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Title: A Pulsed Sphere Tutorial

Abstract

Here I attempt to explain what physically happens when we pulse an object with neutrons, specifically what we expect the time dependent behavior of the neutron population to look like. Emphasis is on the time dependent emission of both prompt and delayed neutrons. I also describe how the TART Monte Carlo transport code models this situation; see the appendix for a complete description of the model used by TART. I will also show that, as we expect, MCNP and MERCURY, produce similar results using the same delayed neutron model (again, see the appendix).

Authors:
 [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1349015
Report Number(s):
LLNL-TR-726839
DOE Contract Number:
AC52-07NA27344
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Cullen, Dermott E. A Pulsed Sphere Tutorial. United States: N. p., 2017. Web. doi:10.2172/1349015.
Cullen, Dermott E. A Pulsed Sphere Tutorial. United States. doi:10.2172/1349015.
Cullen, Dermott E. Mon . "A Pulsed Sphere Tutorial". United States. doi:10.2172/1349015. https://www.osti.gov/servlets/purl/1349015.
@article{osti_1349015,
title = {A Pulsed Sphere Tutorial},
author = {Cullen, Dermott E.},
abstractNote = {Here I attempt to explain what physically happens when we pulse an object with neutrons, specifically what we expect the time dependent behavior of the neutron population to look like. Emphasis is on the time dependent emission of both prompt and delayed neutrons. I also describe how the TART Monte Carlo transport code models this situation; see the appendix for a complete description of the model used by TART. I will also show that, as we expect, MCNP and MERCURY, produce similar results using the same delayed neutron model (again, see the appendix).},
doi = {10.2172/1349015},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 30 00:00:00 EST 2017},
month = {Mon Jan 30 00:00:00 EST 2017}
}

Technical Report:

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  • Two plutonium-alloy hemispheres were cast, machined, and canned for use in pulsed-sphere experiments. LLL physicists will use the data from these experiments to improve physics codes. The total mass of Pu--1.0 wt percent Ga was 9.3 kg. The hemispherical shapes had a radius of 53.7 mm. Both hemispheres were cast with hollow polar cones. In one casting the cone was plugged; in the other casting the cone was left to allow fitting to the neutron generator. The hemispheres were electron beam welded into close-fitting stainless steel cans so they could be used in a non-plutonium area. This report describes themore » fabrication of the device, which is expected to have long-term research utility. 14 figures.« less
  • From the late 1960s to about 1985, the Pulsed-Sphere Program at Lawrence Livermore National Laboratory (LLNL) was carried out to measure 14-MeV neutron leakage spectra from target spheres made out of various elements, compounds, and mixtures Data from these experiments have been and continue to be fundamental in the evaluation of neutron Monte Carlo transport codes and cross section data libraries In addition, the data provide important integral information for stockpile stewardship, fusion technology, neutron therapy, and other applications Therefore, comparisons between computer Monte Carlo simulations and the results of these experiments are pivotal for the integral testing of processedmore » nuclear data libraries and transport codes Fortunately, a large subset of data from the pulsed-sphere program (some 70 experiments) is available as a computer file called disp93in Furthermore, in the past few years, there has been a remarkable improvement in computer performance that allows for more realistic simulations by Monte Carlo codes such as TART 4 Previous TART simulations of the pulsed-sphere experiments were performed using simplified models with relatively small numbers of histories and very large solid angle detectors to offset the limitations in computer power. Also, not all the TART input files were created with the same level of detail For example, some input files included the air around the sphere while others did not These factors prompted a study to simulate in more detail all of the available pulsed-sphere experiments using the Monte Carlo transport code, TART, and the LLNL evaluated neutron data library, ENDL The timing of this study is significant because many years have passed since those experiments were done, and only a few people who participated in them are still working at LLNL Their help has been essential for an accurate documentation of the experiments For the Stewardship Program it is important to preserve and make use of as much of the data as possible, because it represents a unique resource and an enormous effort that would be very costly to reproduce The initial part of this study consisted of an analysis of the experimental setup and neutron source characteristics necessary to create the foundation for a TART input file The next task was to create the input files for the various experiments by incorporating particular settings, such as flight path, sphere materials and dimension, etc , to the basic TART input The results of the TART simulations of these experiments will be used to help assess the quality of evaluated data currently in ENDL Further, other nuclear libraries, e g , ENDF/B-VI, JENDL-3, and JEF-2, will be used in the Monte Carlo simulations after being reformatted for TART and other Laboratory codes Finally, this work will be part of the integral check of the new evaluations being prepared for the Stewardship Barn Book by the LLNL Nuclear Data Group« less
  • Livermore's nuclear data group developed a new verification and validation test suite to ensure the quality of data used in application codes. This is based on models of LLNL's pulsed sphere fusion shielding benchmark experiments. Simulations were done with Mercury, a 3D particle transport Monte Carlo code using continuous-energy cross-section libraries. Results were compared to measurements of neutron leakage spectra generated by 14MeV neutrons in 17 target assemblies (for a blank target assembly, H{sub 2}O, Teflon, C, N{sub 2}, Al, Si, Ti, Fe, Cu, Ta, W, Au, Pb, {sup 232}Th, {sup 235}U, {sup 238}U, and {sup 239}Pu). We also testedmore » the fidelity of simulations for photon production associated with neutron interactions in the different materials. Gamma-ray leakage energy per neutron was obtained from a simple 1D spherical geometry assembly and compared to three codes (TART, COG, MCNP5) and several versions of the Evaluated Nuclear Data File (ENDF) and Evaluated Nuclear Data Libraries (ENDL) cross-section libraries. These tests uncovered a number of errors in photon production cross-sections, and were instrumental to the V&V of different cross-section libraries. Development of the pulsed sphere tests also uncovered the need for new Mercury capabilities. To enable simulations of neutron time-of-flight experiments the nuclear data group implemented an improved treatment of biased angular scattering in MCAPM.« less