This review paper gives the brief description on the development of new sophisticated high-energy neutron spectrometers, and the high-energy neutron shielding experiments performed using these spectrometers by our group. For neutrons of energies beyond 100 MeV, the self-TOF detector using the NE102A plastic scintillators, large-scale NE213 organic liquid scintillator, and spallation detectors of C and Bi were developed, and two types of multi-moderator spectrometers, high-efficiency type and gamma-ray insensitive type, were developed for use in wide energy range, all by our group.

  By using these spectrometers, our group performed the shielding experiments using the following five neutron sources: 1) 25, 35MeVp-Li quasi-monoenergetic neutrons at CYRIC, Tohoku university, 2) 43, 68MeVp-Li quasi-monoenergetic neutrons at TIARA, JAERI, 3) 400MeV/nucleon C ion produced neutrons at HIMAC, NIRS, 4) 800MeV proton produced neutrons at ISIS, RAL, and 5) 28.7GeV electron produced neutrons at FFTB, SLAC.

  Recent progress in developments of neutron detectors has been reviewed. Emphases are placed on neutron spectrometers and related sensing materials that have been developed mainly in this decade.

  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. With this new detector system we intended to address the issues of real-time thermal neutron flux measurement and the simultaneous measurement of a wide range of thermal neutron flux in a BNCT irradiation field which were difficult to implement with the gold wire activation method. Clinical trials using paired SOF to measure thermal neutron flux during therapy confirmed that paired SOF detectors were effective as a real-time thermal neutron flux monitor.

  Clinical trials for boron neutron capture therapy (BNCT) are performed using research reactors in world-wide. BNCT is a radiation therapy for refractory cancer as malignant brain tumor. To carry out the BNCT procedure based on proper treatment planning and its precise implementation, a treatment planning system, JCDS has been developed in Japan Atomic Energy Research Institute (JAERI; now restructured to Japan Atomic Energy Agency, JAEA).

  To estimate the dose components given to a patient by neutron irradiation in BNCT, JCDS performs the dosimetry with numerical simulations. A detailed tree-dimensional patient's head model is created by using CT and MRI images, and then input data for neutron and photon transport calculation are generated based on the patient's model. Distributions of the several dose components and gamma-ray dose in the head are computed by Monte Carlo calculations. A proper irradiation condition based on the calculation results is decided, and then a clinical trial of BNCT can be performed.

This report describes requirements for dosimetry in BNCT and the dosimetry method of JCDS.

  The present status and future needs as to exposure to cosmic neutrons in an aircraft are briefly reviewed. Neutron doses at high altitude are still uncertain and model calculations should be verified based on precise energy spectra of high-energy cosmic neutrons.

  Evaluation of high-energy neutron dose is one of the key issues in the shielding design of accelerator facilities and in the planning of long-term space missions. High-energy neutron transport simulation codes play an important role in the evaluation, since large difficulties lie in the precise measurement of high-energy neutron doses. This paper reviews the Monte-Carlo simulation codes applicable to the purpose, and summarizes the requirements for the future development of the codes.

  Dose conversion coefficients for photons, electrons and neutrons based on new ICRP recommendations were cited in the ICRP Publication 74, but the energy ranges of theses data were limited and there are no data for high energy radiations produced in accelerator facilities. For the purpose of designing the high intensity proton accelerator facilities at JAERI, the dose evaluation code system of high energy radiations based on the HERMES code was developed and the dose conversion coefficients of effective dose were evaluated for photons, neutrons and protons up to 10 GeV, and electrons up to 100 GeV. The dose conversion coefficients of effective dose equivalent were also evaluated using quality factors to consider the consistency between radiation weighting factors and Q-L relationship. The effective dose conversion coefficients obtained in this work were in good agreement with those recently evaluated by using FLUKA code for photons and electrons with all energies, and neutrons and protons below 500 MeV. There were some discrepancy between two data owing to the difference of cross sections in the nuclear reaction models. The dose conversion coefficients of effective dose equivalents for high energy radiations based on Q-L relation in ICRP Publication 60 were evaluated only in this work. The previous comparison between effective dose and effective dose equivalent made it clear that the radiation weighting factors for high energy neutrons and protons were overestimated and the modification was required.