“Quality Control of 137Cs and 90Sr Estimation During Dosimetry Certification in Population Centers of Ukraine”

Customer: State Agency on Exclusion Zone Management, Ukraine (SAU EZM)

Objective: external quality control over 137Cs and 90Sr specific activity measurements performed by local laboratories, and measurement of 90Sr specific activity in milk samples from the Kyiv Region.

According to SAU EZM letter of May 30, 2013 No. 01-1718/1.4.1 “On performing the activities for dosimetry certification of Ukrainian population centers in 2013”, in the period since August till November 2013, milk and potatoes were sampled in the Ukrainian population centers, which are classified by the legislation as radioactively contaminated zones. During the project, 432 population centers in the six regions of Ukraine, which have been radioactively contaminated as a result of the Chornobyl accident, were surveyed.

In accordance with the approved guidelines on dosimetry certification works in the population centers of Ukraine, 9 radiological laboratories in the six regions of Ukraine were involved in taking the measurements of 90Sr and 137Cs content in milk and potatoes. Mainly, these included regional and district laboratory centers under the State Sanitary and Epidemiology Service of Ukraine, as well as laboratories under the Ministry of Agricultural Policy of Ukraine. Totally, 4826 samples were analyzed, including 2448 milk samples and 2378 potato samples. Samples for the external control were selected in local laboratories, by their experts in villages or in district sanitary and epidemiology services. Then, the samples were transferred to the regional sanitary and epidemiology services or to the regional subordination laboratories under the Ministry of Agrarian Policy.

ChC staff took the samples, which were prepared for the external control. Simultaneously, they performed visual survey of equipment and facilities in the local laboratories, studied organization of measurement processes, checked availability of relevant certificates confirming a laboratory qualification to perform radiological measurements and also radiometric equipment verification certificates. 257 samples were delivered to the Chornobyl Center and monitored there, including 207 samples for 137Cs content and 50 ones for 90Sr content. Prior to testing, the samples were stored in special refrigeration cabinets and in a freezer.

The content of 137Cs was assessed using γ-spectrometer SEG-002 AKP-P with a detector base made of pure germanium produced by “Atom Komplex Prylad” and using gamma spectrometer produced by the U.S. Canberra Industries. Inc. with a detector made of pure germanium, GC3019. The content of 90Sr was estimated using beta-spectrometer SEB-01 produced by “Atom Komplex Prylad”.

Based on the external survey results, all local laboratories have adequate equipment to perform estimations of 90Sr and 137Cs content in samples. All equipment is in good working condition and is calibrated. All the laboratories have qualification certificates. Personnel of the laboratories possess adequate experience in analyzing food samples. Most of the doctors and engineers-radiologists were previously involved in dosimetry certifications in population centers of Ukraine during 1991-1997, 2005-2006 and in 2008, 2011 2012.

Results for Comparative Measurement of Standard Samples
In order to assess quality of the measurements, we additionally performed comparative measurement of the Chornobyl Center’s standard samples with known activity. With due regard to the previous experience, the comparative measurements were performed twice: prior to milk and potato samples measurements in the local laboratories and at the final stage of research, during sampling for the external control. The comparative measurements were performed in the presence of a Chornobyl Center’s representative and documented as a separate measurement record sheet. The performed assessment demonstrated that deviations of measurement data for specific activity of 90Sr and 137Cs in standard samples do not exceed 20% in most of the local laboratories. This is in line with the regulatory requirements concerning radioactivity monitoring in food and with the requirements stated in Order of the Ministry of Emergencies of Ukraine No. 116 of August 10, 2012.

External Quality Control of 90Sr and 137Cs Measurements in Milk and Potato Samples
5% of the samples were subject to quality control of 90Sr specific activity measurement. The majority of specific activity values are equal to the so-called minimum measurable activity (MMA), i.e. minimal value that can be measured using a given spectrometer under certain conditions. As for the samples with specified MMA, the IRL experts confirm this based on their own assessments: such values do not exceed 1.5 Bq/kg, which corresponds to the procedure for 90Sr activity measurement using beta spectrometers of SEB series produced by “Atom Komplex Prylad”, Kyiv. The information obtained suggests that local laboratories take high-quality measurements of 90Sr specific activity in milk and potato samples.

Results of the comparison also demonstrate that all local laboratories take high-quality measurements of 137Cs specific activity. The differences between the results obtained in the ChC do not exceed 20% (the criterion was established by MOE order No..116 of August 10, 2012).

The detailed report on the research results was submitted to the customer.