Tatsuhiko Sato

Development of Dose Monitoring System Applicable to Various Radiations with Wide Energy Ranges

A new inventive radiation dose monitor, designated as DARWIN (Dose monitoring system Applicable to various Radiations with WIde energy raNges), has been developed for monitoring doses in workspaces and surrounding environments of high energy accelerator facilities. DARWIN is composed of a phoswitch-type scintillation detector, which consists of liquid organic scintillator BC501A coupled with ZnS(Ag) scintillation sheets doped with 6Li, and a data acquisition system based on a Digital-Storage-Oscilloscope. Scintillations from the detector induced by thermal and fast neutrons, photons and muons were discriminated by analyzing their waveforms, and their light outputs were directly converted into the corresponding doses by applying the G-function method. Characteristics of DARWIN were studied by both calculation and experiment. The calculated results indicate that DARWIN gives reasonable estimations of doses in most radiation fields. It was found from the experiment that DARWIN has an excellent property of measuring doses from all particles that significantly contribute to the doses in surrounding environments of accelerator facilities—neutron, photon and muon with wide energy ranges. The experimental results also suggested that DARWIN enables us to monitor small fluctuation of neutron dose rates near the background-level owing to its high sensitivity.

Study on Response Function of Organic Liquid Scintillator for High‐Energy Neutrons

Response functions of liquid organic scintillator for neutrons up to 800 MeV have been measured at the Heavy‐Ion Medical Accelerator in Chiba (HIMAC) of National Institute of Radiological Sciences (NIRS). 800‐MeV/u Si ions and 400‐MeV/u C ions bombarded a thick carbon target to produce neutrons. The kinetic energies of emitted neutrons were determined by the time‐of‐flight (TOF) method. Light output for neutrons was evaluated by eliminating events due to gamma‐rays and charged particles. The measured response functions were compared with calculations using SCINFUL‐QMD and CECIL codes. It was found that SCINFUL‐QMD reproduced our experimental data adequately.

Systematics of Differential Photoneutron Yields Produced from Al, Ti, Cu, Sn, W, and Pb Targets by Irradiation of 2.04 GeV Electrons

Differential photoneutron yields produced from Al, Ti, Cu, Sn, W, and Pb targets by an irradiation of 2.04 GeV electrons were measured at the angle of 90° relative to the incident beam. The neutron energy range measured in this experiments was between 10 and 400 MeV. The systematics of the yields was studied for two target conditions : a target element and a target thickness. The neutron productions by a photonuclear reaction and by a hadron cascade due to secondary particles were considered to develop semi-empirical formula for the application of shielding calculation.

Study of light output and response function of liquid organic scintillator for high-energy neutron spectrometry

In order to investigate the relationship between kinetic energy of charged particles and light output of liquid organic scintillator, response functions for proton, deuteron, triton, /sup 3/He nucleus and alpha particle have been measured at heavy-ion medical accelerator in Chiba (HIMAC) of National Institute of Radiological Sciences (NIRS). The charged particles were generated by 400 MeV/u C ion bombardment with a thick graphite target. Kinetic energies were determined by time-of-flight (TOF) technique. Energy loss during their flight was calculated by PHITS code and taken into account at energy-correction. Light output for proton was also measured using mono-energy proton beam of 100 and 160 MeV supplied by accelerator. Kinetic energy of proton beam was changed by inserting Al plates onto beam axis as an energy absorber. The experimental results gave a new database of light output.

Secondary Charged Particle Measurement from 2‐GeV Electron‐Induced Reactions with a Current Time‐of‐Flight Technique

The energy spectra of secondary charged particles from 2.04 and 2.5 GeV electron‐induced reactions were measured using a current time‐of‐flight technique at the Pohang accelerator Laboratory. A long flight path and the current time of flight method were adopted to measure the pulse height of each event that reached the detectors in a short period. Secondary proton and deuteron energy spectra were obtained at 90 degrees with respect to the electron incident angle. The results were compared with those calculated by the MCNPX‐2.5e code.