 at.% at temperatures from 150 to 550 deg. C. The specimens were tensile tested at room temperature and at the respective implantation temperatures. Subsequently the fracture surfaces were analysed by scanning electron microscopy and some of the specimens were examined in an instrumented hardness tester. The implanted helium caused hardening and embrittlement which both increased with increasing helium content and with decreasing implantation temperature. Fracture surfaces showed intergranular brittle appearance with virtually no necking at the highest implantation doses, when implanted below 250 deg. C. The present tensile results can be scaled to tensile data after irradiation in spallation sources on the basis of helium content but not on displacement damage. An interpretation of this finding by microstructural examination is given in a companion paper [J. Nucl. Mater., these Proceedings

2003-05-15

433

Effect of implanted helium on tensile properties and hardness of 9% Cr martensitic stainless steels  

Science.gov (United States)

Hundred micrometer thick specimens of 9% Cr martensitic steels EM10 and T91 were homogeneously implanted with He 4 to concentrations up to 0.5 at.% at temperatures from 150 to 550 °C. The specimens were tensile tested at room temperature and at the respective implantation temperatures. Subsequently the fracture surfaces were analysed by scanning electron microscopy and some of the specimens were examined in an instrumented hardness tester. The implanted helium caused hardening and embrittlement which both increased with increasing helium content and with decreasing implantation temperature. Fracture surfaces showed intergranular brittle appearance with virtually no necking at the highest implantation doses, when implanted below 250 °C. The present tensile results can be scaled to tensile data after irradiation in spallation sources on the basis of helium content but not on displacement damage. An interpretation of this finding by microstructural examination is given in a companion paper [J. Nucl. Mater., these Proceedings].

Jung, P.; Henry, J.; Chen, J.; Brachet, J.-C.