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

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The nuclear structure of 67 Co has been investigated through 67 Fe β-decay. The 67 Fe isotopes were produced at the LISOL facility in proton-induced fission of 238 U and selected using resonant laser ionization combined with mass separation. The application of a new correlation technique unambiguously revealed a 496(33) ms isomeric state in 67 Co at an unexpected low energy of 492 keV. A 67 Co level scheme has been deduced. Proposed spin and parities suggest a spherical (7/2 − ) 67 Co ground state and a deformed first excited (1/2 − ) state at 492 keV, interpreted as a proton 1p − 2h prolate intruder state.

The neutron-rich isotopes 65,67 Fe and 65 Co have been produced at the LISOL facility, Louvain-La-Neuve, in the proton-induced fission of 238 U. Beams of these isotopes have been extracted with high selectivity by means of resonant laser ionization combined with mass separation. Yrast and near-yrast levels of 65 Co have also been populated in the 64 Ni+ 238 U reaction at Argonne National Laboratory. The level structure of 65 Co could be investigated by combining all the information from both the 65 Fe and 65 Co β decay and the deep-inelastic reaction. The 65 Fe, 65 Co, and 67 Fe decay schemes and the 65 Co yrast structure are fully established. The 65,67 Co level structures can be interpreted as resulting from the coexistence of core-coupled states with levels based on a low-energy proton-intruder configuration.

We report the first observation of the 108 Xe → 104 Te → 100 Sn α-decay chain. The α emitters, 108 Xe [Eα = 4.4(2) MeV, T1 /2 = 58 +106 −23 µs] and 104 Te [Eα = 4.9(2) MeV, T1 /2 <18 ns], decaying into doubly magic 100 Sn were produced using a fusion-evaporation reaction 54 Fe(58 Ni,4n) 108 Xe, and identified with a recoil mass separator and an implantation-decay correlation technique. This is the first time α radioactivity has been observed to a heavy self-conjugate nucleus. A previous benchmark for study of this fundamental decay mode has been the decay of 212 Po into doubly magic 208 Pb. Enhanced proton-neutron interactions in the N = Z parent nuclei may result in superallowed α decays with reduced α-decay widths significantly greater than that for 212 Po. From the decay chain, we deduce that the α-reduced width for 108 Xe or 104 Te is more than a factor of 5 larger than that for 212 Po.