A personal dosimetry system by Optically Stimulated Luminescence (OSL) was developed and widely commercialized. In normal uses, the upper limit of this measurement is reported to be 10 Sv for137Cs gamma rays. Above this upper limit, the counting system saturates to go beyond its measuring capability. However, far larger radiation doses are applied to transfusion blood. A simple and reliable dosimetry system is required for this extremely large dose measurement. The possibility to realize such a system has been studied and application of the prevailing OSL dosemeters for this purpose has been proposed. The OSL dosemeter has the capability for storing large amount of irradiation defects in its crystals and also has such good characteristic of emitting luminescence that decreases exponentially at every repeated measurement. This particular performance was utilized for large dose evaluation. Continuous measurement of the dosemeter irradiated largely but sufficiently below the saturation level would enable to evaluate the irradiation dose by the number of measurement and each dose. In this experiment, a common blood irradiation facility and personal dosemeters were used. The largest dose was 30 Gy. Ordinary routine readers were adopted to measure the doses, which showed fairly good agreement with the delivered ones.
A crime prevention and safety system using the image was built for the radiation handling facilities. The system employs an internet network. A specific surveillance monitor would be unnecessary in those facilities where the internet is prepared. The following conclusions were derived as a result of applying this system. (1) Because images were preserved by the digital style, those at the time of accident could be searched easily. (2) The system combined with sensor light and sign deterrent has high ability for warning. (3) A real-time surveillance in the night time can be easily realized.
An Automatic drawing system for a report of surface contamination check in a radiation controlled area has been developed. The system can print out the report applied for the format provided by the law from the raw data that is the output from measuring instruments. The task of a worker is only to insert an FD storing the data into a PC and to push a button. The system also yields contamination maps to indicate contamination points clearly. With this system the time to complete the report from the raw data could be decreased from more than two hours to 4 minutes.
With the revision of the law in April, 2001, the effective dose at the boundary of the controlled area was set at 1.3 mSv/3M. Whether the shielding capability of the CT room satisfied the provisions ofthe law or not was confirmed by actual measurements. Both thermo luminescence dosemeter (TLD) and electronic dosemeter were used to measure the radiation doses. The shielding capability of the gantry was studied both inside andoutside the room for a week as a basic experiment. On the basis of the data thus obtained doses accumulated in 3 months were estimated. According to the results of 3 month-measurement, the doses outside the wall of the CT room were about 200μSv. This numerical value was comparable to the background level of the evaluation point.The results above assured that the shielding capability of the CT room satisfied the provisions of the law well.
The educational program for radiation workers is essential for the safety of radiation facility that stands on radiation protection practice by each worker. However, there appears no distinct criterion for quantitative evaluation of the education effect on radiation safety. The effectiveness of education was assessed by the number and the frequency (number of contamination/number of users) of contamination, a major incident involving radioactive materials, based on the long-term contamination surveillance data from 1996 to 2001 in Nagasaki University Radioisotope Center. Facility staffs monitored contamination in the facility every day. In 1996 and 1997, the yearly total number and the frequency of contamination found in a molecular biology room, a most frequently-used laboratory, were 150 and 1.21, respectively. The improvement of education program, including introduction of technical procedures to avoid contamination in molecular biological experiments, pre-entry instruction for fresh workers to demonstrate radiation safety practices on site, and spreading the new concept “contamination happens by all means” through the radiation workers, markedly reduced both the number and the frequency of contamination to 33 and 0.48, respectively. This reduction seemed to be attributable for two different reasons; improvement of skills to avoid contamination, and thorough execution of monitoring and decontamination. These results suggested that contamination was a possible criterion for evaluating effectiveness of education program for radiation workers.
In order to estimate the effective dose (E) of a person who may come into close contact to the 123I-IMP patients, exposure rates around 30 adult patients (male: 15, female: 15) were measured with three ionization survey meters (Aloka, ICS-301) at distances of 0.05, 0.5, 1.0 and 1.5m from the patients. Measurements were carried out in 1, 3, 6 and 24h after the administrations of 123I-IMP. Survey meters were set up to the first cervical vertebrae (Level I), xiphoid process (Level II) and anterior superior iliac spine (Level III) of the patients who were standing erect. The maximum dose equivalent (H1cm) rate of107.9μSv/h per 222MBq was recorded in the level II at 0.05m from the patients. Effective half life of 123I-IMP was 11.0h. The E around the 123I-IMP patient increases in time approaching to a saturated value, which is defined as total E. The tota1 E was calculated from initial H1cm rates and the effective half life; estimated values/222MBq are 949μSv at 0.05m, 195μSv at 0.5m, 76μSv at 1.0m and41μSv at 1.5m.
The safety control system of the X-ray generator was established on the National Personnel Authority rule. The safety control system was built by consulting the Law Concerning Prevention from Radiation Hazards due to Radioisotopes, etc. A new designation of the X-ray protection supervisor was founded after the radiation protection one. Only the inside of the device was set up as the controlled area. All radiation workers were required to measure the radiation exposure. The periodic inspection of facilities comes to be carried out once a year.
On the basis of many human tritium metabolic data accumulated in the Intense 14MeV Neutron Source Facility OKTAVIAN of Osaka University, Japan, until now, the characteristics of the measured data have been analyzed for bioassay samples of urine, exhaled water and water distilled from urine. It has been found that the tritium concentration of exhaled water is equal to that in water distilled from urine. A new method has been developed to follow up each metabolism of two chemical forms, that is, free water tritium (FWT) and organically bound tritium (OBT) in urine. In case of repeated tritium intake, it was found that the tritium concentration could be approximated by single exponential function corresponding to the fastest excretion component for about 50 days after each intake. In this approximate method, the biological half-life of second intake exceeded compared with that of first intake. The distribution ratio of FWT and OBT components changed at the next intake compared with the previous intake. Consequently, the ratio of the OBT component increased and brought the apparent increase of the biological half-life.