Search

Excited states in the neutron-rich nucleus Fe 68 were populated using a Be 9 ( Co 68 , 68 Fe + γ ) X charge-exchange reaction at 95 MeV/u. The new γ -ray transitions reported here for the first time complement data from β -decay studies and nucleon knockout reactions. In comparison to shell-model calculations with the LNPS effective interaction, two candidate states for the 6 1 + level emerge. The distinct population pattern of excited states and the magnitude of the cross section, σ inc = 0.51 ( 6 ) mb, make this reaction a promising one for future in-beam γ -ray spectroscopy. Reaction calculations with nuclear structure input from a new, locally optimized Hamiltonian, f 7 j 4 a , together with general considerations for heavy-ion-induced charge-exchange reactions appear consistent with most of the observations, although challenges remain.

The low-lying dipole strength in the 90,94Zr nuclei was investigated via (p,p′γ) at 80 MeV and (α,α′γ) at 130 MeV. The experiments, made at RCNP, used the magnetic spectrometer Grand Raiden for the scattered particles and the array CAGRA with HPGe detectors for the γ-decay. For 94Zr these are the first data for both reactions and for 90Zr these are the first data with (p,p′γ) and the first ones at high resolution for (α,α′γ). The comparison of the present results for the two nuclei with existing (γ,γ′) data shows that both nuclear probes produce an excitation pattern different than that of the electromagnetic probes. DWBA calculations were made using form factors deduced from transition densities, based on RPA calculations, characterized by a strong neutron component at the nuclear surface. A combined analysis of the two reactions was performed for the first time to investigate the isoscalar character of the 1− states in 90,94Zr. The (p,p′γ) cross section was calculated using values for the isoscalar electric dipole energy-weighted sum rule (E1 ISEWSR) obtained from the (α,α′γ) data. The isoscalar strength for 90Zr was found to exhaust 20 ± 2.5% of the EWSR in the energy range up to 12 MeV. In case of 94Zr, a strength of 9 ± 1.1% of the EWSR was found in the range up to 8.5 MeV. Although an overall general description was obtained in the studied energy intervals, not all proton cross sections were well reproduced using the isoscalar strength from (α,α′γ). This might suggest mixing of isoscalar and isovector components and that this mixing and the degree of collectivity are not the same for all the 1− states below the particle binding energy.

Proton capture on the excited isomeric state of ^{26}Al strongly influences the abundance of ^{26}Mg ejected in explosive astronomical events and, as such, plays a critical role in determining the initial content of radiogenic ^{26}Al in presolar grains. This reaction also affects the temperature range for thermal equilibrium between the ground and isomeric levels. We present a novel technique, which exploits the isospin symmetry of the nuclear force, to address the long-standing challenge of determining proton-capture rates on excited nuclear levels. Such a technique has in-built tests that strongly support its veracity and, for the first time, we have experimentally constrained the strengths of resonances that dominate the astrophysical ^{26m}Al(p,γ)^{27}Si reaction. These constraints demonstrate that the rate is at least a factor ∼8 lower than previously expected, indicating an increase in the stellar production of ^{26}Mg and a possible need to reinvestigate sensitivity studies involving the thermal equilibration of ^{26}Al.

Inelastic ${}^{6}$Li scattering at 100 MeV/u on ${}^{12}$C and ${}^{93}$Nb have been measured with the high-resolution magnetic spectrometer Grand Raiden. The magnetic-rigidity settings of the spectrometer covered excitation energies from 10 to 40 MeV and scattering angles in the range $0^\circ < \theta_{\text{lab.}}< 2^\circ$. The isoscalar giant monopole resonance was selectively excited in the present data. Measurements free of instrumental background and the very favorable resonance-to-continuum ratio of ${}^{6}$Li scattering allowed for precise determination of the $E0$ strengths in ${}^{12}$C and ${}^{93}$Nb. It was found that the monopole strength in ${}^{12}$C exhausts $52 \pm 3^\text{(stat.)} \pm 8 ^\text{(sys.)}$\% of the energy-weighted sum rule (EWSR), which is considerably higher than results from previous $\alpha$-scattering experiments. The monopole strength in ${}^{93}$Nb exhausts $92 \pm 4^\text{(stat.)} \pm 10 ^\text{(sys.)}$\% of the EWSR, and it is consistent with measurements of nuclei with mass number of $A\approx90$. Such comparison indicates that the isoscalar giant monopole resonance distributions in these nuclei are very similar, and no influence due to nuclear structure was observed.

