WorldWideScience

Sample records for absolute thermal fission

  1. Absolute calibration technique for spontaneous fission sources

    An absolute calibration technique for a spontaneously fissioning nuclide (which involves no arbitrary parameters) allows unique determination of the detector efficiency for that nuclide, hence of the fission source strength

  2. Study on the effect factor of the absolute fission rates measured by depleted uranium fission chamber

    The absolute fission rates was measured by the depleted uranium fission chamber. The efficiency of the fission fragments recorded in the fission chamber was analyzed. The factor influencing absolute fission rates was studied in the experiment, including the disturbing effect between detectors and the effect of the structural material of the fission chamber, etc

  3. Determination of fission cross-section and absolute fission yields using track-cum gamma-ray spectrometric technique

    The fission cross-section of 233Pa(2nth, f) using fission track technique has been determined for the first time using thermal neutron flux of the reactor APSARA. This is important from the point of view of advance heavy water reactor (AHWR), which is to be described. On the other hand, the yields of fission products in the fast neutron induced fission of minor actinides are important from the point accelerator driven sub critical system (ADSS). In view of that, absolute yields of fission products in the fast neutron induced fission of 238U, 237Np, 238,240Pu, 243Am and 244Cm have been determined using the fission track-cum gamma-ray spectrometric technique. The total number of fission occurring in the target was estimated by track technique, whereas the activities of the fission products have been determined using gamma-ray spectrometric technique. Detailed procedure and its importance are to be discussed. (author)

  4. Thermal fission rates with temperature dependent fission barriers

    Zhu, Yi; Pei, Junchen

    2016-01-01

    The fission processes of thermal excited nuclei are conventionally studied by statistical models which rely on inputs of phenomenological level densities and potential barriers. Therefore the microscopic descriptions of spontaneous fission and induced fission are very desirable for a unified understanding of various fission processes. We propose to study the fission rates, at both low and high temperatures, with microscopically calculated temperature-dependent fission barriers and collective ...

  5. Thermal fission rates with temperature dependent fission barriers

    Zhu, Yi

    2016-01-01

    \\item[Background] The fission processes of thermal excited nuclei are conventionally studied by statistical models which rely on inputs of phenomenological level densities and potential barriers. Therefore the microscopic descriptions of spontaneous fission and induced fission are very desirable for a unified understanding of various fission processes. \\item[Purpose] We propose to study the fission rates, at both low and high temperatures, with microscopically calculated temperature-dependent fission barriers and mass parameters. \\item[Methods] The fission barriers are calculated by the finite-temperature Skyrme-Hartree-Fock+BCS method. The mass parameters are calculated by the temperature-dependent cranking approximation. The thermal fission rates can be obtained by the imaginary free energy approach at all temperatures, in which fission barriers are naturally temperature dependent. The fission at low temperatures can be described mainly as a barrier-tunneling process. While the fission at high temperatures ...

  6. Absolute measurement of $sup 235$U fission cross-section for 2200 m/sec neutrons

    Borcea, C.; Borza, A.; Buta, A.

    1973-12-31

    The results of an absolute fission cross-section measurement of /sup 235/ U are presented; the thermal neutrons were selected by the time-of-flight method. The principle of the method and the experimental apparatus are described. The method had the advantage of avoiding the use of an intermediate cross section in the neutron flux determination by choice of a B target thick enough to absorb all thermal neutrons. Target preparation, efficiency determination, corrections, etc., are reported. The value determined was 581.7 plus or minus 7.8 barns. (6 figures, 4 tables) (RWR)

  7. Fission yields in the thermal neutron fission of plutonium-239

    Fission yields for 27 mass numbers were determined in the thermal neutron fission of 239Pu using high resolution gamma ray spectrometry and radiochemical method. The results obtained using gamma ray spectrometry and from the investigations on the fission yield of 99Mo using radiochemical method were reported earlier. These data along with fission yields for 19 mass numbers determined using radiochemical method formed a part of Ph.D. thesis. The data given here are a compilation of all the results and are presented considering the neutron temperature correction to 239Pu fission cross-section which is used for calculating the total number of fissions in these studies. A comparison is made of the resulting fission yield values with the latest experimentally determined values and those given in two recent compilations. (author)

  8. Improved Calculation of Thermal Fission Energy

    Ma, X. B.; Zhong, W. L.; Wang, L. Z.; Y. X. Chen; Cao, J

    2012-01-01

    Thermal fission energy is one of the basic parameters needed in the calculation of antineutrino flux for reactor neutrino experiments. It is useful to improve the precision of the thermal fission energy calculation for current and future reactor neutrino experiments, which are aimed at more precise determination of neutrino oscillation parameters. In this article, we give new values for thermal fission energies of some common thermal reactor fuel isotopes, with improvements on three aspects. ...

  9. FFTF (FAST FLUX TEST FACILITY) REACTOR CHARACTERIZATION PROGRAM ABSOLUTE FISSION RATE MEASUREMENTS

    FULLER JL; GILLIAM DM; GRUNDL JA; RAWLINS JA; DAUGHTRY JW

    1981-05-01

    Absolute fission rate measurements using modified National Bureau of Standards fission chambers were performed in the Fast Flux Test Facility at two core locations for isotopic deposits of {sup 232}Th, {sup 233}U, {sup 235}U, {sup 238}U, {sup 237}Np, {sup 239}Pu, {sup 240}Pu, and {sup 241}Pu. Monitor chamber results at a third location were analyzed to support other experiments involving passive dosimeter fission rate determinations.

  10. FFTF (Fast Flux Test Facility) Reactor Characterization Program: Absolute Fission-rate Measurements

    Fuller, J.L.; Gilliam, D.M.; Grundl, J.A.; Rawlins, J.A.; Daughtry, J.W.

    1981-05-01

    Absolute fission rate measurements using modified National Bureau of Standards fission chambers were performed in the Fast Flux Test Facility at two core locations for isotopic deposits of {sup 232}Th, {sup 233}U, {sup 235}U, {sup 238}U, {sup 237}Np, {sup 239}Pu, {sup 240}Pu, and {sup 241}Pu. Monitor chamber results at a third location were analyzed to support other experiments involving passive dosimeter fission rate determinations.

  11. Fission product release and thermal behaviour

    Release of fission products from the fuel matrix is an important aspect in relation to performance and safety evaluations. Of particular importance amongst fission products are the isotopes of iodine for radiological considerations and the isotopes of xenon and krypton for fuel thermal behaviour. It is believed that the main mechanism for fission gas release is diffusion but the magnitudes of the relevant diffusion coefficients, which exhibit strong temperature dependences, are not well established. The conductivity of the main gaseous fission product, xenon, is much lower than that of the fill gas helium and hence fission gas release may lead to a deterioration of the fill gas conductivity resulting in higher fuel temperatures and consequently higher fission product release. The two effects, thermal response of fuel to fill gas composition and fission gas/product release are thus intimately connected and have been investigated in a number of instrumented fuel assemblies in the Halden reactor. In such an assembly, the instrumentation includes fuel centre thermocouples, pressure sensors and neutron detectors. In addition pins in the assembly may be swept, whilst at power, with various gases, for example Xe, He or Ar or mixtures thereof. A gamma spectrometer is incorporated into the gas circuit to facilitate the performance of on-line fission product release measurements. At various stages in the lifetime of the assembly thermal tests and fission product release measurements have been made. At low operating temperatures and up to moderate burn-ups, no major fuel restructuring phenomena have been observed and consequently the fission product release has remained at low level dictated by the exposed surfaces of the fuel. Axial gas flow measurements indicate that fuel cracking and irreversible relocation occurred as early as the first ramps to power. The processes have continued throughout life and an absence of any change in response pressurization tests indicates that

  12. Fission product decay heat for thermal reactors

    Dickens, J. K.

    1979-01-01

    In the past five years there have been new experimental programs to measure decay heat (i.e., time dependent beta- plus gamma-ray energy release rates from the decay of fission products) following thermal-neutron fission of /sup 235/U, /sup 239/Pu, and /sup 241/Pu for times after fission between 1 and approx. 10/sup 5/ sec. Experimental results from the ORNL program stress the very short times following fission, particularly in the first few hundred sec. Complementing the experimental effort, computer codes have been developed for the computation of decay heat by summation of calculated individual energies released by each one of the fission products. By suitably combining the results of the summation calculations with the recent experimental results, a new Decay Heat Standard has been developed for application to safety analysis of operations of light water reactors. The new standard indicates somewhat smaller energy release rates than those being used at present, and the overall uncertainties assigned to the new standard are much smaller than those being used at present.

  13. Thermal annealing of fission tracks in synthetic apatites

    Carpena, J.; Lacout, Jean-Louis

    2010-01-01

    Synthetic analogues of poor-silicated natural apatites have been doped with uranium. These minerals have been irradiated with a thermal neutron dose in the aim to induce the 235U fission and to obtain a fission track population. Thermal annealing experiments have been performed on the fission track population and allow us to compare the ability of the synthetic minerals to anneal such nuclear damages with their natural analogues. The thermal of the fission tracks in the synthetic minerals nee...

  14. Absolute fission rate measurement of 238U induced by 14 MeV neutrons penetrated composite material

    In order to prove the model calculation method and parameter, the 238U absolute fission rate in the case of 14 MeV neutrons penetrating through the special composite material was measured by minitype slab uranium fission chambers. The measuring spots are distributed in the surface of iron ball hull along the different position of equator. The calculated results are compared with the experiment results. The total error of measured 238U absolute fission rate is 6.1%. (author)

  15. Absolute Energy Calibration of Solid-State Detectors for Fission Fragments and Heavy Ions

    Detailed measurements of the pulse-height response of silicon solid-state detectors to energetic heavy ions and fission fragments have been made. These studies have now led to a reliable method of absolute energy calibration of solid-state detectors for fission fragments, as well as to a better understanding of the somewhat peculiar response characteristics of the detectors to fission fragments and heavy ions. The use of silicon solid-state detectors in fragment kinetic energy measurements in recent years has been widespread; at the same time, questions have been raised about the detailed interpretation of such measurements because of the increasing evidence for anomalous behaviour in charge production, charge collection and charge multiplication in the case of densely ionizing particles. The present report discusses systematics and possible origins of these effects. Application of the absolute energy calibration method, which takes into account the mass and energy dependence of the response, is based simply on a Cf252 or U235 fragment pulse- height spectrum. Our studies were carried out with mono-energetic Br71, Br81 and I127 ions of energies from 30 to 120 MeV, and with fission fragments from spontaneous fission of Cf252 and neutron-induced fission of U235 and Pu239. It is shown that for a given fragment mass, over a wide energy range, the fragment energy versus pulse-height relationship is of the form E = ax + b, where E is the fragment energy and x is the measured pulse height. A dependence of pulse height on fragment mass has also been established, which leads to an energy versus pulse-height relationship, for the range of fission-fragment masses and energies, of the form E = (a + a'm)x + b + b'M, where M is the fragment mass. The effect of detector window and of detector type, resistivity and electric field have been studied. Guides to the selection of detectors and to their use with fission fragments are given. The effect of the more exact calibration

  16. Thermal Energetic Reactor with High Reproduction of Fission Materials

    Vladimir M. Kotov

    2012-01-01

    On the base of thermal reactors with high fission materials reproduction world atomic power engineering development supplying higher power and requiring smaller speed of raw uranium mining, than in the variant with fast reactors, is possible.

  17. Testing and evaluation of thermal cameras for absolute temperature measurement

    Chrzanowski, Krzysztof; Fischer, Joachim; Matyszkiel, Robert

    2000-09-01

    The accuracy of temperature measurement is the most important criterion for the evaluation of thermal cameras used in applications requiring absolute temperature measurement. All the main international metrological organizations currently propose a parameter called uncertainty as a measure of measurement accuracy. We propose a set of parameters for the characterization of thermal measurement cameras. It is shown that if these parameters are known, then it is possible to determine the uncertainty of temperature measurement due to only the internal errors of these cameras. Values of this uncertainty can be used as an objective criterion for comparisons of different thermal measurement cameras.

  18. Electroweak absolute, meta-, and thermal stability in neutrino mass models

    Lindner, Manfred; Patel, Hiren H.; Radovčić, Branimir

    2016-04-01

    We analyze the stability of the electroweak vacuum in neutrino mass models containing right-handed neutrinos or fermionic isotriplets. In addition to considering absolute stability, we place limits on the Yukawa couplings of new fermions based on metastability and thermal stability in the early Universe. Our results reveal that the upper limits on the neutrino Yukawa couplings can change significantly when the top quark mass is allowed to vary within the experimental range of uncertainty in its determination.

  19. Multigroup fast fission factor treatment in a thermal reactor lattice

    A multigroup procedure for the studies of the fast fission effects in the thermal reactor lattice and the calculation of the fast fission factor was developed. The Monte Carlo method and the multigroup procedure were combined to calculate the fast neutron interaction and backscattering effects in a reactor lattice. A set of probabilities calculated by the Monte Carlo method gives a multigroup spectrum of neutrons coming from the moderator and entering the fuel element. Thus, the assumptions adopted so far in defining and calculating the fast fission factor has been avoided, and a new definition including the backscattering and interaction effects in a reactor lattice have been given. (author)

  20. Measurement of Absolute Cross-Sections of Fission Induced by 156-MeV Protons, Using Mica as a Fission Fragment Detector

    The fission of elements of medium Z induced by 156-MeV protons is difficult to demonstrate, owing to the particularly small cross-section of the reaction. The detection of fission fragments by means of sheets of mica seemed to be a technique well suited to this type of experiment. In the sheets of synthetic mica that we used it was only the fission fragments that left microscopically identifiable traces. Moreover, these samples contain very few impurities likely to undergo fission, so practically no parasitic traces are observed. The targets consisted of metals of not less than 99.999% purity. We determined the absolute cross-sections.of fission induced by 156-MeV protons in the case of lanthanum (5 μb) and praseodymium (6 μb), and estimated those of cadmium, indium, tin and antimony (≤ 0.1 μb). The sheets of mica were placed on each side of the metal sheet. The kinetics of the reaction explain why more traces were found on the mica sheets placed on the from face. As thick targets were used to take account of self-absorption, we determined (in the case of uranium and gold) the ratio of yields between a thin target and a thick target, and then extrapolated our results to the other elements. We made checks by comparing the absolute cross-sections for fission (induced by 156-MeV protons) in uranium, bismuth, gold and tantalum, as obtained by this method, with those obtained by counters at this energy. The observed agreement was very good. (author)

  1. Some Yields in the Thermal- and Epi-Cadmium-Neutron Fission of Pu239

    The yields of several nuclides in the thermal- and epi-cadmium-neutron fission of Pu239 have been measured and are reported. In epi-cadmium-neutron fission a decrease, relative to thermal fission, in the yields of Ag111 and Ag113, i.e. an increased peak-to-valley ratio, was found. The yield of As77 and As78, which represent, highly unsymmetrical fission, were found to be greater in epi-cadmium-neutron fission than in thermal fission. This result is' shown to be inconsistent with the simple two mode of fission hypothesis. (author)

  2. Absolute rate of thermal desorption from first-principles simulation

    We present a technique for computing by first-principles simulation the absolute desorption rate γ of adsorbate molecules from a surface for any coverage and temperature. The technique is valid when the thermal equilibration rate on the surface is faster than γ, and is based on an exact expression for γ in terms of the difference of non-configurational chemical potentials of gas-phase and adsorbed molecules. This difference is expressed in terms of a potential of mean force, which is computed by constrained first-principles molecular dynamics. The technique is applied to D2O on the MgO(001) surface at low coverage, using the generalized gradient approximation (GGA) for exchange-correlation energy. Comparisons with experimental temperature programmed desorption data allow an assessment of the accuracy of the GGA for the adsorption of D2O on MgO(001). (letter to the editor)

  3. Absolute Thermal SST Measurements over the Deepwater Horizon Oil Spill

    Good, W. S.; Warden, R.; Kaptchen, P. F.; Finch, T.; Emery, W. J.

    2010-12-01

    Climate monitoring and natural disaster rapid assessment require baseline measurements that can be tracked over time to distinguish anthropogenic versus natural changes to the Earth system. Disasters like the Deepwater Horizon Oil Spill require constant monitoring to assess the potential environmental and economic impacts. Absolute calibration and validation of Earth-observing sensors is needed to allow for comparison of temporally separated data sets and provide accurate information to policy makers. The Ball Experimental Sea Surface Temperature (BESST) radiometer was designed and built by Ball Aerospace to provide a well calibrated measure of sea surface temperature (SST) from an unmanned aerial system (UAS). Currently, emissive skin SST observed by satellite infrared radiometers is validated by shipborne instruments that are expensive to deploy and can only take a few data samples along the ship track to overlap within a single satellite pixel. Implementation on a UAS will allow BESST to map the full footprint of a satellite pixel and perform averaging to remove any local variability due to the difference in footprint size of the instruments. It also enables the capability to study this sub-pixel variability to determine if smaller scale effects need to be accounted for in models to improve forecasting of ocean events. In addition to satellite sensor validation, BESST can distinguish meter scale variations in SST which could be used to remotely monitor and assess thermal pollution in rivers and coastal areas as well as study diurnal and seasonal changes to bodies of water that impact the ocean ecosystem. BESST was recently deployed on a conventional Twin Otter airplane for measurements over the Gulf of Mexico to access the thermal properties of the ocean surface being affected by the oil spill. Results of these measurements will be presented along with ancillary sensor data used to eliminate false signals including UV and Synthetic Aperture Radar (SAR

  4. Event-by-event study of neutron observables in spontaneous and thermal fission

    R. Vogt; Randrup, J.

    2011-01-01

    The event-by-event fission model FREYA is extended to spontaneous fission of actinides and a variety of neutron observables are studied for spontaneous fission and fission induced by thermal neutrons with a view towards possible applications for detection of special nuclear materials.

  5. distributions for the thermal neutron induced fission of 234U

    Al-Adili A.

    2016-01-01

    In addition, the analysis of thermal neutron induced fission of 234U(n,f will be discussed. Currently analysis of data is ongoing, originally taken at the ILL reactor. The experiment is of particular interest since no measurement exist of the mass and energy distributions for this system at thermal energies. One main problem encountered during analysis was the huge background of 235U(nth,f. Despite the negligible isotopic traces in the sample, the cross section difference is enormous. Solution to this parasitic background will be highlighted.

  6. Inverse modelling of thermal histories with apatite fission tracks

    The problem of modelling thermal histories lies in the exploration of a time-temperature space, usually so broad, in order to identify the optimal paths. For overcoming this difficulty, many approaches were proposed, using linear and non-linear optimisation algorithms. Generally, these approaches do not take into account the experimental data (fission track age [FTA] and fission track length distribution [FTLD]) to better aim the search strategy. The present work shows that experimental data hold some precious information, for which it should be known how to extract it. In fact, it allows us to tighten the time-temperature space of search, supposed to contain the optimal solutions. A genetic algorithm is also used in this work to perform the search for these optimal solutions. (authors)

  7. A fission fragment reactor concept for nuclear thermal propulsion

    Suo-Anttila, Ahti J.; Parma, Edward J.; Pickard, Paul S.; Wright, Steven A.; Vernon, Milton E.

    1992-01-01

    The Space Exploration Initiative requires the development of nuclear thermal and nuclear electric technologies for space propulsion for future Luna and Mars missions. Sandia National Laboratories has proposed a new nuclear thermal propulsion concept that uses fission fragments to directly heat the propellant up to 1000 K or higher above the material temperatures. The concept offers significant advantages over traditional solid-core nuclear rocket concepts because of higher propellent exit temperatures, while at the same time providing for more reliable operation due to lower structure temperatures and lower power densities. The reactor can be operated in either a steady-state or pulsed mode. The steady-state mode provides a high thrust and relatively high specific impulse, as compared to other nuclear thermal concepts. The pulsed mode requires an auxillary radiator for cooling, but has the possibility of achieving very high specific impulses and thrust scaleable to the radiator size. The propellant temperatures are limited only by thermal radiation and transient heat conduction back to the substrate walls.

  8. Low-Cost Radiator for Fission Power Thermal Control

    Maxwell, Taylor; Tarau, Calin; Anderson, William; Hartenstine, John; Stern, Theodore; Walmsley, Nicholas; Briggs, Maxwell

    2014-01-01

    NASA Glenn Research Center (GRC) is developing fission power system technology for future Lunar surface power applications. The systems are envisioned in the 10 to 100kW(sub e) range and have an anticipated design life of 8 to 15 years with no maintenance. NASA GRC is currently setting up a 55 kW(sub e) non-nuclear system ground test in thermal-vacuum to validate technologies required to transfer reactor heat, convert the heat into electricity, reject waste heat, process the electrical output, and demonstrate overall system performance. Reducing the radiator mass, size, and cost is essential to the success of the program. To meet these goals, Advanced Cooling Technologies, Inc. (ACT) and Vanguard Space Technologies, Inc. (VST) are developing a single facesheet radiator with heat pipes directly bonded to the facesheet. The facesheet material is a graphite fiber reinforced composite (GFRC) and the heat pipes are titanium/water. By directly bonding a single facesheet to the heat pipes, several heavy and expensive components can be eliminated from the traditional radiator design such as, POC(TradeMark) foam saddles, aluminum honeycomb, and a second facesheet. A two-heat pipe radiator prototype, based on the single facesheet direct-bond concept, was fabricated and tested to verify the ability of the direct-bond joint to withstand coefficient of thermal expansion (CTE) induced stresses during thermal cycling. The thermal gradients along the bonds were measured before and after thermal cycle tests to determine if the performance degraded. Overall, the results indicated that the initial uniformity of the adhesive was poor along one of the heat pipes. However, both direct bond joints showed no measureable amount of degradation after being thermally cycled at both moderate and aggressive conditions.

  9. Absolute dating of the youngest sediments of the Swiss Molasse basin by apatite fission track analysis

    A set of ash layer samples within the uppermost Upper Freshwater Molasse (OSM) sediments (N and E of Frauenfeld, Switzerland) was dated by apatite fission track (FT) means. The ages indicate an early Tortonian (perhaps latest Serravallian) eruption and sedimentation age of 11.5 ± 0.3 Ma. The age is in agreement with time constraints by Mammalian relicts which point to MN7-8. Due to the position of the ash layers close to the erosional gap and overlying Quaternary cover, the age represents a maximum age for the cessation of OSM sedimentation in the Swiss Molasse Basin. However, the end of Molasse sedimentation in this region had not stopped before the cover of OSM sediments by volcanic ash layers at the Hoewenegg volcano (southern Germany), an event further constrained by an apatite FT age of 9.8 (-0.7/+0.8) Ma from a hornblende-bearing ash layer at Hoewenegg. An isolated bentonitic ash layer occurring 25 km to the WSW of the main set of dated ashes (near Humlikon) has an age component identical to the OSM ash layers near Frauenfeld. The age suggests a source for this material within the Hegau, but is too young to be related to the volcanic activity at the Kaiserstuhl. The apatites from the ash layer samples show two distinct compositional populations, one very close to a Cl end member and one with apatites of equal proportions of Cl and OH end member. These populations are interpreted to have possibly originated from at least two distinct igneous sources for the ashes, separated by their eruption site or eruption time or both. The distinct compositional data on the volcanic apatites may provide a basis to clarify their origin in future work. (author)

  10. Beta decay of the fission product 125Sb and a new complete evaluation of absolute gamma ray transition intensities

    Rajput, M. U.; Ali, N.; Hussain, S.; Mujahid, S. A.; MacMahon, D.

    2012-04-01

    The radionuclide 125Sb is a long-lived fission product, which decays to 125Te by negative beta emission with a half-life of 1008 day. The beta decay is followed by the emission of several gamma radiations, ranging from low to medium energy, that can suitably be used for high-resolution detector calibrations, decay heat calculations and in many other applications. In this work, the beta decay of 125Sb has been studied in detail. The complete published experimental data of relative gamma ray intensities in the beta decay of the radionuclide 125Sb has been compiled. The consistency analysis was performed and discrepancies found at several gamma ray energies. Evaluation of the discrepant data was carried out using Normalized Residual and RAJEVAL methods. The decay scheme balance was carried out using beta branching ratios, internal conversion coefficients, populating and depopulating gamma transitions to 125Te levels. The work has resulted in the consistent conversion factor equal to 29.59(13) %, and determined a new evaluated set of the absolute gamma ray emission probabilities. The work has also shown 22.99% of the delayed intensity fraction as outgoing from the 58 d isomeric 144 keV energy level and 77.01% of the prompt intensity fraction reaching to the ground state from the other excited states. The results are discussed and compared with previous evaluations. The present work includes additional experimental data sets which were not included in the previous evaluations. A new set of recommended relative and absolute gamma ray emission probabilities is presented.

  11. Strong thermal leptogenesis and the absolute neutrino mass scale

    Di Bari, Pasquale; Fiorentin, Michele Re

    2014-01-01

    We show that successful strong thermal leptogenesis, where the final asymmetry is independent of the initial conditions and in particular a large pre-existing asymmetry is efficiently washed-out, favours values of the lightest neutrino mass $m_1 \\gtrsim 10\\,{\\rm meV}$ for normal ordering (NO) and $m_1 \\gtrsim 3\\,{\\rm meV}$ for inverted ordering (IO). We show analytically why lower values of $m_1$ require a high level of fine tuning in the seesaw formula and/or in the flavoured decay parameters (in the electronic for NO, in the muonic for IO). We also show how this constraint exists thanks to the measured values of the neutrino mixing angles and can be tighten by a future determination of the Dirac phase. Our analysis also allows to place more stringent constraint for a specific model or class of models, such as $SO(10)$-inspired models, and shows that some models cannot realise strong thermal leptogenesis for any value of $m_1$. A scatter plot analysis fully supports the analytical results. We also briefly di...

  12. Measurement of fission yields far from the center of isotopic distributions in the thermal neutron fission of 235U

    The main purpose of this work was to measure independent yields, in the thermal neutron fission of 235U, of fission products which lie far from the centers of the isotopic and isobaric yield distributions. These measurements were used to test the predictions of semi-empirical systematics of fission yields and theoretical fission models. Delay times were measured as a function of temperature in the range 1200-2000degC. The very low delay times achieved in the present work permitted expanding the measurable region to the isotopes 147,148Cs and 99Rb which are of special interest in the present work. The delay times of Sr and Ba isotopes achieved were more than two orders of magnitude lower than values reported in the literature and thus short-lived isotopes of these elements could be separated for the first time by mass spectrometry. The half-lives of 147Ba, 148Ba, 149La and 149Ce were measured for the first time. The isotopic distributions of fission yields were measured for the elements Rb, Sr, Cs and Ba in the thermal neutron fission of 235U, those of 99Rb, 147Cs and 148Cs having been measured for the first time. A comparison of the experimental yields with the predictions of the currently accepted semi-empirical systematics of fission yields, which is the odd-even effect systematics, shows that the systematics succeeds in accounting for the strong odd-even proton effect and the weaker odd-even neutron effect and also in predicting the shape of the distributions in the central region. It is shown that prompt neutron emission broadens the distribution only slightly in the wing of heavy isotopes and more significantly in the wing of light isotopes. But the effect of prompt neutron emission cannot explain the large discrepancies existing between the predictions of fission models and the experimentally measured fission yield in the wings of the isotopic distributions. (B.G.)

