Ionization in Pure Gases and the Average Energy to Make an Ion Pair for Alpha and Beta Particles

Abstract

A series of measurements has been made of the relative currents produced in different gases by beta particles from Ni 63 and from tritium sources in an ionization chamber. In all cases only relative current measurements with argon as a standard gas have as yet been made. The value of W, the average energy to make an ion-pair computed relative to argon as a standard, is found to be the same for Ni 63 and tritium sources. If these relative Wp values are plotted as abscissas against previously determined W a values for polonium alpha particles as ordinates, a marked difference is observed in the gases investigated. For hydrogen and the noble gases the plotted points lie closely on a 45 degree straight line through the origin. Thus for these gases the ratio W a /Wp is constant. This constant may well be unity, but this is not proved as yet by these results. For all other gases so far investigated, the plotted points lie above the 45 degree line, indicating a higher efficiency of ionization (and a lower W) for the beta particles than for the polonium alpha particles. These results are in accord with the findings of Gray and Gurney. Gurney's results have been extended here to include a greater variety of gases for reduced alpha particles of approximately 1-Mev energy. Two postulates are advanced to explain the behavior of W a and Wp here found. E XPERIMENTS have been in progress for some time in which the relative ionization for different gases has been measured for beta particles emitted from tritium and Ni 63 sources. Although the results are as yet preliminary, a comparison of them with the corresponding alpha-particle values is of interest and would seem to warrant publication at this time. EXPERIMENTAL METHODS AND RESULTSThe ionization chamber used was a cylindrical one of brass of inside diameter 9.5 cm and height 7 cm (Fig. 1). The collecting electrode at the center of the cylinder was in the form of a wire ring 5 cm in diameter, supported by three wire stays rising from the central insulated shaft. In the plane of the collecting ring and filling the interior was a square gridwork of copper wires spaced 6 mm apart in each direction. In some experiments the individual wires were 2 mils in diameter and in others 6 mils. The wires in the central area of the collecting disk were coated with the beta-emitting substance under investigation. For Ni 63 this coating was accomplished by electroplating. The tritium, in the form of a solution of tritiated polystyrene, was applied with DETAIL OF ELECTRODE FACECopper wires with 6mm spacing in each direction-FIG. 1. Schematic diagram of ionization chamber for beta-particle current measurements. a brush to the gridwork and was made conducting when dry by a light application of graphite-soft lead pencil. The employment of the gridded electrode came as the result of a series of experiments where the source was applied to the extended surface of a plate electrode. The expected ionization seemed to be reduced by what we believe to be a process of backscattering of the very soft bet...

Carbon monoxide yields in the radiolysis of carbon dioxide at very high dose rates

“…These have not been observed (23), so we must assume that reaction [I61 does not occur to any great extent. It should be noted that reaction [16] is spin forbidden (to give 0z3C) and is unlikely on these grounds.…”

Effect of an electric field on superfluid helium scintillation produced byα-particle sources

“…The deposited energy also goes to promoting atoms to excited states. The W value, the average energy required to produce one electron-ion pair, in liquid helium is W ∼ 43 eV [9]. Electrons and ions then thermalize with the liquid helium.…”

Looking at electrons

“…28 The ionization energy for helium is 24.6 eV. In pure helium gas the average energy to produce an electron-ion pair has been measured for an electron 29 to be W = 42.3Ϯ 0.5 eV and for an alpha particle 30 to be slightly larger, 43.3Ϯ 0.3 eV. It is reasonable to assume a comparable average energy needed for muons to produce an electron-ion pair.…”