We present mass excesses (ME) of neutron-rich isotopes of Ar through Fe, obtained via TOF-$B\rho$ mass spectrometry at the National Superconducting Cyclotron Laboratory. Our new results have significantly reduced systematic uncertainties relative to a prior analysis, enabling the first determination of ME for $^{58,59}{\rm Ti}$, $^{62}{\rm V}$, $^{65}{\rm Cr}$, $^{67,68}{\rm Mn}$, and $^{69,70}{\rm Fe}$. Our results show the $N=34$ subshell weaken at Sc and vanish at Ti, along with the absence of an $N=40$ subshell at Mn. This leads to a cooler accreted neutron star crust, highlighting the connection between the structure of nuclei and neutron stars., Comment: Accepted for publication as a Rapid Communication in Physical Review C

Spin–isospin excitations in Nb 100 were studied via the Mo 100 ( t , He 3 ) charge-exchange reaction at 115 MeV/u with the goal to constrain theoretical models used to describe the isovector spin response of nuclei. The experiment was performed with a secondary beam of tritons, and 3He particles were analyzed in the S800 magnetic spectrometer. Decay by neutron emission from excited states in Nb 100 was observed by using plastic and liquid scintillator arrays. Differential cross sections were analyzed and monopole excitations were revealed by using a multipole decomposition analysis. The Gamow–Teller transition strength observed at low excitation energies, which is important for estimating the electron-capture rate in astrophysical scenarios, was strongly fragmented and reduced compared to single-particle and spherical mean-field models. The consideration of deformation in the theoretical estimates was found to be important to better describe the fragmentation and strengths. A strong excitation of the isovector spin giant monopole resonance was observed, and well reproduced by the mean-field models. Its presence makes the extraction of Gamow–Teller strengths at high excitation energies difficult. The branches for statistical and direct decay by neutron emission were identified in the spectra. The upper limit for the branching ratio by direct decay (integrated over all observed excitations) was determined to be 20 ± 6 % . Even though the statistical uncertainties in the neutron-coincident data were too large to perform detailed studies of the decay by neutron emission from individual states and resonances, the experiment demonstrates the feasibility of the method.

Excited states of the neutron-rich isotopes $^{42,44}\mathrm{S}$ and $^{41,43}\mathrm{P}$ have been studied via inverse-kinematics proton scattering from a liquid hydrogen target, using the GRETINA $\ensuremath{\gamma}$-ray tracking array to extract inelastic-scattering cross sections. Deformation lengths of the ${2}_{1}^{+}$ excitations in $^{42,44}\mathrm{S}$ have been determined and, when combined with deformation lengths determined with electromagnetic probes, yield the ratio of neutron-to-proton matrix elements ${M}_{n}/{M}_{p}$ for the ${2}_{1}^{+}$ excitations in these nuclei. The present results for $^{41,43}\mathrm{P}(p,{p}^{\ensuremath{'}})$ are used to compare two shell-model interactions, SDPF-U and SDPF-MU. As in a recent study of $^{42}\mathrm{Si}$, the present results on $^{41,43}\mathrm{P}$ favor the SDPF-MU interaction.

Angle-integrated cross-section measurements of the $^{56}$Ni(d,n) and (d,p) stripping reactions have been performed to determine the single-particle strengths of low-lying excited states in the mirror nuclei pair $^{57}$Cu-$^{57}$Ni situated adjacent to the doubly magic nucleus $^{56}$Ni. The reactions were studied in inverse kinematics utilizing a beam of radioactive $^{56}$Ni ions in conjunction with the GRETINA $\gamma$-array. Spectroscopic factors are compared with new shell-model calculations using a full $pf$ model space with the GPFX1A Hamiltonian for the isospin-conserving strong interaction plus Coulomb and charge-dependent Hamiltonians. These results were used to set new constraints on the $^{56}$Ni(p,$\gamma$)$^{57}$Cu reaction rate for explosive burning conditions in x-ray bursts, where $^{56}$Ni represents a key waiting point in the astrophysical rp-process., Comment: Final version accepted and published. 5 pages, 2 figures

The key parameter to discuss the possibility of the pion condensation in nuclear matter, i.e., the so-called Landau-Migdal parameter g^{'}, was extracted by measuring the double-differential cross sections for the (p,n) reaction at 216 MeV/u on a neutron-rich doubly magic unstable nucleus, ^{132}Sn with the quality comparable to data taken with stable nuclei. The extracted strengths for Gamow-Teller (GT) transitions from ^{132}Sn leading to ^{132}Sb exhibit the GT giant resonance (GTR) at the excitation energy of 16.3±0.4(stat)±0.4(syst) MeV with the width of Γ=4.7±0.8 MeV. The integrated GT strength up to E_{x}=25 MeV is S_{GT}^{-}=53±5(stat)_{-10}^{+11}(syst), corresponding to 56% of Ikeda's sum rule of 3(N-Z)=96. The present result accurately constrains the Landau-Migdal parameter as g^{'}=0.68±0.07, thanks to the high sensitivity of the GTR energy to g^{'}. In combination with previous studies on the GTR for ^{90}Zr and ^{208}Pb, the result of this work shows the constancy of this parameter in the nuclear chart region with (N-Z)/A=0.11 to 0.24 and A=90 to 208.

A search for the K − p p bound state (the lightest kaonic nucleus) has been performed using the γ d → K + π − X reaction at E γ = 1.5 – 2.4 GeV at LEPS/SPring-8. The differential cross section of the K + π − photo-production off deuterium ( d 2 σ / d cos θ K + l a b / d cos θ π − l a b ) has been measured for the first time in this energy region. A peak structure was searched for in the inclusive missing mass spectrum. A statistically significant peak structure was not observed in the region from 2.22 to 2.36 GeV/c2. The upper limits of the differential cross section of the K − p p bound state production were determined to be (0.17–0.55), (0.55–1.7) and (1.1–2.9) μb at 95% confidence level with the assumed widths of 20 MeV, 60 MeV and 100 MeV.

