Radionuclides Al24, P28, Cl32, and Sc40

Abstract

Three new short-lived positron emitters, ${\mathrm{P}}^{28}$, ${\mathrm{Cl}}^{32}$, and ${\mathrm{S}\mathrm{c},}^{40}$ of the nuclear series $Z=2n+1\mathrm{}$, $A=4n$ have been produced by $p-n$ reactions using 20-Mev protons from the UCLA 41-in. FM cyclotron. ${\mathrm{Al}}^{24}$ has also been investigated. ${\mathrm{Al}}^{24}$ has a half-life of 2.10±0.04 sec and five gamma rays from 1.39 Mev to 7.12 Mev. 2-Mev alpha particles are emitted in a small fraction of the decays. ${\mathrm{P}}^{28}$ has a half-life of 0.280±0.010 sec, threshold of 15.6±0.5 Mev, eight gamma rays from 1.79 Mev to 7.59 Mev, and positrons of maximum energy 10.6±0.4 Mev. No heavy particles were detected in the decay. ${\mathrm{Cl}}^{32}$ has a half-life of 0.306±0.004 sec, threshold of 14.3±0.5 Mev, four gamma rays from 2.21 Mev to 4.77 Mev, and positrons of maximum energy 9.5±0.4 Mev. 2-3 Mev alpha particles are emitted in a small fraction of the decays. ${\mathrm{Sc}}^{40}$ has a half-life of 0.22±0.03 sec, threshold of 15.9±1.0 Mev, a 3.75±0.04 Mev gamma ray, and maximum positron energy of 9.0±0.4 Mev. No heavy particles were detected in the decay. Possible decay schemes can be set up which involve favored positron transitions to calculated analog levels in the daughters in the cases of ${\mathrm{Al}}^{24}$, ${\mathrm{P}}^{28}$, and ${\mathrm{Cl}}^{32}$. In the ${\mathrm{P}}^{28}$ decay, the positron component to the 1.78-Mev level in ${\mathrm{Si}}^{28}$ has the same $\mathrm{ft}$ value as the negatron decay to this level from ${\mathrm{Al}}^{28}$, thus indicating the similarity of the nuclear wave functions of ${\mathrm{P}}^{28}$ and ${\mathrm{Al}}^{28}$.