Radioactive substances and their radiations / by E. Rutherford.

  • Ernest Rutherford
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Radioactive substances and their radiations / by E. Rutherford. Source: Wellcome Collection.

    53/724 (page 41)
    Value of a. Gas Townsend McClung Langevin Air . 3420 x e 3384 x e 3200 x e Carbon Dioxide 3500 x e 3492 x e 3400 x e Hydrogen 3020 x e Assuming that the value of e (see section 20) is 4’65 x 10-10 e.s. units, a = 1'5 x 10~6. Using this value, it can readily be shown from the equation of recombination that, if 106 ions are present per c.c., half of them recombine in about 0*7 sec. and 99 °/0 in 70 secs. The effect of pressure of the gas on the recombination constant has been examined by McClung and Langevin. The results indicate that the rate of recombination diminishes rapidly with lowering of the pressure. Erikson* and Phillips j- have shown that the value of a decreases rapidly with rise of temperature. In experiments on recombination it is essential that the gas should be free from dust or other suspended particles. In dusty air, the coefficient of recombination is much greater than in dust- free air, as the ions diffuse rapidly to the comparatively large dust particles distributed throughout the gas. The effect of the suspension of small particles in a conducting gas is very well illustrated by an experiment of Owens|. If tobacco smoke is blown between two parallel plates as in Fig. 1, the current at once diminishes to a small fraction of its former value, although a voltage is applied sufficient to produce saturation under ordinary conditions. A much larger voltage is then necessary to produce saturation. If the smoke particles are removed by a stream of air, the current returns at once to its original value. 17. Mobility of the ions. Determinations of the mobility of the ions, i.e. the velocity of the ions under a potential gradient of 1 volt per cm., have been made by a number of observers for gases exposed to Rontgen rays. Although widely different methods have been employed, the results have been very concordant, and fully support the view that the ions move with a velocity pro¬ portional to the strength of the field. On the application of a * Erikson, Phil. Mag. 18, p. 328, 1909. f Phillips, Proc. Roy. Soc. A, 83, p. 246, 1910. X Owens, Phil. Mag. 48, p. 360, 1899.