Five types of ionization chamber survey meters and a type of GM counter survey meter were calibrated for measuring the β-ray absorbed dose rate due to a skin contamination, using natural uranium, ¹⁹⁸Au and ²⁰⁴Tl circular sources. To estimate the β-ray absorbed dose rate of a contaminated skin, measurements were done twice by a survey meter without and with a filter, keeping the distance from the contaminated skin surface to the survey meter at 10mm. The absorbed dose rate was obtained by multiplying a net reading (a difference between a reading of survey meter's indicator measured without the filter and a reading measured with the filter) by a multiplying factor.
Multiplying factors varied approximately in proportional to the inverse square of source diameter when the source diameter was smaller than the detector's diameter, and approached gradually to a constant value as the value of source diameter increased over the detector's diameter. The multiplying factors of each ionization chamber survey meter were equal to one another within ±30% independently of type (manufacturer) and the maximum energies of sources. The multiplying factors of GM counter survey meter to ²⁰⁴Tl and ¹⁹⁸Au sources were three times as large as those to natural uranium sources. The change in the multiplying factor was less than ±20%, when the measuring distance was 10±2mm.