Nuclear Instruments and Methods in Physics Research A 530 (2004) 493–504 Filtered fast neutron irradiation system using Texas A&M University Nuclear Science Center Reactor S.Y. Jang a, *, C.H. Kim b , W.D. Reece a , L.A. Braby a a Department of Nuclear Engineering, Texas A&M University, 3133 TAMU, College Station, TX 77843-3133, USA b Department of Nuclear Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, South Korea Received 9 February 2004; received in revised form 19 April 2004; accepted 26 April 2004 Available online 15 June 2004 Abstract A heavily filtered fast neutron irradiation system (FNIS) was developed for a variety of applications, including the study of long-term health effects of fast neutrons by evaluating the biological mechanisms of damage in cultured cells and living animals such as rats or mice. This irradiation system includes an exposure cave made with a lead–bismuth alloy, a cave positioning system, a gamma and neutron monitoring system, a sample transfer system, and interchangeable filters. This system was installed in the irradiation cell of the Texas A&M University Nuclear Science Center Reactor (NSCR). For a realistic modeling of the NSCR, the irradiation cell, and the FNIS, this study used the Monte Carlo N-Particle (MCNP) code and a set of high-temperature ENDF/B-VI continuous neutron cross-section data. Sensitivity analysis was performed to find the characteristics of the FNIS as a function of the thickness of the lead–bismuth alloy. A paired ion chamber system was constructed with a tissue-equivalent plastic (A-150) and propane gas for total dose monitoring and with graphite and argon for gamma dose monitoring. This study, in addition, tested the Monte Carlo modeling of the FNIS system, as well as the performance of the system by comparing the calculated results with experimental measurements using activation foils and paired ion chambers. r 2004 Elsevier B.V. All rights reserved. PACS: 28.41.Ak; 28.20.Gd; 28.50.Dr Keywords: Fast neutron irradiator; Neutron spectrum shifter; Foil activation method; Paired ion chamber method; Monte Carlo modeling 1. Introduction Although a great deal of work has been done on the biological effectiveness of neutrons in animals and cell culture systems, very little of this can be used to evaluate the significance of the bystander cell effect or to guide development of mechanistic risk evaluation models. Most of the mechanistic studies were done with mammalian cells grown as a monolayer on a plastic substrate. This irradia- tion configuration, and the cellular and molecular endpoints that were utilized, limited the results to ARTICLE IN PRESS *Corresponding author. Tel: +1-979-845-7551; fax: +1-979- 862-2667. E-mail address: syjang@cedar.ne.tamu.edu (S.Y. Jang). 0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.04.232