摘要:

AbstractAn angular biasing procedure is presented for use in Monte Carlo radiation transport with discretized scattering angle data. As in more general studies, the method is shown to reduce statistical weight fluctuations when it is combined with the exponential transformation. This discrete data application has a simple analytic form that is problem independent. The results from a sample problem illustrate the variance reduction and efficiency characteristics of the combined biasing procedures, and a large neutron and gamma-ray integral experiment is also calculated. A proposal is given for the possible code generation of the biasing parameter p and the preferential directionΩ0used in the com-bined biasing schemes.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23530

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractThe method of“antithetic variates”for Monte Carlo sampling was invented and named by Hammersley and Morton in 1956 and has been generalized by Halton and Handscomb, and Laurent. Given only that a Monte Carlo estimator possesses derivatives up to a certain order, in the sample space, transformations of the estimator are supplied (independent of the particular estimator used), which reduce the variance of the resulting estimates in a very marked degree. The explicit forms of these transformations are derived. It is demonstrated that, contrary to common belief, the transformations of Halton and Handscomb are more efficient than those proposed by Laurent.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23531

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractAn improved correction for distortions of the electric field in recoil-proton detectors, applied in neutron energy spectrum measurements, was developed. It utilizes a simple analytical expression for the representation of the response function for the entire interval of the electric charge, thus avoiding the previous separate treatment of the upper 20 to 30% of the charge range. The simplicity of the functional expression for the response function allowed the integral equation of the unfolding problem to be solved analytically. This refined unfolding technique apparently provides a better resolution, as it shows the spectrum deformation due to the large scattering resonances to be more pronounced. This highly accurate analytical unfolding procedure is likely to be applicable in other areas as well.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23532

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractGrooved moderators provide greater neutron leakage currents from their channeled surfaces than flat moderators of the same volume. Operated in conjunction with pulsed sources to provide beams of slow neutrons, their pulse widths depend in a complicated way on the groove parameters, as does the leakage current. A one-speed diffusion theory treatment of the asymmetric grooved moderator is described, the eigenfunctions and eigenvalues are presented, and a simple graphical method for eigenvalue calculation is provided. The leakage from the bottoms of the grooves and from the tips of the fins are separately determined and the lowest order functions for a cold polyethylene moderator are calculated. The results for the lowest order time eigenvalue are in good agreement with a measurement obtained at the Intense Pulsed Neutron Source.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23533

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractA sensitive search for a dependence of composite (aggregate) delayed neutron spectra on the energy of neutrons inducing fission of235U was performed for eight nearly contiguous delay time intervals between 0.17 to 85.5 s. The experimental arrangement combined a helium jet and tape transfer system with a beta-neutron time-of-flight spectrometer. Thermal and fast neutron measurements were performed successively. Results are compared with spectra derived from individual precursor data complemented by theoretical estimates of missing spectra.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23534

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractThe181Ta(n,xγ) reaction has been measured for neutron energies En= 2 to 100 MeV and for gamma-ray energies Eγ= 2 to 25 MeV using an array of bismuth germanate detectors and the pulsed neutron source at the Los Alamos Meson Physics Facility. The integrated photon production cross section reaches a maximum at∼7.5 MeV. Above 20 MeV, the cross section increases slowly with energy. The angular distributions of the photon production cross sections for different neutron energies are isotropic. At all measured neutron energies the gamma-ray spectra have the simple evaporation form.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23535

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractA procedure for the determination of neutron-induced photon production cross sections is described, including corrections for the neutron-induced photon background and the unfolding of the gamma-ray spectra. As an example, data have been obtained for tantalum and beryllium with five bismuth germanate detectors and the high-energy white neutron source at the Los Alamos Meson Physics Facility. Calculations and measurements indicate that a beryllium sample may be used to simulate a neutron-induced photon background. Results for the Ta(n,xγ) reaction for neutron energies below En= 20 MeV are compared with previous measurements at the Oak Ridge Electron Linear Accelerator.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23536

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE88-A23537

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE88-A23538

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor