ISSN 00109525, Cosmic Research, 2011, Vol. 49, No. 4, pp. 319–324. © Pleiades Publishing, Ltd., 2011. Original Russian Text © T. Sato, K. Niita, V.A. Shurshakov, E.N. Yarmanova, I.V. Nikolauev, H. Iwase, L. Sihver, D. Mankusi, A. Endo, N. Matsuda, Y. Iwamoto, H. Nakashima, Y. Sakamoto, H. Yasuda, M. Takada, T. Nakamura, 2011, published in Kosmicheskie Issledovaniya, 2011, Vol. 49, No. 4, pp. 329–334. 319 INTRODUCTION Astronauts in a space flight are subject to enhanced radiation effect as compared to terrestrial conditions. One possible way to reduce a dose rate received by them is the use of a local shield in the frequently visited compartment of a manned spacecraft. For example, Russian specialists proposed to put on the exterior wall of the cabin of the ISS Service Module a protective shutter with a thickness of 10 cm consisting of water soaked hygienic napkins and towels, available onboard in sufficient amounts but stored in other compart ments. Evaluation of dose rates for astronauts, including the case of applying local shields, is an issue of primary importance when longterm space missions are planned. The simulation of particle propagation through the spacecraft shield is one of complicated problems at such an evaluation. The radiation filed inside a spacecraft is a result of transformation of the external radiation field in the process of ionization losses and nuclear reactions in the spacecraft shield matter. It is common practice to use for description of the propagation of external radiation through a space craft shield onedimensional deterministic calculation models, for example HZETRN [1], which is caused by their relative simplicity and realistic computing time necessary to perform estimate calculations. At the same time, there exist programs operating with the threedimensional geometry and using the statistical sampling method (Monte Carlo) [2], which can be applied for calculating the radiation field inside a spacecraft, especially for calculating the neutron con tribution to the dose rate, since transport of neutrons cannot be described in onedimensional approach with sufficient accuracy. The software package PHITS (Particle and Heavy Ion Transport code System) [3, 4] using the Monte Carlo method is characterized by the following three specific features (making it preferable when shielding properties of a spacecraft are estimated): (1) one can consider propagation of all kind of hadrons and heavy ions with energies of up to 100 GeV per nucleon in the shielding matter, (2) nucleus–nucleus interaction is correctly described with the help of quantum model JQMD [5, 6], and (3) in the program there is a special function for calculation of the distribution of dose rate 5 Evaluation of Dose Rate Reduction in a Spacecraft Compartment due to Additional Water Shield T. Sato 1 , K. Niita 2 , V. A. Shurshakov 3 , E. N. Yarmanova 3 , I. V. Nikolauev 4 , H. Iwase 5 , L. Sihver 6 , D. Mankusi 6 , A. Endo 1 , N. Matsuda 1 , Y. Iwamoto 1 , H. Nakashima 1 , Y. Sakamoto 1 , H. Yasuda 7 , M. Takada 7 , and T. Nakamura 7 1 Japan Atomic Energy Agency (JAEA), Tokai, Japan 2 Research Organization for Information Science and Technology, Tokai, Japan 3 State Research Center – Institute for Biomedical Problems, Moscow, Russia 4 S.P. Korolev Rocket Space Corporation, Moscow oblast, Russia 5 GSI, Darmstadt, Germany 6 Chalmers University of Technology, Gothenburg, Sweden 7 National Institute of Radiological Sciences (NIRS), Chiba, Japan Email corresponding address: sato.tatsushiko@jaea.go.jp Received April 19, 2007; revised version July 20, 2010 Abstract—The dose reduction rates brought about by the installation of additional water shielding in a space craft are calculated in the paper using the particles and heavy ion transport code system PHITS, which can deal with transport of all kinds of hadrons and heavy ions with energies up to 100 GeV/n in threedimensional phase spaces. In the PHITS simulation, an imaginary spacecraft was irradiated isotropically by cosmic rays with charges up to 28 and energies up to 100 GeV/n, and the dose reduction rates due to water shielding were evaluated for 5 types of doses: the dose equivalents obtained from the LET and linear energy spectra, the dose equivalents to skin and red bone marrow, and the effective dose equivalent. The results of the simulation indi cate that the dose reduction rates differ according to the type of dose evaluated. For example, 5 g/cm 2 water shielding reduces the effective dose equivalent and the LET dose equivalent by approximately 14% and 32%, respectively. Such degrees of dose reduction can be regarded to make water shielding worth the efforts required to install it. DOI: 10.1134/S0010952511040083 5