The dependence of the m value on applied voltage in the collection efficiency of ionisation chambers

Values of m - which are equal to (α/eK+K-)1/2 where α is the recombination coefficient, e the charge per ion, K+ the mobility of positive ions and K- that of negative ions - were measured using a double X-ray beam method. By this method, one value for m is obtained from a set of data on currents at each polarisation voltage. Values obtained are for a recombination region 2.65 cm wide. It was shown that these values decrease from 1.85 x 106 to 1.65 x 106 V s1/2 C-1/2 cm-1/2 with an increase in electric field strength from 4.8 to 48 V cm-1. This means that the value of m increases with ion age. (author)