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We measured both the differential cross section ($\sigma_{p,p^\prime}$ $=d^2\sigma/d\Omega dE_{x}$) and the $\gamma$-ray emission probability ($R_\gamma(E_x)$ $=\sigma_{p,p^\prime\gamma}$/$\sigma_{p,p^\prime}$) from the giant resonances excited by $\rm^{12}C$(\textit{p,p}$^\prime$) reaction at 392 MeV and 0$^\circ$, using a magnetic spectrometer and an array of NaI(Tl) counters. The absolute value of $R_\gamma(E_x)$ was calibrated by using the well-known $\gamma$-ray emission probability from $\rm^{12}C^* ( 15.11$ MeV, $ 1^+$, $T=1$) and $\rm^{16}O^* ( 6.9$ MeV, $2^+$, $T=0$) states within 5\% uncertainty. We found that $R_\gamma(E_x)$ starts from zero at $E_x=16$ MeV, increases to a maximum of 53.3$\pm$0.4$\pm$3.9\% at $E_x=27$ MeV and then decreases. We also compared the measured values of $R_\gamma(E_x)$ with statistical model calculation based on the Hauser-Feshbach formalism in the energy region $E_x=$ 16-32 MeV and discussed the features of $\gamma$-ray emission probability quantitatively.

The ϕ-Λ(1520) interference effect in the γp→K^{+}K^{-}p reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between ϕ and Λ(1520) production amplitudes were obtained in the kinematic region where the two resonances overlap. The measurement results support strong constructive interference when K^{+}K^{-} 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 GeV bump structure in forward differential cross sections for ϕ 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.

Decay via proton emission of isobaric analog states (IAS’s) in 91 Nb was studied using the 90 Zr(α, t) reaction at E�=180 MeV. This study provides information about the damping mechanism of these states. Decay to the ground state and low-lying phonon states in 90 Zr was observed. The experimental data are compared with theoretical predictions wherein the IAS ‘single-particle’ proton escape widths are calculated in a continuum RPA approach. The branching ratios for decay to the phonon states are explained using a simple model.

Polarization transfer (PT) observables in the 12 C (p,p′) reaction at 0° for 392 MeV protons have been measured. The excitation strengths are decomposed into the spin-flip part and the non-spin-flip part by using the obtained PT observables. The PT observables for excitation of the 1+, T=0 and 1+, T=1 states are compared with distorted wave impulse approximation calculations. The strength ratios of the isoscalar spin-dependent term to the isovector tensor term and the isovector tensor term to the isovector spin-dependent term are reasonably consistent with the Franey and Love interaction.

Spin-isospin excitations in ${}^{12}$B and ${}^{12}$N have been studied using the ${}^{12}$C$(d$,${}^{2}$He)${}^{12}$B and ${}^{12}$C${(}^{3}$He,$t)$${}^{12}$N charge-exchange reactions at $\ensuremath{\theta}$ = 0$\ifmmode^\circ\else\textdegree\fi{}$ and at ${E}_{d}$=200 MeV and $E$${(}^{3}$He)=450 MeV, respectively. Neutron decay from ${}^{12}$B to ${}^{11}$B and proton decay from ${}^{12}$N to ${}^{11}$C have been measured with detector arrays consisting of liquid-scintillation counters and silicon detectors, respectively. Microscopic structures of the spin-dipole resonances in ${}^{12}$B and ${}^{12}$N are discussed on the basis of the experimental observations of particle decays and their angular correlations.

A high-resolution measurement of inelastic proton scattering off (90)Zr near 0° was performed at 295 MeV with a focus on a pronounced strength previously reported in the low-energy tail of giant dipole resonance. A forest of fine structure was observed in the excitation energy region 7-12 MeV. A multipole decomposition analysis of the angular distribution for the forest was carried out using the ECIS95 distorted-wave Born approximation code with the Hartree-Fock plus random-phase approximation model of E1 and M1 transition densities and inclusion of E1 Coulomb excitation. The analysis separated pygmy dipole and M1 resonances in the forest at E(PDR)=9.15±0.18 MeV with Γ(PDR)=2.91±0.64 MeV and at E(M1)=9.53±0.06 MeV with Γ(M1)=2.70±0.17 MeV in the Lorentzian function, respectively. The B(E1)↑ value for pygmy dipole resonance over 7-11 MeV is 0.75±0.08 e(2)fm(2), which corresponds to 2.1±0.2% of the Thomas-Reiche-Kuhn sum rule.

