Promotion of the lower limit of detection of gamma emitting nuclides in radioaerosol samples after Fukushima accident
Through placement in a few hours after collecting radioaerosol samples (in Shanghai) after Fukushima nuclear power plant (NPP) accident, radionuclides with gamma-emitting rays can be found to be nuclides (132I/132Te, 129I/129Te) other than 131I, 134,137Cs because of the decrease in background baseline after the daughter nuclides (i.e. 214Bi, 214Pb and etc.) of radon makes decay sharply. Based on aerosol sample collected by passing through 1,300 M3 air in 24 h, the lower limit of detection (LLD) of 132I/132Te, 129I/129Te can be decreased from 6.11 × 10−5, 3.46 × 10−4 Bq m−3 after half an hour sampling to 1.64 × 10−5, 8.19 × 10−5 Bq m−3 after sampling 48 h sampling. Similarly, LLD can be decreased from 9.63 × 10−5 to 1.41 × 10−5 Bq m−3 for 131I, 7.72 × 10−5 to 9.96 × 10−6 Bq m−3 for 134Cs and 9.67 × 10−5 to 1.45 × 10−5 Bq m−3 for 137Cs after the same time sampling. In the same time, the activities of daughter nuclides such as 214Pb and 212Bi from the decay of their parent nuclides 222Rn and 220Rn can sharply decrease from 2.45 × 10−2, 2.57 × 10−2 Bq m−3 to be ~10−4 Bq m−3 while the activities of the concerned nuclides 132I/132Te, 129Te, 131I, 134,137Cs were almost constant. As our knowledge, it is the first time to report such case which is very helpful to monitor the leaked nuclides from NPP by aerosol sampling in both normal operation case and emergency case.