Collinear Laser Spectroscopy on Neutron-rich Mn Isotopes Approaching $N=40$

Abstract

We have studied 51,53−64 Mn (Z = 25) via bunched-beam collinear laser spectroscopy at ISOLDE, CERN. Model-independent information on the ground-and isomeric state spins, as well as their g-factors is obtained from the measured hyperfine spectra. The spins are essential for further establishing the level schemes in the mass region, while the g-factors reveal the changing ground state wave functions in the Mn chain approaching N = 40.

Low-energy Coulomb excitation of 62Fe and 62Mn following in-beam decay of 62Mn

“…A number of experiments have been performed at ISOLDE recently that allow us to shed light on this question. Firstly, the spins of both β-decaying states were confirmed in a laser-spectroscopy experiment at the COLLAPS setup [30,58]. In this experiment, the longer-lived 4 + state (T 1/2 = 671(5) ms [14]) was observed to have been extracted with a much higher intensity than the 1 + state (T 1/2 = 92(13) ms [56,59]).…”

“…In both 58 Mn and 60 Mn there are a number of positive-parity states that lie above the isomeric 4 + state, the first of which is a I = (2 + ) states at 54 keV and 76 keV, respectively [70]. This represents a good candidate for the state that we observe in 62 Mn from both its energy and decay behaviour.…”

“…A scenario similar to "forced isomer depopulation" [69] factor in -ray decay, and that the electron conversion can be considered negligible. While the 3 + states in 58,60 Mn have a non-negligible branch to the 2 + , it is expected that we populate the state that is lowest in energy and therefore a 100% branch is also assumed for the 3 (+) possibility. The results of such calculations are plotted in Figure 9, where it is shown that the most likely position of the new state is ⇡ 72(3) keV above the -decaying 4…”

“…The gosia2 version of the code allows for a simultaneous least-squares fit of matrix elements in the target and projectile systems, as well as a common set of normalisation constants, to the observed -ray intensities [37]. The target system is over-determined by a complete set of spectroscopic data [54][55][56][57][58][59] plus the observed 5/2 1 ! 1/2 1 intensity, which therefore provides the constraint on the normalisation constant.…”

“…However, it can be shown that the B(E2)" value is relatively independent of the assumption of the spin of the final state and in all cases results in a value of ⇡ 30 W.u., more than double that observed for the 2 62 Fe. This large B(E2) value would imply an intrinsic quadrupole moment, Q 2 (4 + ) ⇡ 122 efm 2 , within the rigidrotor model [62], which can be compared to the limits extracted from the spectroscopic quadrupole moment measured in recent laser-spectroscopy measurements, |Q 2 (4 + )| < 40 efm 2 [30,58]. Such a strong transition is 62 Fe projected from the ellipse obtained using the full data set, including the lifetimes of Refs.…”