摘要:

AbstractThe mathematical model of age-dependent branching processes is used to describe neutron slowing down and multiplication in an infinite medium. To construct the probability measure of the neutron branching process, it is necessary to determine the probability densityfor a neutron of ageθ(=time elapsed since birth of the fission neutron) to have energyE.This problem, which is equivalent to the time-dependent slowing down problem, is solved for a scattering law of the formv(E)Σs(E→E′)dE′= aEµh(E′/E) (dE′/E) and an absorption cross section satisfying the relationv(E)Σa(E) =bEµ+ c.In this case, it is proved that there always exist particular“invariant”probability densitiessuffering only contraction during ageing, i.e., having the form. For the time-dependent slowing down problem with a Greuling-Goertzel kernel, the results are compared with those of Koppel. Particular attention is paid to stationary energy spectra.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19713

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA detailed experimental study on the kinetics of a238U sphere is described. The measurements involve the use of nanosecond electronics and silicon solid-state detector with two fission conversion foils:235U and237Np. Thus, some information on the time-energy coupling was obtained. The results show a nonexponential behavior over all time ranges. At longer times, the space and time coupling was small. At early times, the coupling between energy space and time was strong. The early time behavior of the high-energy neutrons (above237Np threshold) appears to be exponential. The decay constant, however, is a function of position. It is shown that this exponential behavior is a result of a“pseudo-trapping”of neutrons between the fast fission threshold in237Np and the large step in the inelastic scattering cross section of238U.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19714

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA generalized digital computer approach to analyze the loss-of-coolant accident in pressurized water reactors requires a systematic specification of the plant geometric, physical, and topological characteristics and initial conditions. The solution of the problem is hampered by numerical stability and convergence problems which can be remedied by first classifying the problem variables into three categories: 1) numerically-integrated; 2) analytically-integrated; and 3) auxiliary algebraic variables. Second, in view of the occurrence of the acoustic wave phenomenon, the maximum allowable integration time step should be kept much smaller than the subharmonics present in the solution. Another distinctive feature of this study is the treatment of stratified elements, such as the pressurizer or the steam generator secondary. Allowance for mass exchange between the top and bottom control volumes in these elements is made by the introduction of bubble rise and condensate drop velocity concepts. Furthermore, to eliminate unrealistic pressure fluctuations in the ruptured elements at the onset of two-phase blowdown, critical flow models including inertia effects are introduced. To verify the sensitivity of the solution to various two-phase frictional loss correlations, five well-known correlations are reviewed. A comparison of the analytical results against LOFT experimental data demonstrates a good agreement and shows that a more accurate prediction would require the introduction of metastability analysis.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19715

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA nuclear model pertinent to the generation of certain classes of nuclear data is described. The analysis is structured so as to minimize difficulties in its numerical implementation. The model involves the simultaneous treatment of particle excitations in a deformed potential well, together with rotational and vibrational collective excitations. Details of certain aspects of the theory are presented with comparisons of calculated and measured level structures for several nuclei of interest in shielding technology.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19716

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA new method, utilizing a modulated neutron source operated in antisynchronism with a long counter, has been used to measure the absolute and relative delayed-neutron yields of five fissionable isotopes for neutron-induced fission at 3.1 and 14.9 MeV. The results, in units of delayed neutrons per fission, for 14.9-MeV fission are: The measured ratios of delayed-neutron yields at 3.1-MeV to those at 14.9-MeV fission are: These new delayed-neutron yield data are in accord with qualitative theoretical predictions but are in marked disagreement with earlier measurements.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19717

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractAn experimental method of determining the ratio of the epicadmium238U neutron-capture rate to the subcadmium238U capture rate in a fuel rod, (ρ28), is presented. The precision is∼0.3% on the cadmium ratio. The relative239Np and fission-product activities induced in a representative cross section of the fuel material (a thin bare foil of natural uranium) are compared with those induced in a cadmium-covered identical foil in a“flux symmetric”position in the rod. The239Np gamma activity is counted by a coincidence method with and without the application of chemical separation. The results from the coincidence method are compared with two single-channel and one hundred-channel analyzer results obtained by chemical separation.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19718

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA simplified cascade model for the calculation of neutron-capture gamma-ray spectra is compared with experiment. In the context of the model, the simplifying assumptions involve extrapolations of measured multipole transition probabilities and equal spin-branching probabilities. Calculated and measured neutron capture gamma-ray spectra are compared for 25 elements spanning virtually the entire mass scale. Substantial agreement between calculated and measured spectra is obtained for medium and heavy nuclei. An analytical method for obtaining neutron energy-dependent capture gamma-ray production cross sections is developed. A comparison between calculated and measured fast neutron capture gamma-ray yields in64Cu is presented.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19719

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractThe nonfission (NF) heating and thermal-neutron flux were measured in copper as a function of distance from the core center line of the ORR Reactor at different times of a reactor cycle. Above the core, the NF heating is a linear function of the thermal-neutron fluxφexpressed by Within the core the relation between the measured thermal-neutron flux and the NF heating is influenced by other factors.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19720

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractDose rates of gamma rays from a60Co cylindrical source surrounded coaxially by a cylindrical shield were measured in the radial direction in a plane passing through the midpoint of the axis of the source. The60Co was uniformly distributed in a water-like medium. The shield was composed of water and iron, each in a single layer, and of water and iron in a double layer. The concept of the dose buildup factor for a volume source was introduced and the behavior of gamma rays scattered from the shielded cylindrical source was considered. The variation of the dose buildup factor for the shielded cylindrical source as a function of the distance from the source is less than the variation for the unshielded source. The dose buildup factor for a cylindrical source, with and without shields, shows many features that differ from those generally observed, i.e., an infinite medium surrounding a point source and one obtained from the total gamma-ray dose rates calculated by integration of an attenuation kernel with dose buildup factors for a point isotropic source. The unique behavior of the dose buildup factor for the cylindrical source with a cylindrical shield is shown by supplemental experiments with a60Co point source to be due to the cylindrical shape of the source and shields.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19721

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA semiempirical formula for the gamma-ray albedo of alternating layers is proposed. The values of the albedo calculated by this formula agree with the experimental ones for alternating layers of tin-aluminum and lead-aluminum slabs within∼10%, except for the case of very thin alternating layers. This formula was applied to the angular distribution of photons backscattered by the alternating layers and the difference between experimental and calculated values was<18%.

ISSN:0029-5639    

DOI:10.13182/NSE69-A19722

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor