Instrumental estimates of accumulated external dose using method of single grain retrospective luminescence dosimetry with quartz microcrystals: first results of international study for samples - "witness" of nuclear tests (Semey city, Republic of Kazakhstan)

Semey city (former Semipalatinsk city), Republic of Kazakhstan, is the largest settlement, located in the vicinity of Semipalatinsk nuclear test site (SNTS) and on the traces of several nuclear tests dated by 23.10.1954, 29.07.1955, 16.03.1956, 25.09.1962 and 15.01.1965. There are very essential discrepancies (more than order of value) between different published external accumulated dose estimations related to Semey city. In this paper retrospective instrumental external accumulated dose estimates were performed with aim to clarify these discrepancies. The results are presented in this paper. The first results of application of retrospective luminescence method (RLD) using single grain technique for instrumental estimation of external accumulated radiation dose in the Semey city, Republic of Kazakhstan, are presented in this paper on the base of quartz containing samples - bricks, which are were “witness” of the nuclear tests” in SNTS. The sampled bricks were located at 50°24'57.9"N, 80°15'27.5"E in Semey city. One sample was sampled from external wall of the building (height of sampling place is 172 cm above the ground level), and second sample was sampled from the very good shielded internal part of the wall (in order to measure the “background” level of accumulated dose). The RLD method with optical stimulated luminescence (OSL) and single quartz grains technique was used for instrumental estimation of external accumulated radiation dose. First external slice with 3 mm thickness was excluded from the analysis in order to avoid possible influence of solar irradiation. Each extracted grain was separately calibrated for accumulated dose estimation. The application of single grain technique was performed in order to separate dosimetrical signal of each quartz grain from non dosimetrical (interfered) signals from other grains, which were impossible chemically and mechanically remove from the analyzed aliquots. The obtained results are the following: a) Very good expressed decrease of accumulated dose VS distance from the exterior wall was found (after subtraction of background dose). It was assumed that there was the presence of external exposure in this location. b) The estimated accumulated dose of external irradiation related to 5.5 mm depth in the brick at the location of sampling is equal to 68±11 mGy (after subtraction of background accumulated dose). As a result, accumulated dose of external dose in free air (recalculated from the dose in 5.5 mm depth in the brick) is equal to 120±21 mGy at the location of sampling. c) Note: these dose estimates are related only to the place of brick's sampling and cannot be extended to all Semey city, as far as radioactive traces, possible, were narrow and did not cover of entire city. Maybe narrow traces of radioactive fallout are the reason of large differences between the different previously published estimated doses of external exposure in the city of Semey (as it was, for example, in a case of Dolon village, which is located near the SNTS). Further investigations are in process.