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Absolute calibration of TFTR neutron detectors for D-T plasma operation

Description: The two most sensitive TFTR fission-chamber detectors were absolutely calibrated in situ by a D-T neutron generator ({approximately}5 {times} 10{sup 7} n/s) rotated once around the torus in each direction, with data taken at about 45 positions. The combined uncertainty for determining fusion neutron rates, including the uncertainty in the total neutron generator output ({plus_minus}9%), counting statistics, the effect of coil coolant, detector stability, cross-calibration to the current mode or log Campbell mode and to other fission chambers, and plasma position variation, is about {plus_minus}13%. The NE-451 (ZnS) scintillators and {sup 4}He proportional counters that view the plasma in up to 10 collimated sightlines were calibrated by scanning. the neutron generator radially and toroidally in the horizontal midplane across the flight tubes of 7 cm diameter. Spatial integration of the detector responses using the calibrated signal per unit chord-integrated neutron emission gives the global neutron source strength with an overall uncertainty of {plus_minus}14% for the scintillators and {plus_minus}15% for the {sup 4}He counters.
Date: March 1, 1995
Creator: Jassby, D.L.; Johnson, L.C.; Roquemore, A.L.; Strachan, J.D.; Johnson, D.W.; Medley, S.S. et al.
Partner: UNT Libraries Government Documents Department

Theory of neutron emission in fission

Description: A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and some examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated in detail for the Los Alamos model. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of the ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. This paper is an extension of a similar paper presented at the International Centre for Theoretical Physics in 1996.
Date: August 1998
Creator: Madland, D. G.
Partner: UNT Libraries Government Documents Department

Statistics to Identify and quantify Pure Radionuclides by Their Neutron Emission Patterns

Description: Perfect knowledge of emission time for every neutron from a radionuclide allows identification of the material and estimation of the quantity present via nondestructive assay. In practice, the authors lack this perfect knowledge. Detector efficiency is less than unity, thermalized neutron arrival is delayed randomly, and neutron showers triggered by cosmic rays in the atmosphere add noise to the process. They compare two classes of statistical estimators capable of recovering characteristic parameters for radionuclides from this imperfect information: method of moments (the current standard) and maximum likelihood, which holds the advantage as the number of parameters to be estimated simultaneously increases.
Date: July 27, 1999
Creator: Kiffe, J. & Rock, J.C.
Partner: UNT Libraries Government Documents Department

Post-scission fission theory: Neutron emission in fission

Description: A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N (E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N (E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N (E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches.
Date: November 1, 1997
Creator: Madland, D. G.
Partner: UNT Libraries Government Documents Department

Measured Delayed Neutron Spectra from the Fission of U-235 and Np-237

Description: Texas A&M University, in collaboration with Oak Ridge National Laboratory / the Japan Atomic Energy Research Institute, have been actively studying the delayed neutron emission characteristics of the higher actinide isotopes for several years. 1-3 Recently, a proton recoil detector system was designed, built, and characterized for use in measuring delayed neutron energy spectra following neutron induced fission. The system has been used to measure aggregate delayed neutron energy spectra from neutron induced fission of U-235 and Np-237. These spectra have also been compared to that calculated using individual precursor P, values, yields, and spectra from the ENDF/B-VI file. A proton recoil detector array consisting of three LND Model 28305 high- -pressure proton recoil detectors has been constructed at the Texas A&M University Nuclear Science Center. The array was characterized using several neutron and gamma- ray sources to check for efficiency, gamma-ray response, and reliability of the unfolding techniques. Resultant measured proton recoil distributions were unfolded using a modified version of the spectrum unfolding code PSNS (the new code was renamed SAC). SAC used response functions calculated using MCNP 4A. This feature allowed the inclusion of several inches of lead between the detector and the source to decrease the detector's sensitivity to gamma-rays, while appropriately accounting for the effect on the transmitted neutron spectrum. Following proper calibration of the array, highly-purified sources of U-235 were irradiated in the Nuclear Science Center Reactor (NSCR) at a power of 1 MW for 200
Date: November 15, 1998
Creator: Charlton, W.S.; Comfort, C.; Parish, T.A. & Raman, S.
Partner: UNT Libraries Government Documents Department

Neutron Emission Characteristics of a High-Current Plasma Focus: Initial Studies

Description: The Texas A and M University plasma focus machine is operational and is beginning to provide good experimental data. It has its origins in several earlier machines and is located in a former service station building with a shield wall that provides a good geometry for neutron measurements. We are operating in the high pressure mode for a plasma focus, similar to previous efforts in the US. Early neutron measurements are providing some insight for the machine's operation.
Date: June 1, 2002
Creator: Ziegler, L. H.; Freeman, B. L. & Boydston, J. C.
Partner: UNT Libraries Government Documents Department

Hiroshima Air-Over-Ground Analysis: Comparison of DORT and MCNP Calculations

Description: Monte Carlo (MCNP4B) and Discrete Ordinates (DORT) calculations were carried out to estimate {sup 60}Co and {sup 152}Eu activation as a function of ground range due to neutrons emitted from the Hiroshima A-bomb. Results of ORNL DORT and MCNP calculations using RZ cylindrical air-over-ground models are compared with LANL MCNP results obtained with an XYZ air-over-ground model. All of the calculations were carried out using ENDF/B-VI cross-section data and detailed angle and energy resolved neutron emission spectra from the weapon. Favorable agreement was achieved for the {sup 60}Co and {sup 152}Eu activation for ground ranges out to 1000m from the three calculations.
Date: September 4, 2001
Creator: Santoro, RT
Partner: UNT Libraries Government Documents Department

Evaluating Fission Neutron-Multiplicity Data

Description: The present work had its origins in the practical need to obtain P{sub {nu}} for the purpose of calculating the theoretical response of instrumentation that used a correlation technique to assay spontaneously fissioning nuclides. The assay results are proportional to the factorial moments calculated with the P{sub {nu}} distribution. Obtaining experimentally derived sets of P{sub {nu}} from many sources reported over several decades led immediately to the problem of evaluating the data: Aside from the trivial problem of sometimes not being properly normalized, the first moments ({nu}) = ({nu}) = {Sigma}{nu}P{sub {nu}} were typically not in accord with the best recent evaluations, or the calibration of detector efficiency was based on obsolete values for ({nu}) for supposedly well-characterized ``standard`` nuclides such as {sup 252}Cf. The problem of evaluating P{sub {nu}} is unusual in that, compared to the usual situation where the quantities being evaluated are single numbers, the P{sub {nu}} are sets of numbers, that moreover, are constrained so that {Sigma}P{sub {nu}}{triple_bond} 1 and {Sigma}{nu} P{sub {nu}} = ({nu}), where ({nu}) is usually determined more accurately from a separate experiment than it can be calculated from the experimentally derived P{sub {nu}} distribution.
Date: 1992~
Creator: Zucker, M. S. & Holden, N. E.
Partner: UNT Libraries Government Documents Department

Analysis of (n,2n) cross-section measurements for nuclei up to mass 238

Description: All suitable measurements of the energy dependence of (n,2n) cross sections of all isotopes up to mass 238 have been analyzed. The objectives were to display the quality of the measured data for each isotope and to examine the systematic dependence of the (n,2n) cross section upon N, Z, and A. Graphs and tables are presented of the ratio of the asymptotic (n,2n) and nonelastic cross section to the neutron-asymmetry parameter (N--Z)/A. Similar data are presented for the derived nuclear temperature, T, and level-density parameter, $alpha$, as a function of N, Z, and A. This analysis of the results of over 145 experiments on 61 isotopes is essentially a complete review of the current status of (n,2n) cross-section measurements. (auth)
Date: June 1, 1975
Creator: Davey, W.G.; Goin, R.W. & Ross, J.R.
Partner: UNT Libraries Government Documents Department

Bulk Properties of Iron Isotopes

Description: Nuclear level densities and radiative strength functions (RSF) in {sup 56}Fe and {sup 57}Fe were measured using the {sup 57}Fe({sup 3}He,{alpha}{gamma}) and {sup 57}Fe({sup 3}He, {sup 3}He{prime}{gamma}) reactions, respectively, at Oslo Cyclotron Laboratory. A low-energy enhancement in the RSF below 4 MeV energy was observed. This finding cannot be explained by common theoretical models. In a second experiment, two-step cascade intensities with soft primary transitions from the {sup 56}Fe(n,2{gamma}) reaction were measured. The agreement between the two experiments confirms the low-energy enhancement in the RSF. In a third experiment, the neutron evaporation spectrum from the {sup 55}Mn(dn,N){sup 56}Fe reaction was measured at 7-MeV deuteron energy at John Edwards Accelerator Laboratory at Ohio University. Comparison of the level density of {sup 56}Fe obtained from the first and third experiments gives an overall good agreement. Furthermore, observed enhancement for soft {gamma} rays is supported by the last experiment.
Date: July 27, 2006
Creator: Algin, E; Schiller, A; Voinov, A; Agvannluvsan, U; Belgya, T; Bernstein, L et al.
Partner: UNT Libraries Government Documents Department

Beta-decay half-lives and beta-delayed neutron emisison probabilities of nuclei in the region A. 110, relevant for the r-process

Description: Measurements of the {beta}-decay properties of A {approx}< 110 r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory, at Michigan State University. {beta}-decay half-lives for {sup 105}Y, {sup 106,107}Zr and {sup 108,111}Mo, along with ,B-delayed neutron emission probabilities of 104Y, 109,11OMo and upper limits for 105Y, 103-107Zr and 108,111 Mo have been measured for the first time. Studies on the basis of the quasi-random phase approximation are used to analyze the ground-state deformation of these nuclei.
Date: January 1, 2009
Creator: Moller, Peter; Pereira, J; Hennrich, S; Aprahamian, A; Arndt, O; Becerril, A et al.
Partner: UNT Libraries Government Documents Department

Study of the characteristics of high-energy proton-induced gamma ray and neutron emission from materials that imitate surface of planets.

Description: A proposed ISTC Project is discussed in the present paper. The proposal is aimed at experiments to determine the space-energy characteristics of the neutron and gamma ray emission fields generated by 0.2-0.8 GeV proton irradiation of thick targets composed of various elements. At present, reliable data on physical properties of secondary radiation from materials irradiated by intennediate- and high-energy protons for some fundamental and applied researches in astrophysics, space physics, atomic and nuclear physics, as well as for designing and operating the latest accelerators are lacking.
Date: January 1, 2003
Creator: Titarenko, Y. E. (Yury E.); Batyaev, V. F. (Vyacheslav F.); Karpikhin, E. I. (Evgeny I.); Zhivun, V. M. (Valery M.); Koldobsky, A. B. (Aleksander B.); Mulambetov, R. D. (Ruslan D.) et al.
Partner: UNT Libraries Government Documents Department

Cross-calibration of neutron detectors for deuterium-tritium operation in TFTR

Description: During the initial deuterium-tritium experiments on TFTR, neutron emission was measured with {sup 235}U and {sup 238}U fission chambers, silicon surface barrier diodes, spatially collimated {sup 4}He proportional counters and ZnS scintillators, and a variety of elemental activation foils. The activation foils, {sup 4}He counters and silicon diodes can discriminate between 14 MeV and 2.5 MeV neutrons. The other detectors respond to both DD and DT neutrons but are more sensitive to the latter. The proportional counters, scintillators, and some of the fission chambers were calibrated absolutely, using a 14-MeV neutron generator positioned at numerous locations inside the TFTR vacuum vessel. Although the directly calibrated systems were saturated during the highest power deuterium-tritium operation, they allowed cross-calibration of less sensitive fission chambers and silicon diodes. The estimated absolute accuracy of the uncertainty-weighted mean of these cross-calibrations, combined with an independent calibration derived from activation foil determinations of total neutron yield, is {plus_minus}7%.
Date: March 1, 1995
Creator: Johnson, L.C.; Jassby, D.L.; Roquemore, A.L.; Strachan, J.D.; Barnes, C.W.; Duong, H.H. et al.
Partner: UNT Libraries Government Documents Department

MAGO-3 results of the experiment. Final report

Description: In this report the results of joint LANL-VNIIEF experiment MAGO-3 are given. The experiment was aimed to investigate the of magnetized plasma parameters when it overflows trough Laval nozzel. The details of the experiment are described, data obtained by VNIIEF experts are given.
Date: December 31, 1996
Creator: Garanin, S.F.; Mokhov, V.N.; Volkov, G.I. & Ivanov, V.A.
Partner: UNT Libraries Government Documents Department


Description: All the bodies of the solar system that are directly irradiated by the galactic cosmic rays, emit enough neutrons to allow a measurement from space. These leakage neutron fluxes are indexes of the surface composition, depending on the energy of the neutrons [1]. Recent work propose geochemical interpretations of these fluxes: the thermal energy range is sensitive to iron, titanium, rare earth elements and thorium [2, 3], the epithermal energy range is sensitive to hydrogen, samarium and gadolinium [2] and the fast energy range is representative of the average soil atomic mass [4]. Nevertheless these studies make the hypothesis of a composition uniform within the footprint of the spectrometer and independent of depth. We show in this abstract that a stratified composition could change significantly the flux intensity and complicate the interpretation of the measurements. The neutron leakage flux is a competition between production effects (sensitive at high energy) and diffusion-capture effects (mostly sensitive at low energy). On one hand, it happens to be that the elements which produce the higher number of neutrons in typical lunar compositions are iron and titanium, which have also large cross section of absorption with the neutrons. On the other hand, the maximum of neutron intensity does not occur at the surface but at about 180 g cm{sup {minus}2} in depth. Therefore, if we have an iron- and/or titanium-rich soil (important production of neutrons) with a top layer having less iron and/or titanium (i.e. more transparent to the neutrons), we can expect an enhancement of the flux compared to a uniform composition.
Date: January 1, 2001
Creator: GASNAULT, O. & AL, ET
Partner: UNT Libraries Government Documents Department

Neutronics studies for a long-wavelength target station at SNS.

Description: The Spallation Neutron Source (SNS), under construction at Oak Ridge National Laboratory, will be the premier facility for neutron scattering studies in the United States. From the outset the SNS can achieve additional flexibility and accommodate a broader range of scientific investigation than would be possible with only the High Power Target Station by utilizing two target stations, each operating under a separate set of conditions and optimized for a certain class of instruments. A second target station, termed the Long-Wavelength Target Station (LWTS), would operate at a lower pulse rate (e.g., 10 vs. 60 Hz) and utilize very cold moderators to emphasize low-energy (long wavelength) neutrons. The LWTS concept discussed here obtains the highest low-energy fluxes possible for neutron scattering instruments by using a heavy-water-cooled solid tungsten target with two moderators in slab geometry and one in a front wing position. The primary focus has been on solid methane moderators, with liquid methane and hydrogen also considered. We used MCNPX to conduct a series of optimization and sensitivity studies to help determine the optimal neutronic parameters of the LWTS. We compared different options based on the thermal and epithermal fluxes as determined by fitting the spectral intensity of the moderators with a Maxwellian peak and a modified Westcott function. The primary parameters are the moderator positions and composition and the target size. We report results for spectral intensity, pulse shapes, high-energy neutron emission, heating profiles in the target, and target activation.
Date: September 21, 2001
Creator: Micklich, B. J.; Iverson, E. B. & Carpenter, J. M.
Partner: UNT Libraries Government Documents Department

Measurements of delayed neutron emission from Np-237, Am-241, and Am-243

Description: Isotopes of transuranic elements are produced as a result of successive radiative capture reactions in the fuel of a nuclear reactor. Typically, these transuranic isotopes decay through long chains, have long half lives and dominate the long term toxicity of the spent reactor fuel. One of the options for waste management is to remove the transuranic from spent fuel by chemical processing, to load them into new special fuel elements, and to transmute them by neutron induced fission into shorter-lived fission fragments. Previous studies have shown the feasibility of actinide transmutation in either Light Water Reactors or Liquid Metal Fast Reactors. Due to the anticipated high transuranic loadings in the fuel of actinide burner reactors, the neutronic properties of the transuranic isotopes will have a significant effect on the operational and safety characteristics of such reactors. Experiments to determine delayed neutron group yields and decay constants for Np-237, Am-241, and Am-243 have been designed and carried out. The experiments were conducted at Texas A&M University TRIGA reactor using a very fast pneumatic transfer system.
Date: December 1995
Creator: Saleh, H. H.; Parish, T. A. & Raman, S.
Partner: UNT Libraries Government Documents Department

Studies of global energy confinement in TFTR supershots

Description: The global energy confinement time, {tau}{sub E}, from TFTR supershot plasmas has been correlated with the hydrogen recycling and the pressure anisotropy. An expression for the global confinement was obtained that describes its value at the time of peak neutron emission for all TFTR supershots obtained in the 1990 campaign, and simultaneously describes the time evolution of {tau}{sub E} for an extensive subset of the 1990 data. The obtained expression is probably not unique and it can be written with different variables. An analysis of the energy balance for many of these supershots indicates that the primary effect of larger {tau}{sub E} is that the central particle diffusivity is lower.
Date: August 1, 1993
Creator: Strachan, J. D.
Partner: UNT Libraries Government Documents Department

Comment on Li pellet Conditioning in TFTR

Description: Li pellet conditioning in TFTR results in a reduction of the edge electron density which allows increased neutral beam penetration, central heating, and fueling. Consequently the temperature profiles became more peaked with higher central Ti, Te, and neutron emission rates.
Date: May 23, 2011
Creator: Budny, R.V.
Partner: UNT Libraries Government Documents Department

