hp(10) distribution measured at the imroh radiation dosimetry and radiobiology unit FOR 2013 AND 2014
Jerko Šiško, Marija Surić Mihić, Tomislav Meštrović, Ivica Prlić
Radiation Dosimetry and Radiobiology Unit, Institute for Medical Research and Occupational Health, Zagreb, Croatia
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INTRODUCTION
Workers professionally exposed to ionizing radiation likely to receive doses exceeding dose limits for public exposure are considered to be exposed workers[1]. In the Republic of Croatia there is still no categorisation of exposed workers so all exposed workers are systematically monitored based on individual measurements performed by a dosimetry service.One such service operates at the Institute for Medical Research and Occupational Health in Zagreb and usespersonal thermoluminescent dosemeters (TLD) for estimations of the effective doses. Exposed workers can be divided into three major groups based on their field of work: medicine, industry and research. Each of these three groups varies significantly in the measured personal dose equivalent Hp(10) values due to the way of exposure and type of radiation source used.This paper presents the distribution of measured Hp(10) values in 2013 2014 for exposed workers in medicine.
MATERIALS AND METHODS
Personal dose equivalent Hp(10) measurements at the Institute are performedusing a dosimetry method accredited according to the norm ISO/IEC 17025. Natural radiation background dose is also measured and according to national legislation [2], effective doses below 85 µSv in one measuring period (one month) are not recorded.
During 2013,the total number of monitored exposed workers was approx. 2200 and during 2014approx. 1800.
RESULTS
The distribution of exposed workers according to their field of work shows that themajority of monitored workers were in medicine (75%) and the rest were in research (14%) and industry (11%).
The distribution of maximum and average Hp(10) valuesfor every monthis presented in Figures 1 and 2. Average Hp(10) values were calculated only from values above the threshold value of 85 µSv.
In 2013, the average measured valueswere consistent and below 500 µSv, while the maximum measured doses were between 700 µSv and 1600 µSv with the exception of 2600 µSv for September.
In 2014, the average measured doses during the entire year were not consistent as in 2013 because of exceptions in April, October and November, when the maximum measured values of Hp(10) were unusually high.
The distribution for 2013 was done on a sample of approximately 1650 exposed workers and for 2014 on approximately 1400 exposed workers.
The approximate monthly number of exposed workers in medicine who had dose equivalent values above the threshold was around 25 during 2013and 21 during 2014.
DISCUSSION
The highest measured values of Hp(10) in 2014 were in April (19.8 mSv), October (8.8 mSv) and November (8.9 mSv). A value of 19.8 mSv was measured for exposed worker from nuclear medicine, values of 8.8 mSv and 8.9 mSv were measured for radiology technicians. These exposed workers had never before received doses of such magnitude and these were recorded only once. All of the doses were investigated and the conclusion was that these measured values could only have been attributed to a misuse of the issued dosimeter.
The average values of Hp(10) for both years (except for the previously discussed values) are under 500 µSv/month much like in previous years[3].
REFERENCES
[1]Council Directive 2013/59/Euratom of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom, Official Journal of European Union L 013, 2014.
[2]Pravilnik o mjerenju osobnog ozračenja, ispitivanju izvora ionizirajućeg zračenja i uvjeta rada te o izvješćima i očevidnicima; Narodne novine 41/12.
[3]Šiško, Jerko; Surić Mihić, Marija; Idrizi, Selvije; Meštrović, Tomislav; Prlić, Ivica. Raspodjela osobnog doznog ekvivalenta Hp(10) mjerenog u Jedinici za dozimetriju zračenja i radiobiologiju, IMI, za 2011. i 2012. godinu.Proceedings of the Ninth Symposium of the Croatian Radiation Protection Association. Krk, 10.-12. travnja 2013. HDZZ. Zagreb. 2013: 111-115.
Figure 1. Hp(10) distribution in medicinefor 2013
Figure 2. Hp(10) distribution in medicine for 2014