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Action of Slow Neutrons on Rare Earth Elements


IN view of the discrepancy between the values obtained by different workers for the periods and the intensity of radiation emitted by the radio rare earth elements1–5 after neutron bombardment, we carried out a detailed investigation on this subject and also on the absorption of slow neutrons in rare earth elements. The latter measurements were carried out chiefly to ascertain the possible presence of strongly capturing isotopes but leading to the formation of a stable instead of an active isotope, as was actually found to be the case for europium. Our investigations lead to the result that the discrepancies can in most cases be explained through the presence of small amounts of impurities showing a very strong activity, like dysprosium in the sample investigated, while some of the very high absorption data found by different workers are due to the presence of highly absorbing substances like gadolinium, samarium or dysprosium in the samples used.


  1. E. Amaldi, E. Fermi and others, Proc. Roy. Soc., A. 149, 522 (1935).

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  2. S. Sugden, NATURE, 135, 469 (1935).

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  3. I. K. March and S. Sugden, NATURE, 136, 102 (1935).

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  4. G. Hevesy and H. Levi, NATURE, 136, 103 (1935).

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  5. Amaldi, Fermi l.c.; according to Sugden l.c. not active; while McLennan finds a period of 6·4 hours (NATURE, 136, 831 (1935)).

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HEVESY, G., LEVI, H. Action of Slow Neutrons on Rare Earth Elements. Nature 137, 185 (1936).

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