INTERCOMPARISON OF ACTIVITY SIZE DISTRIBUTIONS OF THORON PROGENY BY ALPHA-COUNTING AND GAMMA-COUNTING METHODS

It is difficult to calibrate sampling devices using radon or thoron pr ogeny or particles measuring 1-4 nm; therefore, an interlaboratory com parison is important to verify the performance of graded diffusion bat teries for the activity size distributions of the ''unattached'' proge ny. This paper describes the results of an interlaboratory comparison of Rn-220 progeny size distributions using graded diffusion batteries by alpha- and gamma-counting methods with different data inversion sch emes. Graded diffusion batteries designed at the Inhalation Toxicology Research Institute and at the Environmental Measurement Laboratory we re used in the study. Screens and backup filters from the Environmenta l Measurement Laboratory-graded diffusion batteries were counted simul taneously in alpha counters for total alpha activities, and those of t he Inhalation Toxicology Research Institute-graded diffusion batteries were counted in a gamma detector for gamma activities from Pb-212. Be cause of the different counting methods and data analysis procedures u sed, this interlaboratory study of Rn-220 progeny allows a more rigoro us way of testing instrument performance. Pb-212 particles generated i n well-controlled environments of oxygen, nitrogen, or oxygen with 1 p pm of nitrogen oxide were measured. In general, good agreement in acti vity size distributions was obtained from these two methods. Some diff erences observed in individual size spectra were attributable to the d ata inversion programs used in each laboratory. When the data were ana lyzed by the same computer program, most differences disappeared.