A comprehensive dose assessment of irradiated hand by iridium-192 source in industrial radiography.

Among the various incidents in industrial radiography, inadvertent handling of sources by hands is one of the most frequent incidents in which some parts of the hands may be locally exposed to high doses. An accurate assessment of extremity dose assists medical doctors in selecting appropriate treatments, preventing the injury expansion in the region. In this study, a phantom was designed to simulate a fisted hand of a radiographer when the worker holds a radioactive source in their hands. The local doses were measured using implanted TLDs in the phantom at different distances from a source. Furthermore, skin dose distribution was measured by Gaf-chromic films in the palm region of the phantom. The reliability of the measurements has been studied via analytical as well as Monte-Carlo simulation methods. The results showed that the new phantom design can be used reliably in extremity dose assessments, particularly at the points next to the source.

A root cause analysis of the high occupational doses of industrial radiographers in Iran.

The Iran Nuclear Regulatory Authority has investigated overexposure cases in industrial radiography over a period of three years. Radiographers with thermoluminescence dosimeter (TLD) records of more than 4 mSv in any 2 month routine monitoring period were asked to fill in a questionnaire explaining their points of view of the reasons for such relatively high doses. The responses showed that more than 50% of the radiographers did not agree with their recorded TLD doses, although the majority of the alternative explanations were weak. The main causes of overexposures were found to be difficult working conditions and ignoring safety principles while accidents or device failures were a minor contribution. Also, there was poor correlation between the TLDs and direct reading dosimeters worn by the radiographers, indicating that personal monitoring instructions were not being implemented appropriately.

The cytokinesis-blocked micronucleus assay: dose-response calibration curve, background frequency in the population and dose estimation.

An in vitro study of the dose responses of human peripheral blood lymphocytes was conducted with the aim of creating calibrated dose-response curves for biodosimetry measuring up to 4 Gy (0.25-4 Gy) of gamma radiation. The cytokinesis-blocked micronucleus (CBMN) assay was employed to obtain the frequencies of micronuclei (MN) per binucleated cell in blood samples from 16 healthy donors (eight males and eight females) in two age ranges of 20-34 and 35-50 years. The data were used to construct the calibration curves for men and women in two age groups, separately. An increase in micronuclei yield with the dose in a linear-quadratic way was observed in all groups. To verify the applicability of the constructed calibration curve, MN yields were measured in peripheral blood lymphocytes of two real overexposed subjects and three irradiated samples with unknown dose, and the results were compared with dose values obtained from measuring dicentric chromosomes. The comparison of the results obtained by the two techniques indicated a good agreement between dose estimates. The average baseline frequency of MN for the 130 healthy non-exposed donors (77 men and 55 women, 20-60 years old divided into four age groups) ranged from 6 to 21 micronuclei per 1000 binucleated cells. Baseline MN frequencies were higher for women and for the older age group. The results presented in this study point out that the CBMN assay is a reliable, easier and valuable alternative method for biological dosimetry.

Improvement of Accuracy in Environmental Dosimetry by TLD Cards Using Three-dimensional Calibration Method.

INTRODUCTION: The angular dependency of response for TLD cards may cause deviation from its true value on the results of environmental dosimetry, since TLDs may be exposed to radiation at different angles of incidence from the surrounding area. OBJECTIVE: A 3D setting of TLD cards has been calibrated isotropically in a standard radiation field to evaluate the improvement of the accuracy of measurement for environmental dosimetry. METHOD: Three personal TLD cards were rectangularly placed in a cylindrical holder, and calibrated using 1D and 3D calibration methods. Then, the dosimeter has been used simultaneously with a reference instrument in a real radiation field measuring the accumulated dose within a time interval. RESULT: The results show that the accuracy of measurement has been improved by 6.5% using 3D calibration factor in comparison with that of normal 1D calibration method. CONCLUSION: This system can be utilized in large scale environmental monitoring with a higher accuracy.

Analysing an accident related to orphan sources including dose assessment.

This paper discusses an accident, which occurred in one of the radiation application centres in Iran, follow-up investigations as well as lessons learnt. In January 2004 the Regulatory Authority was informed through a university radiation protection officer of an accident regarding orphan sources. Investigations revealed that one Am-Be and three (137)Cs sources in the container were subject to extensive heat due to burning of the container and melting of the paraffin content of the container; consequently, sources were stuck to the side wall of the container, but they were still undamaged and no radioactive leaking had occurred. Further investigations showed that the container had been given to the above mentioned centre a long time before by a foreign well-logging company without notifying the Regulatory Authority. Follow-up measurements and assessments indicated that the collective effective dose due to the accident is unlikely to be more than 21 mSv; consequently, no severe deterministic effect to individuals was expected. The findings showed that the main reasons for the accident were as follows: (1) violation of obligation under radiation protection regulations by the owner of the sources; (2) leaving the sources in an improper storage condition; (3) unauthorised access to the radiation sources at the owner centre; and (4) lack of an integrated national registration system in the Regulatory Authority.

Promoting the safety performance of industrial radiography using a quantitative assessment system.

The increasing number of industrial radiographers and their considerable occupational exposure has been one of the main concerns of the Iran Nuclear Regulatory Authority (INRA) in recent years. In 2002, a quantitative system of evaluating the safety performance of licensees and a complementary enforcement system was introduced by the National Radiation Protection Department (NRPD). Each parameter of the practice is given a weighting factor according to its importance to safety. Assessment of the licensees is done quantitatively by summing up their scores using prepared tables. Implementing this system of evaluation showed a considerable decrease in deficiencies in the various centres. Tables are updated regularly as a result of findings during the inspections. This system is used in addition to enforcement to promote safety performance and to increase the culture of safety in industrial radiography.

Survey on lost and poorly controlled radioactive sources in non-medical applications in Iran.

Despite well-developed Regulatory Authority systems for radiation protection, there are some concerns about lost-controlled and poorly controlled radioactive sources owing to abundance and dispersion of the users. This survey covers the current situation of the categories 3 through 5 of radioactive sources (based on the categorisation of the IAEA) in non-medical applications in Iran. The investigation performed on a selected group of non-medical users of radioactive sources in different provinces of Iran. Findings show that unauthorised supply and legacy sources in addition to abandonment of sources under regulatory control are the main reasons for lost-controlled sources. Considering the possibility of increasing poorly controlled sources which can lead to increase in the number of lost-controlled sources, further developments are needed in national regulatory control as well as international cooperation and discipline in this regard.