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Excited states with seniority $\ensuremath{\nu}=3$, 5, and 7 have been investigated in odd neutron-rich $^{119,121,123,125}\text{Sn}$ isotopes produced by fusion-fission of 6.9-MeV/$A\phantom{\rule{4pt}{0ex}}^{48}\text{Ca}$ beams with $^{208}\text{Pb}$ and $^{238}\text{U}$ targets and by fission of a $^{238}\text{U}$ target bombarded with 6.7-MeV/$A\phantom{\rule{4pt}{0ex}}^{64}\text{Ni}$ beams. Level schemes have been established up to high spin and excitation energies in excess of 6 MeV, based on multifold gamma-ray coincidence relationships measured with the Gammasphere array. In the analysis, the presence of isomers was exploited to identify gamma rays and propose transition placements using prompt and delayed coincidence techniques. Gamma decays of the known $27/{2}^{\ensuremath{-}}$ isomers were expanded by identifying new deexcitation paths feeding $23/{2}^{+}$ long-lived states and $21/{2}^{+}$ levels. Competing branches in the decay of $23/{2}^{\ensuremath{-}}$ states toward two $19/{2}^{\ensuremath{-}}$ levels were delineated as well. In $^{119}\text{Sn}$, a new $23/{2}^{+}$ isomer was identified, while a similar $23/{2}^{+}$ long-lived state, proposed earlier in $^{121}\text{Sn}$, has now been confirmed. In both cases, isomeric half-lives were determined with good precision. In the range of $\ensuremath{\nu}=3$ excitations, the observed transitions linking the various states enabled one to propose with confidence spin-parity assignments for all the observed states. Above the $27/{2}^{\ensuremath{-}}$ isomers, an elaborate structure of negative-parity levels was established reaching the ($39/{2}^{\ensuremath{-}}$), $\ensuremath{\nu}=7$ states, with tentative spin-parity assignments based on the observed deexcitation paths as well as on general yrast population arguments. In all the isotopes under investigation, strongly populated sequences of positive-parity ($35/{2}^{+}$), ($31/{2}^{+}$), and ($27/{2}^{+}$) states were established, feeding the $23/{2}^{+}$ isomers via cascades of three transitions. In the $^{121,123}\text{Sn}$ isotopes, these sequences also enabled the delineation of higher-lying levels, up to ($43/{2}^{+}$) states. In $^{123}\text{Sn}$, a short half-life was determined for the ($35/{2}^{+}$) state. Shell-model calculations were carried out for all the odd Sn isotopes, from $^{129}\text{Sn}$ down to $^{119}\text{Sn}$, and the results were found to reproduce the experimental level energies rather well. Nevertheless, some systematic deviations between calculated and experimental energies, especially for positive-parity states, point to the need to improve some of the two-body interactions used in calculations. The computed wave-function amplitudes provide for a fairly transparent interpretation of the observed level structures. The systematics of level energies over the broad $A$ = 117--129 range of Sn isotopes displays a smooth decrease with mass $A$, and the observed regularity confirms most of the proposed spin-parity assignments. The systematics of the $B(E2)$ reduced transition probabilities extracted for the $23/{2}^{+}$ and $19/{2}^{+}$ isomers is discussed with an emphasis on the close similarity of the observed $A$ dependence with that of the $E2$ transition rates established for other $\ensuremath{\nu}=2$, 3, and 4 isomers in the Sn isotopic chain.

