Published online by Cambridge University Press: 24 October 2008
The absorption limits for the primary β-particles of mesothorium 2 and uranium X2 have been determined using modified tube counters of various types. Results in good agreement with previous single determinations with gold-leaf electroscopes, and at variance with deductions from expansion chamber observations, show the need for caution in fixing limiting energies in β disintegrations from measurements on a relatively small number of tracks.
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‡ In each determination mesothorium 2 was used when in equilibrium with its long-lived parent substance.
§ Commercial mesothorium generally contains radium and its products to the extent of 20–30% of the total γ-ray activity of the preparation.
* According to present ideas, the emission of a γ-ray quantum of energy 1.65 × 106 e.V. in an appreciable fraction of the disintegrations of the nuclei (but certainly not in all such disintegrations) is strong argument for the emission of the disintegration electron occasionally with more than this amount of energy.