Low-Lying Excited States ofNa22

Abstract

Using the singly and doubly ionized helium beams as well as a ${\mathrm{He}}^3$ beam from our electrostatic generator, we have studied the low-lying level structure of ${\mathrm{Na}}^{22}$ in the ${\mathrm{F}}^{19}(\alpha , n\gamma ){\mathrm{Na}}^{22}$ and ${\mathrm{Ne}}^{20}({\mathrm{He}}^3, p\gamma ){\mathrm{Na}}^{22}$ reactions, respectively. We found one excited state at 666±4 kev in addition to most other states previously discovered in the self-conjugate reaction ${\mathrm{Mg}}^{24}(d, \alpha ){\mathrm{Na}}^{22}$ which presumably yields only states having $T=0\mathrm{}$. We believe this state to be the $0^{+}$ analog of the ground states of the two neighboring even-even nuclei forming the $T=1\mathrm{}$ triplet at $A=22\mathrm{}$. By various coincidence experiments, this state is found to decay by a 73-kev transition, having a probable half-life of 0.014 μsec, to the first-excited state of ${\mathrm{Na}}^{22}$ at 593 kev, which in turn decays to the $3^{+}$ ground state with a half-life of 0.266±0.010 μsec. With the plausible assignment of $1^{+}$ for the 593-kev state ($0^{+}$ being completely ruled out by the half-life) this would represent a pure $M1\mathrm{}$—pure $E2\mathrm{}$ cascade, whose strengths would be 0.0045 and 0.0077 single-particle units, respectively. The location of the first $T=1\mathrm{}$ state occurs exactly as expected from a systematic study of the $A=4n+2\mathrm{}$ series Coulomb-energy differences, lending additional support to the $I=0^{+}$, $T=1\mathrm{}$ assignment.