Shape coexistence near the neutron number N=20: First identification of the E0 decay from the deformed 0^+_2 state in 30Mg

TL;DR

This paper reports the first identification of an E0 decay from the deformed 0^+_2 state in 30Mg, providing insights into shape coexistence and configuration mixing near N=20.

Contribution

It presents the first measurement of E0 decay from the 0^+_2 state in 30Mg and combines experimental data with theoretical calculations to analyze shape coexistence.

Findings

Small E0 transition strength indicates minimal configuration mixing.

Ground state has neutron configurations below N=20 shell closure.

Excited 0^+ state involves neutrons excited into the nu1 f_{7/2} orbital.

Abstract

The 1789 keV level in 30Mg was identified as the first excited 0^+ state by measuring its E0 transition to the ground state. The measured small value of rho^2(E0,0^+_2 --> 0^+_1) = 5.7(14) x 10^-3 implies a very small mixing of competing configurations with largely different intrinsic quadrupole deformation near N=20. Axially symmetric Beyond-Mean-Field configuration mixing calculations identify the ground state of 30Mg to be based on neutron configurations below the N=20 shell closure, while the excited 0^+ state mainly consists of a two neutrons excitated into the nu1 f_{7/2} orbital. Using a two-level model, a mixing amplitude of 0.08(4) can be derived.