摘要:

There is current interest in the possibility that symmetric irradiation of a small pellet of fissionable material by intense laser beams may produce sufficient compression to cause the pellet to become supercritical and thus produce a fission microexplosion. It has been proposed that a repetitive series of such explosions in a suitable chamber could be the basis for an alternative means of generating commercial power from nuclear energy. We present an analysis of this scheme that shows that the energetics do not appear favorable for power generation purposes. Although an input of several hundred megajoules of radiation energy is necessary to trigger a microexplosion, the idea appears to be an interesting physics experiment. Such microexplosions would be unique short-duration sources of nuclear radiations.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26790

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

A representation for structured data is described that does not make use of a resonance parameter formalism and is applicable in a region where resonance parameters cannot be resolved or in a resolved resonance region where the precise location of a resonance is unimportant. Following the Probability Table Method, a representation statistically equivalent to a pointwise description of data is given but extended to characterize energy correlations. In the case of data from which higher order derivatives can be taken, a method for temperature broadening and unbroadening data is presented.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26791

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

Absolute absorption cross sections of232Th and197Au for252Cf spontaneous fission neutrons have been measured. 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 Standard Thermal Flux at the National Bureau of Standards. The results obtained were 79.9±2.9 mb for197Au and 87.8±4.0 mb for232Th. The corresponding values calculated from ENDF/B-III data are 84.3 and 99.3 mb, respectively.A simple ratio technique was also used to obtain an independent estimate of the relative232Th to197Au integral cross sections, yielding a value in good agreement with that above. This technique was extended to181Ta,98Mo, and63Cu.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26792

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

The relative energy dependence of the235U fission cross section has been measured with respect to the (n, p) scattering reaction for neutron energies from 0.8 to 4 MeV. The Lawrence Livermore Laboratory Linac provided a pulsed source of neutrons, and energies were measured by neutron time of flight. The flux monitor consisted of a thin annular polyethylene proton radiator with a shielded recoil detector. The total error in the relative235U (n, f) cross section is<1.5% from 0.8 to 4 MeV.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26793

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractEmpirical expressions are given for the excitation functions of a number of (n, n'), (n, p), and (n, f) reactions useful in the dosimetry of fast neutrons. For fission cross sections, the expressions are fitted to existing evaluations while for activation cross sections, they are fitted to recent experimental data. Average cross sections, derived from these expressions, for various fission neutron spectra are compared with measured values.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26794

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

Samples of233U and of natural thorium have been irradiated in high neutron-flux facilities, in both soft and hard neutron spectra, and for both short and long exposure times. Included are exposures resulting in depletions of more than 90% of the233U in the fissile material and burnups of more than 30 000 MWd/MT in the fertile material. Postirradiation mass analyses of the total and the isotopic uranium, of137Cs, and of the neodymium isotopes generally agree within a few percent with corresponding calculations based on measured exposure histories. Reactivity measurements between irradiation cycles provide experimental results for the fissile content and fission-product poisoning as functions of both irradiation and cooling time. Corresponding results obtained from calculated concentrations agree with measurements to∼1% for the fissile content and 3% for the effective one-group fission-product poison cross section. However, fission-product poison cross sections in two energy groups (thermal and epithermal) exhibit differences between measurement and calculation that are believed to be attributable to a lack of adequate information on important fission products in the literature. Experimental results for transient absorbers in irradiated233U give at least 20 000 b for the neutron absorption resonance integral of149Pm. This is a factor of 15 higher than that obtained by a 1/v extrapolation of the thermal cross section. For transient135Xe, the measured absorption is 7.5% higher than that calculated using ENDF/B-IV data. Information is also provided concerning such matters as fission yields and neutron absorption of neodymium isotopes, the existence of significant transient fission-product poisons other than135Xe and149Sm, and the shielding of233U by232Th. Such shielding suggests the need for a change in the energy dependence of the232Th thermal-neutron cross section.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26795

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractThe yields of 27 mass chains in the fission of235U and the ratio of fast-neutron to thermal-neutron fission yields (the“R”value) of 21 mass chains in the fission of239Pu induced by fast neutrons (median energy∼180 keV) have been measured in the reactor PROTEUS. The yields were obtained by a comparison method using gamma-ray spectroscopy. The data show that, in agreement with other authors, yields in the peaks of the mass distribution do not change compared to thermal-neutron-induced fission.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26796

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

Spectra, calculated by Monte Carlo, are presented for neutrons transmitted through various thicknesses of iron from sources of fission neutrons, H2O-moderated fission neutrons, D2O-moderated fission neutrons, and 14.7-MeV neutrons. The sources were located at the center of iron spheres or were in the form of beams incident normally on slabs. Variations in spectral shapes are discussed from the viewpoint of effects on the response of neutron dosimeters.Effective cross sectionsfor threshold detectors103Rh,115In,32S,237Np,232Th, and238U were obtained by averaging the cross sections over the calculated spectra. Average kerma, dose equivalent, and maximum dose per n/cm2were also calculated. Curves ofshow the sensitivity of these detectors to spectral changes and permit the computation of correction factors to dosimeter readings.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26797

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractGamma-ray spectra from the radioactive decay of140Ba and140La were observed by Ge(Li) spectroscopy. Gamma-ray energies were found to be consistent with literature values, but several of the observed gamma rays were found to have intensities differing significantly from those previously reported. Absolute intensities of prominent gamma rays emitted in the radioactive decay of140Ba and140La have been measured. The 12.8-day140Ba activity was produced by 14.8-MeV neutron fission of238U followed by radiochemical separation and purification.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26798

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractA new continuous slowing-down theory developed is applied to the calculations of neutron spectra for elastic moderation in a fast reactor assembly. Our model is shown to yield very accurate results for the neutron spectra in the resolved resonance region of fuel materials and in the wide scattering resonance region, from comparison with the RABBLE calculations. The characteristic features of our slowing-down parameters are also studied for the anisotropic scattering in the center of mass system.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26799

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor