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The neutron-capture reaction plays a critical role in the synthesis of the elements in stars and is important for societal applications including nuclear power generation and stockpile-stewardship science. However, it is difficult--if not impossible--to directly measure neutron capture cross sections for the exotic, short-lived nuclei that participate in these processes. In this Letter we demonstrate a new technique which can be used to indirectly determine neutron-capture cross sections for exotic systems. This technique makes use of the (d,p) transfer reaction, which has long been used as a tool to study the structure of nuclei. Recent advances in reaction theory, together with data collected using this reaction, enable the determination of neutron-capture cross sections for short-lived nuclei. A benchmark study of the 95Mo(d,p) reaction is presented, which illustrates the approach and provides guidance for future applications of the method with short-lived isotopes produced at rare isotope accelerators. [ABSTRACT FROM AUTHOR]

Background: Neutron-rich, even-mass chromium and iron isotopes approaching neutron number N = 40 have been important benchmarks in the development of shell-model effective interactions incorporating the effects of shell evolution in the exotic regime. Odd-mass manganese nuclei have received less attention, but provide important and complementary sensitivity to these interactions. Purpose:We report the observation of two newγ -ray transitions in 63Mn,which establish the (9/2-) and (11/2-) levels on top of the previously known (7/2-) first-excited state. The lifetime for the (7/2-) and (9/2-) excited states were determined for the first time, while an upper limit could be established for the (11/2-) level. Method: Excited states in 63Mn have been populated in inelastic scattering from a 9Be target and in the fragmentation of 65Fe. γγ coincidence relationships were used to establish the decay level scheme. A Doppler line-shape analysis for the Doppler-broadened (7/2-) → 5/2-, (9/2-)→ (7/2-), and (11/2-) → (9/2-) transitions was used to determine (limits for) the corresponding excited-state lifetimes. Results: The low-lying level scheme and the excited-state lifetimes were compared with large-scale shell-model calculations using different model spaces and effective interactions in order to isolate important aspects of shell evolution in this region of structural change. Conclusions: While the theoretical (7/2-) and (9/2-) excitation energies show little dependence on the model space, the calculated lifetime of the (7/2-) level and calculated energy of the (11/2-) level reveal the importance of including the neutron g9/2 and d5/2 orbitals in the model space. The LNPS effective shell-model interaction provides the best overall agreement with the new data. [ABSTRACT FROM AUTHOR]

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]

The 240Am(n,f) cross section has been measured for the first time above 4 MeV, using the surrogate-ratio method over the neutron energy range of 200 keV to 14 MeV. The reactions 243Am(p,tf) and 238U(p,tf), which proceed through the fissioning excited nuclei 241Am* and 236U*, were used as surrogates for the desired 240Am(n,f) and 235U (n,f) reactions. The experiment was fielded using the STARLiTeR detector system with a recently commissioned VME-based data acquisition system. The 38.4-MeV proton beam used in these measurements was provided by the K150 cyclotron at the Texas A&M Cyclotron Institute. The measured 240Am(n, f) cross section disagrees with many of the most recent evaluations, and a reevaluation is recommended. [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 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]

Background: The 8838Sr and 9040JZr nuclei have been utilized as closed cores for large-scale shell-model calculations in the 28 ≥ Z ≥S 50 region around the N = 50 shell. Measurements of magnetic moments for nuclei in this region would provide microscopic information about the use of 88Sr and 90Zr as stable closed-core nuclei. While the g factors of the T+1 states in the stable Sr isotopes have been previously measured, experimental g factors for the radioactive 82,90Sr have not been obtained to date. Purpose: The purpose was to measure the g factors of the 2+1 and 4+1, states in the unstable 82Sr and 90Sr nuclei in order to extend the systematics along the Sr isotopic chain. A comparison of the structure of the N = 52 isotopes 90Sr and 92Zr will shed light on the relative robustness of proton subshell closures at Z = 38 and Z = 40. Methods: The pickup reaction of α particles in inverse kinematics together with the transient field technique were applied to beams of 78Kr and 86Kr at the Cyclotron Institute of Texas A&M University. Results: The values g(82Sr;2+1) = +0.44(19), g(82Sr;4+1) = +0.53(39), g(90Sr;2+1) = -0.12(11), and g i S r f ) = -0.02(17) were measured for the first time. Simultaneously, the g factors of the low-lying states in the Coulomb-excited beam projectiles were remeasured. The g(4+1) = +1.03(14) in 86Kr was also measured for the first time. Conclusions: For 82Sr both g factors are in agreement with the collective value Z/A expected for nuclei in the middle of a major shell. The g factors in 90Sr are negative but smaller than in the isotone 92Zr. The results also indicate that 88Sr is a proton-soft core nucleus and perhaps even softer than 90Zr. [ABSTRACT FROM AUTHOR]

Single-neutron states in 132Sn and 208Pb , which are analogous to single-electron states outside of closed atomic shells in alkali metals, were populated by the (9Be, 8Be) one-neutron transfer reaction in inverse kinematics using particleγ coincidence spectroscopy. In addition, the s 1/2 single-neutron hole-state candidate in 131 Sn was populated by (9Be, 10Be). Doubly closed-shell 132Sn (radioactive) and 208Pb (stable) beams were used at sub-Coulomb barrier energies of 3 MeV per nucleon. Level energies, γ-ray transitions, absolute cross sections, spectroscopic factors, asymptotic normalization coefficients, and excited-state lifetimes are reported and compared with shell-model expectations. The results include a new transition and precise level energy for the 3p1/2 candidate in 133 Sn, new absolute cross sections for the 1 h9/2 candidate in 133Sn and 3s1/2 candidate in 131Sn, and new lifetimes for excited states in 133Sn and 209Pb. This is the first report on excited-state lifetimes of 133Sn, which allow for a unique test of the nuclear shell model and 132Sn double-shell closure. [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]

The first spectroscopy of excited states in 52Ni (Tz = -2) and 51Co (Tz = -3/2) has been obtained using the highly selective two-neutron knockout reaction. Mirror energy differences between isobaric analogue states in these nuclei and their mirror partners are interpreted in terms of isospin nonconserving effects. A comparison between large-scale shell-model calculations and data provides the most compelling evidence to date that both electromagnetic and an additional isospin nonconserving interactions for J = 2 couplings, of unknown origin, are required to obtain good agreement. [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]

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]

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]

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 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]

We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei 47,48Ar using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly magic Ca to collective S and Si isotopes, a critical region of shell evolution and structural change. The deduced B(E2) transition strengths are confronted with large-scale shell-model calculations in the sdpf shell using the state-of-the-art SDPF-Uand EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around N = 28 remains a challenge. [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]

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]

We present a novel technique for studying the quenching of shell gaps in exotic isotopes. The method is based on extracting Gamow-Teller (&Dgr;L = 0, &Dgr;S = 1) transition strengths [B(GT)] to low-lying states from charge-exchange reactions at intermediate beam energies. These Gamow-Teller strengths are very sensitive to configuration mixing between cross-shell orbitals, and this technique thus provides an important complement to other tools currently used to study cross-shell mixing. This work focuses on the N = 8 shell gap. We populated the ground and 2.24 MeV 0+ states in 12Be using the 12B(1+) (7Li, 7Be) reaction at 80 MeV/u in inverse kinematics. Using the ground-state 5(GT) value from ß-decay measurements (0.184 ± 0.007) as a calibration, the B(GT) for the transition to the second 0+ state was determined to be 0.214 ±0.051. Comparing the extracted Gamow-Teller strengths with shell-model calculations, it was determined that the wave functions of the first and second 0+ states in 12Be are composed of 25 ± 5% and 60 ± 5% (0s)4(0p)8 configurations, respectively. [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]

The neutron-rich N = 28 nucleus 44S was studied using the two-proton knockout reaction from 46Ar at intermediate beam energy. We report the observation of four new excited states, one of which is a strongly prolate deformed 4+ state, as indicated by a shell-model calculation. Its deformation originates in a neutron configuration which is fundamentally different from the "intruder" configuration responsible for the ground-state deformation. Consequently, we do not have three coexisting shapes in 44S, but three coexisting configurations, corresponding to zero-, one-, and two-neutron particle-hole excitations. [ABSTRACT FROM AUTHOR]

Measurements and reaction model calculations are reported for single-neutron pickup reactions onto a fast 22Mg secondary beam at 84 MeV per nucleon. Measurements made on both carbon and beryllium targets, having very different structures, were used to investigate the likely nature of the pickup reaction mechanism. The measurements involve thick reaction targets and γ-ray spectroscopy of the projectile-like reaction residue for final-state resolution, which permit experiments with low incident beam rates compared to traditional low-energy transfer reactions. From measured longitudinal momentum distributions we show that the 12C(22Mg,23Mg+γ)X reaction largely proceeds as a direct two-body reaction, with the neutron transfer producing bound 11C target residues. The corresponding reaction on the 9Be target seems to largely leave the 8Be residual nucleus unbound at excitation energies high in the continuum. We discuss the possible use of such fast-beam one-neutron pickup reactions to track single-particle strength in exotic nuclei and also their expected sensitivity to neutron high-ℓ (intruder) states, which are often direct indicators of shell evolution and the disappearance of magic numbers in the exotic regime. [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]

New experimental data obtained from γ-ray tagged one-neutron and one-proton knockout from 55 Co are presented. A candidate for the sought-after T = 1, Tz = 0, Jπ = 6+ state in 54 Co is proposed based on a comparison to the new data on 54 Fe, the corresponding observables predicted by large-scale-shell-model (LSSM) calculations in the full fp-model space employing charge-dependent contributions, and isospin-symmetry arguments. Furthermore, possible isospin-symmetry breaking in the A = 54, T = 1 triplet is studied by calculating the experimental c coefficients of the isobaric mass multiplet equation (IMME) up to the maximum possible spin J = 6 expected for the (1f7/2)-2 two-hole configuration relative to the doubly magic nucleus 56 Ni. The experimental quantities are compared to the theoretically predicted c coefficients from LSSM calculations using two-body matrix elements obtained from a realistic chiral effective field theory potential at next-to-next-to-next-to-leading order (N³ LO). [ABSTRACT FROM AUTHOR]

We present a high-resolution in-beam γ-ray spectroscopy study of excited states in the mirror nuclei 55Co and 55Ni following one-nucleon knockout from a projectile beam of 56Ni. The newly determined partial cross sections and the γ-decay properties of excited states provide a test of state-of-the-art nuclear structure models and probe mirror symmetry in unique ways. The new experimental data are compared to large-scale shell-model calculations in the full pf space which include charge-dependent contributions. A mirror asymmetry for the partial cross sections leading to the two lowest 3/2- states in the A=55 mirror pair was identified as well as a significant difference in the E1 decays from the 1/2+1 state to the same two 3/2- states. The mirror asymmetry in the partial cross sections cannot be reconciled with the present shell-model picture or small mixing introduced in a two-state model. The observed mirror asymmetry in the E1 decay pattern, however, points at stronger mixing between the two lowest 3/2- states in 55Co than in its mirror 55Ni. [ABSTRACT FROM AUTHOR]

Half of the elements heavier than iron are believed to be produced through the rapid neutron-capture process (r process). The astrophysical environment(s) where the r process occurs remains an open question, even after recent observations of neutron-star mergers and the associated kilonova. Features in the abundance pattern of r-process ashes may provide critical insight for distinguishing contributions from different possible sites, including neutron-star mergers and core-collapse supernovae. In particular, the largely unknown neutron-capture reaction rates on neutron-rich unstable nuclei near 132Sn could have a significant impact on the final r-process abundances. To better determine these neutron-capture rates, the (d,p) reaction has been measured in inverse kinematics using radioactive ion beams of 126Sn and 128Sn and a stable beam of 124Sn interacting with a (CD2)n target. An array of position-sensitive silicon strip detectors, including the Super Oak Ridge Rutgers University Barrel Array, was used to detect light reaction products. In addition to the present measurements, previous measurements of 130,132Sn(d,p) were reanalyzed using state-of-the-art reaction theory to extract a consistent set of spectroscopic factors for (d,p) reactions on even tin nuclei between the heaviest stable isotope 124Sn and doubly magic 132Sn. The spectroscopic information was used to calculate direct-semidirect (n,γ) cross sections, which will serve as important input for r-process abundance calculations. [ABSTRACT FROM AUTHOR]

The 24Mg(p,α)21Na reaction was measured at the Holifield Radioactive Ion Beam Facility of the Oak Ridge National Laboratory to study the spectroscopy of the radionuclide 21Na. A 31-MeV proton beam from the 25 MV tandem accelerator bombarded isotopically enriched 24Mg targets. Recoiling 4He particles were identified by an annular silicon strip detector array. Two energy levels at Ex=6.594 and 7.132 MeV were observed for the first time. By comparing the experimentally obtained angular distributions and distorted wave Born approximation calculations, the spins and parities of 21Na energy levels were constrained. The astrophysically-important 17F(α,p)20Ne reaction rate was also calculated for the first time using resonance parameters for 12 energy levels. [ABSTRACT FROM AUTHOR]

The β-delayed neutron emission of Ga83,84 isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high above the neutron separation energy and previously not observed in the β decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed β decay to Ni78 core-excited states in Ge83,84 favored by shell effects. We developed shell model calculations in the proton fpg9/2 and neutron extended fpg9/2+d5/2 valence space using realistic interactions that were used to understand measured β-decay lifetimes. We conclude that enhanced, concentrated β-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. This leads to intense β-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models. [ABSTRACT FROM AUTHOR]

One-neutron knockout reactions have been performed on a beam of radioactive 53Co in a high-spin isomeric state. The analysis is shown to yield a highly selective population of high-spin states in an exotic nucleus with a significant cross section, and hence represents a technique that is applicable to the planned new generation of fragmentation-based radioactive beam facilities. Additionally, the relative cross sections among the excited states can be predicted to a high level of accuracy when reliable shell-model input is available. The work has resulted in a new level scheme, up to the 11+ band-termination state, of the proton-rich nucleus 52Co (Z = 27, N = 25). This has in turn enabled a study of mirror energy differences in the A = 52 odd-odd mirror nuclei, interpreted in terms of isospin-nonconserving (INC) forces in nuclei. The analysis demonstrates the importance of using a full set of J-dependent INC terms to explain the experimental observations. [ABSTRACT FROM AUTHOR]

Comprehensive spectroscopy of the N=29 nucleus 47Ar is presented, based on two complementary direct reaction mechanisms: one-neutron pickup onto 46Ar projectiles and one-proton removal from the 1- ground state of 48K. The results are compared with shell-model calculations that use the state-of-the-art SDPF-U and SDPF-MU effective interactions. Also, from the 9Be(46Cl,45S+γ)X one-proton-removal reaction, we report the first γ-ray transitions observed from 45S. By using comparisons with shell-model calculations, and from the observed intensities and energy sums, we propose a first tentative level scheme for 45S. [ABSTRACT FROM AUTHOR]

Background: The study of excited states in mirror nuclei allows us to extract information on charge-dependent (i.e., isospin-nonconserving) interactions in nuclei. Purpose: To extend previous studies of mirror nuclei in the fτ/2 region, investigating charge symmetry breaking of the strong nuclear force. Methods: γ-ray spectroscopy has been performed for the mirror (Tz=±3/2) pair 53Ni and 53Mn, produced via mirrored one-nucleon knockout reactions. Results: Several new transitions have been identified in 53Ni from which a new level scheme has been constructed. Cross sections for knockout have been analyzed and compared with reaction model calculations where evidence is found for knockout from high-spin isomeric states. Mirror energy differences between isobaric analog states have been computed, compared to large scale shell-model calculations, and interpreted in terms of isospin-nonconserving effects. In addition, lifetimes for the long-lived Jπ=5/2-1 analog states in both 53Mn and 53Ni have been extracted through lineshape analysis, giving half-lives of t1/2=120(14) ps and t1/2=198(12) ps, respectively. Conclusions: The inclusion of a set of isovector isospin-nonconserving matrix elements to the shell-model calculations gave the best agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The neutron-deficient nucleus 107Sn has been studied by using the one-neutron knockout reaction. By measuring the decay γ rays and momentum distributions of reaction residues, the spins of the ground, 5/2+, and first-excited, 7/2+, states of 107Sn have been assigned by comparisons to eikonal-model reaction calculations. Limits on the inclusive and exclusive cross sections have been measured and transitions due to neutron removals from below the N=50 closed shell have been observed. New excited states up to 5.5 MeV in 107Sn have been identified. [ABSTRACT FROM AUTHOR]

Detection of nuclear-decay γ rays provides a sensitive thermometer of nova nucleosynthesis. The most intense γ-ray flux is thought to be annihilation radiation from the β^{+} decay of ^{18}F, which is destroyed prior to decay by the ^{18}F(p,α)^{15}O reaction. Estimates of ^{18}F production had been uncertain, however, because key near-threshold levels in the compound nucleus, ^{19}Ne, had yet to be identified. We report the first measurement of the ^{19}F(^{3}He,tγ)^{19}Ne reaction, in which the placement of two long-sought 3/2^{+} levels is suggested via triton-γ-γ coincidences. The precise determination of their resonance energies reduces the upper limit of the rate by a factor of 1.5-17 at nova temperatures and reduces the average uncertainty on the nova detection probability by a factor of 2.1.

The β-delayed neutron emission of ^{83,84}Ga isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high above the neutron separation energy and previously not observed in the β decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed β decay to ^{78}Ni core-excited states in ^{83,84}Ge favored by shell effects. We developed shell model calculations in the proton fpg&#95;{9/2} and neutron extended fpg&#95;{9/2}+d&#95;{5/2} valence space using realistic interactions that were used to understand measured β-decay lifetimes. We conclude that enhanced, concentrated β-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. This leads to intense β-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models.