  13. Simultaneous measurement of fission fragments and prompt neutrons for thermal neutron-induced fission of U-235

    Nishio, Katsuhisa; Yamamoto, Hideki; Kimura, Itsuro; Nakagome, Yoshihiro [Kyoto Univ. (Japan)

    1997-03-01

    Simultaneous measurement of fission fragments and prompt neutrons following the thermal neutron induced fission of U-235 has been performed in order to obtain the neutron multiplicity (v) and its emission energy ({eta}) against the specified mass (m{sup *}) and the total kinetic energy (TKE). The obtained value of -dv/dTKE(m{sup *}) showed a saw-tooth distribution. The average neutron energy <{eta}>(m{sup *}) had a distribution with a reflection symmetry around the half mass division. The measurement also gave the level density parameters of the specified fragment, a(m{sup *}), and this parameters showed a saw-tooth trend too. The analysis by a phenomenological description of this parameters including the shell and collective effects suggested the existence of a collective motion of the fission fragments. (author)

  14. Thermal annealing effect on fission fragment track recording properties of polycarbonate

    Polycarbonate Track Detector is a commonly used Solid State Nuclear Track Detector (SSNTD) to identify the fission fragment. The phenomenon of spontaneous fission was discussed in papers. The most useful polycarbonate track detector Makrofol-N for recording fission tracks was used. This detector is insensitive to detect the light particles background such as alpha particle, proton etc. The present paper deals with the study of thermal annealing and the mass distribution of 252Cf fission fragments using unannealed and annealed Makrofol-N detectors

  15. Cold events in thermal-neutron-induced fission of heavy nuclei

    An interpretation of the cold fission events in thermal-neutron-induced fission of heavy nuclei is given. The descent from the saddle point is considered as a dynamical process with reversible coupling between collective and intrinsic degrees of freedom. The distribution function for the collective variables is expressed as a product of two terms: the adiabatical and the dynamical factors. A simple model for symmetric fission to study the mass distribution is presented. As example, the calculations are performed for the nucleus 264Fm. Gross features of the cold fission are discussed as well as the dependence of the theoretical mass distribution on the parameters of the model. (orig.)

  16. Isotopic yield distribution of neutron-rich fragment nuclei produced in thermal neutron induced fission

    Nuclear fission allows us to produce and study the properties of the nuclei with a higher neutron to proton ratio. Spectroscopic studies of such neutron-rich fragment nuclei provide direct information on the nuclear excited states. Such studies help to explore the new regions of nuclear deformations, and to extend the theoretical model(s) to regions which have hitherto been inaccessible. A lot of work has already been done on these set of nuclei by means of spontaneous fission of 252Cf and 248Cm sources, heavy-ion induced fusion-fission reactions, and also using deep-inelastic reactions. More recently, spectroscopic studies were performed using thermal neutron induced fission of 235U using CIRUS reactor facility. Here we report the yield distribution of the isotopes, produced in thermal neutron induced fission of 235U, using prompt γ-γ coincidence measurement technique

  17. Thermal release of volatile fission products from irradiated nuclear fuel

    An effective procedure for removing 3H, Xe and Kr from irradiated fuels was demonstrated using Shippingport UO2 fuel. The release characteristics of 3H, Kr, Xe, and I from irradiated nuclear fuel have been determined as a function of temperature and gaseous environment. Vacuum outgassing and a flowing gas stream have been used to vary the gaseous environment. Vacuum outgassing released about 99% of the 3H and 20% of both Kr and Xe within a 3 h at 15000C. Similar results were obtained using a carrier gas of He containing 6% H2. However, a carrier gas containing only He resulted in the release of approximately 80% of the 3H and 99% of both Kr and Xe. These results indicate that the release of these volatile fission products from irradiated nuclear fuel is a function of the chemical composition of the gaseous environment. The rate of tritium release increased with increasing temperature (1100 to 15000C) and with the addition of hydrogen to the gas stream. Using crushed UO2 fuel without cladding and He as the carrier gas, Kr was completely released at 15000C in 2.5 h. Below 13500C, no Kr-Xe release was observed. Approximately 86% of the 129I and 95% of the cesium was released from a piece (3.9 g) of UO2 fuel at 15000C in He. The zirconium cladding was observed to fracture during heat treatment. A large-scale thermal outgassing system was conceptually designed by the General Atomic Company from an engineering analysis of available experimental data. The direct cost of a 0.5 metric/ton day thermal outgassing system is estimated to be $1,926,000 (1982 dollars), including equipment, installation, instrumentation and controls, piping, and services. The thermal outgassing process was determined to be a technically feasible and cost-competitive process to remove tritium in the head-end portion of a LWR fuel reprocessing plant. Additional laboratory-scale development has been recommended

  18. Thermal annealing of fission fragment radiation damage in CR-39

    The annealing behavior of fission fragment tracks in CR-39 has been studied at different temperatures for various time intervals. Experimental data, obtained in isothermal and isochronal annealing experiments carried out on CR-39 irradiated with fission fragments of 252Cf, has been analyzed on the basis of different annealing models. It has been attempted to find out the validity of these models, developed on the basis of annealing data in minerals and other detectors, to the annealing data of fission fragment tracks in CR-39

  19. Low Cost Radiator for Fission Power Thermal Control Project

    National Aeronautics and Space Administration — NASA Glenn Research Center (GRC) is developing fission power system technology for future space transportation and surface power applications. The early systems are...

  20. Low Cost Radiator for Fission Power Thermal Control Project

    National Aeronautics and Space Administration — NASA GRC is developing fission power system technology for future space transportation and surface power applications. The early systems are envisioned in the 10 to...

  1. Fission-product energy release for times following thermal-neutron fission of 235U between 2 and 14000 seconds

    Fission-product decay energy-releases rates were measured for thermal-neutron fission of 235U. Samples of mass 1 to 10 μg were irradiated for 1 to 100 sec by use of the fast pneumatic-tube facility at the Oak Ridge Research Reactor. The resulting beta- and gamma-ray emissions were counted for times-after-fission between 2 and 14,000 seconds. The data were obtained for beta and gamma rays separately as spectral distributions, N(E/sub γ/) vs E/sub γ/ and N(E/sub beta/) vs E/sub β/. For the gamma-ray data the spectra were obtained by using a NaI detector, while for the beta-ray data the spectra were obtained by using an NE-110 detector with an anticoincidence mantle. The raw data were unfolded to provide spectral distributions of modest resolution. These were integrated over E/sub γ/ and E/sub β/ to provide total yield and energy integrals as a function of time after fission. Results are low compared to the present 1973 ANS Decay-heat standard. A complete description of the experimental apparatus and data-reduction techniques is presented. The final integral data are given in tabular and graphical form and are compared with published data. 41 figures, 13 tables

  2. Thermal stability of fission gas bubble superlattice in irradiated U–10Mo fuel

    To investigate the thermal stability of the fission gas bubble superlattice, a key microstructural feature in both irradiated U–7Mo dispersion and U–10Mo monolithic fuel plates, a focused ion beam-transmission electron microscopy (FIB-TEM) sample of irradiated U–10Mo fuel with a local fission density of 3.5 × 1021 fissions/cm3 was used for an in-situ heating TEM experiment. The temperature of the heating holder was raised at a ramp rate of approximately 10 °C/min up to ∼700 °C, kept at that temperature for about 34 min and further increased to 850 °C with a reduced rate of 5 °C/min. The result shows a high thermal stability of the fission gas bubble superlattice. The implication of this observation on the fuel microstructural evolution and performance under irradiation is discussed

  3. Identifying and quantifying short-lived fission products from thermal fission of HEU using portable HPGe detectors

    Pierson, Bruce D.; Finn, Erin C.; Friese, Judah I.; Greenwood, Lawrence R.; Kephart, Jeremy D.; Kephart, Rosara F.; Metz, Lori A.

    2013-03-01

    Due to the emerging potential for trafficking of special nuclear material, research programs are investigating current capabilities of commercially available portable gamma ray detection systems. Presented in this paper are the results of three different portable high-purity germanium (HPGe) detectors used to identify short-lived fission products generated from thermal neutron interrogation of small samples of highly enriched uranium. Samples were irradiated at the Washington State University (WSU) Nuclear Radiation Center’s 1MW TRIGA reactor. The three portable, HPGe detectors used were the ORTEC MicroDetective, the ORTEC Detective, and the Canberra Falcon. Canberra’s GENIE-2000 software was used to analyze the spectral data collected from each detector. Ultimately, these three portable detectors were able to identify a large range of fission products showing potential for material discrimination.

  4. Determination of isobar composition and yields of 239Pu fission-products by thermal neutrons

    On the research nuclear reactor WWR-SM of INP Uz AS by means of mass-spectrometer the heavy fission-products of 239Pu nuclei induced by thermal neutrons are measured in ranges of mass Ai = 125 -157, kinetic energies Ek = 45 - 87 MeV and effective ionic charges z* = 18 - 30. 102 isobar nuclei in composition of the measured fission-products, also the partial yields of the each element giving the contribution to formation of a total yield of heavy fission-product with mass Ai are defined. (authors)

  5. A numerical model for the thermal history of rocks based on confined horizontal fission tracks

    Jensen, Peter Klint; Hansen, Kirsten; Kunzendorf, Helmar

    1992-01-01

    A numerical model for determination of the thermal history of rocks is presented. It is shown that the thermal history may be uniquely determined as a piece-by-piece linear function on the basis of etched confined, horizontal fission track length distributions, their surface densities, and the...

  6. Influence of thermal and resonance neutron on fast neutron flux measurement by Pu-239 fission chamber

    zeng, Lina; Song, Lingli; Zheng, Chun

    2014-01-01

    The Pu-239 fission chambers are widely used to measure fission spectrum neutron flux due to a flat response to fast neutrons. However, in the mean time the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by using B and Cd covers. At a column enriched uranium fast neutron critical assembly, the fission reaction rates of Pu-239 are measured as 1.791*10-16,2.350*10-16 and 1.385*10-15 per second for 15mm thick B cover, 0.5mm thick Cd cover, and no cover respectively. While the fission reaction rate of Pu-239 is rapidly increased to 2.569*10-14 for a 20mm thick polythene covering fission chamber. The average Pu-239 fission cross-section of thermal and resonance neutrons is calculated to be 500b and 24.95b with the assumption of 1/v and 1/E spectra respectively, then thermal, resonance and fast neutron flux are achieved to be 2.30*106,2.24*106 and 1.04*108cm-2s-1.

  7. Thermal decomposition of fission product nitrates and their reaction with glass batch additives Part A

    Thermal decomposition of fission product nitrates constituting a 'Purex' waste and their reaction with silica, alumina and aluminosilicate (Al2O3.2SiO2) have been studied. Oxides of nitrogen may be released from fission product nitrates in the temperature range (150 - 850degC) either due to their thermal decomposition or due to the reaction of alkali nitrates with silica or alumina of the glass batch additives. Fission product nitrates, CaNO3 and RbNO3 excepting, react very slowly with silica, the principal glass forming additive for a silicate glass, at temperatures of 1000degC. Complete reaction of Gr.II-Gr.IV metal nitrates with silica may be achieved at temperatures of 1400degC which is too high for a fission product immobilisation process. The alkali nitrates react very rapidly with boric oxide, silica, alumina and metakaolin (Al2O3.2SiO2) at subsolidus temperatures forming the alkali metaborate, alkali disilicate, alkali monoaluminate and alkali alumino disilicate respectively. A phenomenological description of the heating-up processes for fission product nitrate with silicate glass batch additives has been included. It has been very strongly recommended, that, if a silicate matrix is selected for incorporation of fission products, the glass melting should be carried out until a homogeneous or nearly homogeneous product is obtained and should not be stopped at a stage where a sintered or semivitreous mass is the resultant product. (author)

  8. Neutronic and thermal hydraulic analysis for production of fission molybdenum-99 at Pakistan Research Reactor-1

    Neutronic and thermal hydraulic analysis for the fission molybdenum-99 production at PARR-1 has been performed. Low enriched uranium foil (235U) will be used as target material. Annular target designed by ANL (USA) will be irradiated in PARR-1 for the production of 100 Ci of molybdenum-99 at the end of irradiation, which will be sufficient to prepare required 99Mo/99mTc generators at PINSTECH and its supply in the country. Neutronic and thermal hydraulic analysis were performed using various codes. Data shows that annular targets can be safely irradiated in PARR-1 for production of required amount of fission molybdenum-99

  9. Axial shortening of fission tracks to response thermally driven volume diffusion of lattice vacancies

    Fission track analysis is a well established analytical methodology used by geologists to determine the range of temperatures a rock has experienced in the past. The technique has been calibrated against an extensive suite of empirical data on the kinetics of fission track annealing. However, despite the techniques widespread use within the earth sciences, there is still no quantitative physical description of the phenomenon of thermally driven track shortening. We have developed a preliminary physical model of fission track annealing based on thermally driven bulk diffusion of vacancies within the crystal lattice. The model is based on current understanding of ion track formation in solids. The initial distribution of lattice defects along the ion trajectory is predicted using current ion-lattice interaction models

  10. Thermal history of Tattapani area (Narmada-Son lineament) as revealed by fission-track technique

    Fission-track ages of core samples from boreholes penetrating basement of Tattapani geothermal area reveal a mean age of 36,796 years. The age records the last thermal impulse due to influx of hot meteoric water. (author). 20 refs., 3 figs., 1 tab

  11. Development of a multiscale thermal conductivity model for fission gas in UO2

    Tonks, Michael R.; Liu, Xiang-Yang; Andersson, David; Perez, Danielle; Chernatynskiy, Aleksandr; Pastore, Giovanni; Stanek, Christopher R.; Williamson, Richard

    2016-02-01

    Accurately predicting changes in the thermal conductivity of light water reactor UO2 fuel throughout its lifetime in reactor is an essential part of fuel performance modeling. However, typical thermal conductivity models from the literature are empirical. In this work, we begin to develop a mechanistic thermal conductivity model by focusing on the impact of gaseous fission products, which is coupled to swelling and fission gas release. The impact of additional defects and fission products will be added in future work. The model is developed using a combination of atomistic and mesoscale simulation, as well as analytical models. The impact of dispersed fission gas atoms is quantified using molecular dynamics simulations corrected to account for phonon-spin scattering. The impact of intragranular bubbles is accounted for using an analytical model that considers phonon scattering. The impact of grain boundary bubbles is determined using a simple model with five thermal resistors that are parameterized by comparing to 3D mesoscale heat conduction results. When used in the BISON fuel performance code to model four reactor experiments, it produces reasonable predictions without having been fit to fuel thermocouple data.

  12. Fission-product yields for thermal-neutron fission of 243Cm determined from measurements with a high-resolution low-energy germanium gamma-ray detector

    Cumulative fission-product yields have been determined for 13 gamma rays emitted during the decay of 12 fission products created by thermal-neutron fission of 243Cm. A high-resolution low-energy germanium detector was used to measure the pulse-height spectra of gamma rays emitted from a 77-nanogram sample of 243Cm after the sample had been irradiated by thermal neutrons. Analysis of the data resulted in the identification and matching of gamma-ray energies and half-lives to individual radioisotopes. From these results, 12 cumulative fission product yields were deduced for radionuclides with half-lives between 4.2 min and 84.2 min. 7 references

  13. Recent Experiments on the Beta Activity of Fission Products from the Thermal-Neutron Fission of U233, U235 and Pu239

    The build-up of beta-activity of fission products from the low-energy fission of U233 and U235 has been measured as a function of the lime t after starting the irradiation of the fissionable material with thermal neutrons. By differentiating the beta-activity divided by the constant fission product rate one obtains the mean beta-decay rate β(t) per fission as a function of the time t after fission. The uranium targets were mounted within a 4π proportional counter, coincident conversion electrons and γ-rays being thereby eliminated. The background of fast neutrons and γ-rays was strongly reduced by using a neutron beam tube with a liquid nitrogen-cooled bismuth single crystal filter. The fission product rate was measured with the same counter. The measurements cover the time interval from 0.01 s to 10 h. The results are compared with other experimental data and existing theories. The total number of beta-decays per fission was found to be 5.25 ± 0.2 and 5.93 ± 0.2 for U233 and U235 respectively compared with theoretical values of 5.27 and 6.10 respectively. (author)

  14. In situ thermal imaging and absolute temperature monitoring by luminescent diphenylalanine nanotubes.

    Gan, Zhixing; Wu, Xinglong; Zhang, Jinlei; Zhu, Xiaobin; Chu, Paul K

    2013-06-10

    The temperature sensing capability of diphenylalanine nanotubes is investigated. The materials can detect local rapid temperature changes and measure the absolute temperature in situ with a precision of 1 °C by monitoring the temperature-dependent photoluminescence (PL) intensity and lifetime, respectively. The PL lifetime is independent of ion concentrations in the medium as well as pH in the physiological range. This biocompatible thermal sensing platform has immense potential in the in situ mapping of microenvironmental temperature fluctuations in biological systems for disease diagnosis and therapeutics. PMID:23679829

  15. Thermal history, thermal state, and related tectonism of a moon of fission origin

    Thermal history of an initially totally molten moon of fission origin properly accounts for (1) the mare basalt epoch, in terms of its duration, the depth of the source region, and degrees of partial melting which produced the magmas; (2) the present-day heat flow of 17--18 ergs cm-2 s-1; and (3) the current high temperatures of the lower mantle as deduced from magnetic and seismic data. The model moon has a radius decrease of 5.4 km (3.1 x 10-3 R) during lunar history. This value is within the rather poorly defined limits for the maximum change of the lunar radius of 10-3-10-2 R. The majority of the thermoelastic stresses produced by the cooling of the moon have been dissipated via aseismic creep in the upper parts of the lunar mantle, not via faulting activity. A lower limit of 1024 P for the viscosity of the mantle of the moon (at subsolidus temperatures) is suggested, based on the apparent absence of solid state convection in the moon at any time during its history. This is 103 times larger than that for the terrestrial mantle. The energy derived from the thermoelastic stresses in the type A moonquake zone is orders of magnitude smaller than the available tidal energy. Hence the thermoelastic stresses are not an important energy source for the tidal moon-quakes. The thermoelastic stresses can easily supply the energy for the high-frequency tele-seismic moonquakes. The relative rarity of HFT's is explained by the long times (108-109 years) needed to accumulate the energy required to initiate faulting in the predicted source regions. These regions are in the uppermost mantle (depths between 80 and 200 km), where tensional quakes can occur, and at 10-km depths in the crust, where compressional quakes can occur. The consistency between our thermal history model results and the corresponding characteristics now known for the moon add further support for the fission model for the origin of the moon

  16. Effects of Fission Yield Data in the Calculation of Antineutrino Spectra for ^{235}U(n,fission) at Thermal and Fast Neutron Energies.

    Sonzogni, A A; McCutchan, E A; Johnson, T D; Dimitriou, P

    2016-04-01

    Fission yields form an integral part of the prediction of antineutrino spectra generated by nuclear reactors, but little attention has been paid to the quality and reliability of the data used in current calculations. Following a critical review of the thermal and fast ENDF/B-VII.1 ^{235}U fission yields, deficiencies are identified and improved yields are obtained, based on corrections of erroneous yields, consistency between decay and fission yield data, and updated isomeric ratios. These corrected yields are used to calculate antineutrino spectra using the summation method. An anomalous value for the thermal fission yield of ^{86}Ge generates an excess of antineutrinos at 5-7 MeV, a feature which is no longer present when the corrected yields are used. Thermal spectra calculated with two distinct fission yield libraries (corrected ENDF/B and JEFF) differ by up to 6% in the 0-7 MeV energy window, allowing for a basic estimate of the uncertainty involved in the fission yield component of summation calculations. Finally, the fast neutron antineutrino spectrum is calculated, which at the moment can only be obtained with the summation method and may be relevant for short baseline reactor experiments using highly enriched uranium fuel. PMID:27081973

  17. Effects of Fission Yield Data in the Calculation of Antineutrino Spectra for 235U (n ,fission) at Thermal and Fast Neutron Energies

    Sonzogni, A. A.; McCutchan, E. A.; Johnson, T. D.; Dimitriou, P.

    2016-04-01

    Fission yields form an integral part of the prediction of antineutrino spectra generated by nuclear reactors, but little attention has been paid to the quality and reliability of the data used in current calculations. Following a critical review of the thermal and fast ENDF/B-VII.1 235U 235 fission yields, deficiencies are identified and improved yields are obtained, based on corrections of erroneous yields, consistency between decay and fission yield data, and updated isomeric ratios. These corrected yields are used to calculate antineutrino spectra using the summation method. An anomalous value for the thermal fission yield of 86Ge generates an excess of antineutrinos at 5-7 MeV, a feature which is no longer present when the corrected yields are used. Thermal spectra calculated with two distinct fission yield libraries (corrected ENDF/B and JEFF) differ by up to 6% in the 0-7 MeV energy window, allowing for a basic estimate of the uncertainty involved in the fission yield component of summation calculations. Finally, the fast neutron antineutrino spectrum is calculated, which at the moment can only be obtained with the summation method and may be relevant for short baseline reactor experiments using highly enriched uranium fuel.

  18. Absolute nuclear material assay

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2010-07-13

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  19. Absolute nuclear material assay

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2012-05-15

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  20. Interface between thermal-hydraulics and fission product transport in severe accident analysis

    Studies of the effectiveness of the containment following hypothetical severe accidents in LWRs have traditionally been split into two separate disciplines. The first is the thermal-hydraulics of the containment atmosphere, leading to an estimate of the magnitudes of the threats to the integrity of the containment building. The second is the study of the transport of the fission products released from the core within and from the building, the ultimate output of which, given a building damage state, is a radiological source term to the environment. In fact, the transport of fission products is strongly influenced by the prevailing thermal-hydraulic conditions, and there are some ways in which the fission products have an influence back on the thermal-hydraulics. The paper describes work funded and co-ordinated by the Commission of the European Communities (CEC) to investigate how the two sorts of calculation, the thermal-hydraulic and the fission product transport, can be made more responsive to the needs of each other. Recent theoretical and experimental work has indicated that the deposition of fission product aerosols is markedly enhanced by the condensation of steam on the particles. The rate of such condensation is a sensitive function of the thermodynamic conditions in the atmosphere, and the release of latent heat because of condensation can in turn significantly change these conditions. The rates of condensation are increased if the particles contain chemical components which are water soluble. To model this effect one requires considerable knowledge of the thermodynamic properties of the relevant aqueous solutions. Recent experience has shown that considerable differences occur between the predictions of different codes. In order to resolve these discrepancies, the CEC has organised a code comparison exercise based on the LACE LA-4 experiment and is currently organising another code comparison based on one of the experiments in the DEMONA series. (author

  1. Mesozoic-Cenozoic thermal history of Turpan-Hami Basin: apatite fission track constraints

    ZHU Wenbin; WAN Jinglin; SHU Liangshu; SUN Yan; GUO Jichun; WANG Feng

    2005-01-01

    Apatite fission track dating is carried out on nine samples collected from the central part (Lianmuqin section) and from both northern and southern margins of Turpan-Hami Basin. The fission-track ages of seven Jurassic samples are distinctly younger than depositional ages. In contrast, the fission-track ages of two Cretaceous samples are older than, or as old as depositional ages. These observations indicate that the Jurassic samples have been annealed or partially annealed, whereas the Cretaceous samples have not been annealed.The further thermal modelling results show that Turpan-Hami Basin experienced a Late Cretaceous period (120-100 Ma) of tectonic uplift with rapid cooling and exhumation of sediments. The samples underwent a Cenozoic period of reburial and re-heating and were exhumed again at 10-8 Ma.

  2. Probing energy dissipation, γ-ray and neutron multiplicity in the thermal neutron-induced fission of 239Pu

    Pahlavani, M. R.; Mirfathi, S. M.

    2016-04-01

    The incorporation of the four-dimensional Langevin equations led to an integrative description of fission cross-section, fragment mass distribution and the multiplicity and energy distribution of prompt neutrons and γ-rays in the thermal neutron-induced fission of 239Pu. The dynamical approach presented in this paper thoroughly reproduces several experimental observables of the fission process at low excitation energy.

  3. A fission-fragment stabilized MHD nuclear thermal rocket concept

    The objective of this effort was to determine how much performance improvement can be obtained from adding an MHD accelerator and auxiliary equipment to a nuclear thermal rocket. The justification for considering the concept is that it promises higher specific impulse than nuclear thermal rockets, with lower specific mass and less complication than with most nuclear electric propulsion systems. The concept is described. Key technical issues are addressed. A system level computer code for preliminary performance assessment is discussed. Performance data and parametric sweeps are presented as computed from the code. Suggestions for future work are make to investigate several remaining key technical issues

  4. A numerical model for the thermal history of rocks based on confined horizontal fission tracks

    Jensen, Peter Klint; Hansen, Kirsten; Kunzendorf, Helmar

    1992-01-01

    A numerical model for determination of the thermal history of rocks is presented. It is shown that the thermal history may be uniquely determined as a piece-by-piece linear function on the basis of etched confined, horizontal fission track length distributions, their surface densities, and the...... measured in transmitted light are biased favouring short tracks compared with measurements in reflected light. Testing of the model is performed on apatites from a tuffaceous sandstone from Bornholm (Denmark) yielding an estimate of the thermal history for the period of about 280 Ma back in time....

  5. Ternary Fission

    The fission process in which heavy nuclei fragment into three large charged panicles, in place of the usual two, has been studied in the case of thermal-neutron-induced fission of U235 and the spontaneous fission of Cf252. Solid-state detectors, a fast triple coincidence system and a three-coincident-parameter analyser were used to measure the three fission fragment energies parallel with the detection of each ternary fission event. Experimental evidence is presented supporting the existence of ternary fission by specifically excluding recoil phenomena and accidental events as contributing to the observed three-fold coincidence events. Mass-energy-angular correlations of ternary fission have been determined and are summarized as follows: The total kinetic energy release in ternary fission appears to be slightly higher (by approximately 10 MeV) than that for binary fission. In the case of the spontaneous ternary fission of Cf252, the frequency of occurrence is observed to be greater than 2.2 x 10-6 ternary fission events per binary fission event. Tripartition of Cf252 results preferentially in division into two medium mass particle (one of which has a mass number near 56) and one larger mass. In the case of thermal-neutron-induced fission of U235, the frequency of occurrence is observed to be greater than 1.2 x 10-6 ternary fission events per binary fission event. Ternary fission of U236: results in the formation of one light fragment (near mass 36) and two large fragments or, as in the case of Cf252, two medium fragments and one large one. These results indicate that axially asymmetric distortion modes are possible in the pre-scission configurations of the fissioning nucleus. A description is given of experiments designed to radiochemically detect the light fragment resulting from ternary fission. (author)

  6. An Absolute Method for Determination of Thermal Conductivities of Thermal Insulators by Microcalorimetry

    ChenXuelin

    1996-01-01

    Microcalorimetry was developed to determine thermal conductivities(λ)of thermal insulators with hollow cylindrical shapes,A special device of speciment with resistance threads wrapped on its surface and electric heater placed in its hole was designed to meet the needs of determining λwithout using standard substances to calibrate the instrument.A formula for calculating the value of λwas derived.By heating in the hole and on the surface of the specimen respectively,the values of λ can be obtained conveniently by this technique.The method was tested with teflon,plexiglass,quartz glass and p[olyethylene.The experimental values of λfor the four substances agree well with the literatures ones.Error analysis was also made on the experimental data.It was founr that the main factors affecting values of λare:(1) The errore of determining the values of heat cumulated in specimen and materials in the space around it and (2) the errore of determining the values of inner and outer radii of cylindrical specimen.λ

  7. Thermal Fission Rate Calculated Numerically by Particles Multi-passing over Saddle Point

    LIU Ling; BAO Jing-Dong

    2004-01-01

    Langevin simulation of the particles multi-passing over the saddle point is proposed to calculate thermal fission rate. Due to finite friction and the corresponding thermal fluctuation, a backstreaming exists in the process of the particle descent from the saddle to the scission. This leads to that the diffusion behind the saddle point has influence upon the stationary flow across the saddle point. A dynamical correction factor, as a ratio of the flows of multi- and firstoverpassing the saddle point, is evaluated analytically. The results show that the fission rate calculated by the particles multi-passing over the saddle point is lower than the one calculated by the particle firstly passing over the saddle point,and the former approaches the results at the scission point.

  8. Measurement of Delayed Neutron Yields from Thermal Neutron Induced Fission of $^{237}$Np

    Gundorin, N A; Pikelner, L B; Revrova, N V; Salamatin, I M; Smirnov, V I; Zhdanova, K V; Zhuchko, V E

    2005-01-01

    This paper reports about the measurement of delayed neutron yields from a thermal neutron induced fission of $^{237}$Np. The method based on periodic irradiation of the sample in pulsed neutron beam with the subsequent registration of neutrons in intervals between pulses is used in the experiment. The method is realized on the "Isomer-M" installation, located on the channel of the IBR-2 pulsed reactor. A description of the installation and a technique of the experiment are presented, a thorough analysis of background processes is performed, results of measurements are shown in this paper. The value of delayed neutron yields from thermal neutron induced fission of $^{237}$Np obtained in the present investigation is $\

  9. Fission track dating and thermal history of Habahe rock body in Altai

    The fission track ages (FTA) of several apatite and zircon samples from Habahe rock body in Altai were determined. The FTA of apatites were 51.1-76.9 Ma, and FTA of zircons were 141-149 Ma. Modelling of the palaeo-temperature evolution [T(t)-path] of rock body relies on confined track length measurements and the annealing equations of Laslett et al. (1987). The thermal and uplift history of this region was discussed

  10. Potentialities and practical limitations of absolute neutron dosimetry using thin films of uranium and thorium applied to the fission track dating

    Bigazzi, G; Hadler-Neto, J C; Iunes, P J; Paulo, S R; Oddone, M; Osorio, A M A; Zúñiga, A G

    1999-01-01

    Neutron dosimetry using natural uranium and thorium thin films makes possible that mineral dating by the fission-track method can be accomplished, even when poor thermalized neutron facilities are employed. In this case, the contributions of the fissions of sup 2 sup 3 sup 5 U, sup 2 sup 3 sup 8 U and sup 2 sup 3 sup 2 Th induced by thermal, epithermal and fast neutrons to the population of tracks produced during irradiation are quantified through the combined use of natural uranium and thorium films. If the Th/U ratio of the sample is known, only one irradiation (where the sample and the films of uranium and thorium are present) is necessary to perform the dating. However, if that ratio is unknown, it can be determined through another irradiation where the mineral to be dated and both films are placed inside a cadmium box. Problems related with film manufacturing and calibration are discussed. Special attention is given to the utilization of thin films having very low uranium content. The problems faced sugg...

  11. Combining apatite fission track and He thermochronology to constrain thermal histories

    Persano, C.; Stuart, F.; Bishop, P.

    2003-04-01

    Apatite fission track thermochronometry (AFTT) has proved an invaluable tool for determining the cooling histories of rocks in the shallow crust. Quantitative models for the time and temperature dependence of the fission track annealing process in apatite demostrate that the combination of fission track apparent age and track length distribution provides a continuous record of the thermal history of the samples from 120 to 60^oC, and possibly, to lower temperatures. However the sensitivity of the technique is poorly constrained below 70-80^oC because annealing rates are slow. The apatite (U-Th)/He system is sensitive to temperatures between 80 and 40^oC irrespective of apatite chemistry, and presents a way to test the ability of AFTT to determine thermal histories below 80^oC. Here we present a novel way of combining apatite fission track and (U-Th)/He data that narrows the number of possible thermal histories and provides better constraints on the landscape evolution of a particular region. We use as an example the southeastern Australia passive margin in NSW, an area where post break-up landscape evolution is poorly resolved despite an extensive fission track database. Fission track and (U-Th)/He ages have been measured on 16 apatite samples from two coast perpendicular traverses across the coastal plain, up the escarpment onto the plateau. The fission track data are modelled using AFTSolve and the individual thermal histories which fit the data are used as parameters for forward modelling the apatite He ages. Only the thermal histories that produce the measured He age, within uncertainty, are considered. For each sample, the choosen time-temperature paths show the same peculiar characteristics, narrowing considerably the number of possible cooling scenarios. This combination shows that the AFT/derived thermal histories for temperatures between 60 to 40^oC may be inconsistent with the (U-Th)/He ages, suggesting that the annealing process at this temperatures

  12. Thermal transport in UO2 with defects and fission products by molecular dynamics simulations

    The importance of the thermal transport in nuclear fuel has motivated a wide range of experimental and modelling studies. In this report, the reduction of thermal transport in UO2 due to defects and fission products has been investigated using non-equilibrium MD simulations, with two sets of empirical potentials for studying the degregation of UO2 thermal conductivity including a Buckingham type interatomic potential and a recently developed EAM type interatomic potential. Additional parameters for U5+ and Zr4+ in UO2 have been developed for the EAM potential. The thermal conductivity results from MD simulations are then corrected for the spin-phonon scattering through Callaway model formulations. To validate the modelling results, comparison was made with experimental measurements on single crystal hyper-stoichiometric UO2+x samples.

  13. Evaluation of thermal, mechanical and fission gas release behavior for BWR fuel rods with Teto

    A computer code (TETO) was developed to carry out thermal-mechanical analysis and fission gas release in fuel rod elements of the BWR type. This program was especially designed for use in the simulations made with the Fuel Management System (FMS) from Scandpower. Using experimental correlations this code models the phenomena of swelling, fission gas release and fracture for fuel pellets and cladding that can occur during irradiation cycles. This code differs from other programs in that it uses a simplified model to obtain the temperature profile along the cooling channel with the supposition that there exists a two-phase flow. This profile is used to determine the radial temperature distribution. The code calculates the axial and radial temperature distributions along the fuel rod at half the distance of the pellet's length; in other words there are as many axial points as pellets. Also, the program models the experimental correlation for swelling and fission gas releases and performs a thermal-elastic analysis for fuel pellets and cladding. (author)

  14. Confined fission track lengths in apatite: A diagnostic tool for thermal history analysis

    A compilation of the lengths of confined fission tracks in a wide variety of apatites from different geological environments has shown that the distribution of confined track lengths can provide unique thermal history information in the temperature range below about 1500C over times of the order of 106 to 109 years. The continuous production of tracks through time, coupled with the fact that the length of each track shrinks to a value characteristic of the maximum temperature it has experienced, gives a final length distribution which directly reflects the nature of the variation of temperature with time. Most distinctive of the myriad possible forms of the final distribution are the bimodal distributions, which give clear evidence of a two-stage history, including high and low temperature phases. The study of confined length distributions therefore offers invaluable evidence on the meaning of any fission-track age, and bears the potential of providing rigorous constraints on thermal history in the temperature regime below about 1500C. The results of this study strongly suggest that any apatite fission-track age determination should be supported by a confined track length distribution. (orig./RB)

  15. The thermal history of the Bowen Basin: a comparison of apatite fission track analysis and vitrinite reflectance

    Vitrinite reflectance and apatite fission-track analysis (AFTA) are two techiques widely used to assess paleotemperatures of the order of 20-120 deg.C. in sedimentary basins. Whereas vitrinite reflectance is essentially a qualitative technique that gives an integrated measure of the entire thermal history, AFTA can reveal information on the variation of paleotemperatures through time because fission-tracks in apatite are continually produced throughout geological time. An apatite fission track study of the Upper Permian units of the Bowen Basin has offered the opportunity to compare the two paleotemperature indicators and place constraints on the timing of maximum paleotemperatures. The regional pattern of apatite fission-track ages closely coincides with the vitrinite reflectance indicating that maximum paleotemperatures have varied across the Basin with the central region of the Bowen Basin experiencing highest paleotemperatures. The reduction in apatite reflectance fission-track age with increasing reflectance represents the progressive annealing at temperatures around 60-120 deg. C. of those fission-tracks formed prior to the time of maximum temperatures. In those samples giving the youngest apatite fission-track ages all tacks were totally annealed at this time, and the fission-track age in these samples, in the range 90-120 Myr, indicate the time of cooling from the thermal maximum in the Early Cretaceous. 1 ref

  16. Thermal-Neutron-Induced Fission of U235, U233 and Pu239

    We have used solid-state detectors to measure the kinetic energies of the coincident fission fragments in the thermal-neutron-induced fission of U235, U233 and Pu239. Special care has been taken to eliminate spurious-events near symmetry to give an accurate measure of such quantities as the average total kinetic energy at symmetry. For each fissioning system over 106 events were recorded. As a result the statistics are good enough to see definite evidence for fine structure over a wide range of masses and energies. The data have been analysed to give mass yield curves, average kinetic energies as a function of mass, and other quantities of interest. For each fissioning system the average total kinetic energy goes through a maximum for a heavy fragment mass of about 132 and for the corresponding light fragment mass. There is a pronounced minimum at symmetry, although not as deep as that found in time-of-flight experiments. The difference between the maximum average kinetic energy and that at symmetry is about 32 MeV for U235, 18 MeV for U233 and 20 MeV for Pu239. The dispersion of kinetic energies at symmetry is also smaller than that found in time-of-flight experiments. Fine structure is apparent in two different representations of the data. The energy spectrum of heavy fragments in coincidence with light fragment energies is greater than the most probable value. This structure becomes more pronounced as the light fragment energy increases. The mass yield curves for a given total kinetic energy show a structure suggesting a preference for fission fragments with masses ∼134, ∼140 and ∼145 (and their light fragment partners). Much of the structure observed can be understood by considering a semi-empirical mass surface and a simple model for the nuclear configuration at the saddle point. (author)

  17. Validation of the neutron and gamma fields in the JSI TRIGA reactor using in-core fission and ionization chambers.

    Žerovnik, Gašper; Kaiba, Tanja; Radulović, Vladimir; Jazbec, Anže; Rupnik, Sebastjan; Barbot, Loïc; Fourmentel, Damien; Snoj, Luka

    2015-02-01

    CEA developed fission chambers and ionization chambers were utilized at the JSI TRIGA reactor to measure neutron and gamma fields. The measured axial fission rate distributions in the reactor core are generally in good agreement with the calculated values using the Monte Carlo model of the reactor thus verifying both the computational model and the fission chambers. In future, multiple absolutely calibrated fission chambers could be used for more accurate online reactor thermal power monitoring. PMID:25479432

  18. The Radiological and Thermal Characteristics of Fission Waste from a Deep-Burn Fusion-Fission Hybrid (LIFE) and Implications for Repository Performance

    We are studying the use of a Laser Inertial-confinement Fusion Engine (LIFE) to drive a hybrid fusion-fission system that can generate electrical power and/or burn nuclear waste. The system uses the neutrons from laser driven ICF to produce tritium and to drive nuclear reactions in a subcritical fission blanket. The fusion neutron source obviates the need for a self-sustaining chain reaction in the fission blanket. Either fissile or fertile could be used as fission fuel, thus eliminating the need for isotopic enrichment. The 'driven' system potentially allows very high levels of burnup to be reached, extracting a large fraction of the available energy in the fission fuel without the need for reprocessing. In this note, we discuss the radionuclide inventory of a depleted uranium (DU) fuel burned to greater than 95% FIMA (Fissions per Initial heavy Metal Atom), the implications for thermal management of the resulting waste, and the implications of this waste for meeting the dose standards for releases from a geological repository for high-level waste. The fission waste discussed here would be that produced by a LIFE hybrid with a 500-MW fusion source. The fusion neutrons are multiplied and moderated by a sequence of concentric shells of materials before encountering the fission fuel, and fission in this region is largely due to thermal neutrons. The fission blanket consists of 40 metric tons (MT) of DU, assumed to be in the form of TRISO-like UOC fuel particles embedded in 2-cm-diameter graphite pebbles. (It is recognized that TRISO-based fuel may not reach the high burnup of the fertile fuel considered here, and other fuel options are being investigated. We postulate the existence of a fuel that can reach >95% FIMA so that the waste disposal implications of high burnup can be assessed.) The engine and plant design considered here would receive one load of fission fuel and produce ∼2 GWt of power (fusion + fission) over its 50- to 70-year lifetime. Neutron and

  19. Fractional independent yields of 141La and 142La from thermal-neutron-induced fission of 233U

    The fractional independent yields of 141La and 142La from thermal-neutron-induced fission of 233U were found to be 0.026 +- 0.006 and 0.068 +- 0.010, respectively. These yields are consistent with charge distributions for which σ = 0.56 +- 0.02 and 0.52 +- 0.02, respectively. These results are in good agreement with similar yields measured for fission of 235U, but not with those from fission of 249Cf. (author)

  20. Kelvin Absolute Temperature Scale Identified as Length Scale and Related to de Broglie Thermal Wavelength

    Sohrab, Siavash

    Thermodynamic equilibrium between matter and radiation leads to de Broglie wavelength λdβ = h /mβvrβ and frequency νdβ = k /mβvrβ of matter waves and stochastic definitions of Planck h =hk =mk c and Boltzmann k =kk =mk c constants, λrkνrk = c , that respectively relate to spatial (λ) and temporal (ν) aspects of vacuum fluctuations. Photon massmk =√{ hk /c3 } , amu =√{ hkc } = 1 /No , and universal gas constant Ro =No k =√{ k / hc } result in internal Uk = Nhνrk = Nmkc2 = 3 Nmkvmpk2 = 3 NkT and potential pV = uN\\vcirc / 3 = N\\ucirc / 3 = NkT energy of photon gas in Casimir vacuum such that H = TS = 4 NkT . Therefore, Kelvin absolute thermodynamic temperature scale [degree K] is identified as length scale [meter] and related to most probable wavelength and de Broglie thermal wavelength as Tβ =λmpβ =λdβ / 3 . Parallel to Wien displacement law obtained from Planck distribution, the displacement law λwS T =c2 /√{ 3} is obtained from Maxwell -Boltzmann distribution of speed of ``photon clusters''. The propagation speeds of sound waves in ideal gas versus light waves in photon gas are described in terms of vrβ in harmony with perceptions of Huygens. Newton formula for speed of long waves in canals √{ p / ρ } is modified to √{ gh } =√{ γp / ρ } in accordance with adiabatic theory of Laplace.

  1. Fission track evidence on thermal history of Jiama polymetallic ore district, Tibet

    袁万明; 侯增谦; 李胜荣; 王世成

    2001-01-01

    It is a new attempt to study thermal evolution related to mineralization using the fission track (FT) method. Apatite and zircon fission track data are reported for 6 samples collected from Jiama ore district as well as its periphery. The FT ages of apatites in the ore district are (16.1±0.9) Ma and (18.8±1.1) Ma and reflect the age of late period of hydrothermal mineralizing event. Apatite FT age of (22.0±4.3) Ma and zircon FT age of (20.9±2.0) Ma are related to the early period of mineralization. Another zircon FT age of (341.6±79.1) Ma, inheriting mineral source characteristic, has no connection with the mineralization. Based on the thermal history analysis, the mineralization began before 25-22 Ma. Cooling rate in the ore district is 5-6℃/Ma averagely, in which a slow cooling occurred at 90-80℃. About 2.7 km has been denuded and the denudation rate is higher than the uplifting rate.

  2. Thermal Characterization of a Simulated Fission Engine via Distributed Fiber Bragg Gratings

    We report the use of distributed fiber Bragg gratings to monitor thermal conditions within a simulated nuclear reactor core located at the Early Flight Fission Test Facility of the NASA Marshall Space Flight Center. Distributed fiber-optic temperature measurements promise to add significant capability and advance the state-of-the-art in high-temperature sensing. For the work reported herein, seven probes were constructed with ten sensors each for a total of 70 sensor locations throughout the core. These discrete temperature sensors were monitored over a nine hour period while the test article was heated to over 700 deg. C and cooled to ambient through two operational cycles. The sensor density available permits a significantly elevated understanding of thermal effects within the simulated reactor. Fiber-optic sensor performance is shown to compare very favorably with co-located thermocouples where such co-location was feasible

  3. Decay Heat Analyses after Thermal-Neutron Fission of 235U and 239Pu by SCALE-6.1.3 with Recently Available Fission Product Yield Data

    The heat reaches about 1.5% after one hour and falls to 0.4% after a day. After a week it will be about 0.2%. The reactor, however, still requires further cooling for several years to keep the fuel rods safe. In general, the decay heat in the reactors can be calculated using a summation calculation method, which is simply the sum of the activities of the fission products produced during the fission process and after the reactor shutdown weighted by the mean decay energies. Consequently, the method is strongly dependent on the available nuclear structure data. Nowadays, the method has been implemented in various burnup and depletion programs such as ORIGEN and CINDER. In this study, the decay heat measurements after thermal-neutron fission of 235U and 239Pu have been evaluated by the ORIGEN-S with the decay data and fission product yield libraries included in the SCALE-6.1.3 software package. The new libraries were applied to the decay heat calculations, and the results were compared with those by the ORIGEN reference calculation. The decay heat measurements for very short cooling times after thermal-neutron fission of 235U and 239Pu have been evaluated by the ORIGEN-S summation calculation. The reference calculation results by the latest ORIGEN data libraries of the SCALE-6.1.3 have been validated with the measurements by ORNL and Studsvik. In addition, the generation of the new ORIGEN yield libraries has been completed based on the ENDF/B-VII.1, JEFF-3.1.1, JENDL/FPY-2011, and JENDL-4.0. The new libraries have been successfully applied to the decay heat calculations and comparative analyses have been devoted to verifying the importance of the fission product yield data when estimating the decay heat values for each isotope in a very short time. The decay data library occupies an important position in the ORIGEN summation calculation along with the fission product yield library

  4. Absolute measurements of total peroxy nitrate mixing ratios by thermal dissociation blue diode laser cavity ring-down spectroscopy.

    Paul, Dipayan; Osthoff, Hans D

    2010-08-01

    Peroxycarboxylic nitric anhydrides (PANs) have long been recognized as important trace gas constituents of the troposphere. Here, we describe a blue diode laser thermal dissociation cavity ring-down spectrometer for rapid and absolute measurements of total peroxyacyl nitrate (SigmaPAN) abundances at ambient concentration levels. The PANs are thermally dissociated and detected as NO2, whose mixing ratios are quantified by optical absorption at 405 nm relative to a reference channel kept at ambient temperature. The effective NO2 absorption cross-section at the diode laser emission wavelength was measured to be 6.1 x 10(-19) cm2 molecule(-1), in excellent agreement with a prediction based on a projection of a high-resolution literature absorption spectrum onto the laser line width. The performance, i.e., accuracy and precision of measurement and matrix effects, of the new 405 nm thermal dissociation cavity ring-down spectrometer was evaluated and compared to that of a 532 nm thermal dissociation cavity ring-down spectrometer using laboratory-generated air samples. The new 405 nm spectrometer was considerably more sensitive and compact than the previously constructed version. The key advantage of laser thermal dissociation cavity ring-down spectroscopy is that the measurement can be considered absolute and does not need to rely on external calibration. PMID:20698583

  5. Partitioning of selected fission products from irradiated oxide fuel induced by thermal treatment

    The release of fission products (FPs) from spent nuclear fuel (SNF) has been studied as a function of the temperature and redox conditions. The present paper concerns essentially the high temperature separation of Cs and Sr from irradiated pressurized (PWR) and boiling water reactor (BWR) fuel of different burn-up levels with use of an in-house designed system for inductive vaporization (InVap). Using thermodynamic calculations with the Module of Fission Product Release (MFPR) code along with annealing experiments on SNF in the InVap it was shown that the speciation of Cs and Sr, hence their release behavior at high temperature, is sensitive to the redox conditions during thermal treatment. It was demonstrated that annealing conditions in the InVap can be adjusted in the way to promote the release of selected FPs without significant loss of the fuel matrix or actinides: complete release of Cs and I was achieved during treatment of irradiated fuel at 1800 °C under reducing atmosphere (0.7% H2/Ar mixture). The developed partitioning procedure can be used for the SNF pretreatment as an advanced head-end step in the hydrometallurgical or pyrochemical reprocessing technology

  6. In-core thermal hydraulic and fission product calculations for severe fuel damage analyses

    Best-estimate calculations of realistic source terms are presented which reduce uncertainties in predicting fission product release from the UO2 fuel over the temperature range between 770 K and 3000 K. The proposed method of correlation includes such fuel morphology effects as equiaxed fuel grain growth and fuel-cladding interaction. The method correlates the product of fuel release rate and equiaxed grain size with the inverse fuel temperature to yield a bulk mass transfer correlation. It was found that less and slower releases are predicted utilizing the bulk mass transfer correlation than such conventional literature correlations as the steam oxidation model and the NUREG-0956 correlation. A Severe Fuel Damage (SFD) analysis code was developed to perform the thermal hydraulic and fission product calculations needed to analyze the Power Burst Facility SFD tests. The predictions utilizing the bulk mass transfer correlations overall followed the experimental time-release histories during the course of the heatup, power hold and cooldown phases of the transients. Good agreements were achieved for the integral releases both in timing and in magnitude. The proposed bulk mass transfer correlations can be applied to both current and advanced light water reactor fuels. 17 refs., 8 figs., 3 tabs

  7. Thermal annealing of fission tracks in fluorapatite, chlorapatite, manganoanapatite, and Durango apatite: experimental results

    It is well known that the optically measured lengths of fission tracks in apatite crystals are a function of etching conditions, crystallographic orientation of the track, composition of the crystal, and the state of thermal annealing. In this study we standardize etching conditions and optimize track length measurability by etching until etch pits formed at the surface of each apatite crystal reached widths of about 0.74 μm. Etching times using 5M HNO3 at 21oC were 31 s for Otter Lake, Quebec, fluorapatite; 47 s for Durango, Mexico, apatite; 33 s for Portland, Connecticut, manganoanapatite; and 11 s for Bamle, Norway, chlorapatite. An etching experiment using two etchant strengths (5M and 1.6M HNO3) revealed that, despite significant differences in etch pit shape, fission-track length anisotropy with respect to crystallographic orientation of the tracks is not a chemical etching effect. A series of 227 constant-temperature annealing experiments were carried out on nuclear reactor induced tracks in oriented slices of the apatites. After etching, crystallographic orientations of tracks were measured along with their lengths. The 200-300 track lengths measured for each slice were ellipse-fitted to give the major (c crystallographic direction) and minor (a crystallographic direction) semi-axes used to calculate equivalent isotropic lengths. The equivalent isotropic length is more useful than mean length for thermal history analysis because the variation caused by anisotropy has been removed. Using normalized etching procedures and equivalent isotropic length data, we found that the fluorapatite anneals most readily, followed by Durango apatite, manganoanapatite, and lastly chlorapatite. (author)

  8. Post Irradiation Evaluation of Thermal Control Coatings and Solid Lubricants to Support Fission Surface Power Systems

    The development of a nuclear power system for space missions, such as the Jupiter Icy Moons Orbiter or a lunar outpost, requires substantially more compact reactor design than conventional terrestrial systems. In order to minimize shielding requirements and hence system weight, the radiation tolerance of component materials within the power conversion and heat rejection systems must be defined. Two classes of coatings, thermal control paints and solid lubricants, were identified as material systems for which limited radiation hardness information was available. Screening studies were designed to explore candidate coatings under a predominately fast neutron spectrum. The Ohio State Research Reactor Facility staff performed irradiation in a well characterized, mixed energy spectrum and performed post irradiation analysis of representative coatings for thermal control and solid lubricant applications. Thermal control paints were evaluated for 1 MeV equivalent fluences from 1013 to 1015 n/cm2. No optical degradation was noted although some adhesive degradation was found at higher fluence levels. Solid lubricant coatings were evaluated for 1 MeV equivalent fluences from 1015 to 1016 n/cm2 with coating adhesion and flexibility used for post irradiation evaluation screening. The exposures studied did not lead to obvious property degradation indicating the coatings would have survived the radiation environment for the previously proposed Jupiter mission. The results are also applicable to space power development programs such as fission surface power for future lunar and Mars missions

  9. Post Irradiation Evaluation of Thermal Control Coatings and Solid Lubricants to Support Fission Surface Power Systems

    Bowman, Cheryl L.; Jaworske, Donald A.; Stanford, Malcolm K.; Persinger, Justin A.; Khorsandi, Behrooz; Blue, Thomas E.

    2007-01-01

    The development of a nuclear power system for space missions, such as the Jupiter Icy Moons Orbiter or a lunar outpost, requires substantially more compact reactor design than conventional terrestrial systems. In order to minimize shielding requirements and hence system weight, the radiation tolerance of component materials within the power conversion and heat rejection systems must be defined. Two classes of coatings, thermal control paints and solid lubricants, were identified as material systems for which limited radiation hardness information was available. Screening studies were designed to explore candidate coatings under a predominately fast neutron spectrum. The Ohio State Research Reactor Facility staff performed irradiation in a well characterized, mixed energy spectrum and performed post irradiation analysis of representative coatings for thermal control and solid lubricant applications. Thermal control paints were evaluated for 1 MeV equivalent fluences from 10(exp 13) to 10(exp 15) n per square centimeters. No optical degradation was noted although some adhesive degradation was found at higher fluence levels. Solid lubricant coatings were evaluated for 1 MeV equivalent fluences from 10(exp 15) to 10(exp 16) n per square centimeters with coating adhesion and flexibility used for post irradiation evaluation screening. The exposures studied did not lead to obvious property degradation indicating the coatings would have survived the radiation environment for the previously proposed Jupiter mission. The results are also applicable to space power development programs such as fission surface power for future lunar and Mars missions.

  10. The absolute chronology and thermal processing of solids in the solar protoplanetary disk

    Connelly, James Norman; Bizzarro, Martin; Krot, Alexander N.; Nordlund, Åke; Wielandt, Daniel Kim Peel; Ivanova, Marina A.

    2012-01-01

    Transient heating events that formed calcium-aluminum - rich inclusions (CAIs) and chondrules are fundamental processes in the evolution of the solar protoplanetary disk, but their chronology is not understood. Using U-corrected Pb-Pb dating, we determined absolute ages of individual CAIs and...

