The use of TLD-700H dosemeters in the assessment of external doses at the former Semipalatinsk nuclear test site

The joint projects performed since 1995 by the Julich Research Centre in co-operation with the Kazakh National Nuclear Centre in the area of the former nuclear test site near Semipalatinsk, in eastern Kazakhstan, have assessed the current dose rate of the population at and around the test site, as well as determining retrospectively the dose rate of persons affected by the atmospheric tests. Measurements of the population by personal dosemeters depend on reliably wearing these dosemeters over prolonged periods of time, and of a sufficient dosemeter return. In the past, such measurements have been particularly successful whenever short wearing times were possible. This requires high sensitivity of the dosemeters. The suitability of the highly sensitive TLD material of the BICRON TLD 700H type for such personal dosimetry measurements was investigated. It was tested in practical field application at the Semipalatinsk nuclear test site in September 2000. Initial results are available from individual doses received by a group of geologists and a group of herdsmen at the test site. For the first time, the individual dose was measured directly in these population groups. Detection limits below 1 muSv permit informative measurements for wearing times of less than two weeks. Most individual doses did not arise significantly out of local fluctuations of natural background. A conservative assessment from the aspect of practical health physics yielded a mean personal dose of 0.55 muSv per day for the herdsmen, whereas the geologists received a mean personal dose of 0.45 muSv per day. For an annual exposure period of, typically, about three months, the radiation dose received by the persons investigated, in addition to the natural radiation exposure, is thus well below the international limit value of I mSv.a(-1) for the population dose.