Radiation detection systems
Continuous Radon Monitor
Continuous Radon Monitor (CRM)
The Continuous Radon Monitor (CRM) is a microprocessor based radiation monitoring system that was developed by RDS for the monitoring of the radon activity concentration in outdoor and indoor air. The CRM connected to the external 12 DC power source can operate continuously for 3 months if a 10 minute logging option is chosen. If the 60 minute logging option is used the system can continuously gather data for about 1.5 years. If short term operation is required the internal battery can support up to 20 hours of continuous monitoring.
Filtered air with radon is continuously sampled by the constant flow rate air sampler. Whilst air flows through the Lucas Cell, alpha particles emitted by radon and radon daughters inside the cell produce scintillations of light within the ZnS(Ag) scintillator coating of the Lucas Cell walls. The light pulses are detected by a Photo Multiplier tube and the voltage pulses are pre-amplified, amplified and logged into a microcontroller memory. The background count is subtracted from the total count and the net count is multiplied by the count to the radon activity concentration conversion factor to obtain the radon activity concentration that is displayed and stored in the memory. The Lowest Limit of Detection (LLD) of the CRM is approximately 5 Bq/m3.
Logged data can be downloaded into a MSWindow Hyperterminal as a text file that can be opened in MSExcel. The net alpha countrate to the radon activity concentration conversion factor is obtained through the system calibration inside the South Australian EPA Radiation Protection Branch Radon Calibration Chamber.