Polyethylene moderator optimized for increasing thermal neutron flux in the NASBEE accelerator-based neutron field

Neutron exposure Accelerator System for Biological Effect Experiments (NASBEE) at National Institute of Radiological Sciences, National Institutes for Quantum and Radiological Science and Technology (NIRS-QST) achieved thermal neutron flux of a therapeutic intensity of (1.75 +/- 0.13) x 10(9) cm(-2) s(-1) by optimizing polyethylene (PE) moderator in the beam port. The dose contamination of gamma rays was 2.37 x 10(-12) Gy cm(2) (the absorbed dose of 14.9 Gy h(-1)). The improved thermal neutron field at the NASBEE facility will be useful in the research and development for boron neutron capture therapy (BNCT).