Production and measurement of 222Rn standards

For the production of radon standards, 222Rn is transferred from a solid 226Ra source located in a vacuum system to different types of vessels such as glass bulbs or stainless steel cylinders. Using this radium source, up to 2 MBq of 222Rn gas can be completely transferred when the radon is condensed in a liquid-nitrogen cooled vessel. The radon activity is determined by measuring the daughter products 214Bi and 214Pb with a Ge gamma spectrometer which has been calibrated with a 226Ra point source of known activity placed in the center of a glass bulb which has the same size as the radon source glass bulb and is located at the same distance from the detector. The energy-dependent difference of the attenuation of photons from radon progeny at the glass surface compared with the attenuation of photons from the calibrated point source in the center of the sphere is calculated by Monte Carlo simulation.