Shielding Experiments at High Energy Accelerators of Fermilab (IV) - Calculation Analyses - Norihiro MATSUDA 1* , Yoshimi KASUGAI 1 , Hiroshi MATSUMURA 2 , Hiroshi YASHIMA 3 , Hiroshi IWASE 2 , Norikazu KINOSHITA 2 , Toshiya SANAMI 2 , Nikolai MOKHOV 4 , Anthony LEVELING 4 , David BOEHNLEIN 4 , Kamran VAZILI 4 , Lautenschlager GARY 4 , Schmitt WAYNE 4 , Takashi NAKAMURA 5 , Koji OISHI 6 , Hideo HIRAYAMA 2 , Kenji ISHIBASHI 7 , Koji NIITA 8 , Yukinori SAKAMOTO 1 , Hiroshi NAKASHIMA 1 , and members of JASMIN corroboration 1 Japan Atomic Energy Agency, 2-4, Shirakata Shirane, Tokai-mura, Ibaraki 319-1195, Japan 2 High Energy Accelerator Research Organization, 1-1, Oho, Tsukuba, Ibaraki 305-0801, Japan 3 Kyoto University Research Reactor Institute, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan 4 Fermi National Accelerator Laboratory, Fermilab, Batavia, IL 60510-5011, USA 5 Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8578, Japan 6 Shimizu Corporation, 4-17, Etchujima 3-chome, Koto-ku, Tokyo 135-8530, Japan 7 Kyushu University, 744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan 8 Research Organization for Information Science & Technology, 2-4, Shirakata Shirane, Tokai-mura, Ibaraki 319-1106, Japan JASMIN - Japanese and American Study of Muon Interaction and Neutron detection - a program for studies of shielding and irradiation effect around high energy accelerators has been started until 2007 using high energy proton accelerators located in Fermi National Accelerator Laboratory (FNAL) as a collaboration of JAPAN and FNAL. The series of the presentations entitled “Shielding experiments at high energy accelerators of Fermilab” describes the part of the results of this collaboration regarding transport of secondary particles, neutron and muon, from 120 GeV proton induced reactions through experimental data and simulation. In this paper, calculation analyses using high energy particle transport Monte Carlo calculation codes, PHITS, MARS and MCNPX, for the experiments carried out at the anti-proton production target station were performed with a simplified two-dimensional geometry to validate the accuracy of spatial distribution of reaction rate in iron shield and the attenuation length. The calculation results were good agreement with the obtained experimental data for the spatial distribution. Neutron attenuation lengths of iron were also given by the data. Tendencies of the attenuation length of iron were found the PHITS and MARS values were larger and the MCNPX values were smaller than the data. KEYWORDS: 120 GeV, Fermi National Accelerator Laboratory, Monte Carlo calculation code, angular distribution, attenuation length I. Introduction 1 The shielding experiments were performed at the anti- proton (pbar) target station in Fermi National Accelerator Laboratory (FNAL) in a collaborative research program of JASMIN (J apanese and A merican S tudy of M uon and N eutron Detection). The obtained experimental data using the activation technique provided the useful information concerning the attenuation phenomenon of high energy neutrons as a shielding data that has never been measured at incident proton energies over a hundred-GeV. These data are also useful to validate high energy particle interaction and transport simulation codes, such as PHITS 1) , MARS 2) and MCNPX 3) in GeV region. An inter-comparison among calculation codes for attenuation length of neutron dose over 20 MeV was done on the SATIF-8 4) (Shielding Aspects of Accelerators, Targets and Irradiation Facilities Eighth Meeting at the PAL, Korea in 2006) under various conditions such as, energies of *Corresponding Author, E-mail:matsuda.norihiro@jaea.go.jp © Atomic Energy Society of Japan incident neutrons from 20 MeV to 100 GeV. In the meeting, the calculation results by major codes including PHITS, MARS and MCNPX etc. were compared for some typical problems. One of the items of the inter-comparisons was an attenuation length of mono-energetic neutrons around a GeV region as incidents for iron and concrete shield. Since the neutron attenuation length make a big impact on shielding design of high-energy proton accelerators, the calculations should be validated properly. Though, in an actual situation, the incident neutrons to a shield are not mono-energetic, the neutron attenuation behavior is determined only by a behavior of high-energy neutrons with more than a GeV. Therefore, using the experimental shielding data for the neutron attenuation, the inter-comparison among the simulation codes can be evaluated. In this work, shielding calculation of pbar target station by PHITS, MARS and MCNPX are carried out, and the calculation results of neutron attenuation behavior for iron shield are compared with the experimental data in a viewpoint of decreasing tendencies of reaction rates, and the neutron attenuation lengths deduced from the calculations ARTICLE Progress in NUCLEAR SCIENCE and TECHNOLOGY, Vol. 1, p.57-60 (2011) 57 DOI: 10.15669/pnst.1.57