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The 9Be(28Mg,27Na) one-proton removal reaction with a large proton separation energy of Sp(28Mg) = 16.79 MeV is studied at intermediate beam energy. Coincidences of the bound 27Na residues with protons and other light charged particles are measured. These data are analyzed to determine the percentage contributions to the proton removal cross section from the elastic and inelastic nucleón removal mechanisms. These deduced contributions are compared with the eikonal reaction model predictions and with the previously measured data for reactions involving the removal of more weakly bound protons from lighter nuclei. The role of transitions of the proton between different bound single-particle configurations upon the elastic breakup cross section is also quantified in this well-bound case. The measured and calculated elastic breakup fractions are found to be in good agreement. [ABSTRACT FROM AUTHOR]

A systematic investigation of the inclusive cross sections for single-nucleon knockout reactions from p-shell nuclei has been performed. A total of seven reactions were studied for projectiles with masses between A =7 and 10, having a wide range of nucleón separation energies. Results were obtained for a range of incident beam energies and targets. These differences were found to have a minimal impact on the deduced cross sections. Experimental results were compared to theoretical predictions based on variational Monte Carlo (VMC) nuclear structure calculations, whose radial overlap functions and neutron and proton densities were included in the reaction description. These results are compared with the conventional model, developed for heavier nuclei, that uses shell-model and Hartree-Fock structure inputs. The VMC-based calculations agreed with the experimental data for several reactions where deeply bound nucleons are removed but does not describe some of the more weakly bound nucleón removal cases with comparable accuracy. [ABSTRACT FROM AUTHOR]

The two-proton removal reaction from 28Mg projectiles has been studied at 93 MeV/u. First coincidence measurements of the heavy 26Ne projectile residues, the removed protons, and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations based on the use of eikonal dynamics and sd-shell-model structure amplitudes. [ABSTRACT FROM AUTHOR]

Excited states in the very neutron-rich nuclei 35Mg and 33Na were populated in the fragmentation of a 38Si projectile beam on a Be target at 83 MeV/u beam energy. We report on the first observation of γ-ray transitions in 35Mg, the odd-N neighbor of 36Mg and 36Mg, 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 = 3Z nucleus 33Na, 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. [ABSTRACT FROM AUTHOR]

The neutron decay of an unbound resonance in 12Be has been measured at 1243 ± 21 keV decay energy with a width of 634 ± 60 keV. This state was populated with a one-proton removal reaction from a 71 MeV/u 13B beam incident upon a beryllium target. The invariant mass reconstruction of the resonance was achieved by measuring the daughter fragment in coincidence with neutrons. Despite being above the 2n separation energy, the state decays predominantly by the emission of one neutron to 1 'Be, setting an upper limit on the branching ratio for the two-neutron decay channel to 10Be of less than 5%. From the characteristics of the population and decay of the resonance, it is concluded that this state cannot correspond to the previously observed state at 4580 ± 5 keV. [ABSTRACT FROM AUTHOR]

The article reports on the observation of neutron decay of a low-lying unbound state in Beryllium isotopes and preliminary limits on its branching ratios. Topics discussed include conduct of the study at the U.S. National Superconducting Cyclotron Laboratory, use of two cathode-readout drift chambers (CRDCs) to measure position of the particles, interpretation of data performed with the Monte Carlo simulation.

The article offers information on a study to determine the neutron decay of a low-lying unbound state in 12Beryllium and preliminary limits on its branching ratios. Topics discussed include determination of resonance energy of beryllium isotopes, neutron decay in two bound states in 11beryllium, and calculation of momentum vectors of the neutrons. Other topic discussed include use of invariant mass method to determine the energy released in the decay of a nucleus.

The article offers information on a study related to the measurement of neutron decay of an unbound resonance in Beryllium (Be) 12Be conducted at the National Superconducting Cyclotron Laboratory in U.S. Topics discussed include interpretation of data with Monte Carlo simulation, the use of charged particle detector to measure position, angle and energy loss and the role of the sweeper dipole magnet to introduce angular correlations.

The article discusses the Low-lying neutron unbound states in Beryllium. It mentions that neutron decay of an unbound resonance in Be has been measured with decay energy along with a width of 634 ± 60 kilo electron volt (keV). It presents that experiment were being carried out at the National Superconducting Cyclotron Laboratory.

The article presents brief information on low-lying neutron unbound states in beryllium isotope. It states that neutron decay of an unbound resonance in beryllium isotope has been measured at particular decay energy. It further mentions that energy, the state decays predominantly by the emission of one neutron to beryllium isotope. Information related to continuum shell mode is also discussed.

The ground state two-proton decay lifetime of l9Mg, populated by the one-neutron knockout of an intermediateenergy 20Mg radioactive beam, was measured utilizing a new experimental technique. A thin silicon detector positioned at varying distances (0.0-1.0 mm) downstream of the reaction target measured the energy loss of l9Mg and the two-proton decay product 17Ne. The lifetime was deduced from fits to the measured energy-loss line shapes and depended upon the contribution of prompt reaction processes to the yield of l7Ne. For relative l7Ne prompt contributions from 82% to 92%, the extracted lifetimes ranged from 1.75+0.43-0.42 to 6.4+2.4-2.7 ps. The results are consistent with the previously reported l9Mg lifetime measurement and serve as both an important complementary study and a validation of this new technique, which can provide lifetime information for short-lived states beyond the proton drip line. [ABSTRACT FROM AUTHOR]

Excited states in 18C were populated by the one-proton knockout reaction of an intermediate energy radioactive 19N beam. The lifetime of the first 2+ state was measured with the KöIn/NSCL plunger via the recoil distance method to be τ(21+) = 22.4 ± 0.9(stat)-2.2+3.3(syst) ps, which corresponds to a reduced quadrupole transition strength of B(E2; 21+ → 01+ = 3.64-0.14+0.15(stat)-0.47+0.40(syst) e²fm4. In addition, an upper limit on the lifetime of a higher-lying state feeding the 21+ state was measured to be τ < 4.6 ps. The results are compared to large-scale ab initio no-core shell model calculations using two accurate nucleon-nucleon interactions and the importance-truncation scheme. The comparison provides strong evidence that the inclusion of three-body forces is needed to describe the low-lying excited-state properties of this A = 18 system. [ABSTRACT FROM AUTHOR]

The article presents the study which examined the lifetime excited-state transition-rate measurements in neutron-rich 18 carbon (C). In the study, the recoil distance method (RDM) lifetime measurements were used due to their reliability as model-independent probes of nuclear structure. The study was carried out at the Michigan State University's National Superconducting Cyclotron Laboratory (NSCL).

Single-neutron-transfer measurements using (p,d) reactions have been performed at 33 MeV per nucleon with proton-rich 34Ar and neutron-rich 46Ar beams in inverse kinematics. The extracted spectroscopic factors are compared to the large-basis shell-model calculations. Relatively weak quenching of the spectroscopic factors is observed between 34Ar and 46Ar. The experimental results suggest that neutron correlations have a weak dependence on the asymmetry of the nucleus over this isotopic region. The present results are consistent with the systematics established from extensive studies of spectroscopic factors and dispersive optical-model analyses of 40-49Ca isotopes. They are, however, inconsistent with the trends obtained in knockout-reaction measurements. [ABSTRACT FROM AUTHOR]

We studied transition rates for the lowest 1/2+ and 5/2+ excited states of C17 through lifetime measurements with the GRETINA array using the recoil-distance method. The present measurements provide a model-independent determination of transition strengths giving the values of B(M1;1/2+→3/2g.s.+)=1.04-0.12+0.03×10-2µN² and B(M1;5/2+3/2g.s.+)=7.12-0.96+1.27×10-2µN². The quenched M1 transition strength for the 1/2+→3/2g.s.+ transition, with respect to the 5/2+3/2g.s.+ transition, has been confirmed with greater precision. The current data are compared to importance-truncated no-core shell model calculations addressing effects due to continuum and three-body forces. [ABSTRACT FROM AUTHOR]

Excited states have been studied in 28Na using the β-decay of implanted 28Ne ions at the Grand Accelerateur National d'lons Lourds/LISE as well as the in-beam γ-ray spectroscopy at the National Superconducting Cyclotron Laboratory/S800 facility. New states of positive (Jπ = 3+,4+) and negative (Jπ = l--5-) parity are proposed. The former arise from the coupling between 0d5/2 protons and 0d3/2 neutrons, while the latter are attributable to couplings of 0d5/2 protons with 1 p3/2 or 0f1/2 neutrons. While the relative energies between the Jπ = l+-4+ states are well reproduced with the USDA interaction in the N = 17 isotones, a progressive shift in the ground-state binding energy (by about 500 keV) is observed between 26F and 30Al. This points to a possible change in the proton-neutron 0d5/2-0d3/2 effective interaction when moving from stability to the drip line. The presence of Jπ = 1--4- negative-parity states around 1.5 MeV as well as of a candidate for a Jπ = 5- state around 2.5 MeV give further support to the collapse of the N = 20 gap and to the inversion between the neutron 0f7/2 and 1p3/2 levels below Z = 12. These features are discussed in the framework of shell-model and energy-density-functional calculations, leading to predicted negative-parity states in the low-energy spectra of the 26F and 25O nuclei. [ABSTRACT FROM AUTHOR]

Background: In neutron-rich nuclei around N=40 rapid changes in nuclear structure can be observed. While Ni68 exhibits signatures of a doubly magic nucleus, experimental data along the isotopic chains in even more exotic Fe and Cr isotopes-such as excitation energies and transition strengths-suggest a sudden rise in collectivity toward N=40. Purpose: Reduced quadrupole transition strengths for low-lying transitions in neutron-rich 58,60,62Cr are investigated. This gives quantitative new insights into the evolution of quadrupole collectivity in the neutron-rich region close to N=40. Method: The recoil distance Doppler-shift (RDDS) technique was applied to measure lifetimes of low-lying states in Cr58,60,62Cr. The experiment was carried out at the National Superconducting Cyclotron Laboratory (NSCL) with the SeGA array in a plunger configuration coupled to the S800 magnetic spectrograph. The states of interest were populated by means of one-proton knockout reactions. Results: Data reveal a rapid increase in quadrupole collectivity for 58,60,62Cr toward N=40 and point to stronger quadrupole deformations compared to neighboring Fe isotopes. The experimental B(E2) values are reproduced well with state-of-the-art shell-model calculations using the LNPS effective interaction. A consideration of intrinsic quadrupole moments and B42 ratios suggest an evolution toward a rotational nature of the collective structures in 60,62Cr. Compared to 58Cr, experimental B42 and B62 values for 60Cr are in better agreement with the E(5) limit. Conclusion: Our results indicate that collective excitations in neutron-rich Cr isotopes saturate at N=38, which is in agreement with theoretical predictions. More detailed experimental data of excited structures and interband transitions are needed for a comprehensive understanding of quadrupole collectivity close to N=40. This calls for additional measurements in neutron-rich Cr and neighboring Ti and Fe nuclei. [ABSTRACT FROM AUTHOR]

Background: Triplet energy differences (TED) can be studied to yield information on isospin-non-conserving interactions in nuclei. Purpose: The systematic behavior of triplet energy differences (TED) of T=1, Jπ=2+ states is examined. The A=62 isobar is identified as having a TED value that deviates significantly from an otherwise very consistent trend. This deviation can be attributed to the tentative assignments of the pertinent states in 62Ga and 62Ge. Methods: An in-beam γ-ray spectroscopy experiment was performed to identify excited states in 62Ga using Gamma-Ray Energy Tracking In-Beam Nuclear Array with the S800 spectrometer at NSCL using a two-nucleon knockout approach. Cross-section calculations for the knockout process and shell-model calculations have been performed to interpret the population and decay properties observed. Results: Using the systematics as a guide, a candidate for the transition from the T=1, 2+ state is identified. However, previous work has identified similar states with different Jπ assignments. Cross-section calculations indicate that the relevant T=1, 2+ state should be one of the states directly populated in this reaction. Conclusions: As spins and parities were not measurable, it is concluded that an unambiguous identification of the first T=1, 2+ state is required to reconcile our understanding of TED systematics [ABSTRACT FROM AUTHOR]

Background: Stellar electron-capture reactions on medium-heavy nuclei are important for many astrophysical phenomena, including core-collapse and thermonuclear supernovae and neutron stars. Estimates of electroncapture rates rely on accurate estimates of Gamow-Teller strength distributions, which can be extracted from charge-exchange reactions at intermediate beam energies. Measured Gamow-Teller transition strength distributions for stable pf:shell nuclei are reasonably well reproduced by theoretical calculations in the shell model, except for lower mass nuclei where admixtures from the sd shell can become important. Purpose: This paper presents a β+ charge-exchange experiment on 45Sc, one of the lightest pf-shell nuclei. The focus was on Gamow-Teller transitions tofinal states at low excitation energies, which are particularly important for accurate estimations of electron-capture rates at relatively low stellar densities. The experimental results are compared with various theoretical models. Method: The double-differential cross section for the 45Sc(t, 3He +γ) reaction was measured using the NSCL Coupled-Cyclotron Facility at 115 MeV/u. Gamow-Teller contributions to the excitation-energy spectra were extracted by means of a multipole-decomposition analysis, γ rays emitted due to the deexcitation of 45Ca were measured using GRETINA to allow for the extraction of Gamow-Teller strengths from very weak transitions at low excitation energies. Results: Gamow-Teller transition strengths to 45Ca were extracted up to an excitation energy of 20 MeV, and that to the first excited state in 45Ca at 174 keV was extracted from the γ-ray measurement, which, even though weak, is important for the astrophysical applications and dominates under certain stellar conditions. Shell-model calculations performed in the pf shell-model space with the GXPF1A, KB3G, and FPD6 interactions did not reproduce the experimental Gamow-Teller strength distribution, and a calculation using the quasiparticle random phase approximation that is often used in astrophysical simulations also could not reproduce the experimental strength distribution. Conclusions: Theoretical models aimed at describing Gamow-Teller transition strengths from nuclei in the lower pf shell for the purpose of estimating electron-capture rates for astrophysical simulations require further development. The likely cause for the relatively poor performance of the shell-model theory is the influence of intruder configurations from the sd shell. The combination of charge-exchange experiments at intermediate beam energy and high-resolution γ-ray detection provides a powerful technique to identify weak transitions to low-lying final states that are nearly impossible to identify without the coincidences. Identification of these weak low-lying transitions is important for providing accurate electron-capture rates for astrophysical simulations [ABSTRACT FROM AUTHOR]

In an experiment at the A1900 spectrometer of the National Superconducting Cyclotron Laboratory at Michigan State University the new isotope 59Ge was identified and the cross section for production of the most neutrondeficient 59-62Ge isotopes in the fragmentation of a78Kr beam at 150 MeV/nucleon measured. This experimental information is relevant for the hunt of new two-proton emitters in the region above the doubly-magic 48Ni. [ABSTRACT FROM AUTHOR]

The structure of semi-magic 7035Ni42, was investigated following complementary multinucleon-transfer and secondary fragmentation reactions. Changes to the higher-spin, presumed negative-parity states based on observed y-ray coincidence relationships result in better agreement with shell-model calculations using effective interactions in the neutron f5/2pg9/2 model space. The second 2+ and (4+) states, however, can only be successfully described when proton excitations across the Z = 28 shell gap are included. Monte Carlo shell-model calculations suggest that the latter two states are part of a prolate-deformed intruder sequence, establishing an instance of shape coexistence at low excitation energies similar to that observed recently in neighboring 68Ni. [ABSTRACT FROM AUTHOR]

Shell evolution is studied in the neutron-rich silicon isotopes 36,38,40Si using neutron single-particle strengths deduced from one-neutron knockout reactions. Configurations involving neutron excitations across the N = 20 and N = 28 shell gaps are quantified experimentally in these rare isotopes. Comparisons with shell model calculations show that the tensor force, understood to drive the collective behavior in 42Si with N = 28, is already important in determining the structure of 40Si with N = 26. New data relating to cross-shell excitations provide the first quantitative support for repulsive contributions to the cross-shell T = 1 interaction arising from three-nucleon forces. [ABSTRACT FROM AUTHOR]

The first lifetime measurement used to study the magnetic response of halo nuclei is presented. The lifetime of the first excited state of the one-neutron halo nucleus 19C has been measured by two complementary Doppler-shift techniques with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA). The B(M 1 ; 3/2+ →1/2g,s+) strength of 3.21(25)x 10-3µ²N determined for this decay represents a strongly hindered M1 transition among light nuclei. Shell-model calculations predict a strong hindrance due to the near-degeneracy of the S1/2 and d5/2 orbitals among neutron-rich carbon isotopes, while tensor corrections and loosely bound effects are necessary to account for the remaining strength. [ABSTRACT FROM AUTHOR]

Lifetimes of low-lying excited states have been measured in 66Ge, 69Se, and 65Ga using a γ-ray lineshape method. The results confirm the previously reported 71- state lifetime in 66Ge. The lifetime of the yrast 5/2- state in 65Ga is measured for the first time. Lifetime measurements of two excited 3/2- states in 69Se are also reported. Two previously unobserved γ rays have been identified in 69Se. γ-γ coincidence measurements have been used to place one of these in the level scheme. 69Se excited state populations are compared to shell-model calculations using the GXPF1A interaction in the fp model space. Theoretical spectroscopic factors to excited states in 69Se have identified three candidate levels for the origin of one of the new transitions. [ABSTRACT FROM AUTHOR]

The lifetimes of the yrast 8+ and 9+ states of 70As have been measured via the γ-ray lineshape method following population by the 9Be(78Rb,70As) reaction at 101.6 MeV/nucleon. The strength of the E18+→7- transition is found to be B(E1)=1.3(5)x 10-5 e²fm² or 1.2(4) x 10-5 Weisskopf units (W.u.) while the 9+→8+ M1 transition is found to have a strength of B(M1)=1.5(8) μN² or 0.85(42) W.u. The implications for the structure of these states is discussed and found to be consistent with an assignment to a πg9/2vg9/2 configuration. [ABSTRACT FROM AUTHOR]

The structure of the neutron-rich silicon isotopes 36,38,40Si was studied by one-neutron and one-proton knockout reactions at intermediate beam energies. We construct level schemes for the knockout residues 35,37,39Si and 35,37,39Al and compare knockout cross sections to the predictions of an eikonal model in conjunction with large-scale shell-model calculations. The agreement of these calculations with the present experiment lends support to the microscopic explanation of the enhanced collectivity in the region of 42Si. We also present an empirical method for reproducing the observed low-momentum tails in the parallel momentum distributions of knockout residues. [ABSTRACT FROM AUTHOR]

Background: Gamow-Teller (GT) transition strengths are key inputs for estimating weak reaction rates of importance for a wide variety of astrophysical applications. (n,p)-type charge-exchange reactions, such as the (t³He) reaction used in this work, are commonly used for extracting the GT strength distribution in the β+(electron-capture) direction. Such studies are important for testing theoretical models used to estimate weak rates for a large number of nuclei for simulations of astrophysical phenomena Purpose: The 56Fe(t,³He) reaction at 115 A MeV was measured in order to extract GT strengths for transitions to 56Mn. The extracted strength distributions were compared with shell-model calculations in the p/-shell model space using the KB3G and GXPFla interactions, and with calculations in the quasi-particle random-phase approximation (QRPA). Method: Differential cross sections and excitation-energy spectra for the 56Fe(t, ³He) reaction were determined by measuring the trajectories of ³He ejectiles through the S800 magnetic spectrograph and deducing their momenta. Contributions corresponding to GT transitions were isolated by using a multipole decomposition analysis. A well-established proportionality between GT strength and differential cross section at zero-linear-momentum transfer was utilized to convert extracted cross sections to GT strengths. Results and Conclusions: GT transition strengths from 56Fe to 56Mn were extracted up to an excitation energy of 10 MeV. Shell-model calculations with the GXPFla interaction reproduced the observed GT strength distribution slightly better than calculations with the KB3G interaction. The calculated strength distribution in the QRPA did not reproduce the observed strength distribution. The new experimental data have an improved precision at low excitation energies compared to previous results obtained from an 56Fe(n,p) experiment. Electron-capture rates based on the experimental and theoretical Gamow-Teller strengths were compared and deviations were included in an assessment of the validity of electron-capture rates based on theoretical models for nuclei in the pf shell. [ABSTRACT FROM AUTHOR]

We have performed measurements of the 0+g.s. → 21+ excitations in the neutron-rich isotopes 48,50Ca via inelastic proton scattering on a liquid hydrogen target, using the GRETINA y-ray tracking array. A comparison of the present results with those from previous measurements of the lifetimes of the 21+ states provides the ratio of the neutron and proton matrix elements for the 0+g.s. → 21+ transitions. These results allow the determination of the ratio of the proton and neutron effective charges to be used in shell model calculations of neutron-rich isotopes in the vicinity of 48Ca. [ABSTRACT FROM AUTHOR]

A measurement of the direct two-proton removal from 42Si has provided the first structural information on the N = 28 isotone 40Mg. The value for the inclusive cross section for two-proton removal from 42Si of 40+27-17 μb is significantly lower than that predicted by structure calculations using the recent SDPF-MU shell-model effective interaction combined with eikonal reaction theory. This observed discrepancy is consistent with the interpretation that only one of the predicted low-lying 0+ states in 40Mg is bound. A two-state mixing analysis describing two-proton knockout cross sections along N = 28 provides support for the interpretation of a prolate-deformed 40Mg ground state. [ABSTRACT FROM AUTHOR]

The applicability of Coulomb dissociation reactions to determine the cross section for the inverse neutron capture reaction was explored using the reaction 8Li(γ,n)7Li. A 69.5 MeV/nucleon 8Li beam was incident on a Pb target, and the outgoing neutron and 7Li nucleus were measured in coincidence. The deduced (n,y) excitation function is consistent with data for the direct capture reaction 7Li(n,γ)8Li and with low-energy effective field theory calculations. [ABSTRACT FROM AUTHOR]

We report on the experimental study of quadrupole collectivity in the neutron-deficient nucleus 104Sn using intermediate-energy Coulomb excitation. The B(E2;01+→ 21+) value for the excitation of the first 2+ state in 104Sn has been measured to be 0.180(37) e2b2 relative to the well-known B(E2) value of 102Cd. This result disagrees by more than one sigma with a recently published measurement [G. Guastalla et at, Phys. Rev. Lett. 110, 172501 (2013)]. Our result indicates that the most modern many-body calculations remain unable to describe the enhanced collectivity below midshell in Sn approaching N = Z = 50. We attribute the enhanced collectivity to proton particle-hole configurations beyond the necessarily limited shell-model spaces and suggest the asymmetry of the B(E2)-value trend around midshell to originate from enhanced proton excitations across Z = 50 as N = Z is approached. [ABSTRACT FROM AUTHOR]

Background: The self-conjugate nuclei of the A ~ 70 mass region display rapid shape evolution over isotopic or isotonic chains. Shape coexistence has been observed in Se and Kr isotopes reflecting the existence of deformed subshell gaps corresponding to different shell configurations. As and Ge isotopes are located halfway between such deformed nuclei and the Z = 28 shell closure. Purpose: The present work aims at clarifying the low-lying spectroscopy of 66Ge and i,7As, and providing a better insight into the evolution of collectivity in light even-even Ge and even-odd As isotopes Methods: We investigate the low-lying levels and collectivity of the neutron deficient 67As and 66Ge through intermediate-energy Coulomb excitation, inelastic scattering, and proton knockout measurements. The experiment was performed using a cocktail beam of 68Se, 67As, and 66Ge nuclei at an energy of 70-80 MeV/nucleon. Spectroscopic properties of the low-lying states are compared to those calculated via shell model with the JUN45 interaction and beyond-mean-field calculations with the five-dimensional collective Hamiltonian method implemented using the Gogny DIS interaction. The structure evolution of the lower-mass Ge and As isotopes is discussed. Results: Reduced electric quadrupole transition probabilities B(E2) have been extracted from the Coulomb-excitation cross sections measured in 66Ge and 67As. The value obtained for the B(E2;01+ → 21+) in 66Cie is in agreement with a recent measurement, ruling out the existence of a minimum at N = 34 in the B(E2) systematics as previously observed. New transitions have been found in 67As and were assigned to the decay of low-lying negative-parity states. [ABSTRACT FROM AUTHOR]

To improve the effective interactions in the pf shell, it is important to measure the single-particle and single-hole states near the N = 28 shell gap. In this paper, the neutron spectroscopic factors of hole states from the unstable neutron-rich 45Ar (Z = 18,N = 27) nucleus have been studied using the ¹H(46Ar,d)45Ar transfer reaction in inverse kinematics. Comparison of our results with the particle states of 45Ar produced in -H(44Ar, p)45Ar reaction shows that the two reactions populate states with different angular momenta. Using the angular distributions, we are able to confirm the spin assignments of four low-lying states of 45Ar. These are the ground state (f7/2), the first-excited state (p3/2), and the s1/2 and d3/2 states. While large basis shell-model predictions describe spectroscopic properties of the ground and p3/2 states very well, they fail to describe the s1/2 and d3/2 hole states. [ABSTRACT FROM AUTHOR]

Production cross sections for neutron-rich nuclei from the fragmentation of a 82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions of 126 neutron-rich isotopes of elements 11 ≼ Z ≼ 32 were scanned using an experimental approach of varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including several isotopes first observed in this work. These are the most neutron-rich nuclides of the elements 22 ≼ Z ≼ 25 (64Ti, 67V, 69Cr, and 72Mn). One event was registered consistent with 70Cr and another one with 75Fe. The production cross sections are correlated with Qg systematics to reveal trends in the data. The results presented here confirm our previous results from a similar measurement using a 76Ge beam and can be explained with a shell model that predicts a subshell closure at N = 34 around Z = 20. This is demonstrated by systematic trends and calculations with the abrasion-ablation model that are sensitive to separation energies. [ABSTRACT FROM AUTHOR]

The structure of 10Be was studied via resonant α-particle scattering of a neutron-rich 6He beam. A time projection chamber, PAT-TPC, was operated in an active-target mode to provide a gaseous 4He target and trace the beam and reaction products traversing its active tracking volume. This significantly lowered the detection threshold of reaction products at low energies. Elastic scattering, inelastic scattering to the 6He 2+ state, and the 6He(α, 2n)8Be reaction were measured below an energy of 6 MeV in the center-of-mass frame. Continuous spectra of excitation functions and angular distributions were obtained from unambiguously-identified recoiling a particles for the elastic and inelastic channels. While a resonance of the 4+ state at 10.15 MeV in 10Be previously reported was confirmed, no other resonances were identified in the elastic channel over the measured energy region. The results are in line with antisymmetric molecular dynamics calculations that predict the limits of a clustering in high-spin states due to a spin-orbit force. [ABSTRACT FROM AUTHOR]

The ground state of neutron-rich unbound 13Li was observed for the first time in a one-proton removal reaction from 14Be at a beam energy of 53.6 MeV/u. The 13Li ground state was reconstructed from "Li and two neutrons giving a resonance energy of 120-80+60 keV. All events involving single- and double-neutron interactions in the Modular Neutron Array (MoNA) were analyzed, simulated, and fitted self-consistently. The three-body ("Li + n + n) correlations within Jacobi coordinates showed strong dineutron characteristics. The decay energy spectrum of the intermediate 12Li system (11Li + n) was described with an s-wave scattering length of greater than --4 fm, which is a smaller absolute value than reported in a previous measurement. [ABSTRACT FROM AUTHOR]

The role of proton shell effects in the structure of the N = 28 isotones 45C1 and 44S has been studied via one-proton knockout from 45Cl. We compare measured γ-ray intensities, inclusive and partial knockout cross sections, and the inclusive momentum distribution of outgoing 44S particles with shell-model and reaction-theory predictions. The strong population in this reaction of the recently identified 4+1 state in 44S, identified through its subsequent y-ray decay energy, makes a compelling case for a JΠ= 3/2+ ground state in 45Cl. [ABSTRACT FROM AUTHOR]

Excited states in 16C were populated via the 9Be(17N,16C + γ)X one-proton knockout reaction. The lifetime of the 21+ state in 16C was measured using the recoil distance method. The extracted lifetime of τ21+ = 11,4-0.9+0.8(stat) ± 0.7(systBp)-1.5+0.0(systfeeding) ps yields a deduced B(E2;21+ → O1+ ) = 4.21-0.26+0.34(stat)-0.24+0.28(systsBp)-0.00+0.64(systfeeding) e²fm4 value in good agreement with a previous measurement. The one-proton knockout cross section is used to extract the proton amplitude of the 16C 21+ state, which confirms the neutron dominant character of this state. Gamma-ray branching ratios between the 22+ state and the 21+ and ground states were also determined. The results are compared with p-sd shell model and no-core shell model (with NN and NN + NNN) calculations. The inclusion of three-body forces are essential in order for the no-core shell model calculations to reproduce the experimental findings on the γ-ray branching ratios. [ABSTRACT FROM AUTHOR]

The ground state of 11Li is the preeminent example of a two-neutron-halo nucleus and is part of an isobaric sextet. Another member of this sextet, the double isobaric analog of 11Lig.s. in 11B, has been identified in the 12Be(p, 2n)11B reaction. The state was discovered through its two-proton decay branch. From detected 2p + 9Li events, its excitation energy was determined to be 33.57(8) MeV using the invariant mass method. With the known masses of 11Li and its isobaric analog state in 11Be, three members of the same sextet have measured masses for the first time, permitting the masses of the remaining members to be extrapolated using the isobaric multiplet mass equation. All members of this multiplet are expected to have a two-nucleon halo structure and this was found consistent with the evolution of the mass across the sextet. The momentum correlations of the detected protons were found to have both "diproton" and "cigar" components. [ABSTRACT FROM AUTHOR]

Background: Gamow-Teller (GT) transition strength distributions in stable and unstable pf '-shell isotopes are key inputs for estimating electron-capture rates important for stellar evolution. Charge-exchange experiments at intermediate beam energies have long been used to test theoretical predictions for GT strengths, but previous experiments were largely restricted to stable nuclei. Since a large fraction of the nuclei relevant for astrophysical applications (including key nuclei such as56Ni) are unstable, new methods are needed to perform charge-exchange experiments in inverse kinematics with unstable isotopes. Purpose: The 56Ni(p, n) and 55Co(p, n) reactions were measured in inverse kinematics in order to extract GT strengths for transitions to 56Cu and 55Ni, respectively. The extracted strength distributions were compared with shell-model predictions in the pf shell using the KB3G and GXPF1J interactions. By invoking isospin symmetry, these strength distributions are relevant for electron captures on the ground states of 56Ni and 55Ni to final states in 56Co and 55Co, respectively. Method: Differential cross sections and excitation energy spectra for the 56Ni(p, n) and 55Co(p, n) reactions were determined by measuring neutrons recoiling from a liquid hydrogen target into the Low Energy Neutron Detector Array. GT contributions to the spectra were extracted by using a multipole decomposition analysis and were converted to strengths by employing the proportionality between GT strength and differential cross section at zero linear momentum transfer. Results: GT strengths from 56Ni and 55Co were extracted up to excitation energies of 8 and 15 MeV, respectively. Shell-model calculations performed in the pf shell with the GXPF1J interaction reproduced the experimental GT strength distributions better than calculations with the KB3G interaction. Conclusions: A new technique for measuring (ρ, ?) charge-exchange reactions on unstable nuclei was successfully developed. It can be used to study the isovector response of unstable nuclei in any mass region and for excitation energies beyond the particle decay threshold. In the first experiment, 56Ni(/?, n) and55Co(p, n) reactions were studied and GT transition strengths were extracted for the purpose of testing shell-model calculations used to estimate electron-capture rates in simulations of late stellar evolution. The calculation using the GXPF1J interaction was found to best reproduce the experimental strength distribution. [ABSTRACT FROM AUTHOR]

The low-energy nuclear structure of the neutron-rich 43-46Cl isotopes is studied via in-beam γ-ray spectroscopy following the fragmentation of 48K projectiles on a 9Be target at intermediate beam energies, γγ coincidence information was used to construct level schemes for these neutron-rich nuclei. For the N = 28 nucleus 45Cl, the lifetime of the first excited state at 130 keV was extracted via γ-ray line shape analysis, yielding an M1 strength an order of magnitude greater than that predicted by theory. The experimental data is compared to the results of large-scale shell-model calculations with effective interactions in the sd-pf model space. [ABSTRACT FROM AUTHOR]

β-delayed proton emission from nuclides in the neighborhood of 100Sn was studied at the National Superconducting Cyclotron Laboratory (NSCL). The nuclei were produced by fragmentation of a 120 MeV/nucleon 112Sn primary beam on a Be target. Beam purification was provided by the A1900 Fragment Separator and the Radio Frequency Fragment Separator. The fragments of interest were identified and their decay was studied with the NSCL Beta Counting System in conjunction with the Segmented Germanium Array. The nuclei 96Cd, 98Ing, 98Inm, and 99In were identified as β-delayed proton emitters, with branching ratios bβp = 5.5(40)%, 5.5-2+3%, 19(2)%, and 0.9(4)%, respectively. The branching ratios for 89Ru, 91.92Rh, 93Pd, and 95Ag were deduced for the first time with bβp = 3-1.7+1.9%, 1.3(5)%, 1.9(1)%, 7.5(5)%, and 2.5(3)%, respectively. The bβp = 22(1)% value for 101Sn was deduced with higher precision than previously reported. The impact of the newly measured bβp values on the composition of the type I x-ray burst ashes was studied. [ABSTRACT FROM AUTHOR]

Intermediate-energy Coulomb excitation measurements were performed on the neutron-rich isotopes 58,60,62Cr. The electric quadrupole excitation strengths, B(E2; 01+ → 21+), of 60,62Cr are determined for the first time. The results quantify the trend of increasing quadrupole collectivity in the Cr isotopes approaching neutron number N = 40. The results are confronted with large-scale shell-model calculations in the f pgd shell using the state-of-the-art LNPS effective interaction. Different sets of effective charges are discussed that provide an improved and robust description of the B(E2) values of the neutron-rich Fe and Cr isotopes in this region of rapid shell evolution. The ratio of the neutron and proton transition matrix elements, ∣Mn/Mp∣, is proposed as an effective tool to discriminate between the various choices of effective charges. [ABSTRACT FROM AUTHOR]

The article presents the study which examined the β-delayed proton emission from nuclides in the neighborhood of 100tin (Sn). The study was conducted at the National Superconducting Cyclotron Laboratory (NSCL) in Michigan. The NSCL Beta Counting System and the Segmented Germanium Array were used to study the decay of the nuclides.

The article presents the study which analyzed the intermediate-energy Coulomb excitation of 58,60,62chromium (Cr). In the study, the electric quadruple excitation strengths of 60,62Cr are determined for the first time. The results showed a trend of increasing quadruple collectivity in the Cr isotopes approaching neutron number N=40.

