摘要:

Electron-photon cascade calculations and photoneutron-production calculations have been carried out for 150-MeV electrons on thick targets of Be and Ta. In the energy region of the giant resonance an evaporation model was used to calculate the production spectrum, and at higher energies (⪞25 MeV) an intranuclear-cascade model was used. The calculated photoneutron-production spectra cover the energy range 0.01 to∼100 MeV and are given for target thicknesses of 1 and 20 radiation lengths in both Ta and Be. A method is described and sufficient information is given so that estimates of the photoneutron-production spectra in targets of intermediate thicknesses may be obtained. Results on the photoproton-production spectra are also given.The spectra from the Ta and Be targets are compared and are found to have very different characteristics in that the number of low-energy (<1 MeV) neutrons produced in the Ta target is much greater than that produced in the Be target and the number of high-energy (⪞a few MeV) neutrons produced in the Be target is larger than that produced in the Ta target.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20187

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

The fission cross-section ratios239Pu:235U,233U:235U have been measured as a function of neutron energy between 5 keV and 1 MeV with an accuracy between 1.5 and 3%. Fission events were detected in 4π-geometry by means of argon-filled gas scintillation chambers. The neutron energy has been determined by the time-of-flight technique.The results were compared with the evaluations of Davey. For the ratio239Pu:235U there is fairly good agreement between the measured values and the evaluation of Davey, except in the energy region between 200 and 800 keV. There, our values are∼2 to 4% lower than those of Davey. The233U:235U ratio agrees with Davey's curve for neutron energies<60 keV. Above this energy, our results are∼5% higher than the evaluated curve of Davey.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20188

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

The ratiosσγ(238U)/σf/(235U),σγ(238U)/σf(239Pu), andσf(239Pu)/σf(235U) have been measured in the energy range 130 to 1400 keV. The activation technique was used to determine the capture rate in238U. The 278 keVγray emitted in the decay of239Np was detected by means of a Ge(Li) detector. The counting efficiencies have been absolutely determined for the measurement ofσγ(238U)/σf(239Pu). For the determination of the ratioσγ(238U)/σf(235U) the counting efficiencies have been eliminated by a measurement of the ratio at thermal-neutron energies. The ratioσf(239Pu)/σf(235U) has been measured in a back-to-back gas scintillation counter using the time-of-flight method for background suppression. The measurements resulted in an overdetermination of two unknown quantities by three measured values. The fitted values derived from the collective results were in good agreement with the individual measured ratios.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20189

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

The total neutron cross section of242Pu has been measured from 0.0015 to 8000 eV, using PuO2powder samples in the Materials Testing Reactor (MTR) fast chopper. The data give 26.9±2.0 and 18.5±2.0 b for the 0.0253 eV total and absorption cross sections, respectively. It was necessary to correct the total cross-section data for water contamination and for the effect of scattering by small particles. To determine the proper forms for these corrections, low-energy total cross-section measurements were made using samples of Al2O3and ThO2. Analysis of resonances below 180 eV gives a resonance absorption integral of 1110±60 b, and a neutrons-wave strength functionof (0.99±0.44)×10−4. (A weighted average of data available on this isotope gives 1175±70 b for the resonance absorption integral and 19.7±1.0 b for the neutron absorption cross section at 0.0253 eV).

ISSN:0029-5639    

DOI:10.13182/NSE70-A20190

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

Measurements of neutron elastic and inelastic scattering from56Fe have been analyzed theoretically. The shape-elastic-scattering cross sections, calculated with an optical-model potential using energy-independent parameters, added to the compound-elastic contribution obtained from a Hauser-Feshbach calculation, including width fluctuation corrections, agree reasonably well with the data from 4 to 7.6 MeV. Inelastic-scattering cross sections from the Hauser-Feshbach calculation agree well with the data from 1 to 7.6 MeV. From the known branching ratios for the decay of the levels of56Fe, calculated gamma-ray-production cross sections are in reasonable agreement with the data. It is suggested that such calculations form the basis for consistent sets of (n, n′) and (n, n′γ) cross sections for shielding calculations.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20191