Entrance-channel effects in odd-Z tranactinide compound nucleus reactions

Description: Swiatecki, Siwek-Wilczynska, and Wilczynski's 'Fusion By Diffusion' description [1] of transactinide (TAN) compound nucleus (CN) formation utilizes a three-step model. The first step is the 'sticking', or capture, which can be calculated relatively accurately. The second step is the probability for the formation of a CN by 'diffusion' analogous to that of Brownian motion. Lastly, there exists the probability of the CN 'surviving' deexcitation by neutron emission, which competes with fission and other de-excitation modes. This model predicts and reproduces cross sections typically within a factor of two. Producing the same CN with different projectile-target pairs is a very sensitive way to test entrance channel effects on heavy element production cross sections. If the same CN is produced at or near the same excitation energy the survival portion of the theory is nearly identical for the two reactions. This method can be used as a critical test of the novel 'diffusion' portion of the model. The reactions producing odd-Z TAN CN such as Db, Bh, Mt, and Rg (Z = 105, 107, 109, and 111, respectively) were first studied using even-Z projectiles on {sup 209}Bi targets (as opposed to odd-Z projectiles on {sup 208}Pb targets) because lower effective fissility [2] was expected to lead to larger cross sections. Many odd-Z projectile reactions producing odd-Z CN had not been studied in-depth until very recently. We have completed studies of these reaction pairs with the 88-Inch Cyclotron and the Berkeley Gas-Filled Separator (BGS) at the Lawrence Berkeley National Laboratory (LBNL), see Figure 1. Cross section ratios for several pairs of reactions will be presented and compared with theory.
Date: September 1, 2007
Creator: Nelson, S.L.; Gregorich, K.E.; Dragojevic, I.; Dullmann, Ch.E.; Eichler, R.; Folden III, C.M. et al.
Partner: UNT Libraries Government Documents Department


Description: The Multi-Step Direct (MSD) module TRISTAN in the nuclear reaction code EMPIRE has been extended in order to account for nuclear deformation. The new formalism was tested in calculations of neutron emission spectra emitted from the {sup 232}Th(n,xn) reaction. These calculations include vibration-rotational Coupled Channels (CC) for the inelastic scattering to low-lying collective levels, ''deformed'' MSD with quadrupole deformation for inelastic scattering to the continuum, Multi-Step Compound (MSC) and Hauser-Feshbach with advanced treatment of the fission channel. Prompt fission neutrons were also calculated. The comparison with experimental data shows clear improvement over the ''spherical'' MSD calculations and JEFF-3.1 and JENDL-3.3 evaluations.
Date: April 22, 2007
Creator: WIENKE,H.; CAPOTE, R.; HERMAN, M. & SIN, M.
Partner: UNT Libraries Government Documents Department

Effect of pre-equilibrium spin distribution on neutron induced 150Sm cross sections

Description: Prompt {gamma}-ray production cross section measurements were made as a function of incident neutron energy (En = 1 to 35 MeV) on an enriched (95.6%) {sup 150}Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Above E{sub n} {approx} 8 MeV the pre-equilibrium reaction process dominates the inelastic reaction. The spin distribution transferred in pre-equilibrium neutron-induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). These preequilibrium spin distributions were incorporated into the Hauser-Feshbach statistical reaction code GNASH and the {gamma}-ray production cross sections were calculated and compared with experimental data. Neutron inelastic scattering populates 150Sm excited states either by (1) forming the compound nucleus {sup 151}Sm* and decaying by neutron emission, or (2) by the incoming neutron transferring energy to create a particle-hole pair, and thus initiating the pre-equilibrium process. These two processes produce rather different spin distributions: the momentum transfer via the pre-equilibrium process tends to be smaller than in the compound reaction. This difference in the spin population has a significant impact on the {gamma}-ray de-excitation cascade and therefore in the partial {gamma}-ray cross sections. The difference in the partial {gamma}-ray cross sections using spin distributions with and without preequilibrium effects was significant, e.g., for the 558-keV transition between 8{sup +} and 6{sup +} states the calculated partial {gamma}-ray production cross sections changed by 70% at E{sub n} = 20 MeV with inclusion of the spin distribution of pre-equilibrium process.
Date: April 16, 2007
Creator: Dashdorj, D; Kawano, T; Mitchell, G E; Becker, J A; Agvaanluvsan, U; Chadwick, M et al.
Partner: UNT Libraries Government Documents Department