Equilibrium charge-state distributions for singly and doubly ionized [sup 3]He ions of energy [ital E]([sup 3]He)=200 MeV ([beta]=0.36) have been measured for atomic targets ranging from carbon to bismuth ([ital Z]=6,14,28,40,50,67,73,83). A magnetic spectrometer was used to simultaneously measure the rate of [sup 3]He[sup +] ions and the current of the incident beam of [sup 3]He[sup 2+] ions. The ratio of the fraction of ions [ital Y]([sup 3]He)[sup +]/[ital Y]([sup 3]He[sup 2+]) was found to increase from 3[times]10[sup [minus]9] for [ital Z]=6 to 2[times]10[sup [minus]7] for [ital Z]=83. Very good agreement with the experimental ratios was obtained for calculated ratios based on theoretical stripping (ionization) and capture cross sections. The cross sections are dominated by capture from [ital K] orbits only for atoms up to about [ital Z]=25. For target atoms with high [ital Z], contributions up to principal quantum numbers [ital n]=4 ([ital N] orbits) must be included.

The γ‐ray strength function (γSF) interconnects radiative neutron capture and photoneutron emission as a common ingredient in the statistical model. Outlined here is an indirect method of determining radiative neutron‐capture cross sections for unstable nuclei based on the γ‐ray strength function. Application examples of the γSF method are demonstrated.

Photoneutron cross sections for 90Zr near neutron threshold were examined with a photon difference technique using laser Compton scattering γ‐ray beams. The cross section decreasing in the vicinity of neutron threshold exhibited a steep rise within 150 keV above the threshold. We draw attention to a possible relation of this striking behavior to the 3P valence neutron resonance known in neutron capture in the mass region A≈90.

Photoneutron cross sections were measured for Au in the entire energy range of the (γ,n) channel based on a direct neutron‐counting technique with quasimonochromatic γ rays produced in inverse Compton‐scattering of laser photons with relativistic electrons. We present results of the measurement in comparison with the past data.

Photoneutron cross sections were measured for 108Pd, 106Pd, and 105Pd with laser‐Compton scattering γ‐ray beams in an application of the γSF method to a radioactive nucleus 107Pd. We present radiative neutron cross sections for 107Pd[6.5×106 y] obtained with the γSF method.

The compression-mode isoscalar giant monopole resonance (ISGMR) has been studied in the Sn, Cd and Pb isotopes using inelastic scattering of 400 MeV {alpha}-particles at extreme forward angles, including 0 deg. We have obtained completely 'background-free' inelastic-scattering spectra for the Sn, Cd, and Pb isotopes for a wide angular and excitation-energy range. The various giant resonances excited with different transferred angular momenta were extracted by a multipole-decomposition analysis (MDA). It was found that the centroid energies of the ISGMR in Sn isotopes are significantly lower than the theoretical predictions. The K{sub {tau}} in the empirical expression for the nuclear incompressibility has been determined to be K{sub {tau}} = -550{+-}100 MeV for the Sn isotopes. The extracted value for the Cd isotopes is K{sub {tau}} = -480{+-}100 MeV. These numbers are consistent with values of K{sub {tau}} = -370{+-}120 MeV obtained from an analysis of the isotopic transport ratios in medium-energy heavy-ion reactions, K{sub {tau}} -500{sub -100}{sup +120} MeV obtained from constraints placed by neutron-skin data from anti-protonic atoms across the mass table, and K{sub {tau}} = -500{+-}50 MeV obtained from theoretical calculations using different Skyrme interactions and relativistic mean field (RMF) Lagrangians. Stringent constraints on interactions employed in nuclear structuremore » calculations are obtained on the basis of the experimentally determined values for K{sub {infinity}} and K{sub {tau}}. These parameters constrain as well the equation of state (EOS) of nuclear matter. However, a significant discrepancy still remains. The ISGMR positions in Sn and Cd isotopes are systematically lower than the predictions obtained on basis of determined from the ISGMR in {sup 208}Pb. This raises the question ''Why are Sn and Cd nuclei so soft?''. For a clue to solve the problem, we discuss the preliminary results on the exact positions of the ISGMR in {sup 204,206,208}Pb.« less

M1 and E1 transition cross sections in the D(y→, n) reaction were separately determined by measuring the analyzing power for emitted neutrons with linearly‐polarized γ rays at four energies between 2.26 MeV and 3.70 MeV near reaction threshold at 2.224 MeV. We compared the experimental result with the JENDL evaluated data.

