Instrument for continuous measurement of 220Rn (and 222Rn) using delayed coincidences between 220Rn and 216Po

An instrument has been developed for continuous monitoring of 220 Rn. The method of data analysis is based on delayed coincidences between 220Rn and 216Po. The instrument basically consists of a scaler equipped with a photomultiplier tube (PMT) to which a scintillation cell (SC) of the flow through type is optically coupled. The scaler is equipped with a pulse output (P/) port which provides a TTL pulse, + 5 V in amplitude and 5 to 10 μs duration for each nuclear event recorded by the SC and its associated electronic circuitry. The P/O port is connected to a 32 bit counter/timer unit operating at 1 MHz which records and stores the time of arrival of pulses. For laboratory use, the counter/timer is connected to the serial port of a laptop PC. However, for field applications, where space and weight pose severe practical limitations, the PC is substituted by an expanded counter/ timer unit which incorporates a microprocessor for data analysis, a LCD for data display, and a keypad to key in function instructions. Furthermore, some additional hardware permits the measurement of 220Rn flux density. J(220Rn), from soils and other materials. Because total α-particle count, as well as delayed (α-α) coincidence rates are recorded in two separate channels, the method permits the measurement of 222Rn in addition to 220Rn. The method is particularly useful for low concentration levels.