Assement of radionuclide concentration in various samples by gamma spectrometry and LSC J. Berzins, D.Riekstina, O. Veveris Institute of Solid State Physics University of Latvia Dresden 2010

The Laboratory was organized as the group of the Laboratory of nuclear reactions in 1986 after the accident in Chernobil NPS with the aim to control via gamma spectrometry the environment and measure the radioactivity in foodstof and other samples. Since 1998 the group was reorganized to the Material radioactivity testing laboratory. The quality assurance system was implemented in our laboratory since the year 2000.

Different contaminate samples: soils, waters, metal scrap and various types of samples, irradiated in the research nuclear reactor, were measured by gamma spectrometer. The concentrations of radionuclide were determined using the high resolution HPGe gamma- spectrometer type Ortec within the energy range of keV. For measuring of large radioactive waste volums in the metal barrel, gamma-spectrometer with NaJ detector were used. The uncertainty of measurements was within the range of 3-10%, but the minimal detectable activity – 0.3 Bq/kg.

The measurements of high tritium activities in reactor basin and for monitoring contaminate groundwater were carried out with the liquid scintillation spectrometer Packard TRI-CARB using the scintillation liquid OptiPhase “HiSafe”3. The measurement time for H-3 didn’t exceed some hours and uncertainty was less than 2%. The credibility of obtained results is ensured by the quality assurance and control. The main requisitions involved in the quality assurance of the laboratory according to the requirements of ISO/IEC 17025:2005 are: 1) the use of calibrated equipment only; 2) the regular long-time use of reference materials for the control of equipment; 3) the regular participation in the interlaboratory intercomparison exercises, organized by the RISO National Laboratory (Denmark) and IAEA (Vienna).

Measurements Free release of reactor materials Monitoring for potentially contaminated territories Water quality control Customer service – J-131 from hospitals - metal scrap from foreign countries - samples from illegal radioactive material transport

HPGe gamma spectrometer

Efficiency of HPGe detectors

NaJ gamma spectrometer

Liquid scintilator spectrometer

iSOLO equipment for alfa and beta measurements

Methods For the measurements we use 15 methods. The most importent are: Determination of the radionuclides concentration by high resolution gamma-ray spectrometry. T Water quality – Determination of the activity concentration of radionuclides by high resolution gamma-ray spectrometry. LVS ISO 10703:2008. Water quality. Determination of the specific activity of tritium. Liquid scintilation counting method. LVA ISO 9698:2003. Building materials quality – Determination of the radionuclides and specific activity of radionuclides in building materials by gamma-ray spectrometry. LVS ISO 257:2000.

Our internal quality audit program covers all requirements of ISO/IEC 17025:2005 standard, but the main attention is paid to the analysis of results of laboratory’s participation in intercomparison measurements, their evaluation, interpretation and determination of uncertainty sources. Since 1999 laboratory is a regular participant in the interlaboratory intercomparison exercises organized by the RISO National Laboratory (Denmark) and IAEA (Vienna). Such nuclides as K-40, Mn-54, Co-57, Co-60, Zn-65, Cs-134, Cs-137, Eu-152, Ra-226, U-238 and Th- 232 were analyzed in following intercomparison samples: soils, sediment, seaweed, aerosol, grass, hay, meat, dray milk, waters.

Quality assurance Quality System Quality control Experienced staff Use of standard samples Premises, surroundings Measurement of background Validated methods Analysis in duplicates Calibrated equipment Control charts: background, standard peak stability Calibrated standards Reference materials Internal audit Staff training Participation in intercalibration

Participation of laboratory in the intercomparison exercises YearOrganizerObjectRadionuclides 1999Risoe National laboratory, Denmark Sediment, milk, meat, seaweed, hay K-40, Mn-54, Co-60, Cs-137, Ra-226, Th Risoe National laboratory, Denmark Milk, aerosols, soil, seaweed K-40, Cs-137, Co- 60, Mn-54, Ra-226, Th IAEA, ViennaMineral matrixMn-54, Co-57, Co- 60, Cs-134, Cs-137, Eu Risoe National laboratory, Denmark milk, mineral matrix, seaweed Cs-137, K Risoe National laboratory, Denmark Sediment, soil, seaweed K-40,, Cs-137, U- 238, Th IAEA, ViennaSoil, grass, waterK-40, Mn-54, Co-60, Zn-65, Cs-134, Cs-137

Figure compares our results with the weighted mean in seaweed. There is a good agreement between them.

Column diagram of sum of z-scores for results from all radionuclides combined showing contributions from individual samples (No. 17-Laboratory of Radiation Physics).

137 Cs content in mushrooms in Latvia (1987)

21 Cs-137 radioactivity of soils in the 3 km zone of the Salaspils nuclear reactor Sample number Bq/kg

22 Shut-down medical facility Dubulti Boring of samples

Pollution with Ra-226 depending on the depth in Dubulti

Ra_226 concentration in the waste from Dubulti (in barrels)

Results of tritium detection in Latvia: Communal water sources – 155 objects 5 Bq/L < T < 10 Bq/L 0,01 Bq/l < α < 0,2 Bq/l 0,1 Bq/l < β < 0,6 Bq/l Water for food industry – 54 objects 5 Bq/L < T < 10 Bq/L 0,01 Bq/l < α < 0,05 Bq/l 0,1 Bq/l < β < 0,4 Bq/l

Conclusions The use of gamma and beta spectrometry methods allow: establish the pollution level in the territories included in the monitoring decrease during the last years however unexpected changes was detected; identify and evaluate the wastes of various origin; control the quality of drinking water according to the Latvian Cabinet of Ministers regulations No.235, adopted in 2003, provision the entry in force of the EU Council Directive 98/83/EC. Only credible and justified results can be the basis for further use in any field, thus making it possible to make legitimate decisions.

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