Letter | Published:

The Mounting of Thin Glass Windows

Naturevolume 120page156 (1927) | Download Citation



RECENTLY (early spring of 1926) it became desirable to produce a source of α-rays free from the disturbing effects of the accompanying emanation. This source was to be used in connexion with a simple α-ray track apparatus designed by the writer (Jour. Optical Society of Amer., vol. 11, No. 2, Aug. 1925; Science, vol. 64, No. 1649, Aug. 6, 1926). The solution came from a suggestion by one of the writer's students, L. P. Garner, a graduate in electrical engineering, University of Illinois, and for the above purpose leaves nothing to be desired. Briefly it is as follows: A cane c (Fig. 1) of solid glass (Pyrex or Monax) is broken off squarely. On the centre of this end is placed a minute film of dilute shellac, which serves to hold a microscopic quantity of radioactive salt (radium bromide was used). Now prepare a film f by blowing it out of the same glass and so thin that it will show Newton's rings. Hold this film with a pair of forceps in front of and distant about 3/4 inch from the tip of the cane bearing the radioactive salt and bring them up to a soft blast b, as shown in Fig. 1, a. Heat carefully, and as soon as the square tip begins to assume a globular form thrust it through the film f. The result is a varnish of glass, as it were, enveloping the front side of the globule as shown in Fig. 1, b, The burr is now brushed off and the emanationless source of -rays is ready for use, providing no mishap was encountered.

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  1. Cavendish Laboratory, Cambridge

    • CHAS. T. KNIPP


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