Life Sciences in Space Research 4 (2015) 79–91 Contents lists available at ScienceDirect Life Sciences in Space Research www.elsevier.com/locate/lssr Shielding evaluation for solar particle events using MCNPX, PHITS and OLTARIS codes S.K. Aghara a,∗ , S.I. Sriprisan a , R.C. Singleterry b , T. Sato c a University of Massachusetts Lowell, Chemical Engineering, 1 University Avenue, Lowell, MA 01854, United States b NASA Langley Research Center, 2 West Reid Street, MS 188E, Hampton, VA 23681, United States c Japan Atomic Energy Agency, 2-4, Shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan a r t i c l e i n f o a b s t r a c t Article history: Received 8 July 2014 Received in revised form 17 December 2014 Accepted 23 December 2014 Keywords: Monte Carlo techniques Solar particle events Space radiation simulation Detailed analyses of Solar Particle Events (SPE) were performed to calculate primary and secondary particle spectra behind aluminum, at various thicknesses in water. The simulations were based on Monte Carlo (MC) radiation transport codes, MCNPX 2.7.0 and PHITS 2.64, and the space radiation analysis website called OLTARIS (On-Line Tool for the Assessment of Radiation in Space) version 3.4 (uses deterministic code, HZETRN, for transport). The study is set to investigate the impact of SPEs spectra transporting through 10 or 20 g/cm 2 Al shield followed by 30 g/cm 2 of water slab. Four historical SPE events were selected and used as input source spectra particle differential spectra for protons, neutrons, and photons are presented. The total particle fluence as a function of depth is presented. In addition to particle flux, the dose and dose equivalent values are calculated and compared between the codes and with the other published results. Overall, the particle fluence spectra from all three codes show good agreement with the MC codes showing closer agreement compared to the OLTARIS results. The neutron particle fluence from OLTARIS is lower than the results from MC codes at lower energies ( E < 100 MeV). Based on mean square difference analysis the results from MCNPX and PHITS agree better for fluence, dose and dose equivalent when compared to OLTARIS results.  2015 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved. 1. Introduction The occurrences of large solar particle events (SPE) have been observed at both ground-level and Earth atmosphere over decades. The SPE events consist primarily of protons emitted from the Sun during coronal mass ejections or solar flares. These events are rare, but when they occur, they can inflict a potentially lethal dose of ra- diation to astronauts and damage critical electronic systems if no protective measures are undertaken. Most of the protons emitted during an SPE have kinetic energies below a few hundred MeV. However, protons with kinetic energies as high as several GeV may also be present. These protons can penetrate a protective space suit and structural materials of spacecraft, posing a health risk to flight crew and damaging microelectronics in satellites and high altitude aircrafts leading to critical failures (Shea and Smart, 1990; Mironova et al., 2012). To perform risk assessment and design ro- bust radiation protection strategies, reliable design tools are nec- essary that can simulate complex problems accurately and con- * Correspondence to: University of Massachusetts Lowell, Perry Hall 310, One Uni- versity Ave, Lowell, MA 01854, United States. Tel.: +1 978 934 3115. E-mail address: sukesh_aghara@uml.edu (S.K. Aghara). sistently. A comprehensive radiation shielding analysis requires characterizing the primary radiation and the resulting secondary radiation. Radiation transport codes have been used to calculate quantities such as dose (D) and dose equivalent (H) and/or dis- tributions of particle fluence or flux in many studies (Wilson et al., 1999, 2006; Parsons and Townsend, 2000; Hoff et al., 2004; Heinbockel et al., 2011; Slaba et al., 2011, 2013b). These particle transport codes are based on two different algorithms: determinis- tic and Monte Carlo (MC). HZETRN (High Z and Energy TRaNsport) is the deterministic transport code developed at NASA Langley Research Center (Wilson et al., 1995, 2006). The HZETRN code solves the Boltzmann trans- port equation within the continuous slowing down and straight- ahead approximations. Recently, the HZETRN code has undergone numerous updates and upgrades, including but not limited to, bi- directional neutron transport algorithms coupling with the expan- sion of the light ion ( A < 4) nuclear cross section (Slaba et al., 2010a). Improvements were also made to underlying numerical methods leading to improved code efficiency, accuracy, and robust- ness (Slaba et al., 2010b, 2013a; Slaba, 2013). The HZETRN trans- port code is the engine behind TARIS (Tool for the Assessment of Radiation in Space) which is a deterministic space radiation analy- sis tool. The latest version of NUCFRG3 is implemented in OLTARIS http://dx.doi.org/10.1016/j.lssr.2014.12.003 2214-5524/ 2015 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.