WorldWideScience

Sample records for beryllia

  1. Neutron Spectra in Subcritical Graphite- and Beryllia-Moderated Assemblies

    International Nuclear Information System (INIS)

    A number of subcritical graphite- and beryllia-moderated assemblies fuelled with plutonium and highly enriched uranium plates have been constructed with ratios of moderator atoms to fissile atoms as low as 300. As part of a general study of these small under moderated systems in which fission takes place predominantly at energies above 0.1 eV , time-of-flight measurements have been carried out using a neutron chopper having a resolution of 4 μs/m. This adequately resolves the spectrum in the thermal region and in the region of the resonance in 239Pu at 0.296 eV. Calculations have been carried out using a multigroup transport code with scattering matrices for graphite and beryllia based on data obtained from the Chalk River scattering law experiments. A correct weighting over the experimental source area of the vector flux in the direction of the extracted beam produces a spectrum which can be compared directly with the observed spectrum. It has been found that in the region 0.4 to 1.0 eV the experimental spectra have fewer neutrons than are predicted and this is particularly noticeable in the BeO-moderated assemblies. The factors which could give rise to the discrepancy are discussed but it has not been possible to attribute it to any particular one. (author)

  2. Kinetic analysis of interstitial atomic hydrogen in a-Si:(H,O,N) and beryllia

    International Nuclear Information System (INIS)

    A method for interpreting thermal decay of interstitial atomic hydrogen Hoi produced by irradiation in a-Si: (H,O,N) and in beryllia was developed. The hypothesis of Hoi were produced from RH type molecules by irradiation effect and trapped in the interstitials of studied elements was considered. The hypothesis of the heating causes the disarming of Hoi, and can be retrapped, recombine with R matrices or react between themselves to form the H2 molecules. The kinetic equations were arranged by a schematic method for each proposed reaction. These equations were solved numerically by RungeKutta method. The adjust parameters show that the Hoi + Hoi -> H2 occurs only for beryllia, because the kinetic occurs at higher temperatures. All the parameters were adjusted to Arrhenius law, allowing to determine the activation energies for each process. (M.C.K.)

  3. Effect of beryllia substitution and addition in a YBa2Cu3O7-δ compound

    International Nuclear Information System (INIS)

    The effect of BeO substitution and addition in the superconducting properties of YBa2Cu3O7-δ superconductors has been investigated by temperature resistance measurements and x-ray diffraction studies. The results revealed that the substitution or addition of BeO in YBa2Cu3O7-δ does not have much detrimental effect on the superconducting properties. Because of this nonpoisoning behavior, beryllia is suggested as a suitable substrate material for the production of superconducting thin films

  4. Study on the bound water of several high specific surface-area oxides (beryllia, alumina, silica-alumina)

    International Nuclear Information System (INIS)

    This study is concerned with the bound water of several oxides (beryllia, alumina, silica-alumina) at different steps of their dehydration (heating temperatures between 150 and 1100 deg. C). The following techniques have been used simultaneously: Thermal analysis (a new method has been developed), nitrogen adsorption (study of the texture), Diborane hydrolysis (qualitative and quantitative analysis of surface water), Infra-red spectrography (in the absorption range of water), Nuclear magnetic resonance (in the resonance range of protons). Thanks to these different techniques, five kinds of bound water have been observed. Attention is called on the great influence of the thermal treatment conditions on the evolution of the products resulting from the decomposition of alumina α-trihydrate Al(OH)3 and beryllium α-hydroxide, in the course of the dehydration. Moreover, the author emphasizes the peculiar properties of the two kinds of oxides (alumina and beryllia) prepared through a new method of treatment under low pressure and constant speed of decomposition. Such particular features concern mainly texture, bound water, and consequently, also catalytic activity. (author)

  5. Corrosion testing of zirconia, beryllia and magnesia ceramics in molten alkali metal carbonates at 900 °C

    Science.gov (United States)

    Kaplan, Valery; Bendikov, Tatyana; Feldman, Yishay; Gartsman, Konstantin; Wachtel, Ellen; Lubomirsky, Igor

    2016-01-01

    An electrochemical cell containing molten Li2CO3-Li2O at 900 °C has been proposed for the conversion of the greenhouse gas CO2 to CO for chemical energy storage. In the current work, we have examined the corrosion resistance of zirconia, beryllia and magnesia ceramics at 900 °C in the Li2CO3-Li2O and Li-Na-K carbonate eutectic mixtures to identify suitable electrically insulating materials. Conclusions regarding material stability were based on elemental analysis of the melt, primarily via X-ray photoelectron spectroscopy, a particularly sensitive technique. It was found that magnesia is completely stable for at least 33 h in a Li2CO3-Li2O melt, while a combined lithium titanate/lithium zirconate layer forms on the zirconia ceramic as detected by XRD. Under the same melt conditions, beryllia shows considerable leaching into solution. In a Li-Na-K carbonate eutectic mixture containing 10.2 mol% oxide at 900 °C under standard atmospheric conditions, magnesia showed no signs of degradation. Stabilization of the zirconia content of the eutectic mixture at 0.01-0.02 at% after 2 h is explained by the formation of a lithium zirconate coating on the ceramic. On the basis of these results, we conclude that only magnesia can be satisfactorily used as an insulating material in electrolysis cells containing Li2CO3-Li2O melts.

  6. Texture study of divided solids by gas adsorption: application to beryllia, alumina and to gels and oxides

    International Nuclear Information System (INIS)

    A certain number of porous materials have been studied in an adsorption apparatus developed by us and leading to a measurement of the surface area with a reproducibility as good as 1/1 000. We have shown that this is only obtained at the cost of a number necessary precautions in the measurement of the gaseous volume adsorbed in a monomolecular layer (especially in the case of microporous solids). It also appears convenient to substitute argon to nitrogen, the latter being sensitive to chemical or electrical interactions with the adsorbent. Calculation methods of the pore size distribution are analyzed and discussed. The experimental data shows that the thickness of the multi-molecular layer must be estimated from the number of layers given by Shull using a layer thickness of 3.6 angstrom. A new method of analysis of the desorption curve is also given. We have also shown that a certain number of lamellar, non porous, systems, such as Be(OH)2 present a hysteresis branch on the adsorption isotherm of type I or II. Using the numerical data obtained by our method together with the information provided by the electronic microscope, we have been able to conclude that this hysteresis can be ascribed to the lack of rigidity of the solid. On the contrary, samples of microporous texture (r < 20 A) of the type of beryllia, provide the case, which we have been able to characterize, of porous materials which do not exhibit a hysteresis phenomenon. The above conclusions have allowed us to describe the evolution of the texture during their progressive dehydration (thermal treatment from 150 to 1100 C) of two series of samples, namely beryllia and alumina. (author)

  7. Study on the bound water of several high specific surface-area oxides (beryllia, alumina, silica-alumina); Etude de l'eau de constitution de plusieurs oxydes a grande surface specifique (glucine, alumine, silice-alumine)

    Energy Technology Data Exchange (ETDEWEB)

    Rouquerol, J. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1964-11-01

    This study is concerned with the bound water of several oxides (beryllia, alumina, silica-alumina) at different steps of their dehydration (heating temperatures between 150 and 1100 deg. C). The following techniques have been used simultaneously: Thermal analysis (a new method has been developed), nitrogen adsorption (study of the texture), Diborane hydrolysis (qualitative and quantitative analysis of surface water), Infra-red spectrography (in the absorption range of water), Nuclear magnetic resonance (in the resonance range of protons). Thanks to these different techniques, five kinds of bound water have been observed. Attention is called on the great influence of the thermal treatment conditions on the evolution of the products resulting from the decomposition of alumina {alpha}-trihydrate Al(OH){sub 3} and beryllium {alpha}-hydroxide, in the course of the dehydration. Moreover, the author emphasizes the peculiar properties of the two kinds of oxides (alumina and beryllia) prepared through a new method of treatment under low pressure and constant speed of decomposition. Such particular features concern mainly texture, bound water, and consequently, also catalytic activity. (author) [French] Ce travail porte sur l'eau de constitution de plusieurs oxydes (glucine, alumine, silice-alumine) aux differents degres de leur deshydratation (temperatures de traitement comprises entre 150 et 1100 deg. C). Cette etude met simultanement en oeuvre: l'analyse thermique (proposition d'une nouvelle methode), l'adsorption d'azote (etude de texture), l'hydrolyse du diborane (analyse qualitative et quantitative de l'eau de surface), la spectrographie infra-rouge (dans le domaine d'absorption de l'eau), la resonance magnetique nucleaire (dans le domaine de resonance des protons). A l'aide de ces differentes techniques, cinq formes d'eau de constitution ont ete observees. L'attention est attiree sur la tres grande influence

  8. Ab-initio investigations of the electronic properties of bulk wurtzite Beryllia and its derived nanofilms

    KAUST Repository

    Goumri-Said, Souraya

    2010-08-01

    In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties. © 2010 Elsevier B.V. All rights reserved.

  9. Structure-property relationships in thermomechanically treated beryllia dispersed nickel alloys

    International Nuclear Information System (INIS)

    BeO dispersed nickel alloys, produced by powder metallurgy techniques, were studied extensively in stress rupture at 815, 982, and 10930C (1088, 1255, and 1366 K) and by transmission electron microscopy. The alloys were subjected to a variety of thermomechanical treatments (TMT) to determine the benefits of TMT on properties. It is shown that the use of intermediate annealing treatments after 10 percent reduction steps is highly beneficial on both low and high temperature properties. It is indicated that the high temperature strength is not primarily dependent on the grain aspect ratio or texture but depends strongly on the dislocation density and distribution of dislocations in a stable substructure which is pinned by the fine oxide dispersion. (22 fig) (U.S.)

  10. Beryllium. Beryllium oxide, obtention and properties. Pt.4

    International Nuclear Information System (INIS)

    As a continuation of the 'Beryllium' series this work reviews several methods of high purity beryllia production. Diverse methods of obtention and purification from different beryllium compounds are described. Some chemical, mechanical and electrical properties related with beryllia obtention methods are summarized. (Author)

  11. A measurement of the response to fast neutrons of several materials dosemeters

    International Nuclear Information System (INIS)

    The response to fast neutrons was measured for three types of materials testing dosemeters: fast neutron dosimetry silicon diodes; beryllia, alumina and calcium fluoride TLDs; graphite walled ionisation chambers. The calibrations were made using a 3MW positive ion accelerator. The arrangement of the target, beam monitor and devices is described, and the measured fast neutron sensitivities are presented. (UK)

  12. Thermal-shock Resistance of a Ceramic Comprising 60 Percent Boron Carbide and 40 Percent Titanium Diboride

    Science.gov (United States)

    Yeomans, C M; Hoffman, C A

    1953-01-01

    Thermal-shock resistance of a ceramic comprising 60 percent boron carbide and 40 percent titanium diboride was investigated. The material has thermal shock resistance comparable to that of NBS body 4811C and that of zirconia, but is inferior to beryllia, alumina, and titanium-carbide ceramals. It is not considered suitable for turbine blades.

  13. Wetting behavior of lead borosilicates on ceramic substrates

    International Nuclear Information System (INIS)

    Wetting characteristics of several lead silicates. lead borates, and lead borosilicates, on alumina, beryllia, aluminum nitride, silicon nitride and silicon carbide substrates, were investigated. Both polycrystalline and single crystal substrates behavior of the liquids was studied with the sensile drop method, and optical and SEM/EDAX microscopy was used for examining interfaces. The results are discussed in relating to interfacial properties and bonding

  14. Spray drying of beryllium oxide powder

    International Nuclear Information System (INIS)

    Forming of beryllia ceramics through dry pressing requires the agglomeration of the powder through spray drying. To produce high quality fired ceramics it is necessary to disperse/grind the primary powder prior to binder addition. Size reduction of the powder is accomplished using an aqueous system in Vibro-Energy mills (VEM) charged with beryllia media to minimize contamination. Two VEM mills of different size were used to characterize the grinding operation. Details of the grinding kinetics are described within the context of the Macroscopic Population Balance Model approach. Spray drying of the ceramic slurry was accomplished with both a centrifugal atomizer and a two fluid nozzle atomizer. Two different spray dryers were used. Important operating parameters affecting the size distribution of the spray dried powder are discussed

  15. Pulsed laser deposition of epitaxial BeO thin films on sapphire and SrTiO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Peltier, Thomas; Takahashi, Ryota; Lippmaa, Mikk, E-mail: mlippmaa@issp.u-tokyo.ac.jp [Institute for Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan)

    2014-06-09

    Epitaxial beryllia thin films were grown by pulsed laser deposition on Al{sub 2}O{sub 3}(001) and SrTiO{sub 3}(111) substrates. Nearly relaxed epitaxial films were obtained on both substrates at growth temperatures of up to about 600 °C. Crystalline films with expanded lattice parameters were obtained even at room temperature. The maximum growth temperature was limited by a loss of beryllium from the film surface. The volatility of beryllium appeared to be caused by the slow oxidation kinetics at the film surface and the re-sputtering effect of high-energy Be and BeO species in the ablation plume. Time-of-flight plume composition analysis suggested that the target surface became Be metal rich at low oxygen pressures, reducing the growth rate of beryllia films.

  16. Self-healing fuse development

    Science.gov (United States)

    Jones, N. D.; Kinsinger, R. E.; Harris, L. P.

    1973-01-01

    The mercury-filled self-healing fuses developed for this program afford very good protection from circuit faults with rapid reclosure. Fuse performance and design parameters have been characterized. Life tests indicate a capability of 500 fuse operations. Fuse ratings are 150 v at 5, 15, 25 and 50 circuit A. A series of sample fuses using alumina and beryllia insulation have been furnished to NASA for circuit evaluation.

  17. Beryllium facilities in India

    International Nuclear Information System (INIS)

    Due to its unique combination of physical, mechanical, thermal and nuclear properties, beryllium is indispensable for many applications in the fields of nuclear and space sciences. Beryllia and copper beryllium alloys have also found extensive applications in the electrical and electronic industries. Beryllium facilities at Bhabha Atomic Research Centre (BARC) have been set up to meet indigenous requirements for these materials. Besides developing beryllium technology, the project team has also designed and developed a number of special purpose equipment. (Author)

  18. Annual report of the Metallurgy Division - period ending December 1975

    International Nuclear Information System (INIS)

    The R and D activities of the Metallurgy Division of the Bhabha Atomic Research Centre, Bombay (India) during 1975 are described. Some of the R and D programmes of particular interest to nuclear technology are: (1) flowsheet development for the production of rare metals and alloys of nuclear use e.g. hafnium, beryllium, zirconium (2) metallurgical, irradiation hardening and corrosion studies on Zr and Zr-base alloys and (3) studies of nuclear ceramic materials such as UO2 and beryllia. (M.G.B.)

  19. The coplanar electron tube. Memorandum file report

    Energy Technology Data Exchange (ETDEWEB)

    Zinn, M.H.

    1976-12-01

    Coplanar electron tubes consisting of emitting, controlling and collecting electrodes on a single heated plane have been proposed as a method of achieving high temperature and high radiation resistant devices. In order to design these devices, the scaling laws must be obtained. Using computer techniques it was determined that while the plate current of a device still followed a general three-halves power curve, the effect of electrode areas and electrode spacing are far less pronounced then in multiplanar tubes. A number of auxiliary problems were studied and data was obtained indicating that both alumina and beryllia would be suitable substrates for these devices. Single crystal alumina (sapphire) was found to be satisfactory, but polycrystalline alumina was not, indicating some reaction with active material from the cathode. Polycrystalline beryllia, on the other hand, was satisfactory. A trough strip line was developed for use in a distributed amplifier, power coplanar tetrode, but time did not permit, nor did results warrant, the construction of such a device.

  20. Prototype design of the ITER ICRF vacuum transmission line dielectric window

    International Nuclear Information System (INIS)

    The dielectric window is an essential and critical component of the ICRF VTL, as it provides primary vacuum and Tritium containment. Although several models of dielectric window have been developed and are currently in use, the severe ITER reliability requirements call for special design and prototyping also to allow a realistic evaluation of the failure modes and rates. An earlier design of the (double) dielectric window of the ITER ICRF transmission line has indicated a best strength and compatibility for the alumina (97.5%) (for weak radiation) and beryllia (-3 dpa) ceramics together with both titanium and niobium conductors. Vacuum brazing has been chosen for joining the ceramics to the conductor. In the present work, the material and dielectric shape definition with respect to nuclear, mechanical, and thermal properties in due consideration of material availability, fabrication issues and response to cyclic loads is completed and summarized. Solutions for the cooling and remote handling arrangements are presented. (author)

  1. Millimeter-wave properties of neutron-irradiated ceramics for RF-window MFE applications

    International Nuclear Information System (INIS)

    In response to materials needs connected with electron cyclotron resonance heating (ECRH) in magnetic fusion energy (MFE) reactors, the facility at Los Alamos for dielectric properties measurements on irradiated materials was upgraded to include a capability in the millimeter-wave region. With it, dielectric constants (K) and loss tangents (tandelta) were measured at frequencies (f) of about 95 GHz for polycrystalline alumina and beryllia specimens inserted into WR-10 waveguide after irradiations in EBR-II at 3850C and an average fluence of 8 x 1025 n/cm2 (E > 0.1 MeV). Relative to annealed controls, the dielectric loss quantity Ktandelta doubled for both ceramic types. Furthermore, the BeO material underwent substantial enough changes in K and mass density rho to indicate the likelihood of millimeter-window thickness detuning

  2. Oxide Fiber Targets at ISOLDE

    CERN Document Server

    Köster, U; Carminati, D; Catherall, R; Cederkäll, J; Correia, J G; Crepieux, B; Dietrich, M; Elder, K; Fedosseev, V; Fraile-Prieto, L M; Franchoo, S; Fynbo, H O U; Georg, U; Giles, T; Joinet, A; Jonsson, O C; Kirchner, R; Lau, C; Lettry, Jacques; Maier, H J; Mishin, V I; Oinonen, M; Peräjärvi, K; Ravn, H L; Rinaldi, T; Santana-Leitner, M; Wahl, U; Weissman, L

    2003-01-01

    Many elements are rapidly released from oxide matrices. Some oxide powder targets show a fast sintering, thus losing their favorable release characteristics. Loosely packed oxyde fiber targets are less critical since they may maintain their open structure even when starting to fuse together at some contact points. The experience with various oxyde fiber targets (titania, zirconia, ceria and thoria) used in the last years at ISOLDE is reviewed. For short-lived isotopes of Cu, Ga and Xe the zirconia and ceria targets respectively provided significantly higher yields than any other target (metal foils, oxide powders, etc.) tested before. Titania fibers, which were not commercially available, were produced in a relic process by impregnation of a rayon felt in a titanium chloride solution and subsequent calcination by heating the dried felt in air. Thoria fibers were obtained either by the same process or by burning commercial gas lantern mantle cloth. In the future a beryllia fiber target could be used to produce...

  3. Radio frequency heating of ceramic windows in fusion applications

    International Nuclear Information System (INIS)

    Ceramic windows will be used as material barriers for radio frequency plasma heating in fusion reactors. This report examines the theory behind rf heating phenomena. Heating calculations are presented for various window materials, thicknesses, wavelengths, and power densities. The most pertinent material properties are loss tangent, thermal conductivity, dielectric constant, strength, and radiation resistance. Calculations indicate that among candidate materials, beryllium oxide offers the most promise because of its large thermal conductivity and relatively low loss tangent and dielectric constant. On the other hand, beryllia is susceptible to neutron damage, and this may adversely affect its electrical properties. Another promising candidate is sapphire, particularly at lower temperatures where the thermal conductivity is high. Fused silica suffers from low thermal conductivity and large positive temperature coefficient for loss tangent, but it may be useful under some conditions. In summary, calculations of heating can lead to elimination of some candidate materials and selection of others for further study

  4. Fabrication methods for beryllium spacecraft components (Series 2)

    International Nuclear Information System (INIS)

    The aims of this paper are to conserve and yet promote the use of one of the most versatile metal elements available to the practising engineer. The scope of the work described involves the selection of candidate components suitable for manufacture in beryllium. Evaluation by mathematical modelling using finite element techniques is used as an aid in determining the principal load paths in a structural component. Cost effective techniques which are objectively analysed suggest that the conservation of raw beryllia can best be achieved using recently developed plasma spray methods. The British Aircraft Corporation have been investigating methods of plasma spraying beryllium with A.W.R.E. and current developments are giving clear indications that for certain future space applications plasma spray is the technique which most nearly meets the conservation objective. (author)

  5. A 240-channel thick film multi-chip module for readout of silicon drift detectors

    Science.gov (United States)

    Lynn, D.; Bellwied, R.; Beuttenmueller, R.; Caines, H.; Chen, W.; DiMassimo, D.; Dyke, H.; Elliott, D.; Grau, M.; Hoffmann, G. W.; Humanic, T.; Jensen, P.; Kleinfelder, S. A.; Kotov, I.; Kraner, H. W.; Kuczewski, P.; Leonhardt, B.; Li, Z.; Liaw, C. J.; LoCurto, G.; Middelkamp, P.; Minor, R.; Mazeh, N.; Nehmeh, S.; O'Conner, P.; Ott, G.; Pandey, S. U.; Pruneau, C.; Pinelli, D.; Radeka, V.; Rescia, S.; Rykov, V.; Schambach, J.; Sedlmeir, J.; Sheen, J.; Soja, B.; Stephani, D.; Sugarbaker, E.; Takahashi, J.; Wilson, K.; STAR-SVT Collaboration

    2000-01-01

    We have developed a thick film multi-chip module for readout of silicon drift (or low capacitance ˜200 fF) detectors. Main elements of the module include a custom 16-channel NPN-BJT preamplifier-shaper (PASA) and a custom 16-channel CMOS Switched Capacitor Array (SCA). The primary design criteria of the module were the minimizations of the power (12 mW/channel), noise (ENC=490 e - rms), size (20.5 mm×63 mm), and radiation length (1.4%). We will discuss various aspects of the PASA design, with emphasis on the preamplifier feedback network. The SCA is a modification of an integrated circuit that has been previously described [1]; its design features specific to its application in the SVT (Silicon Vertex Tracker in the STAR experiment at RHIC) will be discussed. The 240-channel multi-chip module is a circuit with five metal layers fabricated in thick film technology on a beryllia substrate and contains 35 custom and commercial integrated circuits. It has been recently integrated with silicon drift detectors in both a prototype system assembly for the SVT and a silicon drift array for the E896 experiment at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. We will discuss features of the module's design and fabrication, report the test results, and emphasize its performance both on the bench and under experimental conditions.

  6. A 240-channel thick film multi-chip module for readout of silicon drift detectors

    International Nuclear Information System (INIS)

    We have developed a thick film multi-chip module for readout of silicon drift (or low capacitance ∼200 fF) detectors. Main elements of the module include a custom 16-channel NPN-BJT preamplifier-shaper (PASA) and a custom 16-channel CMOS Switched Capacitor Array (SCA). The primary design criteria of the module were the minimizations of the power (12 mW/channel), noise (ENC=490 e- rms), size (20.5 mmx63 mm), and radiation length (1.4%). We will discuss various aspects of the PASA design, with emphasis on the preamplifier feedback network. The SCA is a modification of an integrated circuit that has been previously described [1]; its design features specific to its application in the SVT (Silicon Vertex Tracker in the STAR experiment at RHIC) will be discussed. The 240-channel multi-chip module is a circuit with five metal layers fabricated in thick film technology on a beryllia substrate and contains 35 custom and commercial integrated circuits. It has been recently integrated with silicon drift detectors in both a prototype system assembly for the SVT and a silicon drift array for the E896 experiment at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. We will discuss features of the module's design and fabrication, report the test results, and emphasize its performance both on the bench and under experimental conditions

  7. Kelvin probe measurements: investigations of the patch effect with applications to ST-7 and LISA

    International Nuclear Information System (INIS)

    One of the possible noise sources for the space-based gravitational wave detector LISA (the Laser Interferometer Space Antenna), associated with its test masses, is that due to spatial variations in surface potential (or patch effect) across the surfaces of the test mass and its housing. Such variations will lead to force gradients which may result in a significant acceleration noise term. Another noise source is that due to temporal variations in the surface potential, which in conjunction with any ambient dc voltage or net free charge on the test mass may also produce a significant acceleration noise term. The ST-7 demonstrator mission is designed to test technologies for LISA, including the gravitational reference sensor, which contains a gold-coated gold/platinum (Au/Pt) alloy test mass, surrounded by a housing that carries the electrodes for sensing and control. We have used a Kelvin probe at the Goddard Space Flight Center to make spatial and temporal measurements of contact potential differences for a selection of materials (Au/Pt, beryllia, alumina, titanium) and coatings (gold, diamond-like carbon, indium tin oxide, titanium carbide). Our investigations indicate that subject to certain assumptions all of these coatings appear to satisfy the ST-7 requirement that patch effect spatial variations should be less than 100 mV. The data also revealed evidence of behavioural trends with pressure and possible contamination effects. Regarding temporal variations, the current accuracy of the instrument is limiting the measurements at a level above the likely LISA requirements. We discuss our results and draw some conclusions of relevance to LISA

  8. LiBe-14: A novel microdosimeter using LiF and BeO thermoluminescence dosimeter pairs for clinical and aerospace applications

    International Nuclear Information System (INIS)

    The ratio of thermoluminescence light outputs (TLO) of Beryllium Oxide (BeO) and Lithium Fluoride (LiF) dosimeters increases with increasing LET (Linear Energy Transfer) of the impinging particles on the dosimeter chips. This unique phenomenon was utilized to develop a microdosimeter using the common LiF (TLD-700) and BeO (American Beryllia-CF5427-000) dosimeter chips. The dosimeter pairs were exposed to complex mixed radiation fields produced by bombarding a polystyrene plate phantom with therapeutic proton beams of energies from 81 to 231 MeV at the West German Proton Therapy Centre Essen (WPE), Germany. The linear energy transfer (LET) and quality factor (Q) of the secondary radiation fields were simultaneously estimated using a REM 500B tissue equivalent proportional counter (TEPC). The TLD chips were evaluated and the corresponding LET and Q values were plotted as linear functions of the ratio of the TL-glow curve areas within 100–250 °C of TLD-700 and BeO chips. The TLD pairs embody a passive, solid-state, tissue-equivalent, microdosimeter that enable the delivery of dose equivalent (DE), dose-average LET and Q within a broad dynamic range for a given mixed-radiation field relevant to particle therapy, long haul aviation dose monitoring and human space exploration. - Highlights: • A polystyrene phantom bombarded with energetic protons from a medical cyclotron. • This results in production of secondary mixed radiation fields. • Pairs of TLD-700 (7LiF:Ti,Mg) and BeO dosimeter chips and a TEPC are exposed. • Ratio of main TL glow-peak areas expressed as functions of average LET, Q and H. • LiF and BeO dosimeter pairs constitute a simple passive-microdosimeter