The response functions of the Bonner Sphere Extended spectrometer were calculated using the MCNP program. For incident neutrons above 10MeV, Tungsten was an excellent heavy material layer as it yielded the highest response among tested materials. | TẠP CHÍ KHOA HỌC ĐẠI HỌC ĐÀ LẠT Tập 7, Số 3, 2017 265–275 265 EFFECTS OF COMPONENT AND THICKNESS OF METAL LAYER ON RESPONSE FUNCTIONS OF BONNER SPHERE EXTENDED SPECTROMETER USING MCNP CALCULATION Mai Nguyen Trong Nhana*, Trinh Thi Tu Anhb a The Faculty of Nuclear Engineering, Ulsan National Institute of Science and Technology, Ulsan, South Korea b The Research Management and International Cooperation Department, Dalat University, Lamdong, Vietnam Article history Received: November 15th, 2016 | Received in revised form: November 30th, 2016 Accepted: December 12th, 2016 Abstract The response functions of the Bonner Sphere Extended spectrometer were calculated using the MCNP program. For incident neutrons above 10MeV, Tungsten was an excellent heavy material layer as it yielded the highest response among tested materials. As for the effect of isotopes’ abundance and thickness of the metal layer, the differences in the response function could be neglected in the high-energy region (above several MeV), but the thickness of the heavy-metal layer had a considerable effect on the response. Recommended thickness for Bonner Sphere Extended spectrometers was also discussed. Keywords: Bonner Sphere Extended spectrometer; Isotope abundance; Metal thickness; Response. 1. INTRODUCTION Bonner Sphere spectrometer is used to measure neutron energies stretching from eV to several MeV. With higher neutron energies, the performance of conventional Bonner Sphere spectrometers (BSS) declines dramatically as a result of leakage and low neutron absorption cross section. Bonner Sphere Extended spectrometers (BSE) were introduced to address this issue. By adding a layer of heavy-metal, the response at high energy level (above 10MeV) was improved. This heavy-metal layer acted as a neutron multiplier as high energy neutron induced (n, xn) reactions. Response functions of BSE were an interest in many works, and the recent results could be found from the articles by Burgett (2008); .
