T. W. Stern
V. P. Alekna
F. E. Senftle
1959
<p>JOHNSON AND NIER<sup>1</sup> have measured the atomic masses of some of the rare-earth isotopes and have shown that the mass difference cerium-142—(barium-138 <span class="mb">+</span> helium-4) is equivalent to 1.68 ± 0.10 MeV. Similar results for the naturally occurring samarium and neodymium isotopes show that the <span class="mb">α</span>-active isotope of each element is the one having the largest possible decay energy. Rasmussen and others<sup>2</sup> suggest that the two or three neutrons just beyond the closed shell of 82 neutrons have decreased binding energies and hence the <span class="mb">α</span>-energy has a maximum about 84 neutrons. Johnson and Nier suggest that the <span class="mb">α</span>-decay of cerium-142 may take place with enough energy to be experimentally observable. Porschen and Riezler<sup>3</sup> examined a sample of un-enriched cerium ammonium citrate using nuclear track plates sensitive to <span class="mb">α</span>-particles. No <span class="mb">α</span>-activity was observed after a 30-day exposure of 1.2 mgm. of the cerium salt. In 1957 Riezler and Kauw<sup>4</sup> reported an alpha activity for an enriched sample of cerium-142. From their results they calculated a half-life of 5.1 × 10<sup>15</sup> years with an uncertainty factor of 2.</p>
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10.1038/184630a0
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Nature Publishing Group
α-Radioactivity of cerium-142
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