On the Ionization-energy Relation for Alpha-particles in Air

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Abstract
To investigate the effect of columnar recombination on the ionization measurement in air, the ratio of the specific ionizations at two fixed residual ranges for polonium alpha-particles was measured with a shallow ionization chamber under various field strengths and angles between the field and the alpha-track. It was found that the observed ratio varies appreciably with varying field strength and angle. It was shown that the observed variation of the ratio can be explained by the effect of columnar recombination and agrees qualitatively with Jaffé's theory. The value of the parameter b in Jaffé's formula, which gives the best agreement with the experiments, was newly determined as 9.5×10 -4 for alpha-particles in atmospheric air. The observed specific ionization curve was corrected for recombination by Jaffé's theory. Then, the corrected curve was integrated and the true ionization-range relation free from recombination was determined. By comparing this relation with the fixed points of the range-energy relation obtained from nuclear reaction data, an empirical formula for the average energy loss per ion pair for alpha-particles in air relative to polonium alpha-particles, w , was obtained as; \begin{aligned} w{=}0.948+\frac{0.119}{\sqrt{E}}, \end{aligned} where E is the initial alpha-energy in Mev. This formula is valid at least for the alpha-energy down to 1 Mev.

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