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Excited states in the N = 30 neutron-rich 49K have been studied using multi-nucleon transfer reactions with thin targets and the PRISMA-CLARA spectrometer combined with thick-target - coincidence data from Gammasphere. The d3/2 proton-hole state is located 92 keV above the s1/2 ground state and the proton-particle f7/2 state is suggested at 2104 keV. Three other levels are established as involving the coupling to 2+ of two neutrons above the N = 28 shell. The measured or estimated lifetimes served to reinforce the interpretation of the observed level structure which is found to be in satisfactory agreement with shell model calculations.

Excited states in the N=30 neutron-rich isotope K49 have been studied using multinucleon transfer reactions with thin targets and the PRISMA-CLARA spectrometer combined with thick-target γ-coincidence data from Gammasphere. The d3/2 proton-hole state is located 92 keV above the s1/2 ground state, and the proton-particle f7/2 state is suggested at 2104 keV. Three other levels are established as involving the coupling to 2+ of two neutrons above the N=28 shell. The measured or estimated lifetimes served to reinforce the interpretation of the observed level structure, which is found to be in satisfactory agreement with shell-model calculations.

The one-proton knockout reaction Be9(Ti54,Sc53+γ)X at 72 MeV/nucleon has been measured. The location of the first 3/2- state at 2110(3) keV was confirmed, and new γ-ray transitions were observed at 1111(2), 1273(2), 1539(4), and 2495(5) keV. Large spectroscopic strength to excited states in Sc53 was found and attributed to the knockout of sd-shell protons.

The isomeric and β-decay properties of neutron-rich Sc53-57 and Ca53,54 nuclei near neutron number N=32 are reported, and the low-energy level schemes of Sc53,54,56 and Ti53-57 are presented. The low-energy level structures of the 21Sc isotopes are discussed in terms of the coupling of the valence 1f7/2 proton to states in the corresponding 20Ca cores. Implications with respect to the robustness of the N=32 subshell closure are discussed, as well as the repercussions for a possible N=34 subshell closure.

The yrast structure of the neutron-rich nucleus Zr97 has been studied using fission of targetlike products in the reaction of a Ca48 beam on a thick U238 target. The level scheme, known from previous studies up to an excitation energy and spin-parity of approximately 4619 keV and 23/2-, has been extended by about 3 MeV and a few units of angular momentum. Two states fed in the β decay of the 27/2- high-spin isomer in Y97 were identified at 5570 and 5606 keV. The located level structure can be discussed in terms of shell-model configurations.

Gamma rays from Ti52 have been studied with Gammasphere and the Fragment Mass Analyzer using reactions induced by a Ca48 beam on a Be9 target. The data have been used in combination with information from deep-inelastic reactions of Ca48 beams on a thick U238 target at an energy about 25% above the Coulomb barrier. The Ti52 level scheme was expanded considerably, and the lifetimes of some of the identified states were determined for the first time. The excitation of two protons and two neutrons outside the Ca48 core provide new tests of effective interactions in the full pf-shell model space. The positive-parity states in Ti52 were compared to theoretical predictions obtained with the GXPF1A, FPD6, and KB3G effective interactions. The comparisons favor, to a degree, the results computed with the GXPF1A interaction.

β decay of the Cr6137 ground state has been studied. A new half-life of 233±11 ms has been deduced, and seven delayed γ rays have been assigned to the daughter Mn6136. The low-energy level structure of Mn6136 is similar to that of the less neutron-rich Mn57,59 nuclei. The odd-A25Mn isotopes follow the systematic trend in the yrast states of the even-even, Z+1 26Fe isotopes, and not that of the Z-1 24Cr isotopes, where a possible onset of collectivity has been suggested to occur already at N=36.

β-decay properties of neutron-rich Ca isotopes have been obtained. Half-life values were determined for the first time for Ca54 (86±7 ms), Ca55 (22±2 ms), and Ca56 (11±2 ms). The half-life of 230±60 ms deduced for Ca53 is significantly longer than reported previously, where the decay chain K53 → Ca53 → Sc53 was considered. A delayed γ ray with an energy of 247 keV was identified following β decay of Ca54 and is proposed to depopulate the 11+ level in Sc54. The β-decay properties compare favorably with the results of shell-model calculations completed in the full pf space with the GXPF1 interaction. The half-lives of the neutron-rich Ca isotopes are also compared with gross β-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 level structures of 55V and 55Ti, the two nuclei with a single nucleon outside the semi-magic 5422Ti32 core, have been investigated in order to provide new tests of full pf-shell calculations with the GXPF1A interaction. The addition of a proton does not appear to affect the N = 32 shell gap significantly, although comparisons between calculations and experiment at high spins (Iπ ≥ 21 / 2-) indicate the need for a larger model space for an accurate description of the data in this regime. The energy separation between the ν p1 / 2 and ν f5 / 2 orbitals in neutron-rich Ti isotopes is not large enough to result in an N = 34 shell gap. However, comparisons between the 55Ti data and the calculations argue for the presence of a sizable N = 34 gap in 54Ca.

The odd-odd fp-shell nucleus Sc52 was investigated using in-beam γ-ray spectroscopy following secondary fragmentation of a V55 and Cr57 cocktail beam. Aside from the known γ-ray transition at 674(5) keV, a new decay at Eγ=212(3) keV was observed. It is attributed to the depopulation of a low-lying excited level. This new state is discussed in the framework of shell-model calculations with the GXPF1, GXPF1A, and KB3G effective interactions. These calculations are found to be fairly robust for the low-lying level scheme of Sc52 irrespective of the choice of the effective interaction. In addition, the frequency of spin values predicted by the shell model is successfully modeled by a spin distribution formulated in a statistical approach with an empirical, energy-independent spin-cutoff parameter. © 2006 The American Physical Society.

The structure of the Cr56,58,60 nuclei was investigated at Gammasphere using both deep inelastic and fusion-evaporation reactions. As a result of this work, expanded level schemes are now available for these three neutron-rich, even-even isotopes. Experimental signatures were found for both single-particle and collective excitations whose relative importance varies with neutron number. Together with recent structural information on the odd-A Cr55,57,59 neighbors, the present data highlight the changing role of the g9/2 orbital with neutron number. Comparisons with shell-model calculations using the recently developed GXPF1A interaction and with total Routhian surface calculations are presented.

The one-neutron knockout reaction Be9(Cr57,Cr56+γ)X has been measured in inverse kinematics with an intermediate-energy beam. Cross sections to individual states in Cr56 were partially untangled through the detection of the characteristic γ-ray transitions in coincidence with the reaction residues. The experimental inclusive longitudinal momentum distribution and the yields to individual states are compared to calculations that combine spectroscopic factors from the full fp shell model and nucleon-removal cross sections computed in a few-body eikonal approach.

A value of 0.28±0.02 s has been deduced for the half-life of the ground state of Mn60, in sharp contrast to the previously adopted value of 51±6 s. Access to the low-spin Mn60 ground state was accomplished via β decay of the 0+ Cr60 parent nuclide. New low-energy states in Mn60 have been identified from β-delayed γ-ray spectroscopy. The new, shorter half-life of 60Mng is not suggestive of isospin-forbidden β decay, and new spin and parity assignments of 1+ and 4+ have been adopted for the ground and isomeric β-decaying states, respectively, of Mn60.

β-delayed γ-ray measurements have been part of an experimental program at the NSCL to understand the role of the πf7/2 - νf5/2 proton-neutron monopole interaction in neutron-rich pf-shell nuclei above 48Ca. Central to this study has been an attempt to observe the development of new shell structure at N 32, 34 through the systematic observation of E(2+1 ) as a function of neutron number. Additionally, the ground state spin and parity of odd-odd and odd-A nuclei were interpreted in an extreme single-particle model to follow the monopole migration of the νf5/2 as protons are removed from the πf7/2state.

The even 52-56Ti isotopes have been studied with intermediate-energy Coulomb excitation and absolute B(E2;0+ → 21+) transition rates have been obtained. These data confirm the presence of a subshell closure at neutron number N = 32 in neutron-rich nuclei above the doubly magic nucleus 48Ca and provide no direct evidence for the predicted N = 34 closure. Large-scale shell model calculations with the most recent effective interactions are unable to reproduce the magnitude of the measured strengths in the semimagic Ti nuclei and their strong variation with neutron number.

The β-decay of odd-A, neutron-rich Ti57 and V59 are studied. More precise β-decay half-lives of 98±5 and 97±2 ms are deduced for Ti57 and V59, respectively. In addition, β-delayed γ-ray spectroscopy is used to deduce β-decay branching ratios and establish the low-energy-level structures of the daughter nuclides. The new data for levels in V57 and Cr59 are compared with the results of shell-model calculations completed in the full pf model space. Both V57 and Cr59 show evidence of modest oblate deformation near the ground state.

The subshell closure at N = 34 in Ca, Ti, Cr isotones exhibited low excitation characteristics of shell closure. The β decay of 56Sc was used to populate low-energy level structure of 56Ti. The decay of 56Sc was produced in fragmentation reactions and new γ rays were also identified in daughter N = 34 isotone 56Ti. The results show first 2+ level at an energy of 1127 keV which was below expected position and indicated presence of N = 34 shell closure in 56Ti.

Details regarding the β-decay properties of 54,55,56Sc are reported and compared with shell model predictions. The low-energy level structures of even-even 54,56Ti are presented, and the systematic variation of the energy of the first excited 21+ state is discussed in light of proposed shell closures at N=32,34 for the neutron-rich Ti isotopes.

The level structure of 2254Ti32 has been explored for the first time by combining β-decay measurements from fragmentation products with prompt γ-ray spectroscopy following deep inelastic reactions. The latter technique was also instrumental in tracing 52Ti30 to higher spin. The data provide new tests of effective interactions for full pf-shell calculations in neutron-rich nuclei above 48Ca. The data indicate the presence of a significant subshell gap at N = 32 and comparisons between theory and experiment suggest an additional shell closure at N = 34 in Ca and Ti isotopes.