Nuclear Instruments and Methods in Physics Research A 551 (2005) 448–457 Development of a wide-range paired scintillator with optical fiber neutron monitor for BNCT irradiation field study Masayori Ishikawa a,Ã , Hiroaki Kumada b , Kazuyoshi Yamamoto b , Junichi Kaneko c , Gerard Bengua d , Hironobu Unesaki d , Yoshinori Sakurai d , Kenichi Tanaka e , Toshiso Kosako f a Department of Nuclear Engineering and Management, Graduate school of Engineering, The University of Tokyo, Japan b Japan Atomic Energy Research Institute, Japan c Graduate school of Engineering, Hokkaido University, Japan d Research Reactor Institute, Kyoto University, Japan e Research Institute for Radiation Biology and Medicine, Hiroshima University, Japan f Department of Nuclear Professional School, Graduate school of Engineering, The University of Tokyo, Japan Received 24 May 2005; received in revised form 14 June 2005; accepted 15 June 2005 Available online 6 July 2005 Abstract A wide range thermal neutron detector was developed based on the Scintillator with Optical Fiber (SOF) detector which has been previously used for thermal neutron monitoring during boron neutron capture therapy irradiation. Withthisnewdetectorsystemweintendedtoaddresstheissuesofreal-timethermalneutronfluxmeasurementandthe simultaneousmeasurementofawiderangeofthermalneutronfluxinaBNCTirradiationfieldwhichweredifficultto implement with the gold wire activation method. The dynamic range of linearity of the SOF detector was expanded by using a plastic scintillator with a rapid decay time.Ontheotherhand,thecontributionofgammaraysandfastneutronsinthemeasuredsignalswerecompensated from those obtained by a pair of SOF detectors, one with a 6 LiF neutron converter and the other without. The discriminationlevelforthemeasuredsignalswasalsooptimizedtofurtherreducethecontributionofgammaraysand fast neutrons signals. A non-paralyzable system model was applied to correct for the dead-time in the detector system. A good agreement between the thermal neutron flux measured by the gold wire activation method and the paired SOFdetectorsystemwasobserved.However,measurementswhichwouldnormallytakeafewdaystoperformwiththe ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$-see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2005.06.044 Ã Correspondingauthor.Tel.:+81358412988;fax:+81358412928,+81338158540. E-mail address: masayori@n.t.u-tokyo.ac.jp (M. Ishikawa).