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The Application of the Electron Lens to Cloud Chamber Photography

  • W. T. Davies (a1) and C. O'Ceallaigh (a2)

Extract

During the course of a cloud chamber investigation of the occurrence of rare events accompanying the passage of fast β-particles through matter, it was found* that existing methods of introducing high-energy electrons into the chamber were unsatisfactory. Electrons of sufficiently high energy could only be obtained from sources which emit, in addition, a large amount of γ-radiation. Absorption of this γ-radiation in the walls and gas of the chamber resulted in the ejection of numbers of stray electrons, whose presence rendered the observation of the fast β-ray tracks a matter of some difficulty.

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* By one of us (W. T. D.) with the collaboration of M. A. Fromageot.

Ho, P. C., Proc. Camb. Phil. Soc. 31 (1934), 119.

Terroux, and Alexander, , Proc. Camb. Phil. Soc. 28 (1931), 115.

§ While this work was in progress a description was given by Staub (Helv. Phys. Acta, 9 (1936), 306–16) of a solenoidal electron lens used in conjunction with a Wilson chamber. Many of the considerations studied hereafter do not apply to his arrangement.

Klemperer, , Phil. Mag. 20 (1936), 545.

* Busch, , Arch. Elektrotechnik, 18 (1927), 583; Henriot, , Revue, d'optique, 14 (1935), 146.

* The focused electrons were assumed to have energies distributed between 1 and 2·5 M.V. An energy equivalent to Hp = 7000 is a rough mean value.

* Since the beam of electrons has a width of several cm. φ will vary appreciably (~ 20°) from one edge of the beam to the other.

* The focal length could not be decreased sufficiently, and it was inconvenient to lengthen the tube. A larger object distance would result in the permissible divergence being exceeded.

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