Measurement of the neutron spectra inside and outside the target room of the 65 MeV electron LINAC using an extended Bonner sphere

An extended Bonner Sphere (BS) set consisting of four polyethylene (PE) spheres and three PE spheres with an inserted lead shell to increase the detection efficiency for high energy neutron was used to measure the neutron spectra from the thick Pb target bombarded by 65 MeV electron at the Pohang Accelerator Laboratory (PAL). The response function of the BS was calculated using the MCNPX code and calibrated using a 252Cf neutron source. Active BS using the LiI(Eu) scintillator for detecting of the thermal neutron was implemented outside the target room and passive BS with gold foils was used as the thermal neutron detector due to a high intense field of gamma radiation inside the room. With the results of the spectral measurement, the design and calculation of the response function of a newly modified BS of the Korea Atomic Energy Research Institute (KAERI) are also presented.