  11. Fission product data library

    A library is described of data for 584 isotopes of fission products, including decay constants, branching ratios (both burn-up and decay), the type of emitted radiation, relative and absolute yields, capture cross sections for thermal neutrons, and resonance integrals. When a detailed decay scheme is not known, the mean energies of beta particles and neutrino and gamma radiations are given. In the ZVJE SKODA system the library is named BIBFP and is stored on film No 49 of the NE 803 B computer. It is used in calculating the inventory of fission products in fuel elements (and also determining absorption cross sections for burn-up calculations, gamma ray sources, heat generation) and in solving radioactivity transport problems in the primary circuit. It may also be used in the spectrometric method for burn-up determination of fuel elements. The library comprises the latest literary data available. It serves as the basis for library BIBGRFP storing group constants of fission products with independent yields of isotopes from fission. This, in turn, forms the basis for the BIBDN library collecting data on the precursors of delayed neutron emitters. (author)

  12. Primary Distributions of Nuclear Charge for Fission-Fragment Masses 132, 134, 136 and 137 from Thermal Fission of U235

    By a mass spectrometer fission fragments from thermal fission of U235 are exactly separated with respect to mass and kinetic energy within a time of 10-6 s after fission. The separated fragments are caught in a β-sensitive Ilford G 5 emulsion that is located in the focal plane of the spectrometer. Development of the irradiated emulsions is carried out, if possible, after a time long compared with the longest half-life of the regarded decay chain. Half-lives of days or longer are not taken into account, but corrections can be easily made for them. After development of the emulsions all beta tracks emerging from the end of every fission-fragment track can be seen under the microscope. The possibility of correlating every single β-track with a particular fission-fragment track allows the evaluation of the number n(x) of fission fragments possessing x β-tracks, thus giving not only the mean chain length but also the β-particle distribution. As the stable end product of each decay chain is known, this β-distribution is an exact image of the primary nuclear charge distribution. In the measurements done up to now only β-particles emitted into the half solid angle formed by the emulsion plate were registered, buta simple statistical calculation enables the desired 4π-distribution to be evaluated. By this method β-distributions at fixed kinetic energies near the mean kinetic energy of each fragment mass are given for the masses 132, 134, 136 and 137. For the lower masses 132 and 134 the neutron shell N = 82 is responsible for the most probable primary charges near 50 and 52 respectively. For M = 136 and 137 the primary charge is about 53 and 53.2. Additional approximative corrections in respect of conversion electrons (by omitting very short β-tracks corresponding to very low β-energies) and to delayed neutrons (for mass 137) were not very large. Similar measurements carried out directly in 4π—geometry to avoid the statistical error arising from the

  13. Study of Relationship Between Neutron Energy and Fission Yields of 95Zr, 140Ba and 147Nd From 235U

    2001-01-01

    This work measures fission yields of 235U induced by neutrons with energy of thermal, 3.0, 5.0, 5.5, 8.0 and 14.8 MeV. The main purpose is to study the relationship between neutron energy and fission fields of 95Zr,140Ba and 147Nd from 235U by measuring the radioactivity of foil with direct gamma spectrometry. The fission yields induced by fast neutrons are get by fast-thermal-ratio method which based on yields from thermal neutrons, yields by thermal neutron are come from absolute measurement. Since fast-thermal-ratio method eliminates uncertainties of gamma intensity, gamma

  14. Prognostic value of preoperative absolute lymphocyte count in recurrent hepatocellular carcinoma following thermal ablation: a retrospective analysis

    Li X

    2014-10-01

    Full Text Available Xin Li, Zhiyu Han, Zhigang Cheng, Jie Yu, Xiaoling Yu, Ping Liang Department of Interventional Ultrasound, Chinese PLA General Hospital, Beijing, People's Republic of China Purpose: To investigate the prognostic value of preoperative absolute lymphocyte count (ALC in recurrent hepatocellular carcinoma (RHCC following thermal ablation. Materials and methods: We retrospectively analyzed the relationship between preoperative ALC and the clinicopathologic factors and long-term prognosis in 423 RHCC patients who underwent curative thermal ablation. Correlation analysis, receiver operating characteristic (ROC calculation, Kaplan–Meier curves, and multivariate regression were used for statistical analysis. Results: The median time to recurrence was 12 months for RHCC patients after thermal ablation. On multivariate Cox regression analysis, preoperative ALC was an independent risk factor for cancer recurrence, along with tumor differentiation and α-fetoprotein level. ALC ≥1.64×109/L defined by ROC calculation was associated with prolonged survival (area under the curve 0.741, P<0.001. Patients with ALC ≥1.64×109/L showed a mean survival of 20.2 months versus 11.6 months for patients with ALC <1.64×109/L (P<0.001. Patients were stratified into high and low groups according to ALC status. After excluding the basic parameters between groups, the 1- and 3-year recurrence rates in the high group were 20.9% and 29.5%, respectively, which were significantly lower than those of the low group (58.4% and 71.9%, respectively; P<0.001. The recurrence-free survival rates in the two groups analyzed by Kaplan–Meier curves were significantly different (P<0.001. Conclusion: Preoperative ALC is a powerful prognostic factor for RHCC recurrence after thermal ablation, which suggests that maintaining a high ALC in RHCC patients might improve cancer outcomes. Keywords: absolute lymphocyte count, recurrent hepatocellular carcinoma, thermal ablation, recurrence  

  15. Analysis of fuel rod thermal performance and correlations with fission gas release

    The accurate evaluation of temperature distribution inside the fuel rod is most important for good fuel rod modeling as key phenomena, like Fission Gas Release (FGR), are strongly dependent on temperature. The strong coupling between temperature and FGR implies correlations, useful to provide bounds on thermal effects like degradation of fuel thermal conductivity with burnup. This paper presents thermal and FGR analyses done with COPERNIC, the FRAMATOME fuel rod performance code, based on the TRANSURANUS code. COPERNIC was developed to accurately predict extended-burnup fuel performance while including advanced material models. COPERNIC thermal calculations include new or improved models: porosity increase in the rim region, heat transfer multiplier for the pellet-cladding gap, degradation of fuel thermal conductivity with burnup, gaseous and contact conductances, validated separately. The thermal model is benchmarked with over 1800 fuel centerline temperatures up to a rod average burnup of 80 GWd/tM. UO2, UO2-Gd2O3, and MOX data have been obtained through French or international RandD programs, and, in particular, the use of high burnup irradiated fuels. The key feature of FGR is the presence of an Incubation Threshold (IT): FGR occurs above a threshold temperature, which decreases as burnup increases. The COPERNIC model describes FGR as a two-step diffusion process: the gas atoms diffuse first from inside the grain to the grain boundaries where they accumulate until a saturation threshold is reached. The FGR model predicts well the IT curve, usually derived numerically. An excellent Analytical IT expression (AIT) is found and has the merit of isolating the parameters pertaining to the mechanisms which come into play. The AIT expression includes one term similar to that of the Empirical IT (Eli) and additional terms with parameters sensitive to temperature. The AIT parameters have been fitted on close to 200 FGR measurements from UO2 fuel rods in steady

  16. Prompt Gamma Radiation from Fragments in the Thermal Fission of 235U

    Measurements were made on the gamma radiation emitted from fission fragments in slow neutron induced fission of 235U. The fragments were detected with solid state detectors of the surface barrier type and the gamma radiation with a Nal(Tl) scintillator. Mass selection was used so that the gamma radiation could be measured as a function of fragment mass. Time discrimination between the fission gammas and the prompt neutrons released in the fission process was employed to reduce the background. The gamma radiation emitted during different time intervals after the fission event was studied with the help of a collimator, the position of which was changed along the path of the fission fragments. In this way a decay curve was obtained from which the life-time of one of the gamma-emitting states could be estimated. The relative yield of the gamma-rays was determined as a function of mass for different gamma-ray energy portions and two specific time intervals after the fission events. Comparisons were made with data obtained from 252 Cf-fission. Attention is drawn to some features which seem to be the same in 235U and 252 Cf-fission

  17. The absolute chronology and thermal processing of solids in the solar protoplanetary disk.

    Connelly, James N; Bizzarro, Martin; Krot, Alexander N; Nordlund, Åke; Wielandt, Daniel; Ivanova, Marina A

    2012-11-01

    Transient heating events that formed calcium-aluminum-rich inclusions (CAIs) and chondrules are fundamental processes in the evolution of the solar protoplanetary disk, but their chronology is not understood. Using U-corrected Pb-Pb dating, we determined absolute ages of individual CAIs and chondrules from primitive meteorites. CAIs define a brief formation interval corresponding to an age of 4567.30 ± 0.16 million years (My), whereas chondrule ages range from 4567.32 ± 0.42 to 4564.71 ± 0.30 My. These data refute the long-held view of an age gap between CAIs and chondrules and, instead, indicate that chondrule formation started contemporaneously with CAIs and lasted ~3 My. This time scale is similar to disk lifetimes inferred from astronomical observations, suggesting that the formation of CAIs and chondrules reflects a process intrinsically linked to the secular evolution of accretionary disks. PMID:23118187

  18. Easy Absolute Values? Absolutely

    Taylor, Sharon E.; Mittag, Kathleen Cage

    2015-01-01

    The authors teach a problem-solving course for preservice middle-grades education majors that includes concepts dealing with absolute-value computations, equations, and inequalities. Many of these students like mathematics and plan to teach it, so they are adept at symbolic manipulations. Getting them to think differently about a concept that they…

  19. Absolute measurement of thermal noise in a resonant short-range force experiment

    Yan, H.; Housworth, E. A.; Meyer, H. O.; Visser, G.; Weisman, E.; Long, J. C.

    2014-10-01

    Planar, double-torsional oscillators are especially suitable for short-range macroscopic force search experiments, since they can be operated at the limit of instrumental thermal noise. As a study of this limit, we report a measurement of the noise kinetic energy of a polycrystalline tungsten oscillator in thermal equilibrium at room temperature. The fluctuations of the oscillator in a high-Q torsional mode with a resonance frequency near 1 kHz are detected with capacitive transducers coupled to a sensitive differential amplifier. The electronic processing is calibrated by means of a known electrostatic force and input from a finite-element model. The measured average kinetic energy, Eexp = (2.0 ± 0.3) × 10-21 J, is in agreement with the expected value of 1/2{{k}B}T.

  20. Flux depression and the absolute measurement of the thermal neutron flux density

    The thermal neutron flux depression in a diffusing medium by an absorbing foil has been treated in numerous papers. The results are re-examined in an attempt to find a uniform and physically meaningful representation of the 'activation correction'. This quantity can be split up into a combination of probabilities. Thus, it is possible to determine the activation correction for any moderator and foil material. Measurements confirm the utility of the concepts introduced

  1. Flux depression and the absolute measurement of the thermal neutron flux density

    The thermal neutron flux depression in a diffusing medium by an absorbing foil has been treated in numerous papers. The results are re-examined in an attempt to find a uniform and physically meaningful representation of the 'activation correction'. This quantity can be split up into a combination of probabilities. Thus, it is possible to determine the activation correction for any moderator and foil material. Measurements confirm the utility of the concepts introduced. (orig.)

  2. Thermal-hydraulics deisgn and analysis of water-cooled energy production blanket for a fusion-fission hybrid reactor

    A conceptual design of fusion-fission hybrid reactor for energy production, named FDS-EM (Energy Multiplier), was proposed. It was preliminary designed to generate about an electricity power of about 1.0 GW with self-sustaining tritium cycle. This contribution performed the thermal-hydraulics design and analyses for FDS-EM water-cooled blanket. The typical thermal-hydraulics parameters were designed by using mature technologies of PWR, and temperature and stress analyses were carried out, according to typical parameters of the blanket. The results preliminarily demonstrated the engineering feasibility of the design. (authors)

  3. Sustainable and safe nuclear fission energy technology and safety of fast and thermal nuclear reactors

    Kessler, Günter

    2012-01-01

    Unlike existing books of nuclear reactor physics, nuclear engineering and nuclear chemical engineering this book covers a complete description and evaluation of nuclear fission power generation. It covers the whole nuclear fuel cycle, from the extraction of natural uranium from ore mines, uranium conversion and enrichment up to the fabrication of fuel elements for the cores of various types of fission reactors. This is followed by the description of the different fuel cycle options and the final storage in nuclear waste repositories. In addition the release of radioactivity under normal and possible accidental conditions is given for all parts of the nuclear fuel cycle and especially for the different fission reactor types.

  4. KUGEL: a thermal, hydraulic, fuel performance, and gaseous fission product release code for pebble bed reactor core analysis

    The KUGEL computer code is designed to perform thermal/hydraulic analysis and coated-fuel particle performance calculations for axisymmetric pebble bed reactor (PBR) cores. This computer code was developed as part of a Department of Energy (DOE)-funded study designed to verify the published core performance data on PBRs. The KUGEL code is designed to interface directly with the 2DB code, a two-dimensional neutron diffusion code, to obtain distributions of thermal power, fission rate, fuel burnup, and fast neutron fluence, which are needed for thermal/hydraulic and fuel performance calculations. The code is variably dimensioned so that problem size can be easily varied. An interpolation routine allows variable mesh size to be used between the 2DB output and the two-dimensional thermal/hydraulic calculations

  5. Thermal transport in UO2 with defects and fission products by molecular dynamics simulations

    Liu, Xiang-Yang [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Cooper, Michael William Donald [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Mcclellan, Kenneth James [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lashley, Jason Charles [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Byler, Darrin David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Stanek, Christopher Richard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Andersson, Anders David Ragnar [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-10-14

    The importance of the thermal transport in nuclear fuel has motivated a wide range of experimental and modelling studies. In this report, the reduction of thermal transport in UO2 due to defects and fission products has been investigated using non-equilibrium MD simulations, with two sets of empirical potentials for studying the degregation of UO2 thermal conductivity including a Buckingham type interatomic potential and a recently developed EAM type interatomic potential. Additional parameters for U5+ and Zr4+ in UO2 have been developed for the EAM potential. The thermal conductivity results from MD simulations are then corrected for the spin-phonon scattering through Callaway model formulations. To validate the modelling results, comparison was made with experimental measurements on single crystal hyper-stoichiometric UO2+x samples.

  6. Thermal quenching of electronic shells and channel competition in cluster fission

    Yannouleas, Constantine; Landman, Uzi; Brechignac, C.; Cahuzac, Ph.; Concina, B.; Leygnier, J.

    2002-01-01

    Experimental and theoretical studies of fission of doubly-charged Li, Na, and K clusters in the low fissility regime reveal the strong influence of electronic shell effects on the fission products. The electronic entropy controls the quenching of the shell effects and the competition between magic-fragment channels, leading to a transition from favored channels of higher mass symmetry to the asymmetric channel involving the trimer cation at elevated temperatures.

  7. Sustainable and safe nuclear fission energy. Technology and safety of fast and thermal nuclear reactors

    Kessler, Guenter

    2012-07-01

    Written by one of the world-leading specialists in reactor physics and safety Most comprehensive book on nuclear fission technology, new safety concepts and waste disposal Complete description and evaluation of nuclear fission power generation Covers the whole nuclear fuel cycle, from the extraction of natural uranium, uranium conversion and enrichment up to the fabrication of fuel elements Description of the different fuel cycle options Presents viable solutions for safe and long-term storage of nuclear waste Recently developed new safety concepts for fission reactors Unlike existing books of nuclear reactor physics, nuclear engineering and nuclear chemical engineering this book covers a complete description and evaluation of nuclear fission power generation. It covers the whole nuclear fuel cycle, from the extraction of natural uranium from ore mines, uranium conversion and enrichment up to the fabrication of fuel elements for the cores of various types of fission reactors. This is followed by the description of the different fuel cycle options and the final storage in nuclear waste repositories. In addition the release of radioactivity under normal and possible accidental conditions is given for all parts of the nuclear fuel cycle and especially for the different fission reactor types.

  8. A fission track pilot study of the thermal effects of rifting on the onshore Nova Scotian margin, Canada

    The onshore flanks of the Nova Scotian passive margin record a complex thermal history of Acadian (Devonian) plutonism with an Alleghanian/Hercynian overprint, followed by two phases of mafic dike intrusion in southern Nova Scotia at ca. 230-220 Ma and 195-185 Ma, the latter event accompanied by basaltic volcanism along the Fundy Basin to the west. Preliminary calculations based on new apatite fission track apparent ages and etchable track length data from throughout central and southern Nova Scotia indicate that some apatites appear to contain fission tracks that formed after the Alleghanian/Hercynian thermal disturbance but prior to rift-related igneous activity at about 195-185 Ma, whereas others may have experienced complete annealing during this latter event. This difference may have been due to either an areal effect of the thermal pulse associated with rifting, or the effect of differential erosion, or both. If the geothermal gradients were not strongly affected by thermal events, approximately 4.5 km of erosion may have occurred over the entire Nova Scotian margin since the Permian. (author)

  9. Energy released in fission

    The effective energy released in and following the fission of U-235, Pu-239 and Pu-241 by thermal neutrons, and of U-238 by fission spectrum neutrons, is discussed. The recommended values are: U-235 ... 192.9 ± 0.5 MeV/fission; U-238 ... 193.9 ± 0.8 MeV/fission; Pu-239 ... 198.5 ± 0.8 MeV/fission; Pu-241 ... 200.3 ± 0.8 MeV/fission. These values include all contributions except from antineutrinos and very long-lived fission products. The detailed contributions are discussed, and inconsistencies in the experimental data are pointed out. In Appendix A, the contribution to the total useful energy release in a reactor from reactions other than fission are discussed briefly, and in Appendix B there is a discussion of the variations in effective energy from fission with incident neutron energy. (author)

  10. The evidence of fission-track data for the study of tectonic thermal history in Qinshui Basin

    Ren, Z.L.; Xiao, H.; Liu, L.; Zhang, S.; Qin, Y.; Wei, C.T. [North West University of Xian, Xian (China)

    2005-12-15

    The thermal history of the Qinshui Basin has been studied by using the fission-track analysis of apatite and zircon, integrated analysis of tectonic evolution, magmatic activity and other palaeogeothermal analysis data. Results indicate that the palaeogeothermal gradient between the late-Paleozoic era and the mid-Mesozoic era is relatively low and the palaeogeothermal gradient in the late-Mesozoic is up to 5.56 {sup o}C/100 m in the middle, and the values are relatively higher in the north and south margins of the basin, reaching over 8.00{sup o}C/100 m, which indicates that there was an anomalous tectonic thermal event in the thermal history of Qinshui Basin. This event happened in 110 - 140 Ma, and the main peak value was between 120 and 140 Ma. This anomalous tectonic thermal event is controlled by the strengthening thermal mobility of the lithosphere and magmatic intrusion. The maturity of the Permo-Carboniferous coal series mainly was controlled by this anomalous thermal field. The apatite fission track date of samples across the basin shows that a rapid tectonic uplifting with cooling existed 26.2-11.5 Ma ago and the upliftings in the north and south of the basin happened earlier than that in the middle. The Permo-Carboniferous strata had been completely annealed in the early 50 Ma, palaeotemperature over 125{sup o}C. Since then, especially from Oligocene-Miocene epoch, the strata which experienced large-scale tectonic upliftings with rapid cooling have been kept out of the annealing belt (70-125{sup o}C) in a relative low temperature environment. The late Mesozoic tectonic thermal event control hydrocarbon production peak (late Jurassic to early Cretaceous period) of Permo-Carboniferous strata in Qinshui Basin. When the strata experienced upliftings with rapid cooling since Oligocene-Miocene epoch, the hydrocarbon generation of coal series had stopped.

  11. Thermal History of Rocks in the Shiwandashan Basin, Southern China: Evidence from Apatite Fission-Track Analysis

    Wang Xinwei; Wang Xinwen; Ma Yongsheng

    2005-01-01

    Based on interpretations of the apatite fission-track analysis data for 10 outcrop samples and forward modeling of confined fission-track length distributions, the thermal history of rocks in the Shiwandashan basin and its adjacent area, southern China, has been qualitatively and semi-quantitatively studied. The results reflect several features of the thermal history. Firstly, all the samples have experienced temperatures higher than 60-70 ℃. Secondly, the time that the basement strata (T1b) on the northwestern side of the Shiwandashan basin were uplifted and exhumed to the unannealed upper crust (with a paleogeotemperature of below 60-70 ℃) is much earlier than the basement rocks (γ15) on the southeastern side of the basin. Thirdly, the thermal history of samples from the basin can be divided into six stages, I.e., the fast burial and heating stage (220-145 Ma), the transient cooling stage (145-135 Ma), the burial and heating stage (135-70 Ma), the rapid cooling stage (70-50 Ma), the relatively stable stage (50-20 Ma) and another rapid cooling stage (20 Ma to present).

  12. Thermal Simulator Development: Non-Nuclear Testing of Space Fission Systems

    Bragg-Sitton, Shannon M.; Dickens, Ricky E.

    2006-01-01

    Non-nuclear testing can be a valuable tool in the development of a space nuclear power system. At the NASA MSFC Early Flight Fission Test Facility (EFF-TF), highly designed electric heaters are used to simulate the heat from nuclear fuel to test space fission power and propulsion systems. To allow early utilization, nuclear system designs must be relatively simple, easy to fabricate, and easy to test using non-nuclear heaters to closely mimic heat from fission. In this test strategy, highly designed electric heaters are used to simulate the heat from nuclear fuel, allowing one to develop a significant understanding of individual components and integrated system operation without the cost, time and safety concerns associated with nuclear testing.

  13. Determination of the fission coefficients in thermal nuclear reactors for antineutrino detection

    Araujo, Lenilson M. [Coordenacao dos Programas de Pos-Graduacao de Engenharia (PEN/COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Nuclear; Cabral, Ronaldo G., E-mail: rgcabral@ime.eb.b [Instituto Militar de Engenharia (IME), Rio de Janeiro, RJ (Brazil); Anjos, Joao C.C. dos, E-mail: janjos@cbpf.b [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil). Dept. GLN - G

    2011-07-01

    The nuclear reactors in operation periodically need to change their fuel. It is during this process that these reactors are more vulnerable to occurring of several situations of fuel diversion, thus the monitoring of the nuclear installations is indispensable to avoid events of this nature. Considering this fact, the most promissory technique to be used for the nuclear safeguard for the nonproliferation of nuclear weapons, it is based on the detection and spectroscopy of antineutrino from fissions that occur in the nuclear reactors. The detection and spectroscopy of antineutrino, they both depend on the single contribution for the total number of fission of each actinide in the core reactor, these contributions receive the name of fission coefficients. The goal of this research is to show the computational and mathematical modeling used to determinate these coefficients for PWR reactors. (author)

  14. Mass and Cumulative Yields in Near-Symmetric Fission of U235 with Thermal Neutrons. Part I. The 121-Mass Chain

    Determination of fission yield of mass 121 and of cumulative yields of members of that decay chain have been made as part of a study of symmetric and near-symmetric fission of uranium-235 with thermal neutrons. Fast chemical separation methods have been developed that permit isolation of selected fission product elements in 3-30 s. The methods have been applied to identification and characterization of new, short-lived radionuclides in addition to their use in studies of distribution of nuclear charge in fission. The cumulative fission yield of Sn121 (27.5h) was measured to be (1.1±0.1) 10-2% as compared to the single literature value of 1.5 x 10-2%. Taking the cumulative yield of Sn121m (∼25 yr) as 0,08 x 10-2%, and making the reasonable assumption that the independent fission yield of Sb121 is negligible, we obtain a fission mass yield of (1.2±0.1) 10-2% for mass chain 121 in thermal-neutron fission of uranium-235. Identification of Cd121 was made. Its half-life and cumulative fission yield were determined to be 12.8+0.4-0.3 s and (6.4±0.5) 10-3% respectively. If the nuclear charge distribution curve is Gaussian and if a width parameter o of 0.62 as given by Wahl et al. is taken, the cumulative fission yield of Cd121 leads to a value of 48.35 for the most probable nuclear charge (Zp) for mass chain 121. This value of Zp, combined with published values for other mais chains more removed from symmetric fission, indicates in a preliminary way that the Zp function proceeds towards the point of symmetric fission by a gentle rather than an abrupt approach. Fast chemical separation techniques have been developed based on sublimation of metal chelates, precipitation and metal reduction reactions. Isolation of indium in about 30 s was accomplished by precipitation and sublimation of its acetylacetonate. With this procedure the cumulative fission yield of In121 (3.1 min) was determined to be 3.2 x 10-3%. Cadmium as an ammine complex was separated in 3 s from hydroxide

  15. Variation of the Binary-to-Ternary Fission Ratio for U235 in the Thermal-Neutron-Energy Region

    The slow chopper installed at BRI was used to make an accurate determination of the binary-to-ternary fission ratio for U235 in the neutron-energy range from 0.005 eV to 0.2 eV. Large gold-silicon suríace-barrier detectors are used for the consecutive measurement of long-range α-particles (absorber in) and fission fragments (absorber out). The time analysis is done with a 100-channel time-of-flight analyser. A one-metre flight-path and a rotor speed of 50 rev/s is used. The B/T ratio was also measured with a high statistical accuracy (about 1%) in intense beams with well-defined neutron spectra, i.e. a ''cold neutron'' beam, a beam extracted from a thermal column and a beam of 0.3-eV neutrons produced by crystal diffraction. The B/T ratio exhibits a small and smooth variation in the energy range considered. This effect seems to be correlated with measurements of some other fission parameters in the same neutron-energy range. (author)

  16. Thermal evolution of inverted basins: Constraints from apatite fission track thermochronology in the Cuyo Basin, Argentine Precordillera

    Apatite fission track thermochronology (AFTT) was applied to derive the thermal history of formation and inversion of the oil-bearing Triassic-Cretaceous Cuyo Basin, Argentine Precordillera. The obtained central fission track ages range from 13 to 163Ma, and the mean track lengths from 8.2 to 13.1μm. Based on the integration of AFTT, stratigraphic and structural data, five evolutionary phases are here proposed for the studied area: I-Late Permian cooling related to the extrusion of basement volcanics, and initial extensional regime responsible for the Cuyo Basin formation, II-Triassic-Jurassic heating linked with the filling, and consequent burial, of the Cuyo Basin, III-Jurassic-Paleogene tectonic stabilization, IV-Early Miocene heating related to the load of foreland sedimentation, V-Late Miocene rapid cooling related to the Cuyo Basin inversion. During the Late Miocene, rock units formed in different crustal levels were juxtaposed through thrust, reverse and normal faulting, resulting in contrasting old and very young central fission track ages in closely spaced samples

  17. Study of delayed neutron decay curves from thermal neutron induced fission of 235U and 239Pu

    The results of measurements of decay curves for delayed neutrons, obtained in the thermal neutron induced fission of 235U and 239Pu, are presented. The data were obtained by the periodical irradiation method on the IBR-2 pulsed reactor in the time interval from 5 to 730 msec after the end of irradiation. The comparison of the measured curves with the curves calculated with using several known from literature parameter sets (relative weights and half-lives of 6 or 8 exponents) was carried out. The new 7-group parameter set, which describes experimental data better, is proposed. (author)

  18. The thermal column. A new irradiation position for fission-track dating in the University of Pavia Triga Mark II nuclear reactor

    In the present paper a new irradiation position arranged for fission-track dating in the Triga Mark II reactor of the University of Pavia is described. Fluence values determined using the NIST glass standard SRM 962a for fission-track dating and the traditional metal foils are compared. Relatively high neutron thermalization (cadmium ratio of 85.3 for gold and 643 for cobalt) and lack of significant fluence spatial gradients are very favorable factors for fission-track dating. Finally, international age standards (or putative age standards) irradiated in this new position yielded results consistent with independent reference ages. (author). 9 refs., 2 figs., 4 tabs

  19. A Monte Carlo simulation of a simplified reactor by decomposition of the neutron spectrum into fission, intermediate and thermal distributions

    Barcellos, Luiz Felipe F.C.; Bodmann, Bardo E.J.; Vilhena, Marco T. de, E-mail: luizfelipe.fcb@gmail.com, E-mail: bardo.bodmann@ufrgs.br, E-mail: vilhena@mat.ufrgs.br [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre (Brazil). Grupo de Estudos Nucleares. Escola de Engenharia; Leite, Sergio Q. Bogado, E-mail: sbogado@eletronuclear.gov.br [Eletrobras Termonuclear S.A. (ELETRONUCLEAR), Rio de Janeiro, RJ (Brazil)

    2015-07-01

    In this paper the neutron spectrum of a simulated hypothetical nuclear reactor is decomposed as a sum of three probability distributions. Two of the distributions preserve shape with time but not necessarily the integral. One of the two distributions is due to fission, i.e. high neutron energies and the second a Maxwell-Boltzmann distribution for low (thermal) neutron energies. The third distribution has an a priori unknown and possibly variable shape with time and is determined from parametrizations of Monte Carlo simulation. This procedure is effective in attaining two objectives, the first is to include effects due to up-scattering of neutrons, and the second is to optimize computational time of the stochastic method (tracking and interaction). The simulation of the reactor is done with a Monte Carlo computer code with tracking and using continuous energy dependence. This code so far computes down-scattering, but the computation of up-scattering was ignored, since it increases significantly computational processing time. In order to circumvent this problem, one may recognize that up-scattering is dominant towards the lower energy end of the spectrum, where we assume that thermal equilibrium conditions for neutrons immersed in their environment holds. The optimization may thus be achieved by calculating only the interaction rate for neutron energy gain as well as loss and ignoring tracking, i.e. up-scattering is 'simulated' by a statistical treatment of the neutron population. For the fission and the intermediate part of the neutron spectrum tracking is taken into account explicitly, where according to the criticality condition the integral of the fission spectrum may depend on time. This simulation is performed using continuous energy dependence, and as a rst case to be studied we assume a recurrent regime. The three calculated distributions are then used in the Monte Carlo code to compute the subsequent Monte Carlo steps with subsequent updates

  20. Comparison of the ENIGMA code with experimental data on thermal performance, stable fission gas and iodine release at high burnup

    The predictions of the ENIGMA code have been compared with data from high burn-up fuel experiments from the Halden and RISO reactors. The experiments modelled were IFA-504 and IFA-558 from Halden and the test II-5 from the RISO power burnup test series. The code has well modelled the fuel thermal performance and has provided a good measure of iodine release from pre-interlinked fuel. After interlinkage the iodine predictions remain a good fit for one experiment, but there is significant overprediction for a second experiment (IFA-558). Stable fission gas release is also well modelled and the predictions are within the expected uncertainly band throughout the burn-up range. This report presents code predictions for stable fission gas release to 40GWd/tU, iodine release measurements to 50GWd/tU and thermal performance (fuel centre temperature) to 55GWd/tU. Fuel ratings of up to 38kW/m were modelled at the high burn-up levels. The code is shown to accurately or conservatively predict all these parameters. (author). 1 ref., 6 figs

  1. Numbers of prompt neutrons per fission for U233, U235, Pu239, and Cf252

    An absolute measurement of #-v#, the average number of prompt neutrons emitted per fission, is being made for the spontaneous fission of Cf262. The relative values of #-v# are being measured for neutron-induced fission of U233, U235, and Pu239, and are being compared with the spontaneous fission #-v# of Cf252. Neutrons with energies between thermal and 15 MeV are used. Particular emphasis is put on studying the dependence of #-v# on the incident neutron energy. A fission counter containing the appropriate isotope is placed in the centre of a large cadmium-loade d liquid scintillator. Through the fissionable isotope is passed a collimated beam of neutrons. Fission events, identified by pulses from the fission counter, open an electronic gate between the large liquid scintillator and a scaler. Scintillator pulses due to capture in the scintillating solution of thermalized fission neutrons are counted during the gate. The fission neutrons are detected almost independently of energy and with very high efficiency. With this technique values of #-v# to an accuracy of 1 % are expected. (author)

  2. Absolute measurements of the thermal neutron flux by the foil activation method using the 4πβ-γ coincidence technique

    An analysis of the correction factors required for the β-γ coincidence method is presented together with a listing of the various formulae involved in the determination of radioactive sources. The detection system including the activation detectores are described and the results are shown for the absolute measurements of thermal neutron flux carried out in the core of the Argonaut Reactor, at Instituto de Engenharia Nuclear (IEN), Brazil. (Author)

  3. Use of proportional counter in X-Ray spectrometry between 5 and 100 keV. Application to the detection of fission products and to the determination of absolute X-Ray disintegration rates

    The measurement of electromagnetic radiations is difficult in the energy range 20-100 keV. We made suitable for this purpose a regular proportional counter, modifying both the nature and pressure of the gaseous mixture filling the detector volume. We selected the CPEN-SAIP counter, which is able to withstand such modifications. In the energy range considered, the counter is to be standardized with radioactive sources. Such standards were selected according to their disintegration schemes. We thus defined the conditions of use (resolution, yield) of the CPN counter, filled with an argon-methane mixture under a pressure of about 3 bars, in the energy range 5-100 keV. With such an equipment, we were able to measure the absolute disintegration rate for the X-rays of 133 Ba and 75 Se, then to perform the study of a mixed fission products sample. In the same way, we used xenon-based gaseous mixtures, in order to improve the detector yield; in the later case, we carefully examined the limitations introduced by the presence of many parasite rays emitted by the gas. We thus displayed in addition to the leakage peak, the fluorescence ray of the gas, whose origin is difficult to explain. (author)

  4. Evaluating the 239Pu Prompt Fission Neutron Spectrum Induced by Thermal to 30 MeV Neutrons

    Neudecker D.

