IAEA-447 , Natural and artificial radionuclides in moss-soil

Organic , Moss-Soil

In summer 2007, a sample of three hundred kg of the moss-soil was collected from an abandoned red marble mine in Gerecse Mountain in the north-west part of Hungary by staff of the Radioanalytical Laboratory of the Food and Feed Safety Division (Hungary) in cooperation with the IAEA Terrestrial Environment Laboratory. The groovings in the large marble stone surfaces allowed undisturbed moss growth for the last 40 years, so the 3-5 cm thick fresh soil layer which was produced was mixed with the moss. The mixture of moss-soil accumulated radionuclide fall-out and thus represents the history or memory record of the radioactive fall-out. The cleaned moss-soil was dried overnight in an oven at 80 ºC and then milled in a large volume ceramic drum mill. The milled material was sieved to obtain a maximum particle size distribution of 150 µm. The final volume of the treated material was about 180 kg. The material density was measured in 5 test portions and found to be 1.03±0.05 g cm-3. Bottling of IAEA-447 was carried out under normal laboratory conditions. Portions of 150 g were filled into plastic bottles, sealed with security polyethylene caps and labeled with the code IAEA-447. After bottling, the material was sterilized by gamma ray irradiation with a total dose of 25 kGy using a 60Co source according to EN ISO 13485:2003 to ensure long-term stability of the material by inhibiting microbial action.

Certified values for massic activities (Based on dry mass)

Reference date for decay correction: 15 November 2009

Analyte Certified value [Bq kg-1] Uncertainty* [Bq kg-1]
137Cs 425 10
210Pb 0.42 x 103 0.02 x 103
210Po 423 10
212Pb 37.0 1.5
226Ra 25.1 2.0
228Ac 37.0 2.0
234U 21.8 0.8
238U 22.2 0.8
238Pu 0.15 0.02
239+240Pu 5.3 0.16

* Uncertainty is expressed as a mixture model median based standard deviation S(MM-median), k=1 


Information values for massic activities (Based on dry mass)

Analyte Information value [Bq kg-1] Uncertainty* [Bq kg-1]
40K 0.55 x 103 0.02 x 103
90Sr 5.0 0.3
232Th 37.3 2.0
241Am** 2.2 0.2
241Pu 8.0 1.0

* Uncertainty is expressed as a mixture model median based standard deviation S(MM-median), k=1 
**The value of 241Am should be corrected for in-growth from 241Pu


The certified values listed above were established on the basis of results reported by the IAEA Terrestrial Environment Laboratory in Seibersdorf, Austria. In addition, two expert laboratories  (Radioanalytical Laboratory, Food and Feed Safety Division, Budapest, Hungary, and Laboratory of Radiological Measurements, Jožef Stefan Institute, Ljubljana, Slovenia) analyzed the IAEA-447 moss-soil material. Each  laboratory was asked to determine the measurands of interest in three different bottles. The obtained results from the expert laboratories were used to confirm the IAEA certified values. In total, 30 bottles were analyzed in the Terrestrial Environment Laboratory and expert laboratories during the characterization campaign of the moss-soil material. The IAEA derived reference values were in agreement with the expert laboratories’ results. The measurement uncertainty associated with individually assigned values is expressed as a mixture model median based standard deviation S(MM-median).

 

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