The $\ensuremath{\phi}\text{\ensuremath{-}}\mathrm{\ensuremath{\Lambda}}(1520)$ interference effect in the $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}p$ reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between $\ensuremath{\phi}$ and $\mathrm{\ensuremath{\Lambda}}(1520)$ production amplitudes were obtained in the kinematic region where the two resonances overlap. The measurement results support strong constructive interference when ${K}^{+}{K}^{\ensuremath{-}}$ pairs are observed at forward angles but destructive interference for proton emission at forward angles. Furthermore, the observed interference effect does not account for the $\sqrt{s}=2.1\text{ }\text{ }\mathrm{GeV}$ bump structure in forward differential cross sections for $\ensuremath{\phi}$ photoproduction. This fact suggests possible exotic structures such as a hidden-strangeness pentaquark state, a new Pomeron exchange, or rescattering processes via other hyperon states.

Ratios of equilibrium charge-state yields for singly to doubly ionized He-3 ions at an energy of 420 MeV were measured using the Grand Raiden magnetic spectrometer at RCNP. Targets with atomic numbers of 6, 12, 28, 40, 50 and 82 were used. It is found that theoretical calculations for atomic electron-capture and stripping cross sections, which have been successful in describing the data up to beam energies of 200 MeV, are also applicable at this higher energy. However, where at the lower energies the stripping cross sections were calculated with a combination of models by Bohr and Gillespie, the best description of the data at E(He-3) = 420 MeV is obtained when using only the model by Gillespie. The experimental results are also compared with calculations using the code CHARGE, originally developed for fast, heavy (Z > 29) projectiles, to test the extrapolation to low-Z projectiles. It is found that the code underestimates the production of singly-charged He-3 ions, in particular for heavier target nuclei. (c) 2007 Elsevier B.V. All rights reserved.

The (t,3He) charge-exchange reaction has been developed as a tool to extract Gamow-Teller strengths on nuclei of importance for stellar evolution. A secondary triton beam of 115 MeV/nucleon is used, either produced from a primary α beam, or, since recently, from a primary 16O beam. Here, the (t,3He) reaction is used to study the Gamow-Teller strength distribution in 58Co via the 58Ni(t,3He) reaction. The experimental results are compared with calculations in large-scale shell models using the kb3g and gxpf1 interactions, as well as existing data from 58Ni(n, p) and 58Ni(d,2He) experiments. The differences between the data and theoretical models are studied in terms of electron-capture rates in the pre-collapse stages of core-collapse supernovae.

The ( t , 3 He) reaction at 115 MeV/nucleon has been developed as a tool to extract Gamow-Teller strengths. A secondary triton beam was used, initially produced from a primary α -beam, but since recently from a primary 16 O beam. An important advantage of the ( t , 3 He) probe is that the data can be combined with results from the ( 3 He, t ) reaction, so that studies in the Δ T z = − 1 and Δ T z = + 1 direction can be performed with similar probes and good resolutions. This is important for improving the understanding of the reaction mechanism and associated errors in the extraction of transition strengths.

The level structure of 30 S was studied at the NSCL by using neutron removal reactions with a radioactive 31 S beam. The γ -decay from excited states in 30 S was measured in a Ge-detector array. The results discussed for this work will reduce the uncertainties in the determination of the astrophysical 29 P(p, γ ) 30 S reaction rate under rp -process conditions.

Photon beam asymmetries for the γ → p → K + Λ and γ → p → K + Σ 0 reactions have been measured for the photon energy range from 1.5 GeV to 2.4 GeV and for the angular range of 0 ° Θ cm K + 60 ° at the SPring-8/LEPS facility. The observed asymmetries are found to be positive and increase with increasing the photon energy. Present theoretical calculations do not reproduce the data. To extend our knowledge on the K + photoproduction mechanism including the effect of nucleon resonances, further theoretical development is required to fit both the cross section and asymmetry data.

The photo-production of ϕ mesons from Li, C, Al, and Cu at forward angles has been measured at E γ = 1.5 – 2.4 GeV . The number of events for incoherent ϕ photo-production is found to have a target mass number dependence of A 0.72 ± 0.07 in the kinematical region of | t | ⩽ 0.6 GeV 2 / c 2 . The total cross section of the ϕ –nucleon interaction, σ ϕ N , has been estimated as 35 −11 +17 mb using the A -dependence of the ϕ photo-production yield and a Glauber-type multiple scattering theory. This value is much larger than σ ϕ N in free space, suggesting that the ϕ properties might change in the nuclear medium.

