Equilibrium factor of radon progenies in Norwegian homes

Several hundred deaths each year are caused by radon-induced lung cancer in Norway. Lung cancers are mainly caused by the inhalation of radon and alpha radiation from the airborne short-lived radon or progenies but not by the radon gas itself. Since radon progenies measurements are limited, a value known as the equilibrium factor can estimate radon progeny's contribution to lung dose. UNSCEAR suggests a worldwide value of 0.4 for the equilibrium factor. Stranden measured an equilibrium factor mean of 0.5 in Norway in 1979. A new in-situ instrument from SARAD, EQF 3220, was used to determine indoor radon concentration, equilibrium factor, and unattached fraction. Fourteen dwellings in Bærum, Oslo, Ski, and Ås were used for radon measurements from October 2020 to April 2021. Still, only results of 12 homes in Oslo, Ski, and Ås were used. Indoor radon measurements in the 12 homes were performed using a 24hours-cycle. The excluded dwellings had 1hour, 3hours, 6hours, and 12hours-cycles of the sampling period. Low sampling cycles result in high error and uncertainty. As a brand-new instrument, many measures were carried out as a test before the actual measurements took place- the study's first phase. The measurements started with an instrument that belongs to DSA, and months later, NMBU acquired a new instrument like the one from DSA. The instruments were used in parallel in the same room. The study used a paired sample t-test to compare the results of the devices. It was observed that the results of both instruments in parallel were not statistically different, and therefore, the instruments were used separately in the second phase of the study. Most of the dwellings were selected because they were close to the DSA and NMBU. Most owners are DSA or NMBU employees or students willing to make their homes available for measurements. Within 12 houses, of which 2 of Oslo, 1 of Ski, and 9 of Ås, radon means varied from 24 Bq/m3 to 178 Bq/m3 . The overall regional radon mean value is 145 Bq/m3. The equilibrium factor means varied from 0.21 to 0.26 with an overall equilibrium factor mean value of 0.25. The equilibrium factor mean is a lot lower than the value found in the previous measurements by Stranden in 1979 and the international value suggested by The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The unattached fraction means varied from 0.3 to 0.53. The unattached regional fraction mean value is 0.5. A positive correlation between radon concentration was observed, and a negative one between equilibrium factor and unattached fraction was also observed. The study found a low mean value of the equilibrium factor in the indoor air of the measured dwellings.M-RA