Mathematics – Probability
Scientific paper
May 1930
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1930phrv...35.1196t&link_type=abstract
Physical Review, vol. 35, Issue 10, pp. 1196-1216
Mathematics
Probability
11
Scientific paper
Positive caesium ions with velocities of 3.5 to 600 equivalent volts have been studied in hydrogen and helium. No absorption of the ions in the apparatus used is found for pressures below 0.01 mm of mercury. For the higher velocities this absence of absorption persisted for pressures as high as 0.05 mm of mercury. In all cases the ions were retarded in passing through the gas and there is an approximate probability distribution of ion energies about an average retarded value. The retardation in all cases is found to be proportional to the pressure. For Cs+ ions in helium the percent loss of initial energy varies from 11.5 for 400 volt ions to 55 for ions of 3.5 volts initial energy. Similar results are found for hydrogen. Values of the constant, h, of the error curve which are characteristic of a particular distribution are given for various velocities and pressures. An interpretation of the absence of scattering and the retardation of the ions is given on the basis of elastic collisions between ion and gas molecule. It is found that no absorption of the Cs+ ions would be expected until the pressures are high enough to give rise to multiple scattering. The data on retardation give values of the radius of the Cs+ ion as: 1.78A in helium and 3.09A in hydrogen. The slowing up of the ions offers an explanation of the large absorption of Cs+ in helium found by Ramsauer and Beeck. Probability considerations show that for increasing velocities the energy loss per collision found in the present experiments is less than that to be expected on the basis of elastic collisions. The absorption of Li+ ions has been studied by three methods for velocities of 20 to 900 equivalent volts. The coefficients of absorption, C, representing the effective absorbing cross section have been determined by two methods. The general dependence of C on the ion velocity is the same for the two types of apparatus used, but the values of C are found to depend on the dimensions of the absorbing chamber. The results have led to the interpretation of scattering in which forces other than those due to elastic collisions are effective. No general retardation of the Li+ ions was found. Values of C found by Ramsauer and Beeck are interpreted in terms of the dimensions of their apparatus. It is concluded that no absolute significance may be attached to values of atomic radii determined from measurements of this kind.
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