Range and Specific Ionization of Alpha-Particles

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Abstract
A study of the specific ionization of polonium alpha-particles near the end of their range with a shallow ionization chamber and linear pulse amplifier has resulted in an accurate determination of the single particle specific ionization curve and the range energy relation in this region. The method used is to compare the average single particle ionization in chambers of different depths and from the differences to obtain the ionization of particles of residual range less than the depth of the chambers. The single particle specific ionization curve differs from earlier determinations and shows the necessity of a correction to the accepted values of absolute mean range of all alpha-particle groups. The value suggested for the mean range of Th C′ (at 15°C and 760 mm) is 8.570±0.007 cm; for Po it is 3.842±0.006 cm. It is shown that extrapolated ranges obtained from ionization measurements differ from those obtained from number distance curves; an empirical relation is suggested to convert such values to mean range. A corrected range energy relation for alpha-particles extending down to zero range is obtained by combining the results of the present investigations with earlier determinations.

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