Radiation detection systems
This monitoring method uses the RDS medium flow rate air sampler (MFRAS) coupled with a filter cassette and powered by a small battery and solar panel (Fig. 1). The flow rate of the MFRAS is 1.5 L/min. The RDS Low Background Alpha Counter (LBAC) (Fig. 2) is used to alpha count filters.
The filter cassette with a glass fibre filter (GF: Φ37mm/1.2μm) and/or membrane filter (MF: Φ37mm/1.2μm or 0.8μm) is used for dust/aerosol sampling. Airborne dust particles and aerosols that contain naturally occurring long-lived alpha emitting radionuclides are typically sampled for 1 to 4 weeks.
The alpha counting of filters is carried out at least 5 days after dust sampling ends in order to minimize the effect of short-lived alpha emitters of the radon decay series that are also collected. In order to achieve satisfactory accuracy, the alpha counting interval is usually 12 hours long.
The parameters of the methodology are summarised in the Table below:
| Filter type | BC(12 hours) | Lc* | BC+LC | AACLc (Bq/m3) | AACLLDM(Bq/m3) | GF | 27.9 | 12.3 | 40.2 | 1.10E-06 | 2.46E-06 |
|---|---|---|---|---|---|
| MF | 14.6 | 8.9 | 23.5 | 7.95E-07 | 1.85E-06 |
| * Lc is the a posteriori decision limit ie. the net alpha count that includes statistically significant radioactivity collected on the filter added to the background alpha count (BC); AACLc is the Lc equivalent alpha activity concentration in air and AACLLD is the Lowest Limit of detection (LLD) of the alpha activity concentration in air, based on a 30 day sampling period. | |||||
The RDS LBAC background count is at least 5-10 times lower than that of other commercially available alpha counters and thus it avoids the need for a High-Volume Dust Sampler.
The very low LLD with this method makes it is suitable for the monitoring of long-lived alpha activity in air around uranium mines and mineral sand mining operations.
Provided the filter cassette includes the nuclear track detector film Kodak LR-115 (the Universal Radon Daughter Monitor, URDM, is featured in rdsjk.com) radon daughters in air could also be measured in parallel with the long-lived alpha activity concentration of environmental dust in air.
