Nielsen, Sven Poul1; Andersson, Kasper Grann1; Miller, Arne1
1 Center for Nuclear Technologies, Technical University of Denmark2 Radioecology and Tracer Studies, Center for Nuclear Technologies, Technical University of Denmark3 Radiation Physics, Center for Nuclear Technologies, Technical University of Denmark
The environmental surveillance of the Risø environment was continued in January-June 2012. The mean concentrations in air were: 0.48±0.38 μBq m–3 of 137Cs, 3.69±1.79 mBq m–3 of 7Be and 0.21±0.20 mBq m–3 of 210Pb (±1 S.D.; N = 26). The depositions by precipitation at Risø in the first half of 2011 were: 0.052 Bq m–2 of 137Cs, 420 Bq m–2 of 7Be, 21.5 Bq m–2 of 210Pb and < 0.5 kBq m–2 of 3H. The average background dose rate (TLD) at Risø (Zone I) was 99 nSv h–1 compared with 89 ± 9 nSv h–1 (±1 S.D.; N = 4) in the four zones around Risø. TLD results for the period November 2011 – April 2012 are significantly higher than results for the periods before and after this one. Raw data and calculations have been checked without finding a reason why these results show larger doses. The results are close to the detection limit for these dosimeters and the higher results could be due to measurement uncertainties, but measurement errors cannot be excluded. The increased background dose rates measured with TLD’s are believed to be due to unidentified technical reasons. Increased levels in external gamma radiation at the Risø zones during November 2011 to April 2012 were neither identified from measurements of terrestrial dose rates with a NaI(Tl) detector nor from the permanent monitoring station at Risø operated by the Danish Emergency Management Agency.