摘要:

AbstractNeutron-induced reaction cross sections for carbon are measured in the 11.5- to 19-MeV energy range. The response of an NE-213 scintillation detector is measured in steps of at least 0.5 MeV for monoenergetic neutrons, applying suitable time-of-flight techniques, and compared with Monte Carlo simulations. The total cross sections of all reactions with charged particles (except carbon recoil protons) in the exit channel are determined with respect to the n-p scattering cross section. In addition, the12C(n,n′3α) reaction is investigated for neutron energies of 11.9, 12.9, 14.0, 14.8, 17.0, and 19.0 MeV using the nuclear emulsion technique. As it is kinematically complete, this measurement yields the total and partial cross sections for the various channels of the12C(n,n′3α) reaction. The experimental data show deviations of up to±25% from those recommended in ENDF/B-V, while a recent evaluation by Axton is partially confirmed. Reasonable agreement is found with most of the recent scattering experiments; thus, this data set represents a valuable constraint for further evaluations. The analysis performed, however, has shown that additional data for some partial reaction cross sections are needed.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23777

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe sums of the cross sections12C(n,α0)9Be and12C(n,n′3α) are determined in the neutron energy range between 7.4 and 11 MeV. An NE-213 scintillation detector is simultaneously used as a carbon target, an alpha-particle detector, and a neutron fluence monitor. By comparing the measured and calculated response spectra, the neutron-induced alpha-particle events in the scintillation volume are separated and the cross sectionsσn,α0+σn,n′3αare determined relative to the n-p scattering cross section. The pulse-height distribution due to alpha particles allows the angular distribution to be extracted on the basis of the reaction kinematics and an accurately determined light output function for alpha particles in the NE-213 detector.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23778

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA series of experiments was performed in slab geometry using a mixed aqueous Pu-U nitrate with 173 and 262 g/ℓof plutonium and uranium, respectively. Both the thickness of the slab for an∼71-cm fixed height and the height for a 19.05-cm fixed thickness were varied for this slab, which had a 106.7-cm base length. The plutonium contained 91.1 wt%239Pu while the depleted uranium contained 0.57 wt%235U. These measurements using the252Cf-source-driven neutron noise analysis method are interpreted using modified point kinetics to obtain the subcritical neutron multiplication factors. This paper summarizes the data accumulated in the measurements and their interpretation in this first application of the method to slab geometry.The results and conclusions of these experiments are (a) the capability to measure the subcriticality for a multiplying system of slab geometry by the252Cf-source-driven noise method to a k as low as 0.70 was demonstrated; (b) the reactivities obtained by independent measurements using break-frequency noise analysis agreed with those obtained from the ratio of spectral densities within the experimental uncertainties; (c) the criteria developed in previous experiments for choosing source-detector-system configurations for which the data can be interpreted using modified point kinetics were also satisfactory for this experiment; (d) measurement times for this geometry were not significantly different from those used in cylindrical geometry and were sufficiently short to allow practical measurements; (e) the applicability of the method and understanding of the theory of the measurement method for plutonium solution systems were demonstrated; and (f) calculated neutron multiplication factors agreed with those from experiments within∼0.02.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23779

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractVectorization methods used in Monte Carlo codes for particle transport calculations are examined. Event and zone selection methods developed from conventional all-zone and one-zone algorithms have been implemented in a general-purpose vectorized code, GMVP. Moreover, a vectorization procedure to treat multiple-lattice geometry has been developed using these methods. Use of lattice geometry can reduce the computation cost for a typical pressurized water reactor fuel subassembly calculation, especially when the zone selection method is used. Sample calculations for external and fission source problems are used to compare the performances of both methods with the results of conventional scalar codes. Though the speedup resulting from vectorization depends on the problem solved, a factor of 7 to 10 is obtained for practical problems on the FACOM VP-100 computer compared with the conventional scalar code, MORSE-CG.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23780

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractUsing Monte Carlo calculations, it is shown that the transmission of scattered neutrons or gamma rays from a point source through a plane slab of infinite extent to a point detector depends on the orientation of the slab but varies very little with the slab position. This is also true for reflected radiation if the source is replaced by its image source and the results are interpreted in terms of a transmission problem. It is also shown that the transition from a slab of small extent (narrow beam conditions) to a slab of infinite extent (broad beam conditions) can be characterized by a simple function of the single-scatter angle. This function, too, can be applied to reflected radiation by invoking the image source. Typical results are presented for polyethylene and iron.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23781

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractBecause of the demand for intense neutron beams for applications in basic and applied sciences, several design concepts have appeared in the literature recently. It is, therefore, appropriate to present a theory that connects the large variety of possible designs in order to individualize the main parameters from the neutronic point of view; the theory is validated with results from numerical analysis that simulate the transport of neutrons in such drastically different systems as spallation and fission sources. The theory is used to present scoping studies for the production of thermal neutron fluxes around and beyond 1020/m2·s.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23782

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor