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Rapid shape changes are observed for neutron-rich nuclei with A around 100. In particular, a sudden onset of ground-state deformation is observed in the Zr and Sr isotopic chains at N = 60: Low-lying states in N≤58 nuclei are nearly spherical, while those with N≥60 have a rotational character. Nuclear lifetimes as short as a few picoseconds can be measured using fast-timing techniques with LaBr3(Ce) scintillators, yielding a key ingredient in the systematic study of the shape evolution in this region. We used neutron-induced fission of 241Pu and 235U to study lifetimes of excited states in fission fragments in the A∼100 region with the EXILL-FATIMA array located at the PF1B cold neutron beam line at the Institut Laue-Langevin. In particular, we applied the generalized centroid difference method to deduce lifetimes of low-lying states for the nuclei 98Zr (N = 58), 100Zr, and 102Zr (N≥60). The results are discussed in the context of the presumed phase transition in the Zr chain by comparing the experimental transition strengths with the theoretical calculations using the interacting boson model and the Monte Carlo shell model. ispartof: Physical Review C vol:96 issue:5 status: published

Nuclear spins and precise values of the magnetic dipole and electric quadrupole moments of the ground states of neutron-rich 73–78Cu isotopes were measured using the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the CERN On-Line Isotope Mass Separator (ISOLDE) facility. The nuclear moments of the less exotic 73,75Cu isotopes were remeasured with similar precision, yielding values that are consistent with earlier measurements. The moments of the odd-odd isotopes, and 78 29Cu (N =49) in particular, are used to investigate excitations of the assumed doubly magic 78Ni core through comparisons with large-scale shell-model calculations. Despite the narrowing of the Z =28 shell gap between N∼45 and N =50, the magicity of Z =28 and N =50 is restored toward 78Ni.This is due to weakened dynamical correlations, as clearly probed by the present moment measurements. ispartof: Physical Review C vol:96 issue:4 pages:1-6 status: published

Spectroscopic information has been extracted on the hole-states of 55 Ni, the least known of the quartet of nuclei ( 55 Ni, 57 Ni, 55 Co and 57 Cu), one nucleon away from 56 Ni, the N = Z = 28 double magic nucleus. Using the H1(Ni56,d)Ni55 transfer reaction in inverse kinematics, neutron spectroscopic factors, spins and parities have been extracted for the f7/2 , p3/2 and the s1/2 hole-states of 55 Ni. These new data provide a benchmark for large basis calculations that include nucleonic orbits in both the sd and pf shells. State of the art calculations have been performed to describe the excitation energies and spectroscopic factors of the s1/2 hole-state below Fermi energy. © 2014 The Authors. ispartof: Physics Letters B vol:736 pages:137-141 status: published

Cross sections of 1n-removal reactions from the neutron-rich nucleus (37)Mg on C and Pb targets and the parallel momentum distributions of the (37)Mg residues from the C target have been measured at 240 MeV/nucleon. A combined analysis of these distinct nuclear- and Coulomb-dominated reaction data shows that the (37)Mg ground state has a small 1n separation energy of 0.22(-0.09)(+0.12) MeV and an appreciable p-wave neutron single-particle strength. These results confirm that (37)Mg lies near the edge of the "island of inversion" and has a sizable p-wave neutron halo component, the heaviest such system identified to date. ispartof: Physical Review Letters vol:112 issue:24 ispartof: location:United States status: published

The halo structure of 31Ne is studied using 1n-removal reactions on C and Pb targets at 230 MeV/nucleon. A combined analysis of the cross sections of these nuclear and Coulomb dominated reactions that feed directly the 30Ne ground-state reveals 31Ne to have a small neutron separation energy, 0.15(-0.10)(+0.16) MeV, and spin-parity 3/2-. Consistency of the data with reaction and large-scale shell-model calculations identifies 31Ne as deformed and having a significant p-wave halo component, suggesting that halos are more frequent occurrences at the neutron drip line. ispartof: Physical Review Letters vol:112 issue:14 ispartof: location:United States status: published

In order to study the Gamow-Teller (GT) transitions from the T z=+2 nucleus 44Ca to the Tz=+1 nucleus 44Sc, where T z is the z component of isospin T, we performed the (p,n)-type (3He,t) charge-exchange (CE) reaction at 140 MeV/nucleon and the scattering angles 0â̂̃ and 2.5â̂̃. An energy resolution of 28 keV, that was realized by applying matching techniques to the magnetic spectrometer system, allowed the study of fragmented states. The GT transition strengths, B(GT), were derived up to the excitation energy (Ex) of 13.7 MeV assuming the proportionality between cross sections and B(GT) values. The total sum of B(GT) values in discrete states was 3.7, which was 31% of the sum-rule-limit value of 12. Shell model calculations using the GXPF1J interaction could reproduce the gross features of the experimental B(GT) distribution, but not the fragmentation of the strength. By introducing the concepts of isospin, properties of isospin analogous transitions and states were investigated. (i) Assuming isospin symmetry, the Tz=+2→+1 and Tz=-2→-1 mirror GT transitions should have the same properties, where the latter can be studied in the β decay of 44Cr to 44V. First, we confirmed that the β-decay half-life T1/2 of 44Cr can be reproduced using the B(GT) distribution from the 44Ca(3He,t) measurement. Then, the 0â̂̃, (3He,t) spectrum was modified to deduce the "β-decay spectrum" and it was compared with the delayed-proton spectrum from the 44Cr β decay. The two spectra were mostly in agreement for the GT excitations, but suppression of the proton decay was found for the T=2 isobaric analog state (IAS). (ii) Starting from the T=2 ground state of 44Ca, the (3He,t) can excite GT states (state populated by GT transitions) with T=1, 2, and 3. On the other hand, the 44Ca(p,p ′) reaction can excite spin-M1 states (states populated by spin-M1 transitions) with T=2 and 3 that are analogous to the T=2 and 3 GT states, respectively. By comparing the spectra from these two reactions, a T value of 2 is suggested for several GT states in the Ex=11.5-13.7 MeV region. (iii) It has been suggested that the T=2, Jπ=0+ double isobaric analog state (DIAS) at 9.338 MeV in the Tz=0 nucleus 44Ti forms an isospin-mixed doublet with a subsidiary 0+ state at 9.298 MeV. Since no corresponding state was found in the Tz=+1 nucleus 44Sc, we suggest T=0 for the subsidiary state. © 2013 American Physical Society. ispartof: Physical Review C, Nuclear Physics vol:88 issue:1 status: published

Given the importance of Gamow-Teller (GT) transitions in nuclear structure and astrophysical nuclear processes, we have studied T z =+ 3 / 2 →+ 1 / 2, GT transitions starting from the 47 Ti nucleus in the ( 3 He ,t ) charge-exchange reaction at 0 ◦ and at an intermediate incident energy of 140 MeV / nucleon. The experiments were carried out at the Research Center for Nuclear Physics (RCNP), Osaka, using the high-resolution facility with a high-dispersion beam line and the Grand-Raiden spectrometer. With an energy resolution of 20 keV, individual GT transitions were observed and GT strength was derived for each state populated up to an excitation energy ( E x ) of 12.5 MeV. The GT strength was widely distributed from low excitation energy up to 12.5 MeV, where we had to stop the analysis because of the high level density. The distribution of the GT strengths was compared with the results of shell model calculations using the GXPF1 interaction. The calculations could reproduce the experimental GT distributions well. The GT transitions from the ground state of 47 Ti and the M 1 transitions from the isobaric analog state in 47 V to the same low-lying states in 47 V are analogous. It was found that the ratios of GT transition strengths to the ground state, the 0.088-MeV state, and the 0.146-MeV state are similar to the ratios of the strengths of the analogous M 1 transitions from the isobaric analog state (IAS) to these states. The measured distribution of the GT strengths was also compared with those starting from the T z =+ 3 / 2 nucleus 41 Ktothe T z =+ 1 / 2 nucleus 41 Ca. ispartof: Physical Review C, Nuclear Physics vol:87 issue:1 pages:1-12 status: published

For the magnetic moment of the 2083 keV level of 140 Ce, there are four published data, all obtained by applying an external magnetic field of less than 5 T to a liquid sample containing 140 La using the time-differential perturbed angular correlation (TDPAC) technique. Although these four values are consistent within two times their uncertainties (2 σ ), the range of values in 2 σ extends from μ =+ 3 . 0to + 5.2 (in units of nuclear magneton, μ N ).Thistime,theTDPACtechniquewassuccessfullyappliedtothe2083keVlevelof 140 Ceimplanted in an Fe foil. The magnetic moment of this level was determined to be μ =+ 4 . 00(20) μ N , employing the known hyperfine field at 141 Ce in Fe, − 41(2) T, which agrees very well with one of the values, μ =+ 4 . 06(15) μ N .The present value is compared with two shell-model calculations. ispartof: Physical Review C, Nuclear Physics vol:87 issue:4 pages:1-5 status: published

In order to study the Gamow-Teller (GT) transitions from the T z =+ 2 nucleus 44 Ca to the T z =+ 1 nucleus 44 Sc, where T z is the z component of isospin T , we performed the ( p, n )-type ( 3 He ,t ) charge-exchange (CE) reaction at 140 MeV / nucleon and the scattering angles 0 ◦ and 2 . 5 ◦ . An energy resolution of 28 keV, that was realized by applying matching techniques to the magnetic spectrometer system, allowed the study of fragmented states. The GT transition strengths, B (GT), were derived up to the excitation energy ( E x ) of 13.7 MeV assuming the proportionality between cross sections and B (GT) values. The total sum of B (GT) values in discrete states was 3.7, which was 31% of the sum-rule-limit value of 12. Shell model calculations using the GXPF1J interaction could reproduce the gross features of the experimental B (GT) distribution, but not the fragmentation of the strength. By introducing the concepts of isospin, properties of isospin analogous transitions and states were investigated. (i) Assuming isospin symmetry, the T z =+ 2 →+ 1and T z =− 2 →− 1 mirror GT transitions should have the same properties, where the latter can be studied in the β decay of 44 Cr to 44 V. First, we confirmed that the β -decay half-life T 1 / 2 of 44 Cr can be reproduced using the B (GT) distribution from the 44 Ca( 3 He ,t ) measurement. Then, the 0 ◦ ,( 3 He ,t ) spectrum was modified to deduce the “ β -decay spectrum” and it was compared with the delayed-proton spectrum from the 44 Cr β decay. The two spectra were mostly in agreement for the GT excitations, but suppression of the proton decay was found for the T = 2 isobaric analog state (IAS). (ii) Starting from the T = 2 ground state of 44 Ca, the ( 3 He ,t ) can excite GT states (state populated by GT transitions) with T = 1, 2, and 3. On the other hand, the 44 Ca( p, p ) reaction can excite spin- M 1 states (states populated by spin- M 1 transitions) with T = 2 and 3 that are analogous to the T = 2 and 3 GT states, respectively. By comparing the spectra from these two reactions, a T value of 2 is suggested for several GT states in the E x = 11 . 5–13.7 MeV region. (iii) It has been suggested that the T = 2, J π = 0 + double isobaric analog state (DIAS) at 9.338 MeV in the T z = 0 nucleus 44 Ti forms an isospin-mixed doublet with a subsidiary 0 + state at 9.298 MeV. Since no corresponding state was found in the T z =+ 1 nucleus 44 Sc, we suggest T = 0 for the subsidiary state. ispartof: Physical Review C, Nuclear Physics vol:85 issue:2 pages:1-15 status: published

Excited states in the very neutron-rich nuclei 35 Mg and 33 Na were populated in the fragmentation of a 38 Si projectile beam on a Be target at 83 MeV / u beam energy. We report on the first observation of γ -ray transitions in 35 Mg, the odd- N neighbor of 34 Mg and 36 Mg, which are known to be part of the ‘island of inversion” around N = 20. The results are discussed in the framework of large-scale shell-model calculations. For the A = 3 Z nucleus 33 Na, a new γ -ray transition was observed that is suggested to complete the γ -ray cascade 7 / 2 + → 5 / 2 + → 3 / 2 + gs connecting three neutron two-particle–two-hole intruder states that are predicted to form a close-to-ideal K = 3 / 2 rotational band in the strong-coupling limit. ispartof: Physical Review C, Nuclear Physics vol:83 issue:4 status: published

The neutron-rich N = 50 isotones 82 Ge and 84 Se were investigated using intermediate-energy Coulomb excitation on a 197 Au target and inelastic scattering on 9 Be. As typical for intermediate-energy Coulomb excitation with projectile energies exceeding 70 MeV / nucleon, only the first 2 + states were excited in 82 Ge and 84 Se. However, in the inelastic scattering on a 9 Be target, a strong population of the first 4 + state was observed for 84 Se, while there is no indication of a similarly strong excitation of the corresponding state in the neighboring even-even isotone 82 Ge. The results are discussed in the framework of systematics and shell-model calculations using three different effective interactions ispartof: Physical Review C, Nuclear Physics vol:81 issue:6 status: published

