Image from page 148 of "The Bell System technical journal" (1922)
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the sym-metrical case aforesaid. This experiment was first performed by Kirchner of Munich, whogot several pictures of paired fragments from lithium bombarded byprotons. Fig. 13 shows an example. (The third track is rather CONTEMPORARY ADVANCES IN PHYSICS 135 annoying, but it was quite an achievement so to adjust the conditionsas to get so few as three.) Many splendid examples have lately beenpublished by Dee and Walton of the Cavendish, and Fig. 14 is out-standing among them because the bombarding stream was a mixtureof protons and deutons, and the picture shows two pairs of fragments,one apparently due to each of the processes which I have been de-scribing. Those of the pair marked &1&2 have the range of 8.4 cm.agreeing with equation (1), while those marked aia2 go definitelyfarther and even escape from the chamber, which makes it impossibleto measure their ranges. Dee and Walton therefore made the wallsof the target-capsule thicker, so that more of the energy of the frag-
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Fig. 13âTracks of paired fragments, He nuclei resulting from impact of a proton on aLi nucleus. (Kirchner; Bdyrische Akademie) ments should be consumed in them; the pairs which were obtainedwith bombarding deutons now ended in the chamber and in the fieldof view, and their ranges agreed with the 13.2 cm. obtained from thecurve of Fig. 9. At least two more of these pairs appear in Fig. 15.Verification of a theory could scarcely go further or be more vivid!Yet there is the additional point, that Kirchner found the anglebetween the paired paths in his pictures to differ from 180Â° by justabout the amount required by the momentum of the proton. However not every fragment observed when lithium is bombarded,either by protons or by deutons, results from these superbly simpleinteractions. Notice in Fig. 8 the two very much rounded steps,suggesting groups of short ranges (1.15 cm. and 0.65 cm.); these areconfirmed by the maxima in the curve of Fig. 10 which has already 136 BELL SYSTEM TECHNI
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