Abstract
The low-energy structure of the neutron-rich nucleus Ni68 has been investigated by measuring the β decay of the low-spin isomer in Co68 selectively produced in the decay chain of Mn68. A revised level scheme has been built based on the clear identification of β-γ-E0 delayed coincidences. Transitions between the three lowest-lying 0+ and 2+ states are discussed on the basis of measured intensities or their upper limits for unobserved branches and state-of-the-art shell model calculations.
Figures
![FIG. 1. Time spectrum between two consecutive signals in the plastic detectors in the time region [−1000, −125] ns and [+50, +1000] ns, outside the prompt time distribution to exclude β scattering from one detector to another.](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/b7a1bcee-b40f-35d8-b729-a1ba7c2424fa/thumbnail-e4eb833a-15ea-477a-bc70-613f737028e7-0.png)
![FIG. 3. (Color online) β-gated γ -ray spectrum in the time window [350, 2200] ms after the proton pulse impinged on the target when (blue) lasers are tuned to resonantly ionize Mn and (red) lasers are off. The laser-off spectrum was scaled to the laser-on one using the 1313-keV peak from 136I for comparison. Symbols indicate lines associated with: 68Co decay (stars), 68Fe decay (squares), 67Fe and 67Co decay after β-delayed neutron emission (triangles), laser off 68Ga and 136I contaminants decay (circles).](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/b7a1bcee-b40f-35d8-b729-a1ba7c2424fa/thumbnail-104c9eb1-c3ea-4212-8393-3634c2398005-2.png)
![FIG. 4. Decay scheme of 68Co. All the β-feeding percentages should be considered as upper limits (see text) and the missed feeding (possibly β, E0, or γ feeding) was determined using the method of Ref. [27]. Tentative spin-parity assignments in brackets for higher spin states (4−,3−,4+) comes from Refs. [12,23]. When indicated with a 1u exponent, logf t values were taken assuming a first-forbidden unique transition. Asterisk (∗) from Ref. [11], upsidedown triangle (∇ ) from Ref. [32].](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/b7a1bcee-b40f-35d8-b729-a1ba7c2424fa/thumbnail-8af29ddf-0c16-4870-9db1-96a89042e904-3.png)
![TABLE I. (top) Summary of γ energies and intensities in 68Ni relative to the (2+1 → 0+1 ) γ -ray transition obtained in this work compared to the published results of Muelleret al. for the decay of the low-spin isomer of 68Co [11]. (bottom) Intensities and 2σ upper limits (95% CL) determined for different 0+ to 0+ decays.](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/b7a1bcee-b40f-35d8-b729-a1ba7c2424fa/thumbnail-2eb2df56-2429-466b-afea-3a6a44631686-4.png)
![TABLE II. Absolute B(E2) in e2fm 4 and B(E2) ratios R(Eγ ) for low-lying transitions in 68Ni. Theoretical values for MCSM calculations using the revised A3DA interaction (see Ref. [6] for details) and SM calculations using the LNPS interaction from Ref. [8] are compared to experimental values. Effective charges en = 0.5e and ep = 1.5e were used in the A3DA calculations.](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/b7a1bcee-b40f-35d8-b729-a1ba7c2424fa/thumbnail-bdbd3713-38c4-40d1-9177-ab27dfbf48fd-5.png)
![FIG. 5. (Color online) Level scheme of 68Ni focused on the lowlying 0+ and 2+ states with their experimental B(E2) ratios [R(Eγ )] normalized to ground state transitions for each level. For the 0+3 state at 2511 keV, limits on branching ratios are quoted instead of B(E2) ratios (indicated with an asterisk).](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/b7a1bcee-b40f-35d8-b729-a1ba7c2424fa/thumbnail-8dc4b00a-880c-4594-91eb-2802e23ce354-6.png)
![FIG. 6. (Color online) Potential energy surfaces (PESs) obtained fromMCSM calculations [6] for the 0+ and 2+ states of 68Ni, coordinated by the usual quadrupole momentsQ0 andQ2 (or γ ). Circles on the PES represent shapes of MCSM basis vectors (see Ref. [6] for more details).](https://s3-eu-west-1.amazonaws.com/com.mendeley.prod.article-extracted-content/images/b7a1bcee-b40f-35d8-b729-a1ba7c2424fa/thumbnail-94015871-85f9-44bb-87e1-d817ad824a79-7.png)
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CITATION STYLE
Flavigny, F., Pauwels, D., Radulov, D., Darby, I. J., De Witte, H., Diriken, J., … Wimmer, K. (2015). Characterization of the low-lying 0+ and 2+ states in Ni 68 via β decay of the low-spin Co 68 isomer. Physical Review C - Nuclear Physics, 91(3). https://doi.org/10.1103/PhysRevC.91.034310
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