The excitation and subsequent decay by proton emission of the isovector spin-flip giant monopole resonance are studied via the Pb-208 (He-3, t) reaction at 410 MeV. In the tritonsingles spectrum 60 +/- 5% of the non-energy-weighted sum-rule strength for this 2hw resonance is found in the region 29

We have performed measurements of the ${0}_{\mathrm{g}.\mathrm{s}.}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$ excitations in the neutron-rich isotopes $^{48,50}\mathrm{Ca}$ via inelastic proton scattering on a liquid hydrogen target, using the GRETINA $\ensuremath{\gamma}$-ray tracking array. A comparison of the present results with those from previous measurements of the lifetimes of the ${2}_{1}^{+}$ states provides the ratio of the neutron and proton matrix elements for the ${0}_{\mathrm{g}.\mathrm{s}.}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$ 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 $^{48}\mathrm{Ca}$.

Discrete Gamow-Teller (GT) transitions ${}^{176}\mathrm{Yb}{\ensuremath{\rightarrow}}^{176}\mathrm{Lu}$ at low excitation energies have been measured via the ( ${}^{3}\mathrm{He},t$) reaction at 450 MeV and at $0\ifmmode^\circ\else\textdegree\fi{}$. For ${}^{176}\mathrm{Yb}$, two low-lying states are observed, setting low thresholds $Q(\ensuremath{\nu})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}301$ and 445 keV for neutrino ( $\ensuremath{\nu}$) capture. Capture rates estimated from the measured GT strengths, the simple two-state excitation structure, and the low $Q(\ensuremath{\nu})$ in Yb-Lu indicate that Yb-based $\ensuremath{\nu}$ detectors are well suited for a direct measurement of the sub-MeV solar electron-neutrino ( ${\ensuremath{\nu}}_{e}$) spectrum including $\mathrm{pp}$ neutrinos.

The Pb-nat(He-3, tp) reaction at E(He-3) = 177 MeV was studied to identify 2hw isovector monopole strength in Bi isotopes. Monopole strength was found in the region -45

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 as ${}^{56}$Ni) are unstable, new methods are needed to perform charge-exchange experiments in inverse kinematics with unstable isotopes.Purpose: The ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were measured in inverse kinematics in order to extract GT strengths for transitions to ${}^{56}$Cu and ${}^{55}$Ni, 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 ${}^{56}$Ni and ${}^{55}$Ni to final states in ${}^{56}$Co and ${}^{55}$Co, respectively.Method: Differential cross sections and excitation energy spectra for the ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) 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 ${}^{56}$Ni and ${}^{55}$Co 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 ($p,n$) 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, ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) 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.

Background: Electron-capture reaction rates on medium-heavy nuclei are an important ingredient for modeling the late evolution of stars that become core-collapse or thermonuclear supernovae. The estimation of these rates requires the knowledge of Gamow-Teller strength distributions in the ${\ensuremath{\beta}}^{+}$ direction. Astrophysical models rely on electron-capture rate tables largely based on theoretical models, which must be validated and tested against experimental results.Purpose: This paper presents a systematic evaluation of the ability of theoretical models to reproduce experimental Gamow-Teller transition strength distributions measured via ($n$,$p$)-type charge-exchange reactions at intermediate beam energies. The focus is on transitions from stable nuclei in the $pf$ shell ($45\ensuremath{\le}A\ensuremath{\le}64$). In addition, the impact of deviations between experimental and theoretical Gamow-Teller strength distributions on derived stellar electron-capture rates is investigated.Method: Data on Gamow-Teller transitions from 13 nuclei in the $pf$ shell measured via charge-exchange reactions and supplemented with results from $\ensuremath{\beta}$-decay experiments where available, were compiled and compared with strength distributions calculated in shell models (using the GXPF1a and KB3G effective interactions) and quasiparticle random-phase approximation (QRPA) using ground-state deformation parameters and masses from the finite-range droplet model. Electron-capture rates at relevant stellar temperatures and densities were derived for all distributions and compared.Results: With few exceptions, shell-model calculations in the $pf$ model space with the KB3G and GXPF1a interactions qualitatively reproduce experimental Gamow-Teller strength distributions of 13 stable isotopes with $45\ensuremath{\le}A\ensuremath{\le}64$. Results from QRPA calculations exhibit much larger deviations from the data and overestimate the total experimental Gamow-Teller strengths. For stellar densities in excess of ${10}^{7}$ g/cm${}^{3}$, ground-state electron-capture rates derived from the shell-model calculations using the KB3G (GXPF1a) interaction deviate on average less than 47$%$ (31$%$) from those derived from experimental data for which the location of daughter states at low excitation energies are well established. For electron-capture rates derived from Gamow-Teller strengths calculated in QRPA, the deviations are much larger, especially at low stellar densities.Conclusions: Based on the limited set of test cases available for nuclei in the $pf$ shell, shell-models using the GXPF1a and KB3G interactions can be used to estimate electron-capture rates for astrophysical purposes with relatively good accuracy. Measures of the uncertainties in these rates can serve as input for sensitivity studies in stellar evolution models. Ground-state electron-capture rates based on the QRPA formalism discussed in the paper exhibit much larger deviations than those based on the shell-model calculations and should be used with caution, especially at low stellar densities.

A ${}^{76}$Ge(${}^{3}$He,$t$)${}^{76}$As charge-exchange experiment at an incident energy of 420 MeV has been performed with an energy resolution of 30 keV. The Gamow-Teller GT${}^{\ensuremath{-}}$ strength distribution in ${}^{76}$As, which is the intermediate nucleus in the double-beta ($\ensuremath{\beta}\ensuremath{\beta}$) decay of ${}^{76}$Ge, has been extracted. An unusually strong fragmentation of the GT${}^{\ensuremath{-}}$ strength is observed even at low excitation energies of ${E}_{x}\ensuremath{\leqslant}5\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$. By combining the data with those for GT${}^{+}$ transitions from a recent ${}^{76}$Se($d$,${}^{2}$He)${}^{76}$As measurement, the nuclear matrix element for the ${}^{76}$Ge $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay has been evaluated. A lack of correlation among the GT transition strengths feeding the same levels from the two different directions is observed. The impact on the ${}^{76}$Ge $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay nuclear matrix element is discussed.

The double-differential cross sections for the (208)Pb and (90)Zr(t,(3)He) reactions at 300 MeV/u have been measured at the RI Beam Factory at RIKEN. This was the first physics experiment with the SHARAQ magnetic spectrometer. The combined analysis of the present (t,(3)He) data and previous (n,p) data provides the clearest identification for the β(+) isovector spin monopole resonance both in the (208)Tl and (90)Y nuclei, and puts the observations of this giant resonance on a firm foundation. The measured distributions of the (t,(3)He) monopole cross sections were well reproduced by the distorted-wave Born approximation calculation, where the target transition density was calculated with the self-consistent Hartree-Fock plus random-phase approximation using the T43 Skyrme interaction. A major part of the expected β(+) isovector spin monopole strength was found in the measured cross section spectra.

We present a novel technique for studying the quenching of shell gaps in exotic isotopes. The method is based on extracting Gamow-Teller ($\ensuremath{\Delta}L=0$, $\ensuremath{\Delta}S=1$) transition strengths [$B(\mathrm{GT})$] 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 $^{12}\mathrm{Be}$ using the $^{12}\mathrm{B}({1}^{+})$ ($^{7}\mathrm{Li}$, $^{7}\mathrm{Be}$) reaction at $80\text{ }\text{ }\mathrm{MeV}/u$ in inverse kinematics. Using the ground-state $B(\mathrm{GT})$ value from $\ensuremath{\beta}$-decay measurements ($0.184\ifmmode\pm\else\textpm\fi{}0.007$) as a calibration, the $B(\mathrm{GT})$ for the transition to the second ${0}^{+}$ state was determined to be $0.214\ifmmode\pm\else\textpm\fi{}0.051$. 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 $^{12}\mathrm{Be}$ are composed of $25\ifmmode\pm\else\textpm\fi{}5%$ and $60\ifmmode\pm\else\textpm\fi{}5%$ $(0s{)}^{4}(0p{)}^{8}$ configurations, respectively.

A new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate energies on unstable isotopes was successfully developed and used to study the (56)Ni(p,n) reaction at 110 MeV/u. Gamow-Teller transition strengths from (56)Ni leading to (56)Cu were obtained and compared with shell-model predictions in the pf shell using the KB3G and GXPF1A interactions. The calculations with the GXPF1A interaction reproduce the experimental strength distribution much better than the calculations that employed the KB3G interaction, indicating deficiencies in the spin-orbit and proton-neutron residual potentials for the latter. The results are important for improving the description of electron-capture rates on nuclei in the iron region, which are important for modeling the late evolution of core-collapse and thermonuclear supernovae.

The isomeric and $\ensuremath{\beta}$ decays of the $N=Z+2$ nucleus ${}^{96}\phantom{\rule{-0.16em}{0ex}}$Ag were investigated at the National Superconducting Cyclotron Laboratory. A cascade of $\ensuremath{\gamma}$-ray transitions originating from the deexcitation of a microsecond isomer was observed for the first time and was found in coincidence with two previously known transitions with energies of 470 and 667 keV. The isomeric half-life was determined as 1.45(7) $\ensuremath{\mu}$s, more precise than previously reported. The existence of a second, longer-lived microsecond isomer, associated with a 743-keV $\ensuremath{\gamma}$ transition, is also proposed here. Shell model results within the $({p}_{3/2}{p}_{1/2}{f}_{5/2}{g}_{9/2})$ model space, using the jj44b interaction, reproduced level energies and isomeric decay half-lives reasonably well.

A high-energy-resolution $^{9}\mathrm{Be}$($^{3}\mathrm{He}$,$t$)$^{9}\mathrm{B}$ charge-exchange reaction was performed around a scattering angle of ${0}^{\ifmmode^\circ\else\textdegree\fi{}}$ and at an intermediate incident energy of 140 MeV/nucleon for the study of precise Gamow-Teller (GT) transition strengths. The energy resolution of 30 keV allowed a precise deconvolution of the spectrum and the determination of angular distributions of cross sections, excitation energies, and decay widths. The GT strength of 10 states has been determined for the first time using the GT strength of the analogous $\ensuremath{\beta}$ decays of $^{9}\mathrm{Li}$ and $^{9}\mathrm{C}$ as standards. The large difference between the GT strengths going to the low-lying $T=1/2$ and the highly excited $T=3/2$ states is interpreted as a result of their different spatial structures. The obtained GT strength distribution is compared to the results of a ($p$,$n$) experiment with lower resolution performed in the 1980s. In particular, the width of the 16.8 MeV, ${J}^{\ensuremath{\pi}}=(5/{2}^{+}$) state has been determined for the first time.

The {sup 150}Nd({sup 3}He,t) reaction at 140 MeV/u and {sup 150}Sm(t,{sup 3}He) reaction at 115 MeV/u were measured, populating excited states in {sup 150}Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) {beta}{beta} decay of {sup 150}Nd to {sup 150}Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of the quasiparticle random-phase approximation, which is one of the main methods employed for estimating the half-life of the neutrinoless {beta}{beta} decay (0{nu}{beta}{beta}) of {sup 150}Nd. The present results thus provide useful information on the neutrino responses for evaluating the 0{nu}{beta}{beta} and 2{nu}{beta}{beta} matrix elements. The 2{nu}{beta}{beta} matrix element calculated from the Gamow-Teller transitions through the lowest 1{sup +} state in the intermediate nucleus is maximally about half that deduced from the half-life measured in 2{nu}{beta}{beta} direct counting experiments, and at least several transitions through 1{sup +} intermediate states in {sup 150}Pm are required to explain the 2{nu}{beta}{beta} half-life. Because Gamow-Teller transitions in the {sup 150}Sm(t,{sup 3}He) experiment are strongly Pauli blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the 2({h_bar}/2{pi}){omega}, {Delta}L=0, {Delta}S=1 isovector spin-flipmore » giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR.« less

The proportionality between differential cross sections at vanishing linear momentum transfer and Gamow-Teller transition strength, expressed in terms of the unit cross section (${\mathrm{\ensuremath{\sigma}\ifmmode \hat{}\else \^{}\fi{}}}_{\mathit{GT}}$), was studied as a function of target mass number for ($t$,$^{3}\mathrm{He}$) and ($^{3}\mathrm{He}$,$t$) reactions at $115A$ MeV and $140A$ MeV, respectively. Existing ($^{3}\mathrm{He}$,$t$) and ($t$,$^{3}\mathrm{He}$) data on targets with mass number $12\ensuremath{\leqslant}A\ensuremath{\leqslant}120$ were complemented with new and reevaluated ($t$,$^{3}\mathrm{He}$) data on proton, deuteron, $^{6}\mathrm{Li}$, and $^{12}\mathrm{C}$ targets. It was found that in spite of the small difference in beam energies between the two probes, the unit cross sections have a nearly identical and simple dependence on target mass number $A$, for $A\ensuremath{\geqslant}12$: ${\mathrm{\ensuremath{\sigma}\ifmmode \hat{}\else \^{}\fi{}}}_{\mathit{GT}}=109/{A}^{0.65}$. The factorization of the unit cross sections in terms of a kinematical factor, a distortion factor, and the strength of the effective spin-isospin transfer nucleus-nucleus interaction was investigated. Simple phenomenological functions depending on mass number $A$ were extracted for the latter two. By comparison with plane and distorted-wave Born approximation calculations, it was found that the use of a short-range approximation for knock-on exchange contributions to the transition amplitude results in overestimated cross sections for reactions involving the composite ($^{3}\mathrm{He}$,$t$) and ($t$,$^{3}\mathrm{He}$) probes.

Gamow‐Teller (GT) transitions are mediated by the στ operator. Owing to its simplicity and also its spin‐isospin nature, GT transitions play key roles in the studies of nuclear structure as well as astro‐nuclear processes. In violent neutrino‐induced reactions at the core‐collapse stage of type II supernovae, Gamow‐Teller (GT) transitions starting from stable as well as unstable pf‐shell nuclei play important roles. We study GT transitions starting from 47Ti in a high‐resolution (3He,t) charge‐exchange reactions at 0° and at an intermediate incident energy of 140 MeV/nucleon at Research Center for Nuclear Physics (RCNP), Osaka. Individual GT transitions up to high excitations were observed. Assuming the isospin symmetry for the strengths of Tz = ±3/2→±1/2 analogous GT transitions, we can deduce the detailed strength distribution starting from mirror unstable nucleus 47Mn.

We report on the first successful extraction of a ${\ensuremath{\beta}}^{+}$ Gamow-Teller strength distribution from a radioactive isotope in an intermediate-energy charge-exchange experiment in inverse kinematics. The ($^{7}\mathrm{Li},^{7}\mathrm{Be}+\ensuremath{\gamma}(429\text{ }\text{ }\mathrm{keV})$) reaction at $100A\text{ }\text{ }\mathrm{MeV}$ was used to measure Gamow-Teller transition strengths from $^{34}\mathrm{P}$ to states in $^{34}\mathrm{Si}$. The results show that little mixing occurs between $sd$ and $pf$ shell configurations for the low-lying ${0}^{+}$ and ${2}^{+}$ states even though $^{34}\mathrm{Si}$ neighbors the island of inversion and low-lying $2\ensuremath{\hbar}\ensuremath{\omega}$ intruder states exist. Shell-model calculations in the $sdpf$ model space are consistent with these findings.

Differential cross sections and photon-beam asymmetries for the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}(1520)$ reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at $0.6l\mathrm{cos} {\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}^{K}l1$. A new bump structure was found at $W\ensuremath{\simeq}2.11\text{ }\text{ }\mathrm{GeV}$ in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with $J\ensuremath{\le}\frac{3}{2}$. This result suggests that the bump might be produced by a nucleon resonance possibly with $J\ensuremath{\ge}\frac{5}{2}$ or by a new reaction process, for example, an interference effect with the $\ensuremath{\phi}$ photoproduction having a similar bump structure in the cross sections.

We performed a 37Cl(3He, t)37Ar experiment at E = 140 MeV/nucleon and 0° with a resolution of 30 keV. The Gamow‐Teller (GT) strength distribution was obtained up to the excitation energy (Ex) of 14.2 MeV in 37Ar. Under the assumption of isospin symmetry, the GT strengths in the 37Cl→37Ar and 37Ca→37K transitions are analogous. The obtained strength distribution was compared with the mirror 37Ca β decay up to Ex = 8.6 MeV. The overall shapes of the distributions were similar, but the details were not necessary the same. In order to understand those differences, the experimental distribution was compared with the shell model (SM) calculation using the USD interaction. The SM calculation suggests that differences at lower energies can be caused by a large tensor contribution in the charge‐exchange reaction. On the other hand, the differences seen at higher energies are due to the breaking of the mirror symmetry. The neutrino cross section for the 8B solar neutrino source was calculated using the obtained data.

Gamow-Teller and dipole transitions to final states in $^{13}\mathrm{B}$ were studied via the $^{13}\mathrm{C}(t,^{3}\mathrm{He})$ reaction at ${E}_{t}=115A$ MeV. In addition to the strong Gamow-Teller transition to the $^{13}\mathrm{B}$ ground state, a weaker Gamow-Teller transition to a state at 3.6 MeV was found. This state was assigned a spin-parity of $3/{2}^{\ensuremath{-}}$ by comparison with shell-model calculations using the WBP and WBT interactions which were modified to allow for mixing between $n\ensuremath{\hbar}\ensuremath{\omega}$ and $(n+2)\ensuremath{\hbar}\ensuremath{\omega}$ configurations. This assignment agrees with a recent result from a lifetime measurement of excited states in $^{13}\mathrm{B}$. The shell-model calculations also explained the relatively large spectroscopic strength measured for a low-lying $1/{2}^{+}$ state at 4.83 MeV in $^{13}\mathrm{B}$. The cross sections for dipole transitions up to ${E}_{x}$$(^{13}\mathrm{B})=20$ MeV excited via the $^{13}\mathrm{C}(t,^{3}\mathrm{He})$ reaction were also compared with the shell-model calculations. The theoretical cross sections exceeded the data by a factor of about 1.8, which might indicate that the dipole excitations are ``quenched''. Uncertainties in the reaction calculations complicate that interpretation.

The $^{64}\mathrm{Zn}$($t$,$^{3}\mathrm{He}$) reaction has been studied by using a secondary triton beam of 115 MeV/nucleon to extract the Gamow-Teller transition-strength distribution to $^{64}\mathrm{Cu}$. The results were compared with shell-model calculations with the $\mathit{pf}$-shell effective interactions KB3G and GXPF1A and with existing data from the $^{64}\mathrm{Zn}$($d$,$^{2}\mathrm{He}$) reaction. Whereas the experimental results exhibited good consistency, neither of the theoretical predictions managed to reproduce the data. The implications for electron-capture rates during late stellar evolution were investigated. The rates based on the theoretical strength distributions are lower by factors of 3.5--5 compared to the rates based on experimental strength distributions.

The fragment production cross sections of secondary neutron-rich beams of $^{68}\mathrm{Ni}$, $^{69}\mathrm{Cu}$, and $^{72}\mathrm{Zn}$ isotopes at energies of about $95A$ MeV have been measured. We compare the measured cross sections to EPAX, an empirical parametrization of fragmentation cross sections. A reasonable agreement of the experimental data and EPAX predictions suggests that an EPAX parametrization used for stable beams seems to be valid for unstable neutron-rich ion beams. EPAX tends to overestimate the yields of neutron-rich isotopes. This problem is amplified when neutron-rich radioactive beams are employed, leading to overly optimistic estimates of the production of neutron-rich isotopes.

Photoproduction of LAMBDA(1520) with liquid hydrogen and deuterium targets was examined at photon energies below 2.4 GeV in the SPring-8 LEPS experiment. For the first time, the differential cross sections were measured at low energies and with a deuterium target. A large asymmetry of the production cross sections from protons and neutrons was observed at backward K{sup +/0} angles. This suggests the importance of the contact term, which coexists with t-channel K exchange under gauge invariance. This interpretation was compatible with the differential cross sections, decay asymmetry, and photon beam asymmetry measured in the production from protons at forward K{sup +} angles.

Experience NSCL; International audience; We report in this study the nuclear properties of proton-rich isotopes located along the rp-process path. The experiments have recently been performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The level properties above the proton separation energy of the nuclei 30S, 36K and 37Ca were measured with precision of < 10 keV. This will allow a reduction in the determination of the astrophysical (p, ) reaction rate under rp-process conditions.

The {gamma}d{yields}K{sup +}K{sup -}pn reaction has been studied to search for the evidence of the {theta}{sup +} by detecting K{sup +}K{sup -} pairs at forward angles. The Fermi-motion-corrected nK{sup +} invariant mass distribution shows a narrow peak at 1.524{+-}0.002+0.003 GeV/c{sup 2}. The statistical significance of the peak calculated from a shape analysis is 5.1 {sigma}, and the differential cross section for the {gamma}n{yields}K{sup -}{theta}{sup +} reaction is estimated to be 12{+-}2 nb/sr in the photon energy range from 2.0 to 2.4 GeV in the LEPS angular range by assuming the isotropic production of the {theta}{sup +} in the {gamma}n center-of-mass system. The obtained results support the existence of the {theta}{sup +}.

The isovector transitions from the ground state (g.s.) of $^{16}\mathrm{O}$ to the negative parity states in $^{16}\mathrm{F}$, i.e., the ${J}^{\ensuremath{\pi}}={0}^{\ensuremath{-}}$ g.s., the 0.193 MeV, ${1}^{\ensuremath{-}}$ state, the 0.424 MeV, ${2}^{\ensuremath{-}}$ state, the 0.721 MeV, ${3}^{\ensuremath{-}}$ state, and the ${4}^{\ensuremath{-}}$ ``stretched'' state at 6.372 MeV, were studied by using a high resolution $^{16}\mathrm{O}(^{3}\mathrm{He},t)^{16}\mathrm{F}$ reaction at 140 MeV/nucleon. With the help of high energy resolution, these states were, for the first time, clearly resolved in a charge exchange reaction at an intermediate energy, which favorably excites spin-flip states. Angular distributions of the reaction cross sections were measured in the laboratory frame from ${0}^{\ifmmode^\circ\else\textdegree\fi{}}$ to ${14}^{\ifmmode^\circ\else\textdegree\fi{}}$. Parameters of phenomenological effective interactions were derived so as to reproduce these angular distributions in distorted wave Born approximation (DWBA) calculations. The angular distribution of the ${0}^{\ensuremath{-}}$ state could be reproduced well at ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}l{10}^{\ifmmode^\circ\else\textdegree\fi{}}$. The empirical values, however, are larger by a factor of 2--2.5 in the larger angle region, where the contribution of the so-called ``condensed pion field'' is expected. The high resolution also enabled the decay widths of these states to be measured.

A half-life of 2.2 \ifmmode\pm\else\textpm\fi{} 0.2 s has been deduced for the ground-state $\ensuremath{\beta}$ decay of $^{84}\mathrm{Mo}$, more than $1\ensuremath{\sigma}$ shorter than the previously adopted value. $^{84}\mathrm{Mo}$ is an even-even $N=Z$ nucleus lying on the proton dripline, created during explosive hydrogen burning in type I x-ray bursts in the rapid proton capture ($\mathit{rp}$) process. The effect of the measured half-life on $\mathit{rp}$-process reaction flow is explored. Implications on theoretical treatments of nuclear deformation in $^{84}\mathrm{Mo}$ are also discussed.

The $\ensuremath{\Sigma}(1385)$ resonance, or ${\ensuremath{\Sigma}}^{*}$, is well known as part of the standard baryon decuplet with spin $J=\frac{3}{2}$. Measurements of the reaction $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{*0}$ are difficult to extract due to overlap with the nearby $\ensuremath{\Lambda}(1405)$ resonance. However, the reaction $\ensuremath{\gamma}n\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{*\ensuremath{-}}$ has no overlap with the $\ensuremath{\Lambda}(1405)$ due to its charge. Here we report the first measurement of cross sections and beam asymmetries for photoproduction of the ${\ensuremath{\Sigma}}^{*\ensuremath{-}}$ from a deuteron target. The cross sections at forward angles range from 0.4 to $1.2\text{ }\text{ }\ensuremath{\mu}\mathrm{b}$, with a broad maximum near ${E}_{\ensuremath{\gamma}}\ensuremath{\simeq}1.8\text{ }\text{ }\mathrm{GeV}$. The beam asymmetries are negative, in contrast with positive values for the $\ensuremath{\gamma}n\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ reaction.

The excitation and subsequent proton decay of the isoscalar giant dipole resonance (ISGDR) in $^{208}$Pb have been investigated via the $^{208}$Pb($\alpha, \alpha^{\prime}p)^{207}$Tl reaction at 400 MeV. Excitation of the ISGDR has been identified by the difference-of-spectra method. The enhancement of the ISGDR strength at high excitation energies observed in the multipole-decomposition-analysis of the singles $^{208}$Pb($\alpha,\alpha^{\prime}$) spectra is not present in the excitation energy spectrum obtained in coincidence measurement. The partial branching ratios for direct proton decay of ISGDR to low-lying states of $^{207}$Tl have been determined and the results are compared with predictions of continuum random-phase-approximation (CRPA) calculations., Comment: 12 pages, 4 figures; accepted for publication in Physics Letters B