Measurement of the Neutron Energy Spectra by Using Organic Scintillators at the Beam Dump of the 100-MeV Proton Linear Accelerator in the KOMAC

This paper presents the experimental results of neutron spectra measurements with organic scintillators at the copper beam dump of the 100-MeV proton linear accelerator in the Korea Multi-Purpose Accelerator Complex (KOMAC). For the measurement of the fast neutrons generated by the proton-copper nuclear reaction, two organic scintillators made of a stilbene crystal and liquid EJ-309 combined with photomultipliers and fast digitizers were utilized. Both detectors were installed inside radiation shielding structures facing the conical-shaped 100-MeV proton beam dump. The neutron transport was calculated using two Monte-Carlo codes, MCNP6 and GEANT4, with a proper physical model and a nuclear data library, along with the appropriate consideration of the detailed geometrical factors in the vicinity of the beam-dump and the neutron detectors. Each pulse signal measured in the detectors was analyzed to identify whether it was induced by a neutron or a gamma-ray in a mixed radiation field by using pulse shape discrimination technique. For operation of beam current of 5 mA and duty of 0.2%, the neutron yield was measured to be approximately 9.0E+10 n/s, which was 23% smaller than the numerically estimated value. In addition, both the measured and the estimated neutron energy spectra were compared.