Ionization by low energy heavy ions in nitrogen, carbon dioxide, argon and hydrocarbon gases

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Abstract Experimental data on the variation of W, the mean energy expended by a charge particle in producing an ion pair in a gas, with the mass, charge and energy of the particle is examined with a view to discovering how far these variations may be explained in terms of elastic nuclear scattering. In nitrogen and carbon dioxide W appears to depend not only on the elastic nuclear scattering but also on the parameter E/MZ4/3 for ions other than piotons. In argon any relationship is obscured by apparent discrepancies in the data, although it is possible that the variation may be similar to that in nitrogen and carbon dioxide. The data for the hydrocarbon gases is not so extensive as for the other gases and it may be that the variation of W with the mass and charge of the ion is different from that in nitrogen and carbon dioxide. It is speculated that this difference, if real, is due to super-excited states in the hydrocarbon gases. Some empirical relationships are suggested as a practical guide for use in dosimetry.