Excited states above the seniority $\ensuremath{\nu}=2$ isomers have been investigated in even neutron-rich ${}^{118--128}$Sn isotopes produced by fusion-fission of 6.9 MeV/$A$ $^{48}\mathrm{Ca}$ beams with $^{208}\mathrm{Pb}$ and $^{238}\mathrm{U}$ targets and by fission of 6.7 MeV/$A$ $^{64}\mathrm{Ni}$ beams on a $^{238}\mathrm{U}$ target. Level schemes up to excitation energies in excess of 8 MeV have been established based on multifold $\ensuremath{\gamma}$-ray coincidence relationships measured with the Gammasphere array. Isotopic identification of crucial transitions was achieved through a number of techniques, including prompt and delayed cross-coincidence methods. As a result, seniority $\ensuremath{\nu}=4$, 15${}^{\ensuremath{-}}$, and 13${}^{\ensuremath{-}}$ isomers were observed and their half-lives determined. These long-lived states in turn served as steppingstones to delineate the isomeric decays and to locate higher-lying states with good sensitivity. As the observed isomeric decays feed down to 10${}^{+}$ and 7${}^{\ensuremath{-}}$ isomers, firm spin-parity assignments could be proposed for most of the seniority $\ensuremath{\nu}=4$ states. Higher-lying, seniority $\ensuremath{\nu}=6$ levels were assigned tentatively on the basis of the observed deexcitation paths as well as of general yrast population arguments. Shell-model calculations were carried out down to $^{122}\mathrm{Sn}$ in the ${g}_{7/2}$, ${d}_{5/2}$, ${d}_{3/2}$, ${s}_{1/2}$, and ${h}_{11/2}$ model space of neutron holes with respect to a $^{132}\mathrm{Sn}$ core. Effective two-body interactions were adjusted such that satisfactory agreement with data was achieved for $^{130}\mathrm{Sn}$. The results reproduce the experimental level energies and spin-parity assignments rather well. The intrinsic structure of the states is discussed on the basis of the calculated wave functions which, in many instances, point to complex configurations. In a few cases, the proposed assignments lead to unresolved issues. The smooth, systematic decrease of the level energies with mass $A$ is accompanied by the similarly regular behavior with $A$ of the reduced transition probabilities extracted from the isomeric half-lives. This $A$ dependence is discussed for the $E1$ and $E2$ transitions in the decay of the seniority $\ensuremath{\nu}=4$ isomers and is compared to that determined in earlier work for the $E2$ transition rates from the $\ensuremath{\nu}=2,3$ isomers.

Excited states in ${}^{64}$Ni, ${}^{66}$Ni, and ${}^{68}$Ni were populated in quasielastic and deep-inelastic reactions of a 430-MeV ${}^{64}$Ni beam on a thick ${}^{238}$U target. Level schemes including many nonyrast states were established up to respective excitation energies of 6.8, 8.2, and 7.8 MeV on the basis of \ensuremath{\gamma}-ray coincidence events measured with the Gammasphere array. Spin-parity assignments were deduced from an angular-correlation analysis and from observed \ensuremath{\gamma}-decay patterns, but information from earlier \ensuremath{\gamma}-spectroscopy and nuclear-reaction studies was used as well. The spin assignments for nonyrast states were supported further by their observed population pattern in quasielastic reactions selected through a cross-coincidence technique. Previously established isomeric-state decays in ${}^{66}$Ni and ${}^{68}$Ni were verified and delineated more extensively through a delayed-coincidence analysis. A number of new states located above these long-lived states were identified. Shell-model calculations were carried out in the ${p}_{3/2}{f}_{5/2}{p}_{1/2}{g}_{9/2}$ model space with two effective interactions using a ${}^{56}$Ni core. Satisfactory agreement between experimental and computed level energies was achieved, even though the calculations indicate that all the states are associated with rather complex configurations. This complexity is illustrated through the discussion of the structure of the negative-parity states and of the M1 decays between them. The best agreement between data and calculations was achieved for ${}^{68}$Ni, the nucleus where the calculated states have the simplest structure. In this nucleus, the existence of two low-spin states reported recently was confirmed as well. Results of the present study do not indicate any involvement of collective degrees of freedom and confirm the validity of a shell-model description in terms of neutron excitations combined with a closed $Z$ $=$ 28 proton shell. Further improvements to the calculations are desirable.

Excited states in ${}^{67}$Ni were populated in deep-inelastic reactions of a ${}^{64}$Ni beam at 430 MeV on a thick ${}^{238}$U target. A level scheme built on the previously known 13-$\ensuremath{\mu}$s isomer has been delineated up to an excitation energy of 5.3 MeV and a tentative spin and parity of (21/2${}^{\ensuremath{-}}$). Shell model calculations have been carried out using two effective interactions in the ${f}_{5/2}p{g}_{9/2}$ model space with a ${}^{56}$Ni core. Satisfactory agreement between experiment and theory is achieved for the measured transition energies and branching ratios. The calculations indicate that the yrast states are associated with rather complex configurations, herewith demonstrating the relative weakness of the $N=40$ subshell gap and the importance of multi-particle-hole excitations involving the ${g}_{9/2}$ neutron orbital.

Half-life (${T}_{1/2}$) and \ensuremath{\beta}-delayed neutron branching (${P}_{n}$) values of 492(25) ms and 49(8)$%$, 350(15) ms and 72(8)$%$, and 93(13) ms and 90(10)$%$ for the $r$-process nuclei ${}^{137,138,139}$Sb, respectively, have been measured at the CERN On-Line Isotope Mass Separator (ISOLDE) facility by counting \ensuremath{\beta}-delayed neutrons. More precise ${T}_{1/2}$ and ${P}_{n}$ values of 300(15) ms and 27(4)$%$, and 273(7) ms and 50(8)$%$ for ${}^{136,137}$Sn, respectively, have also been measured. The sources were prepared by using the selective ionization of Sb or Sn with the Resonance Ionization Laser Ion Source and the high-resolution mass separator. The new data for Sb isotopes are compared with calculated ${T}_{1/2}$ and ${P}_{n}$ values for both spherical and nonspherical shapes. The data have been incorporated into parametrized nucleosynthesis calculations of the $r$ process in high-entropy winds of core-collapse supernovae in order to study the properties of the $A$ $=$ 130 solar-system $r$-process abundance peak.

Level structures in $^{61,62}\mathrm{Mn}{}_{36,37}$ were studied with Gammasphere in the reaction of a $430$-MeV $^{64}\mathrm{Ni}$ beam and a thick $^{238}\mathrm{U}$ target. The newly identified levels decrease in excitation energy compared to the analogous structures in the lighter Mn isotopes and behave similarly to states in the corresponding Fe isotones that involve ${g}_{9/2}$ neutron excitations. This behavior illustrates the importance of the inclusion of the $\ensuremath{\nu}{g}_{9/2}$ orbital in any realistic shell-model calculations in this region.

Level structures in $^{60,62}\mathrm{Fe}{}_{34,36}$ and adjacent nuclei were studied with Gammasphere using the reaction of a $430$-MeV $^{64}\mathrm{Ni}$ beam on a 55-mg/cm${}^{2}$ thick $^{238}\mathrm{U}$ target. High-spin level schemes were deduced from singly- and doubly-gated prompt coincidence events. Levels populated in the $\ensuremath{\beta}$ decay of $^{60,62}\mathrm{Mn}$ isomers were studied in singly- and doubly-gated delayed coincidences. Spin and parity assignments were deduced from angular correlations of $\ensuremath{\gamma}$ rays observed in both nuclei, leading to firm positive-parity yrast assignments up through ${8}^{+}$ in $^{62}\mathrm{Fe}$. The observed levels for $^{60}\mathrm{Fe}$ up to $~3.5$ MeV compare well with $\mathit{pf}$ shell-model calculations available in the literature. Calculations performed in a limited $\mathit{pfg}$ basis exhibit reasonable agreement for the ${2}^{+}$, ${4}^{+}$, and ${6}^{+}$ levels in $^{62}\mathrm{Fe}$. However, theoretical descriptions that include the newly identified negative-parity levels in $^{62}\mathrm{Fe}$ require a much larger basis, necessarily including ${g}_{9/2}$ neutrons, as well as improved interactions leading to negative-parity levels.

$\ensuremath{\beta}$ decay of the $^{61}\mathrm{Cr}{}_{37}$ ground state has been studied. A new half-life of $233\ifmmode\pm\else\textpm\fi{}11$ ms has been deduced, and seven delayed $\ensuremath{\gamma}$ rays have been assigned to the daughter $^{61}\mathrm{Mn}{}_{36}$. The low-energy level structure of $^{61}\mathrm{Mn}{}_{36}$ is similar to that of the less neutron-rich $^{57,59}\mathrm{Mn}$ nuclei. The odd-${A}_{25}$Mn isotopes follow the systematic trend in the yrast states of the even-even, $Z+1$ ${}_{26}$Fe isotopes, and not that of the $Z\ensuremath{-}1$ ${}_{24}$Cr isotopes, where a possible onset of collectivity has been suggested to occur already at $N=36$.

The neutron-rich isotopes {sup 65,67}Fe and {sup 65}Co have been produced at the LISOL facility, Louvain-La-Neuve, in the proton-induced fission of {sup 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 {sup 65}Co have also been populated in the {sup 64}Ni+{sup 238}U reaction at Argonne National Laboratory. The level structure of {sup 65}Co could be investigated by combining all the information from both the {sup 65}Fe and {sup 65}Co{beta} decay and the deep-inelastic reaction. The {sup 65}Fe, {sup 65}Co, and {sup 67}Fe decay schemes and the {sup 65}Co yrast structure are fully established. The {sup 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.

Two prompt $\ensuremath{\gamma}$ rays of energies 2020 and 554 keV were observed in coincidence with delayed transitions depopulating the ${19/2}^{\ensuremath{-}}$ isomer in the $Z=29$, $N=42$ $^{71}\mathrm{Cu}$ nucleus. The newly identified transitions are proposed to deexcite the 4776- and 5330-keV levels above the ${19/2}^{\ensuremath{-}}$ isomer. Based on the comparison with the low-lying positive-parity states observed in the $Z=42$, $N=50$ $^{92}\mathrm{Mo}$ nucleus, spin and parity ${23/2}^{\ensuremath{-}}$ are proposed for the 4776-keV level in $^{71}\mathrm{Cu}$. The high-energy, 2020-keV transition is interpreted as arising from the breaking of the $N=40$ neutron core. Shell-model calculations with a $^{56}\mathrm{Ni}$ core reproduce the $(23/{2}^{\ensuremath{-}})\ensuremath{\rightarrow}(19/{2}^{\ensuremath{-}})$ gap well, suggesting that the ${23/2}^{\ensuremath{-}}$ state is dominated by $\ensuremath{\pi}{p}_{3/2}\ensuremath{\nu}((\mathit{fp}){}^{10}({g}_{9/2}){}^{4})$ configurations. The present result constitutes further evidence supporting the view that the $N=40$ subshell closure persists in $^{71}\mathrm{Cu}$, herewith challenging recent suggestions that the coupling of two or more proton or neutron quasiparticles induces a large polarization of the $^{68}\mathrm{Ni}$ core.

New levels have been established above the 861-keV, $9/{2}^{+}$ isomeric state in $^{61}\mathrm{Fe}$. The observations can be reproduced satisfactorily by shell model calculations, but only after a significant lowering of the $\ensuremath{\nu}{g}_{9/2}$ single-particle energy with respect to the value determined empirically from levels outside a $^{48}\mathrm{Ca}$ core. The results are also described well within the scope of the particle-triaxial-rotor model assuming a deformation ${\ensuremath{\beta}}_{2}~0.24$. The present findings, together with the recently measured magnetic and quadrupole moments of this state, point toward a structure possibly associated with a prolate shape.

The first in-beam γ-ray spectroscopy study of Al24 is presented. A complete level structure of Al24 incorporating all states below the proton-emission threshold, has been constructed. The first excited state above the proton threshold has also been identified as a 3+ state at 2345.1 ± 1.4 keV. This state, corresponding to a resonance energy of 473 ± 3 keV, has been suggested to be the dominant resonance contributing to the Mg23(p,γ)Al24 stellar reaction rate. The improved precision of the level energy and unambiguous assignment of the state has reduced the uncertainty of the Mg23(p,γ)Al24 stellar reaction rate, which constrains the production of A>20 nuclei in ONe novae. © 2008 The American Physical Society.

\ensuremath{\beta}-decay properties of neutron-rich Ca isotopes have been obtained. Half-life values were determined for the first time for $^{54}\mathrm{Ca}$ ($86\ifmmode\pm\else\textpm\fi{}7$ ms), $^{55}\mathrm{Ca}$ ($22\ifmmode\pm\else\textpm\fi{}2$ ms), and $^{56}\mathrm{Ca}$ ($11\ifmmode\pm\else\textpm\fi{}2$ ms). The half-life of $230\ifmmode\pm\else\textpm\fi{}60$ ms deduced for $^{53}\mathrm{Ca}$ is significantly longer than reported previously, where the decay chain $^{53}\mathrm{K}$ \ensuremath{\rightarrow} $^{53}\mathrm{Ca}$ \ensuremath{\rightarrow} $^{53}\mathrm{Sc}$ was considered. A delayed \ensuremath{\gamma} ray with an energy of 247 keV was identified following \ensuremath{\beta} decay of $^{54}\mathrm{Ca}$ and is proposed to depopulate the ${1}_{1}^{+}$ level in $^{54}\mathrm{Sc}$. The \ensuremath{\beta}-decay properties compare favorably with the results of shell-model calculations completed in the full $\mathit{pf}$ space with the GXPF1 interaction. The half-lives of the neutron-rich Ca isotopes are also compared with gross \ensuremath{\beta}-decay theory. The systematic trend of the neutron-rich Ca half-lives is consistent with the presence of a subshell gap at $N=32$.

The presence of isomeric levels with half-lives in the microsecond range has been identified in $^{125,126,127,128}\mathrm{Cd}$. Neutron-rich Cd isotopes were produced from the fragmentation of a 120 MeV/nucleon $^{136}\mathrm{Xe}$ beam and uniquely identified through their time-of-flight, energy loss, and total kinetic energy. \ensuremath{\gamma} rays from these isomeric levels were measured with an array of Ge detectors that were gated for 15 \ensuremath{\mu}s by a particle implantation trigger from a stack of Si detectors. The \ensuremath{\gamma} rays observed in the decay of $^{126,128}\mathrm{Cd}$ isomers populate low-energy levels previously identified in the \ensuremath{\beta} decay of $^{126,128}\mathrm{Ag}$. The \ensuremath{\gamma} rays found in the decay of $^{125,127}\mathrm{Cd}$ isomers are consistent with expected yrast structures observed in lighter, odd-mass Cd isotopes. The appearance of these isomers at the point where $N/Z$ exceeds 1.6 is interpreted as an indication of the onset of a weakened neutron-neutron interaction that has been proposed for $^{134}\mathrm{Sn}$, whose $N/Z$ also exceeds 1.6.

The level structure of the $N=38$ isotone $^{64}\mathrm{Fe}$ was studied with the $^{64}\mathrm{Ni}$ + $^{238}\mathrm{U}$ reaction at 430 MeV. Several new levels were identified and compared to shell model calculations. Results show no evidence for deformation in the ground state, but a possible contribution from intruder orbitals at higher energy and spin.

The {alpha} decay of the neutron-deficient nuclide {sup 105}Te was observed. The {sup 50}Cr({sup 58}Ni,3n) reaction was used to produce {sup 105}Te nuclei. The {sup 105}Te residues were selected with the Argonne Fragment Mass Analyzer and implanted into a double-sided Si strip detector where their subsequent {alpha} decay was detected. An {alpha}-decay Q value of Q{sub {alpha}}=4900(50) keV and a half life of T{sub 1/2}=0.70(-0.17+0.25){mu}s were measured for {sup 105}Te and a reduced {alpha}-decay width of W{sub {alpha}}=3.3(-1.7+2.1) was deduced. The decay properties of {sup 105}Te are compared with those of heavier Te isotopes and theoretical predictions.

The low-energy levels of $^{120}\mathrm{Pd}_{74}$ were populated by $\ensuremath{\beta}$ decay of $^{120}\mathrm{Rh}_{75}$, which was produced via projectile fragmentation of a $^{136}\mathrm{Xe}_{82}$ beam at $120\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\text{nucleon}$. Delayed $\ensuremath{\beta}$-gated $\ensuremath{\gamma}$ rays with energies of 438 and $618\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ were observed in coincidence with $^{120}\mathrm{Rh}_{75}$ fragments and assigned to the ${2}_{1}^{+}\ensuremath{\rightarrow}{0}^{+}$ and ${4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$ transitions, respectively, in $^{120}\mathrm{Pd}_{74}$. Isomeric $\ensuremath{\gamma}$-ray transitions are also reported for $^{120}\mathrm{Rh}_{75}$ and $^{126}\mathrm{Cd}_{78}$. The low-energy structure of $^{120}\mathrm{Pd}_{74}$ shows remarkable similarity to those of the isotopic $^{108}\mathrm{Pd}_{62}$ and isotonic $^{128}\mathrm{Xe}_{74}$ suggesting that these nuclides share the same $Z=50$ and $N=82$ closed shell structures with neutron-rich $^{120}\mathrm{Pd}_{74}$.