A description follows of an operational-standard irradiation field that has been established by using gamma-ray sources installed at the Radioisotope Research Center of Osaka University. The irradiation system is composed of an irradiator mounted with 60Co (3.7GBq) and 137Cs (11.1GBq and 111GBq), and a mobile exposure deck having a lead shield sandwiched with iron at the back side. The irradiator was provided with three kinds of square collimators around the irradiator beam exit. It is the purpose of the present study to utilize the irradiation system for the calibration of commercially manufactured gamma-ray dosimeters. Estimation of the scattered radiation of an irradiation field was achieved by both measurements and calculations. The absorbed dose rates due to the sources mounted in the irradiator were determined with a calibrated ionization chamber, and the contribution of scattered photons from the irradiator equipment was confirmed to be minimal by calculations with a radiation transport code.
This paper describes a summary of results in a series of 10 international intercomparisons of environmental dosimeters held during 1974-1993 and another series of domestic Intercomparison studies held in Taiwan during 1980-1984. The field conditions were harsh. Even in semitropical Taiwan where high humidity and temperature in the field is usual, the performance of our TLD could pass all the rigid tests. The ANSI N13-29 (American National Standards Institute publication N13-29) dealing with standards for environmental dosimetry and the Horlick's triangle dealing with the accuracy and the precision of TLD were used to analyze the dosimeterc data.
The present status of calibration fields for neutron measuring instruments in Japan has been summarized according to the classification of International Standard ISO/DIS 8529, which specifies the neutron reference radiations produced by radioactive sources, electrostatic accelerators and nuclear reactors in an energy range from thermal energy up to 20MeV, for calibration of neutron measuring devices used for radiation protection purposes. The neutron sources of 252Cf and 241Am-Be are often used for the calibration of neutron measuring instruments in several domestic facilities. The electrostatic accelerators providing protons and deuterons up to an energy of 4MeV can generate monoenergetic neutrons in the energy range from 10keV to 20MeV. Only limited facilities can provide the calibration services to determine the sensitivities or response functions for neutron detectors. Unidirectional beams of thermal and filtered neutrons can be provided by several research reactors. The calibration fields based on the units of neutron emission rate and monoenergetic neutron fluence have been established in some limited facilities but the calibration method for neutron dose equivalent instruments has not been established satisfactorily. It is highly desirable to establish a traceability system for the calibration of neutron measuring instruments used for radiation protection purposes.