We measured the differential cross sections for the 02+ state at Ex = 7.654 MeV in 12C via the (p,p′) reaction at an incident energy of 300 MeV, and in an angular range from 2.7° to 40°. We analyzed the data with the distorted‐wave Born‐approximation (DWBA) employing transition densities obtained in a macroscopic collective model, a microscopic α‐cluster model, and a microscopic α‐cluster condensation model. It is concluded that the present results for the 12C(p,p′) reaction at 300 MeV is quite consistent with the assumption that the 02+ state at Ex = 7.654 MeV has the wave function with the α‐cluster condensation.We measured the differential cross sections for the 02+ state at Ex = 7.654 MeV in 12C via the (p,p′) reaction at an incident energy of 300 MeV, and in an angular range from 2.7° to 40°. We analyzed the data with the distorted‐wave Born‐approximation (DWBA) employing transition densities obtained in a macroscopic collective model, a microscopic α‐cluster model, and a microscopic α‐cluster condensation model. It is concluded that the present results for the 12C(p,p′) reaction at 300 MeV is quite consistent with the assumption that the 02+ state at Ex = 7.654 MeV has the wave function with the α‐cluster condensation.

Photoneutron cross sections were measured for 117Sn and 116Sn near neutron thresholds with quasi‐monochromatic laser Compton scattering γ‐rays. The measured cross sections for 117Sn and 116Sn are strongly enhanced from the threshold behavior expected for L = 1 neutron emissions after E1 photoexcitation. This suggests the presence of extra γ‐ray strength in the low‐energy tail of the giant dipole resonance. The present cross sections were analyzed together with radiative neutron capture cross sections for 116Sn within the framework of the statistical model calculation. It is shown that the extra γ‐ray strength can be interpreted as pygmy E1 resonance which was previously reported in the nuclear resonance fluorescence experiment for 116Sn and 124Sn.

We measured photoneutron cross sections for 197Au with quasi‐monochromatic laser inverse‐Compton scattering gamma rays. We present results of the measurement in comparison with the existing data.We measured photoneutron cross sections for 197Au with quasi‐monochromatic laser inverse‐Compton scattering gamma rays. We present results of the measurement in comparison with the existing data.

Photoneutron cross sections for three Pb isotopes (206Pb, 207Pb, 208Pb) near neutron threshold were measured with the laser inverse‐Compton scattering gamma rays at the National Institute of Advanced Industrial Science and Technology. The cross section data are presented.

Differential cross sections and photon-beam asymmetries for the gamma(p)--K{+}Lambda(1520) reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at 0.6cos(theta){c.m.}{K}1. A new bump structure was found at W approximately 2.11 GeV in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with Jor=3/2. This result suggests that the bump might be produced by a nucleon resonance possibly with Jor=5/2 or by a new reaction process, for example, an interference effect with the phi photoproduction having a similar bump structure in the cross sections.

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+/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+ angles.

The γ‐ray strength function is a key statistical nuclear ingredient to the s‐, r‐ and p‐process nucleosynthesis of heavy elements. It has recently become apparent that extra γ‐ray strengths that appear near neutron threshold on top of the low‐energy tail of GDR play an important role in neutron capture and photodisintegration. We discuss extra γ‐ray strengths of pigmy E1 and giant M1 nature based on the latest experimental photoneutron cross sections measured with laser Compton scattering γ‐rays.

