New Isotope,Al30

Abstract

Scintillation measurements were made of the beta and gamma radiation from high-purity natural silicon targets after bombardment with fast neutrons produced by the ${\mathrm{Li}}^{7}(d, n){\mathrm{Be}}^{8}$ reaction (${E}_{n}\ensuremath{\lesssim}24$ Mev). In addition to well-known radiations, a beta spectrum with an end point of 5.05\ifmmode\pm\else\textpm\fi{}0.25 Mev and two gamma rays with energies of 2.26\ifmmode\pm\else\textpm\fi{}0.03 and 3.52\ifmmode\pm\else\textpm\fi{}0.03 Mev were observed. These gamma rays and the beta group decayed, within experimental error, with the same half-life, 3.27\ifmmode\pm\else\textpm\fi{}0.20 sec. The assignment of this activity to ${\mathrm{Al}}^{30}$ and the proposed decay scheme are supported by considerations involving the decay schemes of the well-known isotopes produced, half-life studies using portions of both the beta and gamma spectra, the features of experimental beta and gamma spectra, and nuclear systematics. Strong beta transitions to the first and second excited states of ${\mathrm{Si}}^{30}$ are inferred from the experimental gamma spectrum and nuclear systematics. A weak beta transition (2%) to the ground state cannot be excluded by this investigation. Possible spin and parity assignments for the ground state of ${\mathrm{Al}}^{30}$ are 1+, 2+, and 3+. A weak argument is made against a spin 1 assignment. The results of this investigation cannot be used to reduce the ambiguity of the spin assignment further. The resulting ${\mathrm{Al}}^{30}$-${\mathrm{Si}}^{30}$ mass difference is 7.29\ifmmode\pm\else\textpm\fi{}0.25 Mev.