DOSIMETRIC ASPECTS OF OPTIMIZATION OF PROTECTION IN IRAN INDUSTRIAL RADIOGRAPHY PRACTICE.

According to the worldwide reports, industrial radiography is one of the highest risk radiation practices due to handling high activity sources. Therefore, an optimization of protection along with appropriate investigation level and/or dose constraint is required to achieve appropriate radiological safety. This research, presents some statistical aspects of this optimization using frequency distributions and percentiles of individual recorded dose of industrial radiographers from the years 2002 to 2016 in Iran. The results show that, considering an investigation level of 4 mSv for bimonthly monitoring periods, 3-7% of population of workers has been investigated during these years. Moreover, an overall reduction on average annual and collective doses is observed, despite of the relative increasing in the number of workers. Since the frequency of periodical recorded dose at lower dose range (e.g. <4 mSv) causes greater impacts on the reduction of collective dose than the higher ranges, a retrospective average dose of non-investigated workers can also be substitute with a constant value as a dose constraint. It can be concluded that all the past measures of regulatory body and attempts of the employers have been effective improving the radiological protection in this practice in Iran. However, establishing a dose constraint seems to be essential to continue and improve this optimization of protection.

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.

Public exposure due to external gamma background radiation in boundary areas of Iran.

A monitoring program in boundary areas of a country is an appropriate way to indicate the level of public exposure. In this research, gamma background radiation was measured using TL dosimeters at 12 boundary areas as well as in the capital city of Iran during the period 2010 to 2011. The measurements were carried out in semi-annual time intervals from January to June and July to December in each year. The maximum average dose equivalent value measured was approximately 70 µSv/month for Tehran city. Also, the average dose values obtained were less than 40 µSv/month for all the cities located at the sea level except that of high level natural radiation area of Ramsar, and more than 55 µSv/month for the higher elevation cities. The public exposure due to ambient gamma dose equivalent in Iran is within the levels reported by UNSCEAR.