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

Critical parameters are reported for uranium-solution systems consisting of equally spaced vertical cylinders arranged in a square array resting on the bottom of a 20.3-cm-high square slab tank. Some of these systems were reflected externally. Both the cylinders and the slab contained uranyl-nitrate solution having 490 g of uranium (93.2 wt%235U)/liter.A system of an 87-cm-high array of sixteen 11.0-cm-diam cylinders on an 11.4-cm-thick solution slab was critical. The slab alone was critical at 12.8 cm. Another critical system was a single 22.4-cm-diam cylinder of effectively infinite height on a solution slab 10.8-cm thick. The 22.4-cm diameter is 93.7% of the critical diameter for an infinite cylinder.Monte Carlo calculations, simulating several typical experimental critical systems, yielded values forkeffbetween 0.958±0.012 and 0.986±0.009.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20192

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

An integral transport method was developed and applied to the calculation of the central reactivity worths of various samples measured in a 2700-liter uranium-carbide fast core and in a 4000-liter UO2fast core. The method was used to obtain corrections to multigroup first-order perturbation calculations, incorporating self-shielding effects inside and outside the sample, as well as scattering, fission, and edge-effect perturbations. Resonance interaction between a238U sample and the238U in the core as well as resonance self-shielding in the sample itself were explicitly considered. A similar treatment was used for235U samples. ENDF/B data were used in all of the analyses.The calculated central worths of10B and tantalum were in very good agreement with the measured values, indicating that the calculated value ofβeffused to convert percentΔk/kto period measurements was reasonably accurate. The calculated worths of235U were 5 to 10% greater than the measured values. The discrepancy between the calculated and measured values for238U was 15 to 20%. The discrepancy for graphite in particular and scatterers in general was rather large, indicating that the distribution of the adjoint function is not adequately calculated.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20193

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

The relationis proposed as an approximate solution to the asymptotic slowing down equations in an infinite, homogenous, and weakly absorbing mixture of elements, in the energy range of fast-reactor neutrons.q(E) is the slowing down density;ais the absorption ratioΣa/Σt/;sλ(E) andQλare, respectively, the scattering ratioΣs,λ/Σtand the excitation energy of theλ'th level;ξis equal to the average logarithmic energy loss per elastic scattering with the element containing theλ'th level; the sum extends over all elastic (Qλ= 0) and inelastic (Qλ>0) levels.The above relation is constructed to reduce to the approximate solutions both in the limit of purely elastic scattering and in the limit of inelastic scattering by infinitely heavy scatterers. The relation is shown to be an approximate solution also in intermediate cases, where both target recoil and level excitation are important, provided that the mixture contains a substantial amount of medium-mass or light scatterers. Higher order terms may be included in the relation to better account for the effects of absorption.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20194

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

A Monte Carlo method for the analysis of the Doppler effect has been developed which employs special perturbation techniques to compute effects due to changes in both the temperature and the diameter of fuel rods. These techniques facilitate the application of Monte Carlo to this type of problem and make possible the elimination of approximations inherent in earlier analytic and numerical methods.Numerical results obtained by this method are in good agreement with previously reported measurements on ZPR-III.The method has been applied to the study of the effect of fuel diameter on the Doppler coefficient in a typical fast reactor. Reducing the fuel diameter in a sodium-cooled uranium-carbide reactor from 0.30 to 0.15 cm was found to increase the Doppler coefficient 13%.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20195

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

Space-time nuclear reactor kinetic calculations based on the well-known computer program WIGLE are compared with measurements from neutron-pulse-propagation experiments. Transients were induced in a heavy-water-moderated, natural uranium subcritical assembly using a coupling extending through a graphite thermal column to a pulsed TRIGA reactor. Results are reported for fivekeffvalues ranging from 0 to 0.92, involving cases both with and without cadmium control rods inserted. A unit-cell-homogenization technique was adopted for analysis purposes, with special attention being given to proper parameter assignment, such as neutron velocity averaging. Calculation results compare favorably with experimental results for the interior of the assembly; however, differences as large as 7% are noted near interfaces or boundaries.

ISSN:0029-5639    

DOI:10.13182/NSE70-A20196

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor