Decay of Neutron-Rich Mn Nuclides and Deformation of Heavy Fe Isotopes

Abstract

The use of chemically selective laser ionization combined with b-delayed neutron counting at CERN/ISOLDE has permitted identification and half-life measurements for 623-ms 61 Mn up through 14-ms 69 Mn. The measured half-lives are found to be significantly longer near N 40 than the values calculated with a quasiparticle random-phase-approximation shell model. Gamma-ray singles and coincidence spectroscopy has been performed for 64,66 In addition to the clear nuclear-structure interest, the neutron-rich Fe-group nuclei may also play an important role as possible seed nuclei in the astrophysical r process [13]. In the present paper, we report new measurements for the half-lives of heavy Mn nuclides up to 69 Mn and for the level structure of 64,66 Fe populated in the decays of 64,66 Mn.Manganese isotopes were produced at CERN by 1-GeV proton-induced spallation of uranium in a thick UC 2 target at the ISOLDE facility. The ionization of the Mn atoms was accomplished using a chemically selective, three-step laser resonance excitation scheme as described in detail earlier [14].Beams of Mn nuclides with masses differing by DA $ 4 were transported separately to two different beam lines equipped with moving tape systems where b-delayed neutron (d.n.) multiscaling and g-ray singles and coincidence measurements could be performed independently. In both cases, counting took place directly at the point of deposit, and the tape systems were used to remove the daughter nuclides as well as unavoidable surfaceionized isobaric Ga activities. Because the Mn half-lives being sought are in the millisecond range, data acquisition in both systems was initiated by the proton pulses from the CERN proton-synchrotron booster (PSB), separated by a multiple of 1.2 s, and continued for 1.0 s for each cycle.Beta-delayed neutron data of high statistical quality were collected by multiscaling measurements using the Mainz 4p 3 He neutron counter. The time dependence of the counting rates for 65 69 Mn is shown in Fig. 1. The decay curves were fitted with a constant small d.n.-background component up through A 65. Because there exist no measured d.n.-emission probabilities (P n values) for the A . 65 daughter and granddaughter isobars, the fits of the heavier isotopes were performed using theoretical P n values [10] along with the known half-lives [5,7,8,15]. For A 66 68, the contributions from d.n. emission of the Fe and Co isobars are quite small and actually do not affect the Mn half-life fits. For A 69, however, a multicomponent fit was necessary to account for the significant Fe and Co d.n. branches. The resulting data are summarized in Table I 0031-9007͞99͞82(7)͞1391(4)$15.00

Characterization of the low-lying0+and2+states inNi68Flavigny1, Pauwels2, Radulov3 et al. 2015Phys. Rev. CSelf Cite462420View full textAdd to dashboardCite

“…At ISOLDE, CERN, T 1/2 = 28(3) ms [24] 68 Mn nuclei were produced in a 1.4 GeV proton-induced 238 U fission reaction and selectively ionized with the resonance ionization laser ion source (RILIS) [25]. After mass separation, the 68 Mn ion beam was implanted on an aluminized mylar tape, inside a movable tape station surrounded by three plastic E β detectors and two MiniBall γ -detector clusters [26] in close geometry.…”

Experimental study of theNi66(d,p) Ni67Diriken1, Raabe2, Eberth3 et al. 2015Phys. Rev. C9150View full textAdd to dashboardCite

“…One of the first observations was the β decay of neutron-rich Mn isotopes, which revealed a sharp decrease of the 2 + 1 energies in 64,66,68 Fe (Z = 26) [5,6] and later in the neutron-rich Cr isotopes (Z = 24) [7]. The discovery of a μs isomer in 67 Fe proved to be compatible with enhanced deformation in this nucleus [8].…”

“…In contrast to the properties of 68 Ni [1][2][3][4], recent experiments point to a swift onset of collectivity in the region below the neutron-rich nickel isotopes (Z = 28) between the N = 40 and N = 50 shell gaps [5][6][7][8][9][10][11][12][13][14][15][16]. One of the first observations was the β decay of neutron-rich Mn isotopes, which revealed a sharp decrease of the 2 + 1 energies in 64,66,68 Fe (Z = 26) [5,6] and later in the neutron-rich Cr isotopes (Z = 24) [7].…”

β−decay of65Mn to65Fe

“…However, shell-model calculations using only the pf g neutron valence space fail to correctly describe the collectivity at N = 40 [1,2], and specifically the low energy of the 573-keV 2 + 1 state in 66 Fe [3]. As pointed out in [4], a proper description of the strong quadrupole collectivity in this region requires also an inclusion of the neutron 1d 5/2 orbital.…”