Measurement of the neutron fluence and dose spectra using an extended bonner sphere and a tissue-equivalent proportional counter.

A conventional Bonner Sphere (BS) set consisting of six polyethylene spheres was modified to enhance its response to a high-energy neutron by putting a lead shell inside a polyethylene moderator. The response matrix of an extended BS was calculated using the MCNPX code and calibrated using a 252Cf neutron source. In order to survey the unknown photon and neutron mixed field, a spherical tissue equivalent proportional counter (TEPC) was constructed and assembled as a portable measurement system. The extended BS and the self-constructed TEPC were employed to determine the dosimetric quantities of the neutron field produced from the thick lead target bombarded by the 2.5 GeV electron beam of Pohang Accelerator Laboratory (PAL) and the neutron calibration field of Korea Atomic Energy Research Institute (KAERI).