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 (I-132/Te-132, I-129/Te-129) other than I-131, Cs-134,Cs-137 because of the decrease in background baseline after the daughter nuclides (i.e. Bi-214, Pb-214 and etc.) of radon makes decay sharply. Based on aerosol sample collected by passing through 1,300 M-3 air in 24 h, the lower limit of detection (LLD) of I-132/Te-132, I-129/Te-129 can be decreased from 6.11 x 10(-5), 3.46 x 10(-4) Bq m(-3) after half an hour sampling to 1.64 x 10(-5), 8.19 x 10(-5) Bq m(-3) after sampling 48 h sampling. Similarly, LLD can be decreased from 9.63 x 10(-5) to 1.41 x 10(-5) Bq m(-3) for I-131, 7.72 x 10(-5) to 9.96 x 10(-6) Bq m(-3) for Cs-134 and 9.67 x 10(-5) to 1.45 x 10(-5) Bq m(-3) for Cs-137 after the same time sampling. In the same time, the activities of daughter nuclides such as Pb-214 and Bi-212 from the decay of their parent nuclides Rn-222 and Rn-220 can sharply decrease from 2.45 x 10(-2), 2.57 x 10(-2) Bq m(-3) to be similar to 10(-4) Bq m(-3) while the activities of the concerned nuclides I-132/Te-132, Te-129, I-131, Cs-134,Cs-137 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.