The Sigma(1385) resonance, or Sigma;{*}, is well known as part of the standard baryon decuplet with spin J=3/2. Measurements of the reaction gammap--K;{+}Sigma;{*0} are difficult to extract due to overlap with the nearby Lambda(1405) resonance. However, the reaction gamman--K;{+}Sigma;{*-} has no overlap with the Lambda(1405) due to its charge. Here we report the first measurement of cross sections and beam asymmetries for photoproduction of the Sigma;{*-} from a deuteron target. The cross sections at forward angles range from 0.4 to 1.2 mub, with a broad maximum near E_{gamma} approximately 1.8 GeV. The beam asymmetries are negative, in contrast with positive values for the gamman--K;{+}Sigma;{-} reaction.

Photoneutron cross sections were measured for 80Se near the neutron separation energy with laser Compton‐backscattered γ‐ray beams at AIST. Neutron capture rates are evaluated for 79Se with the photoreaction data as experimental constraints on the El γ‐strength function, a key parameter in the Hauser‐Feshbach statistical model calculation. Solving the set of differential equations under a single neutron exposure, we analyzed the solar abundance ratio of the weak components of 80Kr and 82Kr in terms of the s‐process branching at 79Se. We discuss the region of temperature and neutron density allowed for the weak s‐process nucleosynthesis.

Photoneutron cross sections were measured for 91Zr, 92Zr and 94Zr near the neutron separation energy with quasi‐monochromatic γ rays. Some systematic extra strength is found around the neutron threshold and identified, through a coherent analysis of 92Zr(γ,n)91Zr and 91Zr(n,γ)92Zr cross sections, as being most probably a strong M1 resonance. The microscopic HFB+QRPA model for the E1 strength with the additional contribution of a strong M1 resonance at 9 MeV is found to explain all the reaction cross section data available. With such an M1 resonance strength tuned on the 92Zr(γ,n)91Zr reaction, the photoneutron cross section of 91Zr and 94Zr are also found to be in good agreement with our new experimental data in the vicinity of the threshold and of the M1 peak energy. The present extra component in the photoneutron channel is qualitatively consistent with the M1 giant resonance reported in the inelastic proton scattering.

The decomposition of the intermetallic compound PdSi by adding a small amount of Ag has been investigated by thermal analysis, metallographic measurement, and x-ray photoemission spectroscopy (XPS). Within the range of Ag concentration from 0 to 6 at.%, PdSi is decomposed in linear proportion to the concentration of Ag into Si and the ternary compound Pd2Si(Ag), which has the ratio of 16 PdSi molecules per single Ag atom. The PdSi is fully decomposed at Ag 10 at.%. In the ternary alloy included in the Pd–Si–Ag alloy involving Ag below 12 at. %, the atomic ratio of Si to metal atoms, which are Pd plus Ag, is nearly the same as the ratio in Pd-rich Pd2Si. Metallographic and XPS measurements indicate that the Ag atom included in the PdSi behaves as an electron donor with a large radius of the wave function; the Ag electron transfers to the anti-bonding state of PdSi and acts to decompose the compound. The Ag atoms seem to occupy the sites of Pd atoms in Pd2Si(Ag) which has been decomposed from PdSi.

The phase diagram for the palladium-silicon system is reinvestigated by thermal analysis using a method taking the second derivative of time-dependent temperature and by metallographic measurement, where the cooling rate is about 140‡ C min−1. The second derivative offers a sensitive and accurate means for thermal analysis with aid of a microcomputer. The phase diagram has no peak for PdSi. At silicon concentrations higher than 50 at. %, the alloy appears to be the eutectic for a composition of PdSi and Si, with the eutectic point at 895‡ C and 50 at. % Si, and at silicon concentrations lower than 50 at. %, the alloy appears to be the eutectic for Pd2Si and PdSi, with the eutectic point at 886‡ C and about 48.5 at. % Si. The phase properties appear to be largely affected by the phase stability of PdSi in company with the departure from thermal equilibrium in the thermal analysis. The addition of small amounts of silver impurity causes the collapse of the PdSi phase and the alloy appears to be a eutectic of constitutions Pd2Si and Si in the concentration range from 33 to 100 at. % silicon.