The cross sections for single-nucleon knockout from 36Ca on a 9Be target at 70 MeV/nucleon were measured to be &sgr;exp(--p) = 51.1 ±2.6 mb for proton knockout and &sgr;exp(--n) = 5.03 ± 0.46 mb for neutron knockout. The spectroscopic factors and orbital angular momenta of the neutrons and protons removed from 36Ca, leading to bound A = 35 residues, were deduced by comparison of the experimental cross sections and longitudinal-momentum distributions to those calculated in an eikonal reaction theory, and found to be S(p, 1d3/2) = 0.79 ± 0.04 and S(n, 2s1/2) = 0.23 ± 0.02 (relative to independent-particle-model values and only including experimental contributions to the uncertainties). As found in previous knockout studies, the spectroscopic factor deduced for the deeply bound neutron was significantly reduced relative to shell-model calculations, a result at variance with dispersive optical model (DOM) extrapolations, which suggest a spectroscopic factor closer to 60% of the independent-particle-model value. [ABSTRACT FROM AUTHOR]

A study of 26Si states by neutron removal from a fast radioactive beam of 27si has been performed. A beam of 27si of energy 84.3 MeV/nucleon impinged on a polypropylene foil (C3H6) of 180 mg/cm2 thickness. Deexcitation γ rays were detected with a highly segmented germanium detector array, in coincidence with the 26Si recoils, and the corresponding 26Si level energies were determined. In comparing our results to two previous y-ray spectroscopic studies of 26Si level structures, we find good agreement with a recent measurement of the 12C(16O,2nγ)26Si reaction. Our results support the use of excitation energies from that study in helping determine the important resonance energies for the thermonuclear 25Al(p, γ)26Si reaction rate. We do not observe a bound state at 4093 keV reported in an earlier study of the 24Mg(3He,nγ)26Si reaction. [ABSTRACT FROM AUTHOR]

The lifetimes of the first 2+ states in the neutron-deficient 76,78Sr isotopes were measured using a unique combination of the γ-ray line-shape method and two-step nucléon exchange reactions at intermediate energies. The transition rates for the 2+ states were determined to be B(E2;2+ → 0+) = 2220(270) e2fm4 for 76Sr and 1800(250) e2fm4 for 78Sr, corresponding to large deformation of p\ = 0.45(3) for 76Sr and 0.40(3) for 78Sr. The present data provide experimental evidence for mutually enhanced collectivity that occurs at N = Z = 38. The systematic behavior of the excitation energies and B(E2) values indicates a signature of shape coexistence in 76Sr, characterizing 76Sr as one of most deformed nuclei with an unusually reduced E(4+)/E(2+) ratio. [ABSTRACT FROM AUTHOR]

Background: Momentum distributions of fragmentation products as a function of fragment mass have been used to study the fragmentation mechanism. The parallel component of the momentum distribution has been well studied previously and modeled. The perpendicular component, however, is much less measured or understood. Purpose: Measure both components of the linear momentum of a wide range of fragmentation products and compare the widths of the momentum distributions to previous results and descriptions. Method: The parallel and perpendicular components of the momentum vector have been measured for projectilelike fragments produced in the reactions of 76Ge with 9Be and 197Au at 130 MeV/nucleon in a magnetic spectrometer. Results: The measured parallel momentum distributions of all fragments follow established systematics. The perpendicular momentum distributions of fragments produced by fragmentation by the 197Au target with masses near that of the projectile exhibit a clear peak near the momentum corresponding to the grazing angle that diminishes with decreasing fragment mass. Conclusions: The interplay between Coulomb and nuclear scattering can be used to describe results for the most peripheral collisions. [ABSTRACT FROM AUTHOR]

Background: Thick-target-induced nucleon-adding transfer reactions onto energetic rare-isotope beams are an emerging spectroscopic tool. Their sensitivity to single-particle structure complements one-nucleon removal reaction capabilities in the quest to reveal the evolution of nuclear shell structure in very exotic nuclei. Purpose: Our purpose is to add intermediate-energy, carbon-target-induced one-proton pickup reactions to the arsenal of y-ray-tagged direct reactions applicable in the regime of low beam intensities and to apply these for the first time to fp-shell nuclei. Methods: Inclusive and partial cross sections were measured for the 12C(48Cr, 49Mn + &ggr;)X and 12C(50Fe,51Co + &ggr;)X proton pickup reactions at 56.7 and 61.2 MeV/nucleon, respectively, using coincident particle-/ spectroscopy at the National Superconducting Cyclotron Laboratory. The results are compared to reaction theory calculations using /p-shell-model nuclear structure input. For comparison with our previous work, the same reactions were measured on 9Be targets. Results: The measured partial cross sections confirm the specific population pattern predicted by theory, with pickup into high-l orbitals being strongly favored, driven by linear and angular momentum matching. Conclusion: Carbon-target-induced pickup reactions are well suited, in the regime of modest beam intensity, to study the evolution of nuclear structure, with specific sensitivities that are well described by theory. [ABSTRACT FROM AUTHOR]