Decay ofNa26

Abstract

The bombardment of high-purity natural magnesium targets with fast neutrons from the ${\mathrm{Li}}^7(d, n){\mathrm{Be}}^8$ reaction ($E_n\lesssim 24$ Mev) yielded, in addition to activities associated with well-known isotopes, an activity having an experimental half-life of 1.03±0.06 sec. Scintillation spectrometer measurements showed a (1.82±0.03)-Mev gamma ray and a (6.7±0.3)-Mev beta group decaying with the 1.03-sec half-life. The 6.7-Mev beta group was found to be in coincidence with the 1.82-Mev gamma ray. The assignment of the (1.03±0.06)-sec half-life to ${\mathrm{Na}}^{26}$ produced in the reaction ${\mathrm{Mg}}^{26}(n, p){\mathrm{Na}}^{26}$ and the proposed decay scheme are supported by internally consistent arguments based on the known characteristics of the reaction products and their decay modes; the half-life studies using both beta and gamma radiation; the features of experimental beta and gamma spectra; and nuclear systematics. The decay of the ground state of ${\mathrm{Na}}^{26}$ takes place in part by a (6.7±0.3)-Mev beta transition to the (2+) first excited state of ${\mathrm{Mg}}^{26}$. The intensities of the beta transitions to the (2+) second excited state and (0+) ground state are less than 0.1 of the intensity of the (6.7±0.3)-Mev transition. The possible ground-state spin and parity assignment for ${\mathrm{Na}}^{26}$ is either 1+, 2+, or 3+. A weak theoretical argument against spin 1 is presented. The present experimental measurements alone will not reduce the ambiguity in the spin assignment. A ${\mathrm{Na}}^{26}$—${\mathrm{Mg}}^{26}$ mass difference of 8.5±0.3 Mev is derived from the known level structure of ${\mathrm{Mg}}^{26}$ and the beta transition energy measured in the present investigation.