Measurement of potential alpha energy concentration of radon and thoron daughters using an electret dosemeter

An electret dosemeter was modified to hold an air sampling filter paper at the bottom and air was sampled through it. Nearly 20% of the energy of alpha radiation emitting from the filter paper was dissipated in the volume of the chamber. This energy in turn produced ion pairs which were collected by the electret resulting in a measurable change in charge status of the electret. By proper choice of the thickness of the electret and the total flow, it was possible to measure radon daughter concentrations down to milliworking level units. For thoron decay products, it was shown that the alpha energy concentration measured during sampling and up to a period of 7.7 hours post sampling, yielded 33% of the potential alpha energy concentration due to thoron daughters. An air sample collected and measured in this way registered all of the radon daughter alpha potential energy and one third of thoron daughter alpha potential energy, thus providing and equivalent radon daughter concentration. This procedure is suitable for evaluating any mixture of daughter products whether they originated from radon or thoron. (author)