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.