Independent Benchmarking of a Hybrid Monte Carlo Simulation Cross Section Code Nathan P. DeLauder ndelaude@utk.edu Co-author: Lawrence W. Townsend The University of Tennessee Presented at: SESAPS 2011 – Roanoke, VA October 21, 2011 Hotel Roanoke & Conference Center Hosted by: Dept. of Physics – Virginia Tech

Overview Target material’s cross section (xs) ALICE 2008 xs code ALICE Limitations ENDF/B-VII database Code results Summary

Purpose of Work High energy neutron reactions with certain materials is of interest to space radiation protection Significant biological risk can result from neutron interactions and production with spacecraft materials This work compares code xs results with tabulated data for validating code usage in future high energy neutron investigations.

Material Neutron Cross Section A way to characterize or quantify the probability of a certain reaction occurring as a result of interaction σT = σS + σA Experimentally this is done by measuring the attenuation of a parallel beam for all possible interactions

ALICE 2008 Code Hybrid Monte Carlo (HMS) pre-compound nuclear decay model Weisskopf-Ewing evaporation model Bohr-Wheeler fission model Gives single/double differential emission spectra and product yields caused by particle ranging from photons to heavy ions

ALICE 2008 Limitations Incident particle energy range of 0.2 to 250 MeV per particle (950 MeV/p ‘tolerated’) Pion production channels not yet implemented in the de-excitation phase Targets lighter than Be can present problems in results

Limitations effecting this study While 2-3 GeV upper limit ideal, immediate need is for lower energy investigations Pion production/decay treatment is not of much concern here Light target issues may be of concern for C-12, but not for heavier targets

ENDF/B-VII Database Uses models benchmarked with experimental data Al-27 and Fe-56 have XS data reported to 150 MeV while C-12 data stop at 20 MeV Al-27 and Fe-56 data uses previous ENDF values supplemented by various optical models.

n+12C Total Cross Section Comparison Comparison of n+C-12 total reaction cross-section between ALICE2008 results and ENDF/B-VII data

n+27Al Total Cross Section Comparison Comparison of n+Al-27 total reaction cross-section between ALICE2008 results and ENDF/B-VII data

n+56Fe Total Cross Section Comparison Comparison of n+Fe-56 total reaction cross-section between ALICE2008 results and ENDF/B-VII data

Table 1. Percent error statistics for ALICE2008 vs. ENDF/B-VII ALICE % error Table 1. Percent error statistics for ALICE2008 vs. ENDF/B-VII 12C 27Al 56Fe % error range 0.6 – 51.8 % 15.3 – 54.3 % 11.7 – 56.2 % % error avg 34.6 % 37.9% 43.3%

Benchmarking Results There is a consistent ‘elbow’ in the trends of ALICE and ENDF at 20 – 40 MeV ALICE results for Al-27 trend rather well with the data although at lower values For C-12 and Al-27, σT from ENDF remain rather constant between 10 – 40 MeV while ALICE values gradually fall off.

Summary The ALICE 2008 statistical model was bench marked against the ENDF/B-VII standard XS’s General trends are followed by both code results and XS database Percent error from ENDF accepted values has a large range and averages about 39% The lack of pion production in the ALICE calcs above 250 MeV/n may play a part at lower incident energies (pion production can begin at ~150 MeV/n depending on target mass number)

References M.BLANN, A.Y. KONOBEEV, W.B. WILSON, and S.G. MASHNIK, “Manual for Code Alice, Ver. July 7, 2008” (2008). M.B. CHADWICK and P.G. YOUNG, “ENDF/B-VI MOD 3 Evaluation”, LANL (1997). R.W. FINLAY, W.P. ABFALTERER, G. FINK, et. al., “Neutron Total Cross Sections at Intermediate Energies”, Physical Review C, 47, 237 (1993).

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