    2016-01-01

    Full Text Available We present a new evaluation of the 239Pu prompt fission neutron spectrum (PFNS induced by thermal to 30 MeV neutrons. Compared to the ENDF/B-VII.1 evaluation, this one includes recently published experimental data as well as an improved and extended model description to predict PFNS. For instance, the pre-equilibrium neutron emission component to the PFNS is considered and the incident energy dependence of model parameters is parametrized more realistically. Experimental and model parameter uncertainties and covariances are estimated in detail. Also, evaluated covariances are provided between all PFNS at different incident neutron energies. Selected evaluation results and first benchmark calculations using this evaluation are briefly discussed.

  5. Effects of Neutron Emission on Fragment Mass and Kinetic Energy Distribution from Thermal Neutron-Induced Fission of 235U

    The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of 235U(nth,f) have been studied using a Monte-Carlo simulation. Besides reproducing the pronounced broadening in the standard deviation of the kinetic energy at the final fragment mass number around m = 109, our simulation also produces a second broadening around m = 125. These results are in good agreement with the experimental data obtained by Belhafaf et al. and other results on yield of mass. We conclude that the obtained results are a consequence of the characteristics of the neutron emission, the sharp variation in the primary fragment kinetic energy and mass yield curves. We show that because neutron emission is hazardous to make any conclusion on primary quantities distribution of fragments from experimental results on final quantities distributions

  6. Fission product release from a pressurized water reactor defective fuel rod: effect of thermal cycling

    The emission of fission gases and iodines by a pressurized water reactor fuel rod containing a defect when it is initially put in the reactor is studied experimentally using a pressurized water loop in the Siloe reactor at Grenoble. The initial leakage is simulated by making a small hole near the upper end of the rod. The rare gases and iodines are continuously analyzed, and the source terms of fission products are expressed as the ratio of the release rate of a given isotope from the defective fuel rod to the birth rate of this isotope. The release fractions of rare gases and iodines have been determined in different conditions: steady power level between 120 and 700 W . cm-1, power cycling in the range of 200 to 400 W . cm-1, and in the range 120 to 400 W . cm-1. At steady power level, the amounts of radioactive gases escaped from the rod are 100 times higher than those emitted by a sound fuel submitted to a similar power level. The power cycling favors the emission of all iodines whose release rate is 10 to 20 times higher than at the maximum steady power level

  7. Relative quantifying technique to measure mass of fission plate in a fission chamber

    Under the same neutron radiation conditions, fission counts are proportional to the number of fission nuclei. Based on this concept, a relative quantifying method has been developed to measure the mass of fission plate in fission chamber on a 14 MeV accelerator neutron source at the Neutron Physics Laboratory, INPC, CAEP. The experimental assembly was introduced and mass of the fission material in several fission chambers was measured. The results by this method agree well (within 1%) with the α-quantifying method. Therefore, it is absolutely feasible to quantify the fission plate mass in fission chambers. The measurement uncertainty is 2%-4%. (authors)

  8. Prediction on thermal and fission gas behavior of MOX fuel by FEMAXI-5 code

    Benchmarking Femaxi-5 for MOX fuel irradiated by SCNSCK is presented. The history of fuel burnup shown good prediction as other codes did, Femaxi-5 results for temperature of mid plane rod center-line shown good agreement, in side 5% difference of code majority. Internal rod pressure before ramp. Femaxi show in between 2 groups. Rod fission gas release before ramp predicted by Femaxi-5 less difference to experiment one. FGR after power ramp by Femaxi-5 show it between others. NFC has received Femaxi-5 from NEA data bank. Starting use of Femaxi-5 the source code compilation has been done, and testing run has been performed, graphic plot show test run is well done, numerical results need to be recheck. While continuing elaborating NEA data bank via IAEA, exploitation and exploration of might be continued

  9. Absolute surface energy determination

    Metois, J. J.; Muller, P.

    2007-01-01

    Experimental determination of absolute surface energies remains a challenge. We propose a simple method based on two independent measurements on 3D and 2D equilibrium shapes completed by the analysis of the thermal fluctuation of an isolated step. Using then basic equations (Wulff' theorem, Gibbs-Thomson equation, thermodynamics fluctuation of an isolated step) allows us to extract the absolute surface free energy of a singular face. The so-proposed method can be applied when (i) all orientat...

  10. Fission product yields

    Data are summed up necessary for determining the yields of individual fission products from different fissionable nuclides. Fractional independent yields, cumulative and isobaric yields are presented here for the thermal fission of 235U, 239Pu, 241Pu and for fast fission (approximately 1 MeV) of 235U, 238U, 239Pu, 241Pu; these values are included into the 5th version of the YIELDS library, supplementing the BIBFP library. A comparison is made of experimental data and possible improvements of calculational methods are suggested. (author)

  11. Experimental studies of fission properties utilized in reactor design

    Experimental studies of fission properties utilized in reactor design. A programme of experimental studies of fission parameters useful in reactor design is described including the following: (a) The periods and yields of delayed-neutron groups emitted following the neutron-induced fission of Pu241 are measured. Evidence for systematic isotopic dependence of delayed-neutron yields is presented. An experimental investigation of the relation between the time behaviour of delayed-neutron emission and the energy of the incident neutron inducing fission is described. (b) The cross-section for the inducing, of fission in Am243, Pu242 and Pu241 with neutrons in the energy range 0.030 to 1.8 MeV is measured. Emphasis is placed upon the detailed dependence of the fission cross-section on the incident-neutron energy. The absolute values of the cross-sections are given to a precision of ∼25%. (c) Detailed results of a measurement of the Pu241 fission-neutron spectrum are given, including the spectral shape and average fission-neutron energy. Techniques and methods of measuring prompt-fission-neutron spectra are described. (d) The dependence of #-v# (the average number of neutrons emitted per fission) of U235 on the incident neutron energy is measured from 100 keV to 1.6 MeV. #-v# of U238 and other fissile isotopes is compared to #-v# of U235 (thermal). The relative precision of the measurements is #>approx#1.2%. (author)

  12. Late stage thermal history of the Songliao Basin and its tectonic implications: Evidence from apatite fission track (AFT) analyses

    2007-01-01

    Apatite Fission Track (AFT) data from the Songliao Basin indicates that the late stage tectonic movements in the Songliao Basin have zoning in space and episodes in time. The late stage tectonic movements started from the east part of the basin and migrated westward. AFT ages in the east part of the basin are older than those in the west part of the basin, suggesting that the uplift occurred earlier in the east than in the west. The denudation thickness in the east part of the basin is significantly greater than that in the centre and west. The thermal history evolved two episodes of rapid cooling and subsequent slow cooling processes. Age-depth relationship derived from the AFT data indicates a four-episode denudation history. Further Monte Carlo random simulation of the AFT data reveals the four changing points of the thermal evolution at 65 Ma, 43.5 Ma, 28 Ma and 15 Ma, respectively. The uplifting and denudation rates from different episodes of evolution are proportional to the plate convergence rate. Based on the above analyses and the regional geologic background, it is concluded that the late stage thermal events in the Songliao Basin are the far field response to the subduction of the Pacific Plate under the Eurasian Plate. The first episode of the rapid cooling probably started at the end of the Nenjiang Formation, climaxed at the end of the Cretaceous and ceased at the Late Eocene. The subsequent slow cooling lasts another 15 Ma. The first episode of the evolution is the far field response to the major episode of the Yanshan Movement and subsequent series of the tectonic reorganization, especially the directional change of the Pacific Movement and also the subduction of the Indian Plate underneath the Eurasian Plate. While the second episode of the evolution is the far field response to the extension and closure of the Sea of Japan. Extension led to the migration and converging of the mantle heat flow to the Sea of Japan and resulted in the rapid cooling

  13. The thermal history of the Miocene Ibar Basin (Southern Serbia: new constraints from apatite and zircon fission track and vitrinite reflectance data

    Andrić Nevena

    2015-02-01

    Full Text Available The Ibar Basin was formed during Miocene large scale extension in the NE Dinaride segment of the Alpine- Carpathian-Dinaride system. The Miocene extension led to exhumation of deep seated core-complexes (e.g. Studenica and Kopaonik core-complex as well as to the formation of extensional basins in the hanging wall (Ibar Basin. Sediments of the Ibar Basin were studied by apatite and zircon fission track and vitrinite reflectance in order to define thermal events during basin evolution. Vitrinite reflectance (VR data (0.63-0.90 %Rr indicate a bituminous stage for the organic matter that experienced maximal temperatures of around 120-130 °C. Zircon fission track (ZFT ages indicate provenance ages. The apatite fission track (AFT single grain ages (45-6.7 Ma and bimodal track lengths distribution indicate partial annealing of the detrital apatites. Both vitrinite reflectance and apatite fission track data of the studied sediments imply post-depositional thermal overprint in the Ibar Basin. Thermal history models of the detritial apatites reveal a heating episode prior to cooling that began at around 10 Ma. The heating episode started around 17 Ma and lasted 10-8 Ma reaching the maximum temperatures between 100-130 °C. We correlate this event with the domal uplift of the Studenica and Kopaonik cores where heat was transferred from the rising warm footwall to the adjacent colder hanging wall. The cooling episode is related to basin inversion and erosion. The apatite fission track data indicate local thermal perturbations, detected in the SE part of the Ibar basin (Piskanja deposit with the time frame ~7.1 Ma, which may correspond to the youngest volcanic phase in the region.

  14. The thermal history of the Miocene Ibar Basin (Southern Serbia): new constraints from apatite and zircon fission track and vitrinite reflectance data

    Andrić, Nevena; Fügenschuh, Bernhard; Životić, Dragana; Cvetković, Vladica

    2015-02-01

    The Ibar Basin was formed during Miocene large scale extension in the NE Dinaride segment of the Alpine- Carpathian-Dinaride system. The Miocene extension led to exhumation of deep seated core-complexes (e.g. Studenica and Kopaonik core-complex) as well as to the formation of extensional basins in the hanging wall (Ibar Basin). Sediments of the Ibar Basin were studied by apatite and zircon fission track and vitrinite reflectance in order to define thermal events during basin evolution. Vitrinite reflectance (VR) data (0.63-0.90 %Rr) indicate a bituminous stage for the organic matter that experienced maximal temperatures of around 120-130 °C. Zircon fission track (ZFT) ages indicate provenance ages. The apatite fission track (AFT) single grain ages (45-6.7 Ma) and bimodal track lengths distribution indicate partial annealing of the detrital apatites. Both vitrinite reflectance and apatite fission track data of the studied sediments imply post-depositional thermal overprint in the Ibar Basin. Thermal history models of the detritial apatites reveal a heating episode prior to cooling that began at around 10 Ma. The heating episode started around 17 Ma and lasted 10-8 Ma reaching the maximum temperatures between 100-130 °C. We correlate this event with the domal uplift of the Studenica and Kopaonik cores where heat was transferred from the rising warm footwall to the adjacent colder hanging wall. The cooling episode is related to basin inversion and erosion. The apatite fission track data indicate local thermal perturbations, detected in the SE part of the Ibar basin (Piskanja deposit) with the time frame ~7.1 Ma, which may correspond to the youngest volcanic phase in the region.

  15. On-line mass spectrometry measurement of fission gas release from nuclear fuel submitted to thermal transients

    The work presented in this paper has been performed in the framework of a joint research program between Aix-Marseille University and CEA Cadarache. The aim is to develop a mass spectrometer (MS) device for the MERARG facility. MERARG is devoted to the study of fission gas release measurement, from nuclear fuels submitted to annealing tests in high activity laboratory such as LECA-STAR, thanks to gamma spectrometry. The mass spectrometer will then extend the measurement capability from the γ-emitters gases to all the gases involved in the release in order to have a better understanding of the fission gas release dynamics from fuel during thermal transients. Furthermore, the mass spectrometer instrument combines the capabilities and performances of both on-line (for release kinetic) and off-line implementations (for delayed accurate analysis of capacities containing total release gas). The paper deals with two main axes: (1) the modelling of gas sampling inlet device and its performance and (2) the first MS qualification/calibration results. The inlet device samples the gas and also adapts the pressure between MERARG sweeping line at 1.2 bar and mass spectrometer chamber at high vacuum. It is a two-stage device comprising a capillary at inlet, an intermediate vacuum chamber, a molecular leak inlet and a two-stage pumping device. Pressure drops, conductance and throughputs are estimated both for mass spectrometer operation and for exhaust gas recovery. Possible gas segregation is also estimated and device modification is proposed to attain a more accurate calibration. First experimental results obtained from a standard gas bottle show that the quantitative analysis at a few ppm level can be achieved for all isotopes of Kr and Xe, as well as masses 2 and 4 u. (authors)

  16. Modeling of thermal hydraulic behavior and fission product releases in degraded cores

    When core material reaches melting conditions severe degradation of the core geometry occurs. Data available on the core behavior in a severely degraded state suggest that extensive blockage of the flow channels would occur. If a sufficient bypass is available for the gas flow, such as in the LOFT LP-FP-2 test, severe retardation of the hydrogen and fission product sources from the degraded channel is suggested from the available data. This phenomena is expected to occur in an LWR core and should be considered by core models that are used for severe accident analysis. In the MAAP code it is done by preventing gas flow through molten core regions. Good agreement is obtained with all relevant data that are directly applicable to LWR accident conditions. A more mechanistic model for the freezing of core material and its effect on the coolant channel geometry is currently being investigated by the US Department of Energy Advanced Reactor Severe Accident Program (ARSAP). 8 refs., 2 figs

  17. Temporal evolution of a granitic rock under thermal loads generated by fission products

    The thermal time history of a granitic mass under thermal loads, generated by the terminal subproducts arising from the Argentine nuclear programme is analyzed. This rock will be the final repository of those subproducts. The analysis is based on the consideration of a representative unit cell of the rock's centre using the Heating 5 programme. A preliminary analysis is made in order to obtain criteria with respect to the accuracy of the problem. Temporal evolution curves of the temperature on zones of interest of the unit cell considered are shown. Under the thermal loads considered, 500W by container, a maximum temperature of 55 deg C at the wall of the orifice subproducts' deposit is obtained. (Author)

  18. Temporal evolution of a granitic rock under thermal loads generated by fission products

    A parametric study of the thermal history of a granitic mass under thermal loads originating in terminal subproducts of the fuel cycle is performed. Variations of the conductivity and density of the rock and the unit cell dimensions are considered. In this way it was tried to delimit (for short time intervals of the order of 100 years) the influence of possible uncertainties in the rock's knowledge on the results of interest for the engineering design. In the reasonable situations considered, the maximum temperature in the rock did not rise over 80 deg C. (Author)

  19. Fission product migration in intact fuel rods. S176 experiments 1-5: Fission product deposits on clad specimens and their thermal stability

    This report is the fifth of a group which present the results obtained during the first 5 experiments in the S176 series of irradiation experiments. The aim of this series is to provide informtion on the distribution of fission products in intact irradiated fuel rods, both within the UO2 fuel and on the inside of the Zircaloy clad. Fuel rods, previously irradiated to appreciable burnups in the Aagesta R3 reactor, after cooling, are re-irradiated in the Studsvik R2 test reactor for short periods to build up significant inventories of short-lived fission products of interest. Examination of sections of fuel and clad is performed within a short time after removal from the reactor

  20. The fission power of a conceptual fluidised bed thermal nuclear reactor

    The fluidised bed thermal nuclear reactor investigated in this paper is an innovative reactor design in which 1 mm diameter TRISO-coated fuel particles are fluidised by helium gas coolant in a 2,5 m diameter and 6 m high cylindrical bed. The coolant flow rate provides part of the reactivity control mechanism. The TRISO-coated particles have an enriched uranium oxide kernel surrounded by layers of porous carbon, pyrolytic carbon and silicon carbide. This paper presents detailed transient modelling results of this conceptual fluidised bed thermal nuclear reactor obtained using the FETCH nuclear criticality model. Previous work has provided evidence to suggest that such a reactor can be dynamically stable for low power outputs of ∝20 MWt. This work focuses on a reactor with a much higher thermal output of 100 MWt. To simulate the fluidised bed reactor the FETCH model has been used to solve the neutron transport equation in full-phase space, coupled to multi-phase gas-particle fluid dynamics. The main difficulty in modelling such a reactor is that its reactivity is a sensitive function of the fuel particle distribution inside the inner fluidised bed reactor cavity. This fuel particle distribution varies chaotically with time which is the root cause of the reactor's power variability. (orig.)

  1. Time, absolute.

    Mughal, Muhammad Aurang Zeb

    2009-01-01

    The concept of absolute time is a hypothetical model from the laws of classical physics postulated by Isaac Newton in the Principia in 1687. Although the Newtonian model of absolute time has since been opposed and rejected in light of more recent scholarship, it still provides a way to study science with reference to time and understand the phenomena of time within the scientific tradition. According to this model, it is assumed that time runs at the same rate for all the observers in the uni...

  2. Isotope ratio analysis of actinides, fission products, and geolocators by high-efficiency multi-collector thermal ionization mass spectrometry

    A ThermoFisher 'Triton' multi-collector thermal ionization mass spectrometer (MC-TIMS) was evaluated for trace and ultra-trace level isotoperatioanalysis of actinides (uranium, plutonium, and americium), fission products and geolocators (strontium, cesium, and neodymium). Total efficiencies (atoms loaded to ions detected) of up to 0.5-2% for U, Pu, and Am, and 1-30% for Sr, Cs, and Nd can be reported employing resin bead load techniques onto flat ribbon Re filaments or resin beads loaded into a millimeter-sized cavity drilled into a Re rod. This results in detection limits of 4 atoms to 105 atoms) for 239-242+244Pu, 233+236U, 241-243Am, 89,90Sr, and 134,135,137Cs, and (le) 1 pg for natural Nd isotopes (limited by the chemical processing blank) using a secondary electron multiplier (SEM) or multiple-ion counters (MICs). Relative standard deviations (RSD) as small as 0.1% and abundance sensitivities of 1 x 106 or better using a SEM are reported here. Precisions of RSD ∼ 0.01-0.001% using a multi-collector Faraday cup array can be achieved at sub-nanogram concentrations for strontium and neodymium and are suitable to gain crucial geolocation information. The analytical protocols reported herein are of particular value for nuclear forensic and nuclear safeguard applications.

  3. Neutron emission effects on fragment mass and kinetic energy distribution from fission of 239Pu induced by thermal neutrons

    The average of fragment kinetic energy () and the multiplicity of prompt neutrons (ν(bar sign)) as a function of fragment mass (m*), as well as the fragment mass yield (Y (m*)) from thermal neutron induced fission of 239Pu, have been measured by Tsuchiya et al.. In that work the mass and kinetic energy are calculated from the measured kinetic energy of one fragment and the difference of time of flight of the two complementary fragments. However they do not present their results about the standard deviation σE*(m*). In this work we have made a numerical simulation of that experiment, assuming an initial distribution of the primary fragment kinetic energy (E(A)) with a constant value of the standard deviation as function of fragment mass σE(A)). As a result of that simulation we obtain the dependence σE*(m*) which presents an enhancement between m* = 92 and m* 110, and a peak at m* = 121. (orig.)

  4. Neutron emission effects on fragment mass and kinetic energy distribution from fission of 239Pu induced by thermal neutrons

    The average of fragment kinetic energy (E-bar sign*) and the multiplicity of prompt neutrons (ν(bar sign)) as a function of fragment mass (m*), as well as the fragment mass yield (Y(m*)) from thermal neutron-induced fission of 239Pu have been measured by Tsuchiya et al.. In that work the mass and kinetic energy are calculated from the measured kinetic energy of one fragment and the difference of time of flight of the two complementary fragments. However they do not present their results about the standard deviation σE*(m*). In this work we have made a numerical simulation of that experiment which reproduces its results, assuming an initial distribution of the primary fragment kinetic energy (E(A)) with a constant value of the standard deviation as function of fragment mass (σE(A)). As a result of the simulation we obtain the dependence σE*(m*) which presents an enhancement between m* = 92 and m* = 110, and a peak at m* = 121.

  5. Realistic Testing of the Safe Affordable Fission Engine (SAFE-100) Thermal Simulator Using Fiber Bragg Gratings

    The motivation for the reported research was to support NASA space nuclear power initiatives through the development of advanced fiber optic sensors for space-based nuclear power applications. Distributed high temperature measurements were made with 20 FBG temperature sensors installed in the SAFE-100 thermal simulator at the NASA Marshal Space Flight Center. Experiments were performed at temperatures approaching 800 deg. C and 1150 deg. C for characterization studies of the SAFE-100 core. Temperature profiles were successfully generated for the core during temperature increases and decreases. Related tests in the SAFE-100 successfully provided strain measurement data

  6. Contribution to the study of the thermal fission process for uranium 235 (1964)

    This report deals with the study of the distribution of the masses of the fragments produced by the disintegration of the U-236 nucleus, formed when a U-235 nucleus captures a thermal neutron. The experimental method chosen consists in the simultaneous measurement using p-n silicon junction detectors of the energies of the two fragments emitted in coincidence. This measurement is first made by a conditioned analysis of the energy of one of the fragments and then by a two dimensional analysis of the energies of the two fragments. Systematic results, are obtained concerning the distribution of the masses for different values of the total kinetic energy. The five structures appearing both for the mass distributions and for the energies of the fragments are studied and discussed. Generally speaking, our results are in agreement with those obtained by the time-of-flight method. (author)

  7. Absolute nuclear material assay using count distribution (LAMBDA) space

    Prasad, Mano K.; Snyderman, Neal J.; Rowland, Mark S.

    2015-12-01

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  8. Absolute nuclear material assay using count distribution (LAMBDA) space

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2012-06-05

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  9. Delayed fission

    Delayed fission is a nuclear process that couples beta decay and fission. In the delayed fission process, a parent nucleus undergoes beta decay or electron capture and thus populates excited states in the daughter nucleus. This review covers experimental methods for detecting and measuring delayed fission. Experimental results (ECDF activities and beta-DF activities) and theory are presented. The future prospects for study of delayed fission are discussed. 50 refs., 8 figs., 2 tabs

  10. IFPE/SOFIT, WWER-440 Fuel Thermal Performance and Fission Gas Release

    Description: The SOFIT program is described as a sub-task under the Finnish- Russian co-operation on VVER fuel research and consists of a series of irradiation tests in the MR reactor at the Kurchatov Institute, Moscow. The contracting parties are Imatran Voima Oy (IVO) and the Russian National Research Centre Kurchatov Institute (IRTM), (Reference 1). The program is divided into three distinct phases each addressing specific objectives: SOFIT 1: Parametric fuel rod irradiations with basic steady state power histories up to moderate levels of burn-up as dictated by instrumentation endurance. SOFIT 2: Parametric studies based on irradiation of instrumented high burn-up rods. SOFIT 3: Irradiation testing under transient conditions. The results of 2 assemblies of SOFIT 1 are at present available where the main objective was to obtain well qualified data on VVER-440 fuel for verifying and improving codes. In each assembly, rods of different design were irradiated with in-pile instrumentation to measure fuel centreline temperature, fuel stack and cladding elongation. PIE has been performed to obtain data on microstructural changes and measurement of fission gas release (FGR). The first series of irradiations were completed by May '92 and some destructive PIE has been performed. NEA-1310/01: Description: Pre-characterization and irradiation histories for SOFIT 1.1 rods 1-6, 7 and 12. In-pile temperatures for rods 1-6 and PIE FGR from rods 7 and 12. NEA-1310/03: Description of program or function: Pre-characterization and irradiation histories for SOFIT 1.3 rods 1, 3, 4 and 5. In-pile fuel and clad extension measurements for rods 1 and 3. In-pile temperature data for rods 4 and 5. Method of solution: - Irradiation conditions in the MR reactor: The MR reactor is a pool type research reactor with a total power of 50 MW. The reactor contains several pressurized loops which can be connected to one or more in-pile test channels. These channels are located between blocks of

  11. Absolute beginners

    Costa, Carlos Casimiro da; Costa, Jacinta Casimiro da

    2012-01-01

    Tomorrow, I m recovering my Thursday child as an absolute beginner , Transporting you to the essential touch of surface skin and space, Only for you, i do not regret, looking for education in a materia set. My love is your love , my materiality is you making things, The legacy of our ethnography, craftsmen s old and disappear, make me strong hard feelings, Recovering experiences and knowledge sprinkled in powder of stone, wood and metal ( ) reflecting in your dirty face the ...

  12. Fission Fragments Discriminator

    Nuclear fission reaction between Uranium-235 nucleus and thermal neutron caused the high energy fission fragments with uncertainly direction. The particle direction discrimination was determined. The 2.5 x 3.0 mm2 polyethylene gratings with 1-6 mm thickness were used. The grating was placed between uranium screen that fabricated from ammonium-diurinate compound and polycarbonate nuclear track film recorder irradiated by neutron from Thai Research Reactor (TRR-1/M1) facility. The nuclear track density was inversely with grating thickness. It's only fission fragments normal to uranium screen pass through film recorder when grating thickness was 4-6 mm

  13. Fission product yields from 22 MeV neutron-induced fission of 235U

    The chain yields of 28 product nuclides were determined for the fission of 235U induced by 22 MeV neutrons for the first time. Absolute fission rate was monitored with a double-fission chamber. Fission product activities were measured by HPGe γ-ray spectrometry. Time of flight technique was used to measure the neutron spectrum in order to estimate fission events induced by break-up neutrons and scattering neutrons. A mass distribution curve was obtained and the dependence of fission yield on neutron energy is discussed

  14. Fission product yields from 19.1 MeV neutron induced fission of 238U

    36 chain yields were determined for the fission of 238U induced by 19.1 MeV neutrons for the first time. Absolute fission rate was monitored with a double-fission chamber. Fission product activities were measured by HPGe γ-ray spectrometry. Threshold detector method was used to measure the neutron spectrum in order to estimate the fission events induced by break-up neutrons and scattering neutrons. A mass distribution curve was obtained and the dependence of fission yield on neutron energy was discussed

  15. The latest progress of fission track analysis

    Fission track analysis as a new nuclear track technique is based on fission track annealing in mineral and is used for oil and gas exploration successfully. The west part of China is the main exploration for oil and gas. The oil and gas basins there experienced much more complicated thermal history and higher paleotemperature. In order to apply fission track analysis to these basins, following work was be carried out: 1. The decomposition of grain age distribution of zircon fission tracks. 2. Study on thermal history of Ordos basin using zircon fission track analysis. 3. The fission track study on the Qiang Tang basin in tibet

  16. Absolute Summ

    Phillips, Alfred, Jr.

    Summ means the entirety of the multiverse. It seems clear, from the inflation theories of A. Guth and others, that the creation of many universes is plausible. We argue that Absolute cosmological ideas, not unlike those of I. Newton, may be consistent with dynamic multiverse creations. As suggested in W. Heisenberg's uncertainty principle, and with the Anthropic Principle defended by S. Hawking, et al., human consciousness, buttressed by findings of neuroscience, may have to be considered in our models. Predictability, as A. Einstein realized with Invariants and General Relativity, may be required for new ideas to be part of physics. We present here a two postulate model geared to an Absolute Summ. The seedbed of this work is part of Akhnaton's philosophy (see S. Freud, Moses and Monotheism). Most important, however, is that the structure of human consciousness, manifest in Kenya's Rift Valley 200,000 years ago as Homo sapiens, who were the culmination of the six million year co-creation process of Hominins and Nature in Africa, allows us to do the physics that we do. .

  17. Nuclear fission

    The nuclear fission process is pedagogically reviewed from a macroscopic-microscopic point of view. The Droplet model is considered. The fission dynamics is discussed utilizing path integrals and semiclassical methods. (L.C.)

  18. Nuclear fission

    V.M. STRUTINSKY's semi-classical method is the most precise to determine the energy of the different states along the fission way. The double-humped fission barrier explains fission isomerism. V.M. STRUTINSKY's barrier explains the ''intermediate structure'' observed in the cross section under the threshold; it provides also the observed effect of ''vibrational resonances'' with an interpretation. Taking an asymmetry parameter in consideration, a triple-humped fission barrier seems to be essential now for the light actinides. There is still a microscopic fission barrier to be explained

  19. Investigation of fission layers for precise fission cross-section measurements with a gridded ionization chamber

    An ionization chamber with a Frisch grid is used to determine both the energy (E) of the charged particles emitted from the source positioned coplanar with the cathode, and the cosine of the emission angle (/sigma phi/) with respect to the normal of the cathode. In the plane determined by the variables cos/sigma phi/ and E, it is possible to identify an area that is unaffected by backscattering and self-absorption. Events belonging to this area show an isotropic angular distribution for alpha particles and also for fragments of fission induced by thermal neutrons, which, extrapolated to 90 deg, yields the absolute number of events. The capabilities of this technique are demonstrated by the investigation of four evaporated 235 UF4 layers and one suspension-sprayed 235U3O8 layer. For the UF4 layers, the alpha-particle source strengths were determined, and agreement was found within 0.3% with values independently measured by low-geometry alpha counting. The same method was also applied to fission events induced by thermal neutrons. The determination of the total number of fission events is determined to an accuracy of better than 0.5%. The longstanding doubts on the magnitudes of fragment absorption and scattering are, in principle, circumvented by the present method, and therefore no assumptions on fragment ranges and scattering cross sections are needed. It is emphasized that the present method, within reasonable limits, is insensitive to source shape and homogeneity in its thickness

  20. Investigation of fission layers for precise fission cross section measurements with a gridded ionization chamber

    An ionization chamber with Frisch-grid is used to determine both the energy (E) of the charged particles emitted from the source positioned coplanar with the cathode, and the cosine of the emission angle (theta) with respect to the normal of the cathode. In the plane determined by the variables cos theta and E it is possible to identify an area which is unaffected by backscattering and selfabsorption. Events belonging to this area show an isotropic angular distribution for alpha particles and also for fission fragments induced by thermal neutrons, which, extrapolated to 90 deg., yields the absolute number of events. The capabilities of this technique are demonstrated by the investigation of four evaporated 235UF4 layers and one suspension sprayed 235U3O8 layer. For the UF4 layers the alpha particle source strengths were determined, and agreement was found within 0.3% with values independently measured by low geometry alpha counting. The same method was applied also to fission events induced by thermal neutrons. An accuracy for the determination of the total number of fission events of better than 0.5% is reached. The longstanding doubts on the magnitudes of fragment absorption and scattering are in principle circumvented by the present method and therefore no assumptions on fragment ranges and scattering cross-sections are needed. It is also emphasized that the present method, within reasonable limits, is intensive to source shape and thickness homogeneity. (author)

  1. Beta-decay half-lives of neutron rich Cu and Ni isotopes produced by thermal fission of 235U and 239Pu

    The half-lives of very neutron rich isotopes of Ni and Cu have been measured. The isotopes are produced in very asymmetric thermal fission of 235U and 239Pu at the I.L.L. high flux reactor. They are separated by means of the Lohengrin spectrometer. They are identified with a ΔE-E ionization chamber and implanted in one of the 8 Si planar detectors where the β- particles are also detected. The time correlations between the implantation and the detection of β- particles provide the half-life. The values obtained are compared to current theoretical predictions

  2. The thermal history of the Miocene Ibar Basin (Southern Serbia): new constraints from apatite and zircon fission track and vitrinite reflectance data

    Andrić Nevena; Fügenschuh Bernhard; Životić Dragana; Cvetković Vladica

    2015-01-01

    The Ibar Basin was formed during Miocene large scale extension in the NE Dinaride segment of the Alpine- Carpathian-Dinaride system. The Miocene extension led to exhumation of deep seated core-complexes (e.g. Studenica and Kopaonik core-complex) as well as to the formation of extensional basins in the hanging wall (Ibar Basin). Sediments of the Ibar Basin were studied by apatite and zircon fission track and vitrinite reflectance in order to define thermal events during basin evolution. Vitrin...

  3. Fission gas release (FGASRL)

    During irradiation of water reactor fuel rods, gaseous fission products are produced in the fuel and are slowly released to various voipd volumes in the fuel rods. The released fission gases degrade the initial fill gas thermal conductivity and thus change the thermal response of the fuel rods. Moreover, fuel rod internal pressure is increased so that the cladding mechanical response is affected. The fission gas release subcode FGASRL is intended for use in analytical codes which predict water reactor fuel pin behavior. The development effort was directed primarily at improving code predictions of the gas release model used in FRAP-S3 which overpredicts release of fuels irradiated at relatively low operating temperatures and therefore small gas release fractions. The fission gas release subcode (FGASRL) presented in the report describes a two-step gas release process: (a) fission gas release from fuel grains to the grain boundaries, and (b) fission gas release from the grain boundaries to internal free volume of the fuel pin

  4. Fission fragment driven neutron source

    Miller, Lowell G.; Young, Robert C.; Brugger, Robert M.

    1976-01-01

    Fissionable uranium formed into a foil is bombarded with thermal neutrons in the presence of deuterium-tritium gas. The resulting fission fragments impart energy to accelerate deuterium and tritium particles which in turn provide approximately 14 MeV neutrons by the reactions t(d,n).sup.4 He and d(t,n).sup.4 He.

  5. Spontaneous fission

    Recent experimental results for spontaneous fission half-lives and fission fragment mass and kinetic-energy distributions and other properties of the fragments are reviewed and compared with recent theoretical models. The experimental data lend support to the existence of the predicted deformed shells near Z = 108 and N = 162. Prospects for extending detailed studies of spontaneous fission properties to elements beyond hahnium (element 105) are considered. (orig.)

  6. Application of digital signal-processing technique to delayed-neutron yield measurements on thermal-neutron induced fission of 237Np

    The measurement procedure based on the continuous thermal-neutron beam modulation with a mechanical chopper was developed for delayed-neutron yield measurement of the thermal-neutron induced fission of 237Np. The idea of the procedure is similar to that which is widely used in modern communications for the nonauthorized data access prevention. The data is modulated with predefined pattern before transmission to the public network and only the recipient that has the modulation pattern is able to demodulate it upon reception. For the thermal-neutron induced reaction applications, the thermal-neutron beam modulation pattern was used to demodulate the measured delayed-neutron intensity signals on the detector output resulting in nonzero output only for the detector signals correlated with the beam modulation pattern. A comparison of the method with the conventional measurement procedure was provided, and it was demonstrated that the cross-correlation procedure has special features making it superior over the conventional one when the measured value difference from the background is extremely small. Due to strong sensitivity of measurement procedure on the modulation pattern of the neutron beam, one can implement the modulation pattern of specific shape to separate the effect of the thermal part of the beam from the higher energy one in the most confident way in a particular experiment

  7. Low-energy ternary fission

    With the detector system DIOGENES thermal neutron induced and spontaneous α particle associated fission and spontaneous nuclear tripartition into three fragments of similar masses has been investigated. DIOGENES is a concentric arrangement of toroidal angular position sensitive ionization chambers and proportional counters to measure the kinetic energies and relative angular distributions of the three reaction products of ternary fission. For α-particle accompanied fission some of the many possible α particle fission-fragment parameter correlations will be discussed. For nearly symmetric low-energy nuclear tripartition new upper limits are presented. Former experimental results which pretended evidence for so called true ternary fission could be explained by charged-particle associated fission with a light particle in the mass range of 13 < A < 23

  8. Thermal modeling and geomorphology of the south border of the Sao Francisco Craton: thermochronology by fission tracks in apatites

    Recent developments in Fission Track thermochronology associated to mesozoic-cenozoic erosion and tectonic presented trough thematic maps (isotemperature), permit to model the landscape evolution in the southern border of the Sao Francisco craton, southeastern Brazil. Paleotemperature, obtained by fission track analysis in apatite, is closely related to geomorphologic interpretations. The area suffered a complex imprint of endogenous and exogenous processes resulting diversified and differentiated relieves. The landscape is strongly controlled by exhumation between Jurassic and Lower Cretaceous, uplift with tectonic denudation related to crustal heating at the Upper Cretaceous and reactivation of faults until the Miocene. This scenario is a result of reactivations of different brittle structures that accommodate the deformation in the southern border of the Sao Francisco craton. The landscape reflects denudations of up to 3 km with preserved remains of erosive surfaces in the topographical tops and chronocorrelates deposits in the basins of the region. (author)

  9. Spontaneous Fission

    Segre, Emilio

    1950-11-22

    The first attempt to discover spontaneous fission in uranium was made by [Willard] Libby, who, however, failed to detect it on account of the smallness of effect. In 1940, [K. A.] Petrzhak and [G. N.] Flerov, using more sensitive methods, discovered spontaneous fission in uranium and gave some rough estimates of the spontaneous fission decay constant of this substance. Subsequently, extensive experimental work on the subject has been performed by several investigators and will be quoted in the various sections. [N.] Bohr and [A.] Wheeler have given a theory of the effect based on the usual ideas of penetration of potential barriers. On this project spontaneous fission has been studied for the past several years in an effort to obtain a complete picture of the phenomenon. For this purpose the spontaneous fission decay constants {lambda} have been measured for separated isotopes of the heavy elements wherever possible. Moreover, the number {nu} of neutrons emitted per fission has been measured wherever feasible, and other characteristics of the spontaneous fission process have been studied. This report summarizes the spontaneous fission work done at Los Alamos up to January 1, 1945. A chronological record of the work is contained in the Los Alamos monthly reports.

  10. Fission fragment mass, kinetic energy and angular distribution for 235U(n,f) in the neutron energy range from thermal to 6 MeV

    A double Frisch gridded ionization chamber has been used for the measurements. For both fission fragments the mass, kinetic energy and emission angle is found. Data have been measured at different neutron energies, Esub(n), ranging from thermal to 6.0 MeV in steps of 0.5 MeV. The measured angular anisotropies will be shown. A fit, based on statistical theory, to earlier measurements of negative anisotropies for Esub(n)<=0.2 MeV will be discussed.The measured total kinetic energy averaged over all fragment masses, TKE-bar(Esub(n)), shows a sudden decrease at Esub(n)approx. 4.5 MeV in agreement with earlier measurements. This sudden decrease can not be explained by the measured change in the mass distribution. The present data of TKE-bar(Esub(n)) as function of mass-split reveal that TKE-bar(Esub(n)) decreases with Esub(n) for mass splits around the 104/132 split as predicted by calculations of B.D. Wilkins et al. It is also seen that TKE-bar(Esub(n)) increases with Esub(n) for the symmetric and the extreme asymmetric fissions. The very structured mass distribution from approximately cold fragmentation will be presented. (author)

  11. Relative fission product yield determination in the USGS TRIGA Mark I reactor

    Koehl, Michael A.

    Fission product yield data sets are one of the most important and fundamental compilations of basic information in the nuclear industry. This data has a wide range of applications which include nuclear fuel burnup and nonproliferation safeguards. Relative fission yields constitute a major fraction of the reported yield data and reduce the number of required absolute measurements. Radiochemical separations of fission products reduce interferences, facilitate the measurement of low level radionuclides, and are instrumental in the analysis of low-yielding symmetrical fission products. It is especially useful in the measurement of the valley nuclides and those on the extreme wings of the mass yield curve, including lanthanides, where absolute yields have high errors. This overall project was conducted in three stages: characterization of the neutron flux in irradiation positions within the U.S. Geological Survey TRIGA Mark I Reactor (GSTR), determining the mass attenuation coefficients of precipitates used in radiochemical separations, and measuring the relative fission products in the GSTR. Using the Westcott convention, the Westcott flux, modified spectral index, neutron temperature, and gold-based cadmium ratios were determined for various sampling positions in the USGS TRIGA Mark I reactor. The differential neutron energy spectrum measurement was obtained using the computer iterative code SAND-II-SNL. The mass attenuation coefficients for molecular precipitates were determined through experiment and compared to results using the EGS5 Monte Carlo computer code. Difficulties associated with sufficient production of fission product isotopes in research reactors limits the ability to complete a direct, experimental assessment of mass attenuation coefficients for these isotopes. Experimental attenuation coefficients of radioisotopes produced through neutron activation agree well with the EGS5 calculated results. This suggests mass attenuation coefficients of molecular

  12. Observation of cold fission in 242Pu spontaneous fission

    Coincidence γ-ray data from the spontaneous fission of 242Pu were collected at the Lawrence Berkeley Laboratory high purity Ge (HPGe) array, GAMMASPHERE. Data from several cold-fission (0 neutron emission) isotopic pairs were observed and are presented. An interesting trend in the fractional population of cold-fission events was observed and is discussed. Relative yields of Zr-Xe, Sr-Ba, and Mo-Te pairs were measured. The Zr-Xe system has the most complete data set. Some speculations on the trend in the number of neutrons emitted as a function of the mass of the Xe isotope populated are presented. Comparisons between the yields from the spontaneous fission of 242Pu and the yields from thermal-neutron-induced fission of 241Pu are also presented. copyright 1996 The American Physical Society

  13. Chemical characterization of short-lived selenium and their daughter isotopes from thermal neutron induced fission of 235U at a gas-jet facility

    Selenium nuclides are available from thermal neutron induced nuclear fission of 235U at the gas-jet facility at the Swiss spallation neutron source (SINQ) at Paul Scherrer Institute, Switzerland. The formation of stable selenium compounds, their transport yields using the gas-jet system and their relative thermal decomposition temperature were investigated under oxidizing and reducing conditions in the target chamber. Using O2, H2, CO, and propene as additional gases, the selenium isotopes are suggested to form H2SeO3, H2Se, COSe, and C3H6Se, respectively, with overall 84Se yields of 1.5%, 4.7%, 6.3%, and 21.9%, respectively. Adsorption enthalpy, vapour pressure, solubility and acidity data for these species were collected from the literature or estimated from other known thermochemical properties. Carrier free bromine isotopes (84Br, 86Br) in the form of HOBr were obtained by thermally decomposing H2SeO3 and retaining elemental Se under oxygen rich conditions on quartz at 400 K. (author)

  14. Study of the emission of a light particle charged during the fission of 235U by thermal neutron

    In a first part, this research thesis discusses the existing theories of the mechanism of emission of light particles charged of tri-partition (tri-partition is defined as an event involving two big fragments of masses comparable with those obtained in binary fission, and a charged light particle). Then, the author presents and reports an experiment performed by suing nuclear emulsions. Another type of experiment is then presented which allows the measurement of masses and energies of tri-partition fragments. The author then presents theoretical calculations which have been performed in order to find again some characteristics of tri-partition. These calculations are mainly based on Coulomb repulsion between various fragments

  15. Teaching Absolute Value Meaningfully

    Wade, Angela

    2012-01-01

    What is the meaning of absolute value? And why do teachers teach students how to solve absolute value equations? Absolute value is a concept introduced in first-year algebra and then reinforced in later courses. Various authors have suggested instructional methods for teaching absolute value to high school students (Wei 2005; Stallings-Roberts…

  16. Subroutines to Simulate Fission Neutrons for Monte Carlo Transport Codes

    Lestone, J. P.

    2014-01-01

    Fortran subroutines have been written to simulate the production of fission neutrons from the spontaneous fission of 252Cf and 240Pu, and from the thermal neutron induced fission of 239Pu and 235U. The names of these four subroutines are getnv252, getnv240, getnv239, and getnv235, respectively. These subroutines reproduce measured first, second, and third moments of the neutron multiplicity distributions, measured neutron-fission correlation data for the spontaneous fission of 252Cf, and meas...

  17. Fission track studies of tektites

    The fission track analysis method was used for the age determination of tektites. The tektite samples were obtained from Hainan Island and Leizhou Peninsula. The method consists in cutting and polishing two sections of a sample, irradiating one of these with a known thermal neutron flux (5.90 x 1015/cm2), etching each section identically with hydrofluoric acid, and then comparing the fission track densities in two cases with a microscope. Their fission track age is found to be around 0.7 Ma

  18. Average Number and Energy of Gamma-Rays Emitted as a Function of Fragment Mass in U235 Thermal-Neutron-Induced Fission

    The average number and energy of gamma-rays emitted as a function of fragment mass in U235 thermal-neutron-induced fission have been measured. A three-parameter correlation experimeni was performed in which two silicon suríace barrier detectors were used to measure the fission product energies, and a 5-in-diam., 4-in-thick Nal(Tl) scintillation crystal was used to measure the gamma-ray energies. Extreme care was taken in the experimental arrangement to avoid counting direct fission neutrons, scattered gamma-rays and neutrons, and other false events. Data were recorded event-by-event in a system similar to that used in previous energy correlation experiments at Oak Ridge, and were analysed according to a ''weighting method'' proposed by Maier-Leibnitz. The total number and energy of the gamma- rays for both fragments as a function of mass ratio were obtained directly. The number and energy of gamma- rays for individual fragment masses were determined by making use of the variation in laboratory angular distribution and energy of the gamma-rays emitted from moving fragments. In particular, the 0° to 180° ratio of the number of gamma-rays from a moving source emitting isotropically in its centre-of-mass system is proportional to 1 + 2 x 2v/c; similarly the 0° to 180° ratio in total gamma energy is proportional to 1 + 2 x3v/c. Thus by comparing appropriate ratios in the analysis for light and heavy fragments moving towards or away from the gamma-ray derector, one obtains these quantities as a function of individual fragment mass. Results of preliminary analyses show interesting similarities in behaviour to those for neutrons. Both the total energy and average quantum energy of gamma-rays are essentially constant over most of the range of mass ratios; however a broad minimum is observed for the total energy in the region where Mh ∼ 130, i. e. where ZH ∼ 50 or NH ∼ 82. An increase is observed in the total energy as the mass ratio approaches unity. The number

  19. The microscopic theory of fission

    Younes, W.; Gogny, D.

    2009-01-01

    Fission-fragment properties have been calculated for thermal neutron-induced fission on a $^{239}\\textrm{Pu}$ target, using constrained Hartree-Fock-Bogoliubov calculations with a finite-range effective interaction. A quantitative criterion based on the interaction energy between the nascent fragments is introduced to define the scission configurations. The validity of this criterion is benchmarked against experimental measurements of the kinetic energies and of multiplicities of neutrons emi...

  20. Mesoscale Benchmark Demonstration Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing

    Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert; Gao, Fei; Sun, Xin; Tonks, Michael; Biner, Bullent; Millet, Paul; Tikare, Veena; Radhakrishnan, Balasubramaniam; Andersson , David

    2012-04-11

    A study was conducted to evaluate the capabilities of different numerical methods used to represent microstructure behavior at the mesoscale for irradiated material using an idealized benchmark problem. The purpose of the mesoscale benchmark problem was to provide a common basis to assess several mesoscale methods with the objective of identifying the strengths and areas of improvement in the predictive modeling of microstructure evolution. In this work, mesoscale models (phase-field, Potts, and kinetic Monte Carlo) developed by PNNL, INL, SNL, and ORNL were used to calculate the evolution kinetics of intra-granular fission gas bubbles in UO2 fuel under post-irradiation thermal annealing conditions. The benchmark problem was constructed to include important microstructural evolution mechanisms on the kinetics of intra-granular fission gas bubble behavior such as the atomic diffusion of Xe atoms, U vacancies, and O vacancies, the effect of vacancy capture and emission from defects, and the elastic interaction of non-equilibrium gas bubbles. An idealized set of assumptions was imposed on the benchmark problem to simplify the mechanisms considered. The capability and numerical efficiency of different models are compared against selected experimental and simulation results. These comparisons find that the phase-field methods, by the nature of the free energy formulation, are able to represent a larger subset of the mechanisms influencing the intra-granular bubble growth and coarsening mechanisms in the idealized benchmark problem as compared to the Potts and kinetic Monte Carlo methods. It is recognized that the mesoscale benchmark problem as formulated does not specifically highlight the strengths of the discrete particle modeling used in the Potts and kinetic Monte Carlo methods. Future efforts are recommended to construct increasingly more complex mesoscale benchmark problems to further verify and validate the predictive capabilities of the mesoscale modeling

  1. Ternary fission

    M Balasubramaniam; K R Vijayaraghavan; C Karthikraj

    2015-09-01

    We present the ternary fission of 252Cf and 236U within a three-cluster model as well as in a level density approach. The competition between collinear and equatorial geometry is studied by calculating the ternary fragmentation potential as a function of the angle between the lines joining the stationary middle fragment and the two end fragments. The obtained results for the 16O accompanying ternary fission indicate that collinear configuration is preferred to equatorial configuration. Further, for all the possible third fragments, the potential energy surface (PES) is calculated corresponding to an arrangement in which the heaviest and the lightest fragments are considered at the end in a collinear configuration. The PES reveals several possible ternary modes including true ternary modes where the three fragments are of similar size. The complete mass distributions of Si and Ca which accompanied ternary fission of 236U is studied within a level density picture. The obtained results favour several possible ternary combinations.

  2. Mass and Charge Distribution in Low-Energy Fission

    The mass and charge distributions for thermal-neutron fission of U235 are discussed in considerable detail and compared with the corresponding distributions in other low-energy fission processes. Points discussed in connection with the mass distributions for binary fission include the positions of the peaks, valley and fine structure in a mass yield curve with respect to filled nuclear shells and the changes in the positions that occur with changing fissioning nucleus and excitation energy. The mass distribution from ternary fission is discussed also. For both binary and ternary fission comments are made concerning the mass distributions of primary fragments (before neutron evaporation) and of fission products (after neutron evaporation). Charge distribution is discussed in terms of charge dispersion among fission products with the same mass number and the variation with mass number of Zp, the ''most probable charge'' (non-integral) for a given mass number. Although direct information about charge distribution is limited to fission products, estimates are presented of charge distribution for primary fission fragments. Knowledge and estimates of mass and charge distribution for a fission process allow estimation of primary yields of all fission products or fragments. Although many estimated primary yields are quite uncertain mainly because of lack of knowledge of charge distribution, especially for fission products formed in low yield; some estimates of primary yields are presented to illustrate the need for and possible practicality of further experimentation. Fission processes other than thermal-neutron fission of U235 that are discussed include thermal-neutron fission of U233 and Pu239, spontaneous fission of Pu240 and Cf252, 14-MeV neutron fission of U235 and U238, 11-MeV proton fission of Ra226 and 22-MeV deuteron fission of Bi209. (author)

  3. Benchmarking Nuclear Fission Theory

    G. F. Bertsch(INT, Seattle, USA); Loveland, W.; Nazarewicz, W.; Talou, P.

    2015-01-01

    We suggest a small set of fission observables to be used as test cases for validation of theoretical calculations. The purpose is to provide common data to facilitate the comparison of different fission theories and models. The proposed observables are chosen from fission barriers, spontaneous fission lifetimes, fission yield characteristics, and fission isomer excitation energies.

  4. Modelling of thermal mechanical behaviour of high burn-Up VVER fuel at power transients with special emphasis on the impact of fission gas induced swelling of fuel pellets

    This paper is devoted to the modelling of unsteady state mechanical and thermo-physical behaviour of high burn-up VVER fuel at a power ramp. The contribution of the processes related to the kinetics of fission gas to the consequences of pellet-clad mechanical interaction is analysed by the example of integral VVER-440 rod 9 from the R7 experimental series, with a pellet burn-up in the active part at around 60 MWd/kgU. This fuel rod incurred ramp testing with a ramp value ΔW1 ∼ 250 W/cm in the MIR research reactor. The experimentally revealed residual deformation of the clad by 30-40 microns in the 'hottest' portion of the rod, reaching a maximum linear power of up to 430 W/cm, is numerically justified on the basis of accounting for the unsteady state swelling and additional degradation of fuel thermal conductivity due to temperature-induced formation and development of gaseous porosity within the grains and on the grain boundaries. The good prediction capability of the START-3 code, coupled with the advanced model of fission gas related processes, with regard to the important mechanical (residual deformation of clad, pellet-clad gap size, central hole filling), thermal physical (fission gas release) and micro-structural (profiles of intra-granular concentration of the retained fission gas and fuel porosity across a pellet) consequences of the R7 test is shown. (authors)

  5. Fission Spectrum

    Bloch, F.; Staub, H.

