A humidity resistant radon source developed by ion exchange of radium in a membrane

To develop a humidity resistant radon source on a membrane based on the ion exchange technique. 226 Ra in its standard solution was adsorbed in the HP membrane through cation exchange. The radioactivity of 226 Ra in the membrane was determined through the measurements of 226 Ra activities in the solution before and after the adsorption using a HPGe γ spectrometer. The emanation coefficients of radon from the membrane in different humidity conditions were quantified through the measurements of radon concentrations in a close loop mode using the AlphaGUARD DF2000 radon monitor. Long-term measurements of radon concentrations in the close loop and a standard chamber using the membrane as radon source were performed to verify the stability of radon emanation from the source. A piece (70 ​mm ​× ​20 ​mm) of the HP membrane could adsorb 51.2 kBq of 226 Ra in about 30 ​min. The emanation coefficient of radon from the membrane could reach as high as 0.997, and it was hardly changed in a humidity range from 7.5% RH to 94.5 ​% RH. The variation of the radon production rate from the source was only ±1.2 ​% in two weeks at a general laboratory condition, and its emanation stability was also confirmed in a standard radon chamber by using the membrane source for one month. The radon membrane source developed in this study has a stable emanation coefficient regardless the environmental humidity. It can be used as a flow-through radon source in a standard radon chamber.