The design and evaluation of an automated system for monitoring 133Xe in room air.
The radioactive gas 133Xe is widely used for ventilation imaging. This paper describes a system for continuous monitoring of the air concentration of 133Xe. The instrument consisted of a sodium iodide scintillation detector, a scaler/ratemeter and a data logger. The crystal was mounted inside a lead shield and enclosed in a perspex cylinder. A fan at one end of the cylinder drew room air into a shielded active volume via an inlet aperture designed to generate turbulent flow with no stagnant areas. The instrument was rendered relatively insensitive to external radiation by positioning the energy window over the 31 keV peak in the 133Xe spectrum. The detector sensitivity was approximately 2 s-1 per MBq m-3, with a typical background count rate of 0.12 s-1. The system was therefore capable of detecting a concentration of 0.06 MBq m-3 in a one-minute sampling interval. Results collected at five centres demonstrated that the eight-hour time-averaged concentrations were much less than the derived air concentration (DAC) for occupationally exposed persons (mean values 0.4 to 1.5% of the DAC), but that transient concentrations were extremely variable (mean values 7 to 24% of the DAC).
Meanwell
E F
EF
Regional Medical Physics Department, Dryburn Hospital, Durham, UK.
Gibson
C J
CJ
Saunders
P J
PJ
Diffey
B L
BL
D000395:Air Pollutants, Occupational / Q000032:analysis*; D000396:Air Pollutants, Radioactive / Q000032:analysis; D004784:Environmental Monitoring / Q000295:instrumentation*; D004867:Equipment Design; D006748:Hospital Departments; D009684:Nuclear Medicine Department, Hospital; D014980:Xenon Radioisotopes / Q000032:analysis*
D000395:Air Pollutants, Occupational; D000396:Air Pollutants, Radioactive; D014980:Xenon Radioisotopes