The positron emitters P28 (0.29 ± 01 sec.) and Cl32 (0.32 ± 01 sec.) have been discovered in (p, n) reactions with thresholds at 15.4 ± 0.6 Mev. and 14.5 ± 0.6 Mev. respectively. Identification is realized through threshold and transition energies as well as through the complex γ-ray spectra identified in part with the known levels of the daughters Si28 and S32.The new nuclei represent an extension to the series A = 4k, Z = 2k + 1, whose initial members, B8, N12, Na20, are delayed α-emitters, while the recently reported Al24 is known to emit delayed alphas or protons.Under re-examination of Al24, a half-life of 2.0 ± 1 sec. is obtained for γ-ray activity which identifies the stable daughter Mg24.The results are in substantial agreement with the recent work of Glass, Jensen, and Richardson. Delayed α-particles are not observed with the new isotopes.
A member of the odd–odd Z = N family, Sc42, has been produced by proton bombardment of a calcium target greatly enriched in Ca42. The positron emission, which alone is observed, has a measured half-life of 0.68 second, end point 4.8. Mev., and threshold 6.8 Mev. The superallowed transition is between ground states (J, T) tentatively described as Sc42 (0+, 1) and Ca42 (0+, 1).
Using the McGill 100-Mev proton synchro-cyclotron, the half-life of Ir'Sm has been redetermined and the value 4.53f0.18 s obtained from 55 trials. The mass assignment is here based on the study of the excitation curves for both osmium and iridium targets. The measured CYL = 2 . 0 f 0.3 for the observed 126-16 I;ev ganlma ray is consistent with the M l + E 2 assignment previously nlade. No 42-lrev gamma ray could be detected.
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