Development of a Neutron Detection System using an LGB Scintillator for Precise Measurements of Epi-Thermal Neutrons

Precise measurements of epi-thermal neutrons are important for evaluation of BNCT irradiation facilities. We are developing a new neutron detection system that is nearly independent of nuclear data. The neutron detection system is composed of
⁶
Li
₆
^nat
Gd
¹⁰
B
₃
O
₉
:Ce
⁺
(LGB) and two Bi
₄
Ge
₃
O
₁₂
(BGO) scintillation detectors. The detection system coincidently measures alpha particles and monoenergetic gamma rays with an energy of 478 keV produced by the
¹⁰
B(n,αγ)
⁷
Li reaction in the LGB scintillator. The alpha particles are detected by the LGB scintillation detector and the gamma rays are subsequently detected by the BGO scintillation detectors. The gamma ray detection efficiency of BGO scintillation detector is determined by the coincidence measurements. The neutron fluence is obtained after measurements with a thick
¹⁰
B
₄
C sample that absorbs the almost total number of incident epi-thermal neutrons. Characteristics of the neutron detection system are evaluated by means of the time-of-flight method using a photo neutron source at the Kyoto University. As a result, it is successfully shown that the neutron fluence is obtained without using nuclear data in the detection system.