    1943-08-18

    Measurements of the spectrum of the fission neutrons of 25 are described, in which the energy of the neutrons is determined from the ionization produced by individual hydrogen recoils. The slow neutrons producing fission are obtained by slowing down the fast neutrons from the Be-D reaction of the Stanford cyclotron. In order to distinguish between fission neutrons and the remaining fast cyclotron neutrons both the cyclotron current and the pusle amplifier are modulated. A hollow neutron container, in which slow neutrons have a lifetime of about 2 milliseconds, avoids the use of large distances. This method results in much higher intensities than the usual modulation arrangement. The results show a continuous distribution of neutrons with a rather wide maximum at about 0.8 MV falling off to half of its maximum value at 2.0 MV. The total number of netrons is determined by comparison with the number of fission fragments. The result seems to indicate that only about 30% of the neutrons have energies below .8 MV. Various tests are described which were performed in order to rule out modification of the spectrum by inelastic scattering. Decl. May 4, 1951

  6. Singlet Fission

    Smith, M. B.; Michl, Josef

    2010-01-01

    Roč. 110, č. 11 (2010), s. 6891-6936. ISSN 0009-2665 Grant ostatní: Department of Energy(US) DE-FG36-08GO18017 Institutional research plan: CEZ:AV0Z40550506 Keywords : solar energy conversion * photovoltaics * singlet fission Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 33.033, year: 2010

  7. Ideological Fission

    Christiansen, Steen Ledet

    materialisation of an ideological fission which attempts to excise certain ideological constructions, yet paradoxically casting them in a form that is recognizable and familiar. The monstrous metonomy which is used shows us glimpses of a horrid being, intended to vilify the attack on New York City. However, it is...

  8. Nuclear fission with a Langevin equation

    A microscopically derived Langevin equation is applied to thermally induced nuclear fission. An important memory effect is pointed out and discussed. A strong friction coefficient, estimated from microscopic quantities, tends to decrease the stationary limit of the fission rate and to increase the transient time. The calculations are performed with a collective mass depending on the collective variable and with a constant mass. Fission rates calculated at different temperatures are shown and compared with previous available results. (author) 23 refs.; 7 figs

  9. An absolute measurement of #-v# of Cf252

    An absolute measurement of v of Cf252. An absolute determination of the average number of neutrons, #-v#, emitted in the spontaneous fission of Cf252 has been made by counting the fission neutrons in a large liquid scintillator. The detection efficiency of this counter was measured as a function of neutron energy. Well-collimated neutrons were scattered into the scintillator by an anthracene crystal, which detected the corresponding recoil protons. Pulse-shape discrimination was employed to eliminate γ-ray background. The detection efficiency for Cf252 fission neutrons was found to be 0.703 ± 0.007, giving a value of 3.78 ± 0.04 for the average number of prompt neutrons emitted per Cf252 fission. (author)

  10. Eosinophil count - absolute

    Eosinophils; Absolute eosinophil count ... the white blood cell count to give the absolute eosinophil count. ... than 500 cells per microliter (cells/mcL). Normal value ranges may vary slightly among different laboratories. Talk ...

  11. Intercomparison study of inductively coupled plasma mass spectrometry, thermal ionization mass spectrometry and fission track analysis of μBq quantities of 239Pu in synthetic urine

    Even today, some Marshall Islanders are looking forward to permanently resettling their islands after five decades. The U.S. Department of Energy and the resettled residents require reasonable but cost-prudent assurance that the doses to resident from residual 239Pu will not exceed recognized international standards or recommendations, as estimated from the excretion of 239Pu in urine. The goal of this study was to evaluate the bias, uncertainty and sensitivity of analytical techniques that measure 3-56 μBq 239Pu in synthetic urine. The analytical techniques studied in this work included inductively coupled plasma mass spectrometry, thermal ionization mass spectrometry and fission track analysis. The results of the intercomparison demonstrated that all three techniques were capable of marking the measurements, although not with equal degree of bias and uncertainty. The estimated minimum detectable activity was 1 μBq of 239Pu per synthetic urine sample. This exercise is also the first effort to certify test materials of plutonium in the nBqxg-1 range. (author)

  12. Thermal history of the Jurassic Strata in the Northern Tianshan and its geological significance, revealed by apatite fission-track and vitrinite-reflectance analysis

    Zhang, Z.C.; Guo, Z.J.; Wu, C.D.; Fang, S.H. [Peking University, Beijing (China)

    2007-07-15

    Apatite fission track (AFT) dating is carried on 18 samples collected from Shichang-Manas, Anjihai river and Sikesu area of the Northern margin of Tianshan. Vitrinite reflectance (R{sub o}) data of 10 samples from the Triassic to Jurassic coal seam were obtained to provide maximum paleotemperatures for the stratigraphic strata experiencing. The data suggest that maximum burial and thermal maturity of the Triassic and lower Jurassic rocks occurred at Late Jurassic to Early Cretaceous, and then retained at the same depth till Miocene. This history is consistent with the AFT modeling result of the underlying granite. The cooling of Late Jurassic to Early Cretaceous can be typically interpreted as the result of decreasing of paleothermal gradient at the Cretaceous. The burial and heating of the Middle Jurassic rocks preserved for a long time until late Oligocene. All AFT samples show evidence for Miocene rapid cooling, beginning at about 10 Ma. This cooling is typically interpreted as the result of uplift and erosion of overlying strata. Miocene cooling of Mesozoic and Paleozoic granite suggests that uplift of the northern Tianshan occurred significantly later than previously proposed and is consistent with timing of intense deformation in the southwestern Junggar basin.

  13. Coulomb and even-odd effects in cold and super-asymmetric fragmentation for thermal neutron induced fission of 235U

    Montoya, Modesto

    2015-01-01

    The Coulomb effects hypothesis is used to interpret even-odd effects of maximum total kinetic energy as a function of mass and charge of fragments from thermal neutron induced fission of 235U. Assuming spherical fragments at scission, the Coulomb interaction energy between fragments (C_sph) is higher than the Q-value, the available energy. Therefore at scission the fragments must be deformed, so that the Coulomb interaction energy does not exceed the Q-value. The fact that the even-odd effects in the maximum total kinetic energy as a function of the charge and mass, respectively, are lower than the even-odd effects of Q is consistent with the assumption that odd mass fragments are softer than the even-even fragments. Even-odd effects of charge distribution in super asymmetric fragmentation also are interpreted with the Coulomb effect hypothesis. Because the difference between C_sph and Q increases with asymmetry, fragmentations require higher total deformation energy to occur. Higher deformation energy of the...

  14. Effects of variations on slopes of yield and average kinetic energy curves as a function of fragment mass on standard deviation of final kinetic energy distribution from thermal neutron induced fission of 235U

    The mass and kinetic energy distributions of fragments from thermal neutron induced fission of 233U have been studied using a Monte-Carlo simulation. In our previous work [1] we reproduce the two pronounced broadenings in the standard deviation (SD) of the kinetic energy distribution of the final fragment at mass number around m=109, and m=125, respectively, which is agreement with the experimental data obtained by Belhafaf et al. [2] (author).

  15. Thermal history and age of geological regions obtained by applying the fission track method in apatite samples; Historia termica e idades de regioes geologicas obtidas atraves de tracos de fissao em apatita

    Soares, Cleber J.; Tello Saenz, Carlos A.; Balan, Ana M. Osorio A.; Dias, Airton N.C.; Novaes, Felipe P.; Oliveira, Roger D.; Barra, Beatriz C., E-mail: pccj13@yahoo.com.b, E-mail: amoa@fct.unesp.b [UNESP, Presidente Prudente, SP (Brazil). Dept. de Fisica, Quimica e Biologia

    2007-07-01

    The objective of this work is dating apatite samples using the Fission Track Method (FTM). Samples were collected from different altitudes in Serra da Mantiqueira (Brazil): High Mantiqueira (above 1,000 m) and Low Mantiqueira (below 1,000 m). Data obtained for the ages and thermal history of the samples via FTM have been interpreted and, according to the geological point of view, can be associated with the uplifting of Serra da Mantiqueira after the opening of the Atlantic Ocean

  16. The absolute total delayed neutron yields, relative abundances and half-lives of delayed neutron groups in 6- and 8-group model format from neutron induced fission of 232Th, 233U, 236U, 239Pu, and 241Am in the energy range from 0.35 MeV (or threshold energy) to 5 MeV

    The latest evaluation of delayed neutron constants was made for main fuel nuclides (235U, 238U, 239Pu) within an working group under the auspices of the Nuclear Energy Agency’s (NEA) Working Party on International Evaluation Cooperation (WPEC), Subgroup 6 (SG6) in 1999 [1]. As a result of this work the total delayed yields for the above nuclides were essentially corrected as compared with Tuttle’s recommended data set [2]. For the total delayed yields from 238U correction is +5.6%, for thermal induced fission of 239Pu - +3.4% and for fast neutron induced fission of 239Pu - +3.2%. This is a direct indication that there is a need for a continuing effort on delayed neutron data improving. From now, this will be mainly directed at satisfying new requirements emerging from the current trends in reactor technology, such as: the use of high burn-up fuel, the burning of plutonium stocks, the general growing interest in fuel recycling strategies, and new concept of actinide burners

  17. Thorium-uranium fission radiography

    Haines, E. L.; Weiss, J. R.; Burnett, D. S.; Woolum, D. S.

    1976-01-01

    Results are described for studies designed to develop routine methods for in-situ measurement of the abundance of Th and U on a microscale in heterogeneous samples, especially rocks, using the secondary high-energy neutron flux developed when the 650 MeV proton beam of an accelerator is stopped in a 42 x 42 cm diam Cu cylinder. Irradiations were performed at three different locations in a rabbit tube in the beam stop area, and thick metal foils of Bi, Th, and natural U as well as polished silicate glasses of known U and Th contents were used as targets and were placed in contact with mica which served as a fission track detector. In many cases both bare and Cd-covered detectors were exposed. The exposed mica samples were etched in 48% HF and the fission tracks counted by conventional transmitted light microscopy. Relative fission cross sections are examined, along with absolute Th track production rates, interaction tracks, and a comparison of measured and calculated fission rates. The practicality of fast neutron radiography revealed by experiments to data is discussed primarily for Th/U measurements, and mixtures of other fissionable nuclei are briefly considered.

  18. Fission product revaporization

    One of the major developmental advances in severe accident analysis since the Reactor Safety Study relates to the accounting for radionuclide retention in the reactor coolant system (RCS). The retention is predicted to occur as materials released during core heatup and degradation are transported through the RCS to the break (broken pipe, relief valve, etc.). For accidents involving relatively long RCS-transit times (e.g., station blackout in PWRs), the fraction of released material predicted to remain in the RCS can be large. For example, calculations for the Surry station blackout sequence showed retention of approximately 80% of the cesium and iodine species. Factors affecting fission product revaporization are post-vessel-failure thermal hydraulics, heat loss through vessel and pipe walls, and revaporization chemistry. The accident conditions relevant to this issue range from those present immediately after vessel failure to those present after containment failure. The factors that affect fission product revaporization are discussed

  19. Fission meter

    Rowland, Mark S.; Snyderman, Neal J.

    2012-04-10

    A neutron detector system for discriminating fissile material from non-fissile material wherein a digital data acquisition unit collects data at high rate, and in real-time processes large volumes of data directly into information that a first responder can use to discriminate materials. The system comprises counting neutrons from the unknown source and detecting excess grouped neutrons to identify fission in the unknown source.

  20. Fission-track dating using object-based image analysis

    Full text: Geological dating with the help of fission track analysis is based on a time-consuming counting of the spontaneous and induced tracks in the minerals. Fission tracks are damage trails in minerals caused by fast charged particles, released in nuclear fission. In this study the 950;-method is used for fission-track dating. In order to determine the age, spontaneous tracks in the apatite and induced tracks in the muscovite external detector have to be counted. The automatic extraction and identification would not only improve the speed of track counting and eliminate the personal factor. Pixel values alone are not enough to distinguish between tracks and background. Traditional pixel based approaches are therefore inefficient for fission track counting. Image analysis based on objects, which include shape, texture and contextual information is a more promising method. A procedure for automatic object - based classification is used to extract the track objects. Resolving the individual tracks in a multi-track object is based on morphological operations. The individual track objects are skeletonized and the number of individual tracks in the object is counted by processing the skeletons. To give the right fission track age, there has to be a calibration of every single user manually counting the tracks. We calibrate the automatic approach for counting in the same way. Durango apatite standard samples are used to determine the 950;- and Z-calibration factor. The automatic approach is useful for counting tracks in apatite standards and induced tracks in muscovite external detectors where the quality and quantities of the etched tracks is high. Muscovite detectors irradiated against glasses can also be used to determine the thermal neutron fluence, which is necessary to determine an absolute age. These images are of high quality and free of disturbing background irregularities. Here the automatic approach is a practical alternative. However for natural samples

  1. Advanced Space Fission Propulsion Systems

    Houts, Michael G.; Borowski, Stanley K.

    2010-01-01

    Fission has been considered for in-space propulsion since the 1940s. Nuclear Thermal Propulsion (NTP) systems underwent extensive development from 1955-1973, completing 20 full power ground tests and achieving specific impulses nearly twice that of the best chemical propulsion systems. Space fission power systems (which may eventually enable Nuclear Electric Propulsion) have been flown in space by both the United States and the Former Soviet Union. Fission is the most developed and understood of the nuclear propulsion options (e.g. fission, fusion, antimatter, etc.), and fission has enjoyed tremendous terrestrial success for nearly 7 decades. Current space nuclear research and technology efforts are focused on devising and developing first generation systems that are safe, reliable and affordable. For propulsion, the focus is on nuclear thermal rockets that build on technologies and systems developed and tested under the Rover/NERVA and related programs from the Apollo era. NTP Affordability is achieved through use of previously developed fuels and materials, modern analytical techniques and test strategies, and development of a small engine for ground and flight technology demonstration. Initial NTP systems will be capable of achieving an Isp of 900 s at a relatively high thrust-to-weight ratio. The development and use of first generation space fission power and propulsion systems will provide new, game changing capabilities for NASA. In addition, development and use of these systems will provide the foundation for developing extremely advanced power and propulsion systems capable of routinely and affordably accessing any point in the solar system. The energy density of fissile fuel (8 x 10(exp 13) Joules/kg) is more than adequate for enabling extensive exploration and utilization of the solar system. For space fission propulsion systems, the key is converting the virtually unlimited energy of fission into thrust at the desired specific impulse and thrust

  2. Absorption cross section measurements for 252Cf spontaneous fission neutrons (LWBR development program)

    Absolute absorption cross sections have been measured for 232Th and 197Au for 252Cf spontaneous fission neutrons. Irradiations were performed in an exceptionally low mass source-foil arrangement, providing a ''pure'' spectrum with few corrections. Calibration of the activation detector was achieved by irradiating identical foils in the National Bureau of Standards (NBS) Standard Thermal Flux. A simple ratio technique was also used to obtain an independent estimate of the relative 232Th to 197Au integral cross sections, yielding a value in good agreement with that above. This technique was extended to 181Ta, 98Mo, and 63Cu. (5 tables, 3 figures) (U.S.)

  3. The 235U Prompt Fission Neutron Spectrum in the BR1 Reactor at SCK•CEN

    Wagemans, Jan; Malambu, Edouard; Borms, Luc; Fiorito, Luca

    2016-02-01

    The BR1 research reactor at SCK•CEN has a spherical cavity in the graphite above the reactor core. In this cavity an accurately characterised Maxwellian thermal neutron field is present. Different converters can be loaded in the cavity in order to obtain other types of neutron (and gamma) irradiation fields. Inside the so-called MARK III converter a fast 235U(n,f) prompt fission neutron field can be obtained. With the support of MCNP calculations, irradiations in MARK III can be directly related to the pure 235U(n,f) prompt fission neutron spectrum. For this purpose MARK III spectrum averaged cross sections for the most relevant fluence dosimetry reactions have been determined. A calibration factor for absolute measurements has been determined applying activation dosimetry following ISO/IEC 17025 standards.

  4. The 235U Prompt Fission Neutron Spectrum in the BR1 Reactor at SCK•CEN

    Wagemans Jan

    2016-01-01

    Full Text Available The BR1 research reactor at SCK•CEN has a spherical cavity in the graphite above the reactor core. In this cavity an accurately characterised Maxwellian thermal neutron field is present. Different converters can be loaded in the cavity in order to obtain other types of neutron (and gamma irradiation fields. Inside the so-called MARK III converter a fast 235U(n,f prompt fission neutron field can be obtained. With the support of MCNP calculations, irradiations in MARK III can be directly related to the pure 235U(n,f prompt fission neutron spectrum. For this purpose MARK III spectrum averaged cross sections for the most relevant fluence dosimetry reactions have been determined. A calibration factor for absolute measurements has been determined applying activation dosimetry following ISO/IEC 17025 standards.

  5. Excitation-energy dependence of the nuclear fission characteristics

    Baba, H.; Saito, T.; Takahashi, N. [Osaka City Univ. (Japan). Faculty of Science] [and others

    1996-03-01

    It is known that the width parameter of the fragment mass yield distribution follows a beautiful systematics with respect to the excitation energy. According to this systematics, the fission characteristics following the systematics should disappear when the excitation energy Ex goes down to 14 MeV. The present purpose is to elucidate if, where, how and why a transition takes place in the fission characteristics of the asymmetric fission of light actinide elements. Two types of experiments are performed, one is the double-energy measurement of the kinetic energies of complementary fragments in the thermal-neutron fission of {sup 235,233}U and proton-induced fission of {sup 238}U at 13.3- and 15.7-MeV excitations, and the other is the radiochemical study of proton-induced fission and photofission of {sup 238}U at various excitation energies. In conclusion, it has demonstrated that there are two distinctive fission mechanisms in the low-energy fission of light actinide elements and the transition between them takes place around 14-MeV excitation. The characteristics of proton fission and photofission in the energy range lower than the above transition point are the essentially the same as those of thermal-neutron fission and also spontaneous fission. The results of GDR fission indicates the fission in the high-energy side starts from the nuclear collective states, whereas the lower-energy fission is of non-collective nature. It is likely that thermal-neutron fission is rather of the barrier-penetrating type like spontaneous fission than the threshold fission. (S.Y.)

  6. Burn-up physics in a coupled Hammer-Technion/Cinder-2 system and ENDF/B-V aggregate fission product thermal cross section validation

    The new methodology developed in this work has the following purposes: a) to implement a burnup capability into the HAMMER-TECHNION/9/computer code by using the CINDER-2/10/computer code to perform the transmutation analysis for the actinides and fission products; b) to implement a reduced version of the CINDER-2 fission product chain structure to treat explicity nearly 99% of all original CINDER-2 fission product absorption in a typical PWR unit cell; c) to treat the effect of the fission product neutron absorption in an unit cell in a multigroup basis; d) to develop a tentative validation procedure for the ENOF/C-V stable and long-lived fission product nuclear data based on the available experimental data/11-14/. The analysis will be performed by using the reduce chain in the coupled system CINDER-2 to generate the time dependent effective four group cross sections for actinides and fission products and CINDER-2 to perform the complete transmutation analysis with its built-in chain structure. (author)

  7. ABSOLUTE NEUTRINO MASSES

    Schechter, J.; Shahid, M. N.

    2012-01-01

    We discuss the possibility of using experiments timing the propagation of neutrino beams over large distances to help determine the absolute masses of the three neutrinos.......We discuss the possibility of using experiments timing the propagation of neutrino beams over large distances to help determine the absolute masses of the three neutrinos....

  8. Feasibility study of new microscopic fission chambers dedicated for Ads

    In the frame of the MEGAPIE project we propose to measure the neutron flux inside the molten 1 MW Pb-Bi target at PSI (Switzerland). For this purpose a new type of microscopic fission chambers, developed for on-line measurements of the actinide incineration rates in the high neutron fluxes, will be placed in the central rod of the Pb-Bi target to determine both thermal and fast components of the neutron spectra. In addition to the neutron flux measurements in absolute value, both - time and space dependent variations - of it will be monitored on-line with a precision better than 10%. In this work we show that these measurements are feasible. (author)

  9. Electron spectra from decay of fission products

    Dickens, J K

    1982-09-01

    Electron spectra following decay of individual fission products (72 less than or equal to A less than or equal to 162) are obtained from the nuclear data given in the compilation using a listed and documented computer subroutine. Data are given for more than 500 radionuclides created during or after fission. The data include transition energies, absolute intensities, and shape parameters when known. An average beta-ray energy is given for fission products lacking experimental information on transition energies and intensities. For fission products having partial or incomplete decay information, the available data are utilized to provide best estimates of otherwise unknown decay schemes. This compilation is completely referenced and includes data available in the reviewed literature up to January 1982.

  10. Construction of covariance matrix for absolute fission yield data measurement

    The purpose is to provide a tool for experimenters and evaluators to conveniently construct the covariance based on the information of the experiment. The method used is so called as parameter analysis one. The basic method and formula are given in the first section, a practical program is introduced in the second section, and finally, some examples are given in the third section

  11. Exotic fission properties of highly neutron-rich Uranium isotopes

    Satpathy, L.; Patra, S.K.; Choudhury, R. K.

    2007-01-01

    The series of Uranium isotopes with $N=154 \\sim 172$ around the magic number N=162/164 are identified to be thermally fissile. The thermal neutron fission of a typical representative $^{249}$U of this region amenable to synthesis in the radioactive ion beam facilities is considered here. Semiempirical study of fission barrier height and width shows this nucleus to be infinitely stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. Calculation of p...

  12. Fission yield covariance generation and uncertainty propagation through fission pulse decay heat calculation

    Highlights: • Fission yield data and uncertainty comparison between major nuclear data libraries. • Fission yield covariance generation through Bayesian technique. • Study of the effect of fission yield correlations on decay heat calculations. • Covariance information contribute to reduce fission pulse decay heat uncertainty. - Abstract: Fission product yields are fundamental parameters in burnup/activation calculations and the impact of their uncertainties was widely studied in the past. Evaluations of these uncertainties were released, still without covariance data. Therefore, the nuclear community expressed the need of full fission yield covariance matrices to be able to produce inventory calculation results that take into account the complete uncertainty data. State-of-the-art fission yield data and methodologies for fission yield covariance generation were researched in this work. Covariance matrices were generated and compared to the original data stored in the library. Then, we focused on the effect of fission yield covariance information on fission pulse decay heat results for thermal fission of 235U. Calculations were carried out using different libraries and codes (ACAB and ALEPH-2) after introducing the new covariance values. Results were compared with those obtained with the uncertainty data currently provided by the libraries. The uncertainty quantification was performed first with Monte Carlo sampling and then compared with linear perturbation. Indeed, correlations between fission yields strongly affect the uncertainty of decay heat. Eventually, a sensitivity analysis of fission product yields to fission pulse decay heat was performed in order to provide a full set of the most sensitive nuclides for such a calculation

  13. Fission Research at IRMM

    Al-Adili A.; Fabry I.; Borcea R.; Zeynalov S.; Kornilov N.; Hambsch F.-J.; Oberstedt S.

    2010-01-01

    Fission Research at JRC-IRMM has a longstanding tradition. The present paper is discussing recent investigations of fission fragment properties of 238 U(n,f), 234 U(n,f), prompt neutron emission in fission of 252 Cf(SF) as well as the prompt fission neutron spectrum of 235 U(n,f) and is presenting the most important results.

  14. Fission - track age of the Marjalahti Pallasite

    Full text: Investigation of fossil charged-particle tracks in various mineral phases of extraterrestrial samples is a powerful method for research the early stages of the solar system. Over geological time, meteorites crystals have accumulated a record of tracks produced by heavily charged energetic particles from both internal (spontaneous fission of 238U and some other extinct isotopes) and external sources (galactic cosmic rays with Z>20). The fortunate fact that meteorite grains can accumulate latent and very long-lived tracks since soon after the end of nucleosynthesis in the solar nebula enables one to decode their radiation history and to detect any thermal events in the meteorite cosmic history by revealing these tracks through suitable etching procedures. Only a few minerals in meteorites (mainly phosphates) contain small amount of uranium; the fact that 238U undergoes fission with fission-decay constant λf∼8.2x10-17 yr-1 allows one to use this isotope as a chronometer. By measuring the U concentration in the crystals (by reactor irradiation) and the density of the spontaneous-fission tracks it is relatively easy to calculate the 'fission-track age' if 238U is the main source of fission tracks. However the fission-track dating of extraterrestrial samples compared with the terrestrial ones has some peculiar features due to presence of a number of other potential track sources except the spontaneous fission of 238U, such as the spontaneous fission of presently extinct 244Pu, heavy nuclei of cosmic rays and induced fission by cosmic ray primaries. Only tracks from the spontaneous fission of U and Pu are suitable for fission-track dating. The competing effects of these fissioning elements, whose half-lives differ by a factor of ∼50, form a basis for a fission-track chronology for samples older than ∼ 4.0 Gyr. Over small intervals in time (∼ few x108 yr ) the track density from spontaneous fission of 238U is nearly constant. However, the contribution

  15. Subroutines to Simulate Fission Neutrons for Monte Carlo Transport Codes

    Lestone, J P

    2014-01-01

    Fortran subroutines have been written to simulate the production of fission neutrons from the spontaneous fission of 252Cf and 240Pu, and from the thermal neutron induced fission of 239Pu and 235U. The names of these four subroutines are getnv252, getnv240, getnv239, and getnv235, respectively. These subroutines reproduce measured first, second, and third moments of the neutron multiplicity distributions, measured neutron-fission correlation data for the spontaneous fission of 252Cf, and measured neutron-neutron correlation data for both the spontaneous fission of 252Cf and the thermal neutron induced fission of 235U. The codes presented here can be used to study the possible uses of neutron-neutron correlations in the area of transparency measurements and the uses of neutron-neutron correlations in coincidence neutron imaging.

  16. NGS Absolute Gravity Data

    National Oceanic and Atmospheric Administration, Department of Commerce — The NGS Absolute Gravity data (78 stations) was received in July 1993. Principal gravity parameters include Gravity Value, Uncertainty, and Vertical Gradient. The...

  17. Energy Dependence of Plutonium Fission-Product Yields

    A method is developed for interpolating between and/or extrapolating from two pre-neutron-emission first-chance mass-asymmetric fission-product yield curves. Measured 240Pu spontaneous fission and thermal-neutron-induced fission of 239Pu fission-product yields (FPY) are extrapolated to give predictions for the energy dependence of the n + 239Pu FPY for incident neutron energies from 0 to 16 MeV. After the inclusion of corrections associated with mass-symmetric fission, prompt-neutron emission, and multi-chance fission, model calculated FPY are compared to data and the ENDF/B-VII.1 evaluation. The ability of the model to reproduce the energy dependence of the ENDF/B-VII.1 evaluation suggests that plutonium fission mass distributions are not locked in near the fission barrier region, but are instead determined by the temperature and nuclear potential-energy surface at larger deformation.

  18. Energy Dependence of Plutonium Fission-Product Yields

    Lestone, J. P.

    2011-12-01

    A method is developed for interpolating between and/or extrapolating from two pre-neutron-emission first-chance mass-asymmetric fission-product yield curves. Measured 240Pu spontaneous fission and thermal-neutron-induced fission of 239Pu fission-product yields (FPY) are extrapolated to give predictions for the energy dependence of the n + 239Pu FPY for incident neutron energies from 0 to 16 MeV. After the inclusion of corrections associated with mass-symmetric fission, prompt-neutron emission, and multi-chance fission, model calculated FPY are compared to data and the ENDF/B-VII.1 evaluation. The ability of the model to reproduce the energy dependence of the ENDF/B-VII.1 evaluation suggests that plutonium fission mass distributions are not locked in near the fission barrier region, but are instead determined by the temperature and nuclear potential-energy surface at larger deformation.

  19. Absolute Pitch on Music

    Çuhadar, C.Hakan

    2008-01-01

    Musicians are debated people in the academic circles with the claim of they have both various characteristics and different cognitive personalities on the analogy those other people. One of these different characteristics is absolute pitch ability. Absolute pitch (AP) is a cognitive ability which can be characterized as to identify any tones (labeling) at a given pitch without using any external references. According to the different studies which were held in different times, the prevalence ...

  20. Absolute polarimetry at RHIC

    Okada, H.; Alekseev, I.; Bravar, A; Bunce, G.; Dhawan, S.; Eyser, K. O.; Gill, R; Haeberli, W.; Huang, H.; Jinnouchi, O.; Makdisi, Y.; Nakagawa, I.; Nass, A.; Saito, N; Stephenson, E.

    2007-01-01

    Precise and absolute beam polarization measurements are critical for the RHIC spin physics program. Because all experimental spin-dependent results are normalized by beam polarization, the normalization uncertainty contributes directly to final physics uncertainties. We aimed to perform the beam polarization measurement to an accuracy of $\\Delta P_{beam}/P_{beam} < 5%$. The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Target and left-right pairs of silicon strip detector...

  1. Thermal reference neutron flux irradiation facility development

    The development of the nuclear energy imposed the knowledge with high accuracy of the neutron characteristics in the nuclear reactors, both for control and safety and for the calibration of the apparatus working in the neutron fields. In order to standardize the neutron measurements, different nuclear facilities producing reproducible neutron fields were created with different neutron characteristics. The object of our project is to develop the reference thermal neutron irradiation facility at the steady state core of the Romanian TRIGA Reactor. The reference thermal neutron irradiation facility consists in a dry spherical cavity (50 cm diameter) placed into the graphite thermal column of the TRIGA-SSR core. The implementation of the irradiation facility into the under water thermal column has represented an important challenge in point of instrumentation solutions. In this paper the development of experimental devices, the local flux monitoring system and the thermal flux cavity neutron characterization results are presented. The available neutron flux density ranges between 2·1010 and 5·1014 neutrons/m2·s. The main spectral characteristics are the cadmium ratio for 197Au(n,γ) reaction 52.1±3% and neutron spectrum temperature = (37 ± 4) deg C. The neutron flux and spectrum measurements have been performed using foil activation techniques and fission rate measurements by sealed fission chambers, followed by spectrum unfolding procedure. The absolute fission reaction measurements, using calibrated fission chambers, allows the neutron flux density unit transfer from international reference neutron fields. The fission chambers have been calibrated during international intercomparison programs and have been used for measurements in the reference facilities from CEN/SCK Mol. (authors)

  2. Nuclear Fission as a Markov Process

    Starting from the assumption of a random transfer of nucleons between the two sides of a; fissioning nucleus, during the time from saddle point to scission, it is shown that the mass distribution data in low, intermediate and high energy fission can be given a reasonable -explanation based on the ground state properties of nuclei. The theory is extended to explain the shape of the deformation energy mass curves. These relations follow as a direct consequence of the equilibrium conditions that determine the mass distributions while the gap in the ''zig-zag'' curves is essentially due to the proton transfers. The time of fission is shown to be about 500 nucleonic times in thermal fission and this results from the properties of the transition matrix. The theory is also able to explain the small range of the threshold energies of fission, and the formation of a symmetry axis early in the process. (author)

  3. Absolute reaction rate measurement with D-D neutron source in polyethylene spherical shell

    The absolute reaction rate distribution measurements in a polyethylene spherical shell with 38.6 cm outside diameter and 10 cm thickness were performed with D-D neutron source. By combining fission method and activation method, rich-uranium fission chamber, depleted-uranium fission chamber, 237Np fission chamber and 115In activation foils were placed at several positions on the equatorial line of the inner face of the shell, and the absolute reaction rates were obtained. The uncertainty of fission rates is 2.5%-4.3%, while the uncertainty of activation rates is about 6.3%. The reaction rates were calculated by MCNP and ENDF/B-VII. 0. The calculated results are lower than the measured results and 238U is typical. (authors)

  4. MCNP6 Fission Multiplicity with FMULT Card

    Wilcox, Trevor [Los Alamos National Laboratory; Fensin, Michael Lorne [Los Alamos National Laboratory; Hendricks, John S. [Los Alamos National Laboratory; James, Michael R. [Los Alamos National Laboratory; McKinney, Gregg W. [Los Alamos National Laboratory

    2012-06-18

    With the merger of MCNPX and MCNP5 into MCNP6, MCNP6 now provides all the capabilities of both codes allowing the user to access all the fission multiplicity data sets. Detailed in this paper is: (1) the new FMULT card capabilities for accessing these different data sets; (2) benchmark calculations, as compared to experiment, detailing the results of selecting these separate data sets for thermal neutron induced fission on U-235.

  5. Fission Cross-Sections of Ta181, Re, Pt, Au197, Pb, Bi, Th, And U235 For Protons With An Energy Of 150-660 MeV

    The measurements were carried out on the synchrocyclotron of the Joint Institute for Nuclear Research, wirha maximum proton energy of 660 MeV. The fission events were recorded by visual observation of the fission-fragment tracks left on glass after treating. The absolute recording efficiency was determined by (he number of U2'35 and Pu239 fissions in a known thermal-neutron flux, and the number of U235 fissions in a neutron fluxfroma Ra-α-Be standard source. The proton flux was determined by measuring the absolute number of β-disintegrations of Na24 occurring in the Al27 (p. 3pn) Na24 reaction (whose cross-section is known with an accuracy of ± 5%), using a scintillation gamma-spectrometer. Samples were irradiated both in an external proton beam and within the chamber of the synchrocyclotron. The fission cross-sections were measured in rhe proton energy range 150-660 MeV. The corrections applied are discussed. The results of the measurements are compared with earlier figures, and the dependence of fissility of the nuclei investigated Dn the parameter Z2/A is determined. (author)

  6. Fission tracks - clock and thermometer for rock formations

    The age of fission tracks and the thermal history are closely related. In addition, fission tracks have different sensitivities on different minerals (apatite, zirconium, titanite), and slight thermal alterations of the minerals can be detected by this method. The technique of fission track dating (Rb/Sr and K/Ar dating) is described and applied to the folding of the Alpine region and the heat-up of the Noerdlinger Ries region as a result of a meteorite impact. Fission track dating is a valuable aid in hydrocarbon prospecting. (DG)

  7. Effect of the impurity on the results of the fission rate measurements and elimination method

    The nuclear fission method is an important method for neutron measurement. The 235U and 239Pu fission chamber can be used to measure the thermal neutron, and 238U, 232Th and 237Np fission chamber are often used to measure fast neutron. Because the materials for the fission chambers are got by the isotope separation or artificial method, they can contain a few other impurity atoms. The experimental measurements show that the measurement results for the fast neutron can be obviously affected by the few impurities which can be fissioned by the thermal neutron. The thermal fission can be corrected by the method of the thermal fission correction. It also can be eliminated by using the fast fission chamber with Cd

  8. Absolute measurement of the 242Pu neutron-capture cross section

    Buckner, M. Q.; Wu, C. Y.; Henderson, R. A.; Bucher, B.; Chyzh, A.; Bredeweg, T. A.; Baramsai, B.; Couture, A.; Jandel, M.; Mosby, S.; O'Donnell, J. M.; Ullmann, J. L.; Dance Collaboration

    2016-04-01

    The absolute neutron-capture cross section of 242Pu was measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. The first direct measurement of the 242Pu(n ,γ ) cross section was made over the incident neutron energy range from thermal to ≈6 keV, and the absolute scale of the (n ,γ ) cross section was set according to the known 239Pu(n ,f ) resonance at En ,R=7.83 eV. This was accomplished by adding a small quantity of 239Pu to the 242Pu sample. The relative scale of the cross section, with a range of four orders of magnitude, was determined for incident neutron energies from thermal to ≈40 keV. Our data, in general, are in agreement with previous measurements and those reported in ENDF/B-VII.1; the 242Pu(n ,γ ) cross section at the En ,R=2.68 eV resonance is within 2.4 % of the evaluated value. However, discrepancies exist at higher energies; our data are ≈30 % lower than the evaluated data at En≈1 keV and are approximately 2 σ away from the previous measurement at En≈20 keV.

  9. Overview of research by the fission group in Trombay

    R K Chourdhury

    2015-08-01

    Nuclear fission studies in Trombay began nearly six decades ago, with the commissioning of the APSARA research reactor. Early experimental work was based on mass, kinetic energy distributions, neutron and X-ray emission in thermal neutron fission of 235U, which were carried out with indigenously developed detectors and electronics instrumentation. With the commissioning of CIRUS reactor and the availability of higher neutron flux, advanced experiments were carried out on ternary fission, pre-scission neutron emission, fragment charge distributions, quarternary fission, etc. In the late eighties, heavy-ion beams from the pelletron-based medium energy heavy-ion accelerator were available, which provided a rich variety of possibilities in nuclear fission studies. Pioneering work on fragment angular distributions, fission time-scales, transfer-induced fission, -ray multiplicities and mass–energy correlations were carried out, providing important information on the dynamics of the fission process. More recently, work on fission fragment -ray spectroscopy has been initiated, to understand the nuclear structure aspects of the neutron-rich fission fragment nuclei. There have also been parallel efforts to carry out theoretical studies in the areas of shell effects, superheavy nuclei, fusion–fission dynamics, fragment angular distributions, etc. to complement the experimental studies. This paper will provide a glimpse of the work carried out by the fission group at Trombay in the above-mentioned topics.

  10. Calibration with Absolute Shrinkage

    Øjelund, Henrik; Madsen, Henrik; Thyregod, Poul

    2001-01-01

    In this paper, penalized regression using the L-1 norm on the estimated parameters is proposed for chemometric je calibration. The algorithm is of the lasso type, introduced by Tibshirani in 1996 as a linear regression method with bound on the absolute length of the parameters, but a modification...

  11. Fission Mass Yield Studies

    Mass yields from fission induced by a span of neutron energies up to 18 MeV have been measured for Th232, U235 and U238 target nuclei. Particular attention has been given to the dependence of symmetric fission yields on energy. To study the effect of angular momentum, fission yields from the U236 compound nucleus formed by alpha-particle irradiations of Th232 were also studied over the same span of excitation energies. A standard set of Pd109, Ag111, Pd112 and Ag113 symmetric fission yields was generally measured for all irradiations. In addition, yields of Eu156, Cs136 and 2.3-d Cd115 were measured for some selected combinations of projectile, energy and target nucleus. Assays for Zr97 and sometimes also Ba139 served as fission monitors. Altogether 150 fission yields were measured for these combinations of target nucleus, projectile and incident energy. About one-third of these were checked by replicated irradiations. At highest energies for the U236 compound nucleus the symmetric fission yield from alpha-particle-induced fission is about 13% higher than for neutron-induced fission. Dips in symmetric fission yield were observed at the energy onset of third-chance fission for each target and projectile. Some indication of a small central peak in the mass distribution was observed in the yields from U236 compound nucleus fission, but not from the Th233 compound nucleus fission. Detailed mathematical methods have been developed to separate the effects of fissions preceding and following neutron emission. These methods were used to remove the effects of second- and third-chance fissions from the measured symmetric fission yields. These calculated yields for first-chance fission show no dips with energy. The calculations also show that perhaps half the difference between symmetric yields for alpha- particle-induced fission of Th232 and neutron-induced fission of U235 is attributable to angular momentum effects. Both calculated first-chance yields and measured yields

  12. Complex fission phenomena

    Poenaru, D N; Greiner, W

    2005-01-01

    Complex fission phenomena can be studied in a unified way. Very general reflection asymmetrical equilibrium (saddle-point) nuclear shapes, may be obtained by solving an integro-differential equation without being necessary to specify a certain parametrization. The mass asymmetry in cold fission phenomena can be explained as the result of adding a phenomenological shell correction to the liquid drop model deformation energy. Applications to binary, ternary, and quaternary fission are outlined. Predictions of two alpha accompanied fission are experimentally confirmed.

  13. Fission Research at IRMM

    Al-Adili A.

    2010-03-01

    Full Text Available Fission Research at JRC-IRMM has a longstanding tradition. The present paper is discussing recent investigations of fission fragment properties of 238 U(n,f, 234 U(n,f, prompt neutron emission in fission of 252 Cf(SF as well as the prompt fission neutron spectrum of 235 U(n,f and is presenting the most important results.

  14. SOFIA, a Next-Generation Facility for Fission Yields Measurements and Fission Study. First Results and Perspectives

    Audouin, L.; Pellereau, E.; Taieb, J.; Boutoux, G.; Béliera, G.; Chatillon, A.; Ebran, A.; Gorbinet, T.; Laurent, B.; Martin, J.-F.; Tassan-Got, L.; Jurado, B.; Alvarez-Pol, H.; Ayyad, Y.; Benlliure, J.; Caamano, M.; Cortina-Gil, D.; Fernandez-Dominguez, B.; Paradela, C.; Rodriguez-Sanchez, J.-L.; Vargas, J.; Casarejos, E.; Heinz, A.; Kelic-Heil, A.; Kurz, N.; Nociforo, C.; Pietri, S.; Prochazka, A.; Rossi, D.; Schmidt, K.-H.; Simon, H.; Voss, B.; Weick, H.; Winfield, J. S.

    2015-10-01

    Fission fragments play an important role in nuclear reactors evolution and safety. However, fragments yields are poorly known : data are essentially limited to mass yields from thermal neutron-induced fissions on a very few nuclei. SOFIA (Study On FIssion with Aladin) is an innovative experimental program on nuclear fission carried out at the GSI facility, which aims at providing isotopic yields on a broad range of fissioning systems. Relativistic secondary beams of actinides and pre-actinides are selected by the Fragment Separator (FRS) and their fission is triggered by electromagnetic interaction. The resulting excitation energy is comparable to the result of an interaction with a low-energy neutron, thus leading to useful data for reactor simulations. For the first time ever, both fission fragments are completely identified in charge and mass in a new recoil spectrometer, allowing for precise yields measurements. The yield of prompt neutrons can then be deduced, and the fission mechanism can be ascribed, providing new constraints for fission models. During the first experiment, all the technical challenges were matched : we have thus set new experimental standards in the measurements of relativistic heavy ions (time of flight, position, energy loss).This communication presents a first series of results obtained on the fission of 238U; many other fissioning systems have also been measured and are being analyzed presently. A second SOFIA experiment is planned in September 2014, and will be focused on the measurement of the fission of 236U, the analog of 235U+n.

  15. To fission or not to fission

    Pomorski, Krzysztof; Ivanyuk, Fedir A

    2016-01-01

    The fission-fragments mass-yield of 236U is obtained by an approximate solution of the eigenvalue problem of the collective Hamiltonian that describes the dynamics of the fission process whose degrees of freedom are: the fission (elongation), the neck and the mass-asymmetry mode. The macroscopic-microscopic method is used to evaluate the potential energy surface. The macroscopic energy part is calculated using the liquid drop model and the microscopic corrections are obtained using the Woods-Saxon single-particle levels. The four dimensional modified Cassini ovals shape parametrization is used to describe the shape of the fissioning nucleus. The mass tensor is taken within the cranking-type approximation. The final fragment mass distribution is obtained by weighting the adiabatic density distribution in the collective space with the neck-dependent fission probability. The neck degree of freedom is found to play a significant role in determining that final fragment mass distribution.

  16. Conservation of Isospin in Neutron-rich Fission Fragments

    On the occasion of the 75th anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavyion reactions 238U(18O,f) and 208Pb(18O,f) as well as a thermal neutron fission reaction 245Cm(nth,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon

  17. Conservation of Isospin in Neutron-rich Fission Fragments

    Jain, A. K.; Choudhury, D.; Maheshwari, B.

    2014-06-01

    On the occasion of the 75th anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavyion reactions 238U(18O,f) and 208Pb(18O,f) as well as a thermal neutron fission reaction 245Cm(nth,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

  18. Conservation of Isospin in Neutron-Rich Fission Fragments

    Jain, Ashok Kumar; Maheshwari, Bhoomika

    2014-01-01

    On the occasion of the $75^{th}$ anniversary of the fission phenomenon, we present a surprisingly simple result which highlights the important role of isospin and its conservation in neutron rich fission fragments. We have analysed the fission fragment mass distribution from two recent heavy-ion reactions $^{238}$U($^{18}$O,f) and $^{208}$Pb($^{18}$O,f) as well as a thermal neutron fission reaction $^{245}$Cm(n$^{th}$,f). We find that the conservation of the total isospin explains the overall trend in the observed relative yields of fragment masses in each fission pair partition. The isospin values involved are very large making the effect dramatic. The findings open the way for more precise calculations of fission fragment distributions in heavy nuclei and may have far reaching consequences for the drip line nuclei, HI fusion reactions, and calculation of decay heat in the fission phenomenon.

  19. Tectonic and thermal history of the western Serrania del Interior foreland fold and thrust belt and Guarico Basin, north central Venezuela: Implications of new apatite fission track analysis and seismic interpretation

    Perez de Armas, Jaime Gonzalo

    Structural analysis, interpretation of seismic reflection lines, and apatite fission-track analysis in the Western Serrania del Interior fold and thrust belt and in the Guarico basin of north-central Venezuela indicate that the area underwent Mesozoic and Tertiary-to-Recent deformation. Mesozoic deformation, related to the breakup of Pangea, resulted in the formation of the Espino graben in the southernmost portion of the Guarico basin and in the formation of the Proto-Caribbean lithosphere between the diverging North and South American plates. The northern margin of Venezuela became a northward facing passive margin. Minor normal faults formed in the Guarico basin. The most intense deformation took place in the Neogene when the Leeward Antilles volcanic island arc collided obliquely with South America. The inception of the basal foredeep unconformity in the Late Eocene-Early Oligocene marks the formation of a perisutural basin on top of a buried graben system. It is coeval with minor extension and possible reactivation of Cretaceous normal faults in the Guarico basin. It marks the deepening of the foredeep. Cooling ages derived from apatite fission-tracks suggest that the obduction of the fold and thrust belt in the study area occurred in the Late Oligocene through the Middle Miocene. Field data and seismic interpretations suggest also that contractional deformation began during the Neogene, and specifically during the Miocene. The most surprising results of the detrital apatite fission-track study are the ages acquired in the sedimentary rocks of the easternmost part of the study area in the foreland fold and thrust belt. They indicate an Eocene thermal event. This event may be related to the Eocene NW-SE convergence of the North and South American plates that must have caused the Proto-Caribbean lithosphere to be shortened. This event is not related to the collision of the arc with South America, as the arc was far to the west during the Eocene.

  20. The Energies, Angular Distribution and Yields of the Prompt Neutrons from Individual Fragments in the Thermal-Neutron Fission of U233 and U235

    An apparatus for simultaneously recording the velocities of both fission fragments and the velocity of a neutron at any one of four angles to the fragment direction has been used to investigate the neutron-emission properties of individual fragments. Early results for U233 exhibit the saw-tooth variation of v, the neutron yield per fragment, observed in the spontaneous fission of Cf252 The yields in the vicinity of mass 130 are consistent with no neutrons being emitted from these fragments. Unlike the neutron yields, the average neutron kinetic energy is symmetric about the symmetric mass point, being high near this point and low at the most probable mass division. The paradox between very small yields and high apparent nuclear temperatures has been qualitatively explained on the basis of a model that takes account of shell structure in the level densities and assumes that at the time of scission the fragments are cold but in some cases highly deformed, in others nearly spherical. The model is supported by the fact that in fissions with more than the average total excitation energy, the fragments near mass 130 and 80 receive much less than half the increase in energy and the other fragment of the pair much more. The experiment is now being conducted with U235 under considerably improved conditions. The background per channel under the neutron spectrum has been reduced by nearly a factor of three, so that 0.39 of all recorded events in the 10° detector are useful neutron events with a corresponding increase in statistical accuracy. Better time resolution in the fragment system (1.5 ns, full width at half maximum) has allowed the. flight paths to be shortened to 125 and 100 cm (formerly 145-145 cm) with a concomitant higher countings rate. (author)

  1. Study of fission fragment trapping detector used in neutron detection

    To detect the absolute neutron flux in a weak neutron field and restricted space, the fission fragment trapping detector was fabricated and the properties of the detector were studied. In this paper, the detector and shielding chamber used in neutron detection were described and the experimental measurements of the fission rate in specific condition were performed with the detection system and the result has been compared with that obtained by fission chamber. The influence of the shielding chamber on the measured results was analyzed. (authors)

  2. Absolute Neutrino Masses

    Since the recent convincing evidence for massive neutrinos in oscillation experiments, the next task is to determine the absolute masses of neutrinos. A unique pattern of neutrino masses will be hopefully fixed in the future superbeam experiments and neutrino factories. However, the determination of the exact scale is more complicated and depends on the mass of the lightest neutrino ( mμ )min . If ( mμ)min ≥ 0.35 eV, the future tritium β decay experiments ( e.g. KATRIN) will have a chance to establish absolute neutrino masses. For smaller masses, 0.004 eV ≤ (mμ)min ≤ 0.35 eV, if neutrinos are Majorana particles, an additional information can be derived from the neutrinoless double β decay (ββ)0μ of nuclei and again the absolute neutrino masses can be fixed. If, however, (mμ)min ≤ 0.004 eV, none of the present and foreseeable future experiments is known to be able to fix the mass scale. (author)

  3. Technique of absolute efficiency determination for gamma radiation semiconductor detectors

    Simple technique is suggested to determine the absolute efficiency (E) of semiconductor detectors (SCD) which employes low-intensity neutron sources wide spread in scientific laboratories. The technique is based on using radioactive nuclide gamma radiation in decay chains of heavy element fission fragments, uranium-235, for example. Cumulative yields of a number of nulcides following heavy element fission are measured to a high accuracy (1-5%), which permits to . the value E is determined for a wide energy range (from X- ray to some MeV); using a nuclide with a well known decay scheme and measured to a high accuracy cumulative yield 140La, for example, one can calibrate in absolute values comparatively easily obtained plots of the SCD relative efficiency. The technique allows to determine the E value for extended plane (and volumetric) sources of an arbitrary form. Some nuclides, convenient for the determination of E, and their nuclear characteristics are tabulated

  4. Fission neutron statistical emission

    The statistical model approach FINESSE (FIssion NEutronS' Statistical Emission) for the description of fission neutron multiplicities, energy spectra and angular distributions is described. Based on an extended Weisskopf ansatz and on a realistic temperature distribution it provides a fragment mass number dependent description of fission neutron data. Model parameters (optical potential, n/γ competition) were fixed on the basis of the 252Cf(sf) (nuclear data standard). Combined with a phenomenological fission model for predicting relevant fragment data as function of asymmetry. FINESSE can be applied to any fission reaction of actinides in the Th-Cf region without further parameter adjustment. Results are presented for 252Cf(sf) and neutron induced fission of 235U, 239Pu, 232Th. Effects of multiple-chance fission are discussed for 232Th(n,xnf) reacation. (author). 46 refs, 11 figs

  5. Description of Induced Nuclear Fission with Skyrme Energy Functionals: I. Static Potential Energy Surfaces and Fission Fragment Properties

    Schunck, N.; Duke, DJ; Carr, H.; Knoll, A

    2013-01-01

    Eighty years after its experimental discovery, a description of induced nuclear fission based solely on the interactions between neutrons and protons and quantum many-body methods still poses formidable challenges. The goal of this paper is to contribute to the development of a predictive microscopic framework for the accurate calculation of static properties of fission fragments for hot fission and thermal or slow neutrons. To this end, we focus on the Pu239(n,f) reaction and employ nuclear ...

  6. Total kinetic energy release in the fast neutron-induced fission of $^{235}$U

    Yanez, R; King, J; Barrett, J S; Fotiades, N; Lee, H Y

    2016-01-01

    We have measured the total kinetic energy (TKE) release for the $^{235}$U(n,f) reaction for $E_{n}$=2-100 MeV using the 2E method with an array of Si PIN diode detectors. The neutron energies were determined by time of flight measurements using the white spectrum neutron beam at the LANSCE facility. To benchmark the TKE measurement, the TKE release for $^{235}$U(n$_{th}$,f) was also measured using a thermal neutron beam from the Oregon State University TRIGA reactor, giving pre-neutron emission $E^*_{TKE}=170.7\\pm0.4$ MeV in good agreement with known values. Our measurements are thus absolute measurements. The TKE in $^{235}$U(n,f) decreases non-linearly from 169.0 MeV to 161.4 MeV for $E_{n}$=2-90 MeV. Comparison of the data with the multi-modal fission model of Brosa indicates the TKE decrease is a consequence of the growth of symmetric fission and the corresponding decrease of asymmetric fission with increasing neutron energy. The average TKE associated with the Brosa superlong, standard I and standard II ...

  7. Fission product source term research at Oak Ridge National Laboratory

    The purpose of this work is to describe some of the research being performed at ORNL in support of the effort to describe, as realistically as possible, fission product source terms for nuclear reactor accidents. In order to make this presentation manageable, only those studies directly concerned with fission product behavior, as opposed to thermal hydraulics, accident sequence progression, etc., will be discussed

  8. Application of fission track analysis to hydrocarbon exploration

    The temperature range over which fission tracks in apatite show observable annealing effects coincides with that responsible for the maximum generation of liquid hydrocarbons. Work is currently in progress in a number of Australian and overseas sedimentary basins, applying Apatite Fission Track Analysis (AFTA) to investigate the thermal evolution of these hydrocarbon prospective regions

  9. Study of α and triton particles emission in Uranium 235, Uranium 238, Plutonium 239 fast neutron fission

    Fast neutrons up to 2.5 MeV have been used to induce light particle accompanied fission in 235U, 238U and 239Pu targets. The energy spectra and relative intensities of 3H and 4He have been measured with a ΔE-E telescope. Absolute particle yields were derived from the number of 4He particle per 1000 binary fissions of 235U and 239Pu induced by thermal neutrons measured under the same geometrical conditions. We observe that all the energy distributions are well reproduced by gaussian lineshape, the mean energies of which remain constant while varying the neutron incident energy. (For all nuclei, the 4He mean energies lie close to 16 MeV and the corresponding energies for 3H particle at about 8-9 MeV). The production rates of 3H and 4He show a decrease of about 30% between thermal energy and En = 2 MeV with a small maximum at En = 1 MeV. Conversely the 3H and 4He particle yields obtained in fast neutron fission of 239U remain constant between En = 1.5 MeV and En = 2.5 MeV. Some possible explanation for these observations are briefly and qualitatively explored

  10. Tectonic interpretation of an inverse gradient of zircon fission-track ages with respect to altitude: Alpine thermal history of the Gran Paradiso basement

    Extensive sampling along vertical and north-south cross-sections in the Gran Paradiso basement (internal crystalline massif, Western Alps) reveals an inverse gradient of zircon fission-track ages with respect to altitude, which is explained by an ''inverted metamorphism'' during Eocene time. Subsequent to the obduction of the Schistes Lustres nappe (high pressure Eoalpine phase), the Gran Paradiso massif cooled down 90-80 Myrs ago. The Austro-Alpine nappe of Monte Emilius - Dent Blanche overthrust the Gran Paradiso massif 38-40 Myrs ago, inducing in its basement an inverted metamorphism or, more precisely, a ''nappe emplacement metamorphism'' (greenschist facies). The last cooling below 1000C occurred as early as 35-40 Myrs ago in the southern Gran Paradiso massif; in the northern part, this last cooling occurred 20 Myrs ago, accompanied by an important uplift phase (2 mm/year). (orig.)