Yordanov etal. [ 1 ] reported a measurement of the spin and magnetic moment of the ground state of 33 Mg and inferred a negative parity based on a proposed ground-state configuration whose magnetic moment agrees with the measured value. ispartof: Physical Review Letters vol:104 issue:12 ispartof: location:United States status: published

Excited states in 30 Mg have been populated to ∼ 6 ̄ h and 5 MeV excitation energy with the 14 C( 18 O,2 p ) reaction. Firm spin assignments for states with J> 2 ̄ h have been made in this nucleus. The level scheme is compared to shell-model calculations using the Universal sd effective interaction and the Monte Carlo shell model method. Calculations employing a full sd model space fail to reproduce the observed levels. The results indicate that excitations across the N = 20 gap are required at relatively low excitation energy to achieve a description of the data. The incorporation of the f 7 / 2 and p 3 / 2 orbitals into the model space gives improved results but indicate the need for further refinement of the models to reproduce the observed spectra. ispartof: Physical Review C, Nuclear Physics vol:82 issue:3 status: published

We study the structure of low-lying states of 13 C with a microscopic cluster model. In addition to the 3 α - n model space, the breaking effect of one of the α clusters due to the spin-orbit interaction is also taken into account. The isoscalar E 0 transition probabilities from the ground 1 / 2 − state to the excited ones are discussed associated with the cluster structure of these states ispartof: Physical Review C, Nuclear Physics vol:79 issue:3 status: published

We present a new effective interaction for shell-model calculations in the model space consisting of the single-particle orbits 1 p 3 / 2 ,0 f 5 / 2 ,1 p 1 / 2 ,and0 g 9 / 2 . Starting with a realistic interaction based on the Bonn-C potential, 133 two-body matrix elements and four single-particle energies are modified empirically so as to fit 400 experimental energy data out of 69 nuclei with mass numbers A = 63 ∼ 96. The systematics of binding energies, electromagnetic moments and transitions, and low-lying energy levels are described. The soft Z = 28 closed core is observed, in contrast to the stable N = 50 shell closure. The new interaction is applied to systematic studies of three different chains of nuclei, Ge isotopes around N = 40, N = Z nuclei with A = 64 ∼ 70, and N = 49 odd-odd nuclei, focusing especially on the role of the g 9 / 2 orbit. The irregular behavior of the 0 + 2 state in Ge isotopes is understood as a result of detailed balance between the N = 40 single-particle energy gap and the collective effects. The development of the band structure in N = Z nuclei is interpreted in terms of successive excitations of nucleons into the g 9 / 2 orbit. The triaxial/ γ -soft structure in 64 Ge and the prolate/oblate shape coexistence in 68 Se are predicted, showing a good correspondence with the experimental data. The isomeric states in 66 As and 70 Brare obtained with the structure of an aligned proton-neutron pair in the g 9 / 2 orbit. Low-lying energy levels in N = 49 odd-odd nuclei can be classified as proton-neutron pair multiplets, implying that the obtained single-particle structure in this neutron-rich region appears to be appropriate. These results demonstrate that, in spite of the modest model space, the new interaction turns out to describe rather well properties related to the g 9 / 2 orbit in various cases, including moderately deformed nuclei. ispartof: Physical Review C, Nuclear Physics vol:80 issue:6 status: published

Neutrino-induced reactions on 56 Fe and 56 Ni are investigated based on a new shell-model Hamiltonian for pf shell. The calculated charged current reaction cross section on 56 Fe induced by decay-at-rest (DAR) neutrinos is shown to be consistent with the observation. The Gamow-Teller strength in 56 Ni is found to be more spread compared to previous calculations and result in a considerably large branching ratio for the proton knock-out channel. As a consequence of this, the production yields of heavy elements such as 55 Mn in population III stars are shown to be enhanced for the new Hamiltonian. ispartof: Physical Review C, Nuclear Physics vol:79 issue:6 status: published

Gamma rays from 52 Ti have been studied with Gammasphere and the Fragment Mass Analyzer using reactions induced by a 48 Ca beam on a 9 Be target. The data have been used in combination with information from deep-inelastic reactions of 48 Ca beams on a thick 238 U target at an energy about 25% above the Coulomb barrier. The 52 Ti 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 48 Ca core provide new tests of effective interactions in the full pf -shell model space. The positive-parity states in 52 Ti 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. ispartof: Physical Review C, Nuclear Physics vol:80 issue:2 status: published

The breakdown of the N = 20 magic number in the so-called island of inversion around 32 Mg is well established. Recently developed large-scale shell-model calculations suggest a transitional region between normal- and intruder-dominated nuclear ground states, thus modifying the boundary of the island of inversion. In particular, a dramatic change in single-particle structure is predicted between the ground states of 30 Mg and 32 Mg, with the latter consisting nearly purely of 2p-2h N = 20 cross-shell configurations. Single-neutron knockout experiments on 30 , 32 Mg projectiles have been performed. We report on a first direct observation of intruder configurations in the ground states of these very neutron-rich nuclei. Spectroscopic factors to low-lying negative-parity states in the knockout residues are deduced and compare well with shell-model predictions ispartof: Physical Review C, Nuclear Physics vol:77 issue:1 status: published

Magnetic dipole transitions in 17 C are investigated by shell model calculations. The important role of the tensor interaction for magnetic dipole transitions in this exotic neutron-rich nucleus is pointed out. The recently observed anomalous quenching of the magnetic dipole transition in 1 / 2 + 1 → 3 / 2 + g . s . is shown to be well explained by using a modified shell model Hamiltonian that takes full account of the tensor force and monopole corrections in the isospin T = 1 channel. The predicted quadrupole moment of 17 C is smaller than the value obtained by conventional shell model Hamiltonians ispartof: Physical Review C, Nuclear Physics vol:78 issue:6 status: published

The low-lying yrast states in the 51 Ca and 52 Sc nuclei were investigated to obtain information on the evolution of the p 1 / 2 and f 5 / 2 neutron single-particle orbitals in neutron-rich nuclei near proton number Z = 20. Level structures associated with neutron excitations into these two orbitals and with proton excitations across the Z = 20 shell gap were identified. Shell-model calculations with the recently proposed GXPF1A interaction account reasonably well for the fp -shell states. The energy separation between the νp 1 / 2 and νf 5 / 2 orbitals in the Ca isotopes appears to be overestimated by the GXPF1A Hamiltonian. ispartof: Physical Review C, Nuclear Physics vol:77 issue:1 status: published

The low energy level structure of N = 20 32 Mg obtained via β -delayed γ spectroscopy is reported. The level structure of 32 Mg is found to be completely dominated by intruders. An inversion between the 1p-1h and 3p-3h states is observed for the negative parity states, similar to the 0p-0h and 2p-2h inversion for the positive parity states in these N ∼ 20 nuclei. The intruder excited states, both positive and negative parity, are reasonably explained by Monte Carlo shell model calculations, which suggest a shrinking N = 20 shell gap with decreasing Z ispartof: Physical Review C, Nuclear Physics vol:77 issue:3 status: published

The first 2+ states in 134Ce and 136Nd and the second 2+ state in 136Nd were populated by Coulomb excitation at relativistic energies, and γ-rays were measured using the RISING setup at GSI. For 134Ce an indication of the excitation to the second 2+ state was observed. This experiment performed for the first time Coulomb excitation to second 2+ states with rare isotope beams at relativistic energies. For 136Nd the View the MathML sourceB(E2;21+→0+), View the MathML sourceB(E2;22+→0+), and View the MathML sourceB(E2;22+→21+) values relative to the previously known View the MathML sourceB(E2;21+→0+) value for 134Ce are determined as 81(10), 11(3) and 180(92) W.u., respectively. The results are discussed in the framework of geometrical models that indicate pronounced γ-softness in these nuclei. ispartof: Physics Letters B vol:669 issue:1 pages:19-23 status: published

The decay of 33 Mg ( N ¼ 21 ) presented in this Letter reveals intruder configurations in both the parent and the daughter nucleus. The lowest excited states in the N ¼ 20 daughter nucleus, 33 Al , are found to have nearly 2 p 2 h intruder configuration, thus extending the ‘‘island of inversion’’ beyond Mg. The allowed direct -decay branch to the 5 = 2 þ ground state of the daughter nucleus 33 Al implies positive parity for the ground state of the parent 33 Mg , contrary to an earlier suggestion of negative parity from a g -factor measurement. An admixture of 1 p - 1 h and 3 p - 3 h configurations is proposed for the ground state of 33 Mg to explain all of the experimental observables ispartof: Physical Review Letters vol:101 issue:14 ispartof: location:United States status: published

The level structures of 55 Vand 55 Ti, the two nuclei with a single nucleon outside the semi-magic 54 22 Ti 32 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 ( I π 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 νp 1 / 2 and νf 5 / 2 orbitals in neutron-rich Ti isotopes is not large enough to result in an N = 34 shell gap. However, comparisons between the 55 Ti data and the calculations argue for the presence of a sizable N = 34 gap in 54 Ca. ispartof: Physics Letters B vol:650 issue:2 pages:135-140 status: published

The nucleus 31 P has been studied in the 24 Mg( 16 O,2 αp ) reaction with a 70-MeV 16 O beam. A complex level scheme extended up to spins 17/2 + and 15/2 − , on positive and negative parity, respectively, has been established. Lifetimes for the new states have been investigated by the Doppler shift attenuation method. Two shell-model calculations have been performed to describe the experimental data, one by using the code ANTOINE in a valence space restricted to the sd shell, and the other by applying the Monte Carlo shell model in a valence space including the sd - fp shells. The latter calculation indicates that intruder excitations, involving the promotion of a T = 0 proton-neutron pair to the fp shell, play a dominant role in the structure of the positive-parity high-spin states of 31 P. ispartof: Physical Review C, Nuclear Physics vol:73 issue:2 status: published

High-spin states in the odd-odd 58 Co nucleus have been studied with the fusion-evaporation reaction 51 V( 10 B ,p 2 n ) using the γ -spectrometer Saci-Perere. Thirty-six new excited states up to spin 11 + and an excitation energy of 8.0 MeV have been observed, which are connected by 46 γ -ray transitions. Transition probabilities for 14 excited states were measured through the Doppler-shift attenuation method. The results are compared with shell-model calculations using the GXPF1 effective interaction, developed for use in the pf shell. These results were interpreted by considering particle-hole excitations with respect to the doubly magic N = Z = 28 core. ispartof: Physical Review C, Nuclear Physics vol:74 issue:6 status: published

The energy of the first excited state in the neutron-rich N=28 nucleus 45Cl has been established via in-beam gamma-ray spectroscopy following proton removal. This energy value completes the systematics of the E(1/2^+_1)-E(3/2^+_1) level spacing in odd-mass K, Cl and P isotopes for N=20-28. The results are discussed in the framework of shell-model calculations in the sd-fp model space. The contribution of the central, spin-orbit and tensor components is discussed from a calculation based on a proton single-hole spectrum from G-matrix and pi + rho meson exchange potentials. A composite model for the proton 0d_{3/2}-1s_{1/2} single-particle energy shift is presented., Comment: Phys. Rev. C, in press

We present a full pf -shell spectroscopy of the low-lying states of 56 Ni using the GXPF1A interaction. Both the ground-state band and the first deformed band, as well as the transition probabilities, compare favorably with the experimental data. We analyze the significance of the contributions of N -particle N -hole configurations to the full model calculations, similarly to the analysis obtained for 28 Si in the sd shell some 20 years ago. ispartof: Physical Review C, Nuclear Physics vol:73 issue:6 status: published

The nucleus 34 S has been studied up to relatively high spin ( I = 10 ̄ h ) and up to an excitation energy of 16.64 MeV. Data are compared with different shell model calculations where effective interactions involving two main shells, the sd and the fp , are used. For the first time in an N = Z nucleus, it is observed that the promotion of an isoscalar ( T = 0) proton-neutron pair to the fp shell becomes energetically favored at high spin ispartof: Physical Review C, Nuclear Physics vol:71 issue:1 status: published

The even 52 – 56 Ti isotopes have been studied with intermediate-energy Coulomb excitation and absolute B ( E 2; 0 + → 2 + 1 ) 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 48 Ca 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. ispartof: Physical Review C, Nuclear Physics vol:71 issue:4 status: published

The low-energy level structure of the exotic Na isotopes 28 ; 29 Na has been investigated through -delayed spectroscopy. The N 20 isotones for Z 10 – 12 are considered to belong to the ‘‘island of inversion’’ where intruder configurations dominate the ground state wave function. However, it is an open question as to where and how the transition from normal to intruder dominated configurations happens in an isotopic chain. The present work, which presents the first detailed spectroscopy of 28 ; 29 Na , clearly demonstrates that such a transition in the Na isotopes occurs between 28 Na ( N 17 ) and 29 Na ( N 18 ), supporting the smaller N 20 shell gap in neutron-rich sd shell nuclei. The evidence for inverted shell structure is found in -decay branching ratios, intruder dominated spectroscopy of low- lying states, and shell model analysis. ispartof: Physical Review Letters vol:94 issue:16 ispartof: location:United States status: published

Low-lying excited states of 46 Ar have been studied via inverse-kinematics proton scattering with a thick target. Coupled-channels calculations have been used to extract the deformation length of the 2 + 1 state. This result, combined with existing Coulomb excitation data, yields a ratio of the neutron-to-proton transition matrix elements of M n /M p = 1 . 19(25) N/Z , showing a departure from the proton dominance observed in the N = 28 isotones above 48 Ca. The status of the N = 28 shell below 48 Ca is discussed ispartof: Physical Review C, Nuclear Physics vol:72 issue:2 status: published

The Gamow-Teller β decay of 46 Cr to the N = Z odd-odd nucleus 46 V has been observed for the first time. 46 Cr was produced by the fragmentation of a 50 Cr primary beam at 80 MeV/nucleon. By means of β - γ coincidence measurements, a γ -ray peak at 993 keV corresponding to the decay of the 1 + 1 state in 46 V was observed. The branching ratio of the Gamow-Teller decay to this state was found to be b GT = 0 . 216 ± 0 . 050. The half-life of 46 Cr was measured to be T 1 / 2 = 240 ± 140 ms. The transition strength was determined to be B (GT) = 0 . 64 ± 0 . 20. This result was compared with theoretical values calculated with the shell model and the phenomenological quasideuteron model. ispartof: Physical Review C, Nuclear Physics vol:72 issue:2 status: published

We have measured the cross section of the 7 Be p , g 8 B reaction for E c.m. 185.8 , 134.7, and 111.7 keV using a radioactive 7 Be target (132 mCi). Single and coincidence spectra of b 1 and a particles from 8 B and 8 Be decay, respectively, were measured using a large acceptance spectrometer. The zero en- ergy S factor inferred from these data is 18.5 6 2.4 eV b and a weighted mean value of 18.8 6 1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies ispartof: Physical Review C, Nuclear Physics vol:71 issue:5 status: published

γ rays from neutron-rich Ti nuclei in the vicinity of N = 32 have been studied at Gammasphere using deep-inelastic reactions induced by 48 Ca beams on thick 208 Pb and 238 U targets. The 53 Ti yrast cascade was identified for the first time, and the location in energy of states with spin up to I = 21/2 was determined. The excitations of 53 Ti provide new tests of effective interactions for full- pf -shell calculations. Comparisons between theory and experiment for the highest spin states in 53 Ti favor the recently proposed GXPF1A interaction, which accounts for the appearance of a neutron subshell closure at N = 32 in Ti isotopes as well as for the lack of a similar subshell closure at N = 34, as predicted by earlier calculations with another interaction ispartof: Physical Review C, Nuclear Physics vol:72 issue:4 status: published

Nuclear structure of the neutron rich 25 − 29 Ne nuclei has been investigated through the in-beam γ -ray spectroscopy technique using fragmentation reactions of both stable and radioactive beams. Level schemes have been deduced for these Ne isotopes. In order to examine the importance of intruder fp configurations, they are compared to shell model calculations performed either in the restricted sd or in the larger sdpf valence space. The 25 , 26 Ne and 27 Ne nuclei were found to be in agreement with the sd shell model calculations, whereas 28 Ne exhibits signatures of the intruder fp shell contribution ispartof: Physical Review C, Nuclear Physics vol:72 issue:5 status: published

The first excited 2 + states in 54,56,58 Cr were populated by Coulomb excitation at relativistic energies and γ rays were measured using the RISING setup at GSI. For 56 Cr and 58 Cr the B( E2 , 2 + 1 → 0 + ) values relative to the previously known B( E2 ) value for 54 Cr are determined as 8.7(3.0) and 14.8(4.2) W.u., respectively. The results are consistent with a subshell closure at neutron number N = 32 which was already indicated by the higher energy of the 2 + 1 state in 56 Cr. Recent large-scale shell model calculations using effective interactions reproduce the trend in the excitation energies, but fail to account for the minimum in the B( E2 ) values at N = 32.  2005 Elsevier B.V. All rights reserved ispartof: Physics Letters B vol:622 issue:1 pages:29-34 status: published

The ground and low-lying states of neutron-rich exotic Te and Sn isotopes are studied in terms of the nuclear shell model by the same Hamiltonian used for the spherical-deformed shape phase transition of Ba isotopes, without any adjustment. An anomalously small value is obtained for B s E 2;0 1 + ! 2 1 + d in 136 Te, consistent with a recent experiment. The levels of 136 Te up to yrast 12 + are shown to be in agreement with observed ones. It is pointed out that 136 Te can be an exceptionally suitable case for studying mixed-symmetry 1 + ,2 + , and 3 + states, and predictions are made for energies and M 1 and E 2 properties. Systematic trends of structure of heavier and more exotic Sn and Te isotopes beyond 136 Te are studied by the Monte Carlo shell model, presenting an unusual and very slow evolution of collectivity/deformation ispartof: Physical Review C, Nuclear Physics vol:70 issue:5 status: published

Details regarding the b -decay properties of 54,55,56 Sc are reported and compared with shell model predic- tions. The low-energy level structures of even-even 54,56 Ti are presented, and the systematic variation of the energy of the first excited 2 1 + state is discussed in light of proposed shell closures at N = 32 , 34 for the neutron-rich Ti isotopes ispartof: Physical Review C, Nuclear Physics vol:70 issue:6 status: published

Recent experimental characterization of the subshell closure at N 32 in the Ca, Ti, and Cr isotones has stimulated shell-model calculations that indicated the possibility that the N 34 isotones of these same elements could exhibit characteristics of a shell closure, namely, a high energy for the first excited 2 level. To that end, we have studied the decay of 56 Sc produced in fragmentation reactions and identified new rays in the daughter N 34 isotone 56 Ti . The first 2 level is found at an energy of 1127 keV , well below the expected position that would indicate the presence of an N 34 shell closure in 56 Ti . ispartof: Physical Review Letters vol:92 issue:7 ispartof: location:United States status: published

The collectivity of the odd-mass nucleus 55 Ni was explored via intermediate-energy Coulomb excitation using a powerful combination of particle and g -ray spectroscopy. A g -ray at 2879 ( 18 ) keV was observed and is interpreted to deexcite a member of the core-coupled quintuplet 2 1 + s 56 Ni d ^ n f 7/2 −1 at the same energy. By similarity with the mirror nucleus 55 Co, transition probabilities were calculated assuming J p =9/2 − and J p =11/2 − for this state. Both assumptions lead to a transition strength higher than predicted by a large-scale shell-model calculation using the GXPF1 effective interaction and exceed the value predicted within a simple weak-coupling approach ispartof: Physical Review C, Nuclear Physics vol:70 issue:6 status: published

Low-spin states in the odd-odd N5Z nucleus 58Cu were investigated with the 58Ni(p,ng )58Cu fusion evaporation reaction at the FN-TANDEM accelerator in Cologne. gg-coincidences, gg-angular correlations, and signs of g -ray polarizations were measured. Seventeen low-spin states below 3.6 MeV and 17 new transitions were observed. Ten multipole mixing ratios and 17 g -branching ratios were determined for the first time. New detailed spectroscopic information on the 22 1 state, the isobaric analogue state ~IAS! of the 21 1 ,T51 state of 58Ni, makes 58Cu the heaviest odd-odd N5Z nucleus with known B(E2;21,T51!01,T51) value. The 41 state at 2.751 MeV, observed here for the first time, is identified as the IAS of the 41 1 ,T51 state in 58Ni. The new data are compared to full p f -shell-model calculations with the GXPF1 residual interaction and to calculations within a p f 5/2 configurational space with a residual surface d interaction. The role of the 56Ni core excitations for the low-spin structure in 58Cu is discussed. ispartof: Physical Review C, Nuclear Physics vol:68 issue:3 status: published

b decay of 56,57,58V has been used to populate low-energy levels of 56,57,58Cr, respectively. The low-energy levels of the even-even Cr isotopes and b-decay half-lives and branching ratios of the parent V isotopes are compared to results of shell-model calculations. The Cr energy level calculations were completed in the full p f -model space, using several different interactions. The systematic variation of E(21 1), which is indicative of a subshell closure at N532, was best reproduced in calculations using a pf-shell-model interaction based on effective two-body matrix elements with some replacement by the G matrix ispartof: Physical Review C, Nuclear Physics vol:67 issue:1 status: published