High-sensitivity study of levels in Al30 following β decay of Mg30

Abstract

γ -ray and fast-timing spectroscopy were used to study levels in 30 Al populated following the β − decay of 30 Mg. Five new transitions and three new levels were located in 30 Al. A search was made to identify the third 1 + state expected at an excitation energy of ∼2.5 MeV. Two new levels were found, at 3163.9 and 3362.5 keV, that are firm candidates for this state. Using the advanced time-delayed (ATD) βγ γ (t) method we have measured the lifetime of the 243.8-keV state to be T 1/2 = 15(4) ps, which implies that the 243.8-keV transition is mainly of M1 character. Its fast B(M1; 2 + → 3 + ) value of 0.10(3) W.u. is in very good agreement with the USD shell-model prediction of 0.090 W.u. The 1801.5-keV level is the only level observed in this study that could be a candidate for the second excited 2 + state.

Fast-timing spectroscopy at ISOLDE

“…For instance, neutron-rich aluminium nuclei are placed at an interesting merging point at the border of the island of inversion, and they can serve to test shell-model calculations using sd configurations, and including the intruder fp shell intruders is required. A recent study on 30 Al [30] confirms that it is outside the island of inversion and that no sizeable occupation of the fp orbits is needed to reproduce either the low energy positive parity states, or the measured B(M1) transition rates.…”

“…The 0 2 + intruder state in 30 Mg was suggested by Mach et al [34] to be located at 1788keV, based on the rearrangement of the level scheme and the measured T 1 2 = 3.9(4)ns half life.…”

“…Its origin is linked to modifications of the monopole term of the residual nuclear interaction between valence nucleons and the effect of the quadrupole interaction. For even-even nuclei such as 30,32 Mg, spherical and deformed 0 + states coexist a low energies.…”

“…The 0 2 + intruder state in 30 Mg was suggested by Mach et al [34] to be located at 1788keV, based on the rearrangement of the level scheme and the measured T 1 2 = 3.9(4)ns half life. Recently the lifetime of the 1788 keV 0 + level in 30 Mg, populated in the β-decay of 30 Na has been obtained with higher precision [31], and limits have been established for the 1482 and 2467 keV states.…”

“…Recently the lifetime of the 1788 keV 0 + level in 30 Mg, populated in the β-decay of 30 Na has been obtained with higher precision [31], and limits have been established for the 1482 and 2467 keV states. The excited 0 + state at 1788keV had been confirmed by the direct measurement of the E0 transition [35] together with its monopole strength.…”