Spins, parities and isospins of 26Al levels: Shell-model aspects

Abstract

Abstract Two preceding papers on the 25 Mg(p , γ) 26 Al reaction have presented information on the energies, γ-ray branchings, lifetimes and resonance partial widths of 26Al states in the Ex = 0−9.1 MeV region. These data (combined with information from other reactions) provide new Jπ; T assignments to 127 levels (of which 111 assignments are unambiguous), as discussed in the present paper. The states obtained from a shell-model calculation in the untruncated sd-shell are found to correspond one-to-one with the 30 lowest T = 1 and the 42 lowest T = 0 even-parity states; for many higher T = 0 states the correspondence could also be established. An extensive comparison has been made of experimental and calculated γ-ray strengths. On the average E2IS strengths are calculated correctly, whereas M1IV strengths are high by a factor 1.85. For many levels the decay strengths are in excellent agreement, whereas the poor agreement for some pairs of neighbouring levels with the same Jπ; T value could be ascribed to a poor description of the configuration mixing. In some cases the strength comparison has helped to establish the correspondence between calculated and experimental states. A comparison has also been made between T = 1 levels of 26Al and 26Mg. For one (out of 44) 26Al states the 26Mg parent is unknown, whereas for one 26Mg level the analogue in 26 Al has not been identified.