First -and -spectroscopic decay studies of the N 82 r-process ''waiting-point'' nuclide 130 Cd have been performed at CERN/ISOLDE using the highest achievable isotopic selectivity. Several nuclear-physics surprises have been discovered. The first one is the unanticipatedly high energy of 2.12 MeV for the [g 9=2 g 7=2 1 level in 130 In, which is fed by the main Gamow-Teller transition. The second surprise is the rather high Q value of 8.34 MeV, which is in agreement only with recent mass models that include the phenomenon of N 82 shell quenching. Possible implications of these new results on the formation of the A ' 130 r-process abundance peak are presented.

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

The isotopes 68 74 Ni, of interest both for nuclear physics and astrophysics, have been produced in proton-induced fission of 238 U and ionized in a laser ion guide coupled to an on-line mass separator. Their b decay was studied by means of b-g and g-g spectroscopy. Half-lives have been determined and production cross sections extracted. A partial level scheme is presented for 73 Cu and additional levels for 71 Cu, providing evidence for a sharply lowered position of the p1f 5͞2 orbital as occupancy of the n1g 9͞2 state increases. The latter may have a clear impact on the predicted structure and decay properties of doubly magic 78 Ni. [S0031-9007 (98)07340-2]

The 2ZNe(c~,7)26Mg and 22Ne(cq n)2SMg reactions were investigated for E~(lab) from 0.71 to 2.25 MeV. Neon gas enriched to 99% in 22Ne was recirculated in a differentially pumped gas target system of the extended type. The 7-ray transitions were observed with Ge(Li) detectors and the neutrons with 3He ionization chambers. A previously known resonance at ER(lab)= 2.05 MeV was verified and 15 new resonances were found in the energy range covered, with the lowest at ER(lab)=0.83 MeV. Information on resonance energies, widths, strengths, 7-ray branching ratios, as well as J" assignments, is reported. The energy range investigated corresponds to the important temperature range of T9 from 0.3 to 1.4 (109 K), for which the astrophysical rates were determined for both reactions. The results show that the ratios of the rates for 22Ne(c~,n)2SMg and 22Ne(c~, 7)26Mg are significantly smaller than the previously adopted values, e.g., by at least a factor of 60 near T9=0.65. Thus, the 22Ne(e, n)25Mg reaction will likely play a smaller role as a neutron source for s-process nucleosynthesis, than has frequently been assumed.

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Nuclei with magic numbers serve as important benchmarks in nuclear theory. In addition, neutronrich nuclei play an important role in the astrophysical rapid neutron-capture process (r-process). 78 Ni is the only doubly-magic nucleus that is also an important waiting point in the r-process, and serves as a major bottleneck in the synthesis of heavier elements. The half-life of 78 Ni has been experimentally deduced for the first time at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University, and was found to be 110 +100 −60 ms. In the same experiment, a first half-life was deduced for 77 Ni of 128 +27 −33 ms, and more precise half-lives were deduced for 75 Ni and 76 Ni of 344 +20 −24 ms and 238 +15 −18 ms respectively.Doubly-magic nuclei with completely filled proton and neutron shells are of fundamental interest in nuclear physics. The simplified structure of these nuclei and their direct neighbors allows one to benchmark key ingredients in nuclear structure theories such as single-particle energies and effective interactions. Doubly-magic nuclei also serve as cores for shell model calculations, dramatically truncating the model space, thus rendering feasible shell model calculations in heavy nuclei. All this is of particular importance for nuclei far from stability, where doubly-magic nuclei serve as beachheads in the unknown territory of the chart of nuclides [1,2].When considering the classic nuclear shell gaps and excluding superheavy nuclei, there are only 10 doublymagic nuclei, and only four of these are far from stability: 48 Ni, 78 Ni, 100 Sn, and 132 Sn. Of these, 48 Ni and 78 Ni are the most exotic ones, and the last ones with experimentally unknown properties. 78 Ni therefore represents a unique stepping stone towards the physics of extremely neutron-rich nuclei. In a pioneering experiment, Engelmann et al. Very neutron-rich nuclei play an important role in the astrophysical rapid neutron-capture process (r-process) [5,6]. The r-process is responsible for the origin of about half of the heavy elements beyond iron in nature, yet its site and exact mechanism are still unknown. 78 Ni is the only doubly-magic nucleus that represents an important waiting point in the path of the r-process, where the reaction sequence halts to wait for the decay of the nucleus [7].One popular astrophysical site for the r-process is the neutrino driven wind off a hot, newborn neutron star in a core-collapse supernova explosion [8]. In this case the rprocess begins around mass number A = 90, with lighter nuclei being produced as less neutron-rich species in an α-rich freeze-out. For such a scenario 78 Ni would not be directly relevant. However, the α-rich freezeout fails to accurately reproduce the observed abundances for nuclei with A = 80−90 [9], and the associated r-process does not produce sufficient amounts of the heaviest r-process nuclei around A =195 [10].78 Ni is among the important r-process waiting points in models that try to address these issues. Examples ...

The β-decays of very neutron rich nuclides in the Co-Zn region were studied experimentally at the National Superconducting Cyclotron Laboratory using the NSCL β-counting station in conjunction with the neutron detector NERO. We measured the branchings for β-delayed neutron emission (Pn values) for 74 Co (18±15%), and 75−77 Ni (10±2.8%, 14±3.6%, and 30±24%, respectively) for the first time, and remeasured the Pn values of 77−79 Cu, 79,81 Zn, and 82 Ga. For 77−79 Cu and for 81 Zn we obtain significantly larger Pn values compared to previous work. While the new half-lives for the Ni isotopes from this experiment had been reported before, we present here in addition the first half-life measurements of 75 Co (30±11 ms) and 80 Cu (170 +110 −50 ms). Our results are compared with theoretical predictions, and their impact on various types of models for the astrophysical rapid neutron capture process (r-process) is explored. We find that with our new data the classical rprocess model is better able to reproduce the A = 78 − 80 abundance pattern inferred from the solar abundances. The new data also influence r-process models based on the neutrino driven high entropy winds in core collapse supernovae.

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.