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Abstract

A determination of W, the average energy to produce an ion pair, in dry carbon dioxide-free air was made for the alpha particles from Po/sup 210/. The ionization was measured at air pressures of 5 cm of mercury, where conditions are optimum for a minimum loss by ion recombination. The value obtained was 34.96 plus or minus 0.07 ev/ion pair, a result somewhat lower than in earlier determinations. Comparison measurements under the same conditions yielded absolute values for N/sup 2/ and C/sup 2/R/sup 4/ of 36.39 plus or minus 0.07 and 28.03 plus or minus 0.05 ev/ion pair, respectively, in gocd agreement with older values. This agreement confirms the known fact that columnar recombination difficulties are much less severe in these two gases than in air. The present value for W in air under conditions of minimum ion recombination would seem to present difficulties for the suggestion that W for alpha and beta particles may be the same, the apparent differences being attributed to experimental errors due to ion recombination in the alpha -particle determinations. In the light of recent measurements the W for beta particles is probably not greater than 34.0 ev/ion pair. Such a resuit would seem hardmore » to reconcile with the present value of appronimately 35.0 ev/ion pair for the polonium alpha particle. Such considerations, however, do not rule out the possibility that with increasing alpha particle energy the ratio W/sub alpha /W/sub beta / approaches unity as a limit, as has already been suggested. Less precise measurements of the ionization in air from single alpha particles, ranging in energy from 1 to 5 Mev, are in fairly good accord with older measurements, where gocd ion collection in air at atmospheric pressure is achieved by the use of extremely high fields. (auth)« less

The Ionization by Polonium Alpha Particles in Air and the Average Energy to Make an Ion Pair

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