Temperature dependence of effective area and depth of extrapolation chamber in dosimetry

The variation of the effective area and zero-offset of an extrapolation chamber used for beta-ray and low-energy x-ray dosimetry was measured as a function of temperature in the range 19 °C to 25 °C. The effective area and zero-offset were determined from the capacitance of the extrapolation chamber measured with the chamber depths in the range up to 1.4 mm. The extrapolation chamber was put in a precision thermostatic air bath with a programmable temperature regulator to evaluate the influence of temperature on it. At room temperature we found the thermal expansion coefficients to be (8.55 ± 0.57) × 10−5 K−1 for the effective area and (2.83 ± 0.03) µm K−1 for the depth of the extrapolation chamber. The influence of thermal expansion of the extrapolation chamber on the ionization current measurement was estimated to be about 3 × 10−3 K−1 when the measurement depth was 1 mm.