Photoneutron cross sections were measured for 91Zr, 92Zr, and 94Zr near the neutron separation energy with quasimonochromatic gamma rays. The data exhibit some extra components around the neutron threshold. A coherent analysis of the photoneutron data for 92Zr together with the neutron capture on 91Zr based on the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model for the E1 strength has revealed the presence of an M1 resonance at 9 MeV. The microscopic approach systematically shows the same M1 strength in the photoneutron cross section for 91Zr and 94Zr. The total M1 strength is about 75% larger than the strength predicted by the systematics, being qualitatively consistent with the giant M1 resonance observed in the inelastic proton scattering.

Differential cross sections for transitions of known weak strength were measured with the (3He,t) reaction at 420 MeV on targets of 12C, 13C, 18O, 26Mg, 58Ni, 60Ni, 90Zr, 118Sn, 120Sn and 208Pb. Using this data, it is shown the proportionalities between strengths and cross sections for this probe follow simple trends as a function of mass number. These trends can be used to confidently determine Gamow-Teller strength distributions in nuclei for which the proportionality cannot be calibrated via beta-decay strengths. Although theoretical calculations in distorted-wave Born approximation overestimate the data, they allow one to understand the main experimental features and to predict deviations from the simple trends observed in some of the transitions., 4 pages, 2 figures

We investigated charged‐particle decay from the high‐lying dipole resonances at Ex=24 MeV in 6He and at 18 MeV in 7He via the 6,7Li(7Li,7Be x) reactions at 455 MeV and at 0°. d‐ and t‐decay, and t‐decay was observed as the dominant decay modes for these resonances in 6He and 7He, respectively. The yield ratios observed for charged particle decay were qualitatively consistent with those expected from the assumption that the resonances are the analogs of the dipole resonances in the α cluster in 6Li and 7Li, but could not be explained by simple phase space calculations.

The strength distributions of the giant monopole resonance (GMR) have been measured in the even-A Sn isotopes (A=112--124) with inelastic scattering of 400-MeV $\alpha$ particles in the angular range $0^\circ$--$8.5^\circ$. We find that the experimentally-observed GMR energies of the Sn isotopes are lower than the values predicted by theoretical calculations that reproduce the GMR energies in $^{208}$Pb and $^{90}$Zr very well. From the GMR data, a value of $K_{\tau} = -550 \pm 100$ MeV is obtained for the asymmetry-term in the nuclear incompressibility., Comment: Submitted to Physical Review Letters. 10 pages; 4 figures

Differential cross sections and photon-beam asymmetries have been measured for the gamma n --K+ Sigma- and gamma p --K+Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of E gamma = 1.5-2.4 GeV at 0.6cos ThetacmK1. The cross section ratio of sigma K+ Sigma-/sigma K+ Sigma0, expected to be 2 on the basis of the isospin 1/2 exchange, is found to be close to 1. For the K+ Sigma- reaction, large positive asymmetries are observed, indicating the dominance of K* exchange. The large difference between the asymmetries for the K+ Sigma- and K+ Sigma0 reactions cannot be explained by simple theoretical considerations based on Regge model calculations.

Photoneutron cross sections for (181)Ta(y, n) (180)Ta(m) were determined from simultaneous measurements of total cross sections (sigma(tot) and ground-state cross sections (sigma(gs)) for (180)Ta in photodisintegration of with laser Compton-backscattered rays. Techniques of direct neutron counting and photoactivation were used for the measurement of sigma(tot) and sigma(gs), respectively. The partial cross sections for the isomeric state serves as a novel probe of the nuclear level density of (180)Ta. Implications for the p- and s-process nucleosynthesis of (180)Ta(m) are given.

The isovector giant dipole resonance (GDR) of the α‐clusters in 6Li and 7Li, and the GDR in 4He were investigated by using the 6,7Li(p,p′) and 4He(p,p′) reactions, respectively, at an incident energy of 300 MeV. The cross sections for the excitation of the GDR in the α clusters in 6,7Li normalized with the spectroscopic factors of the α‐particle for 6,7Li agreed to the GDR cross section in 4He. The excitation energies and widths for the GDR in α clusters were larger than those for the GDR in 4He by 2–4 MeV and 0.5–4 MeV, respectively.

The isovector giant dipole resonance (GDR) of an α‐cluster in 6Li and 7Li, and their analogs in 6,7He and 6,7Be were searched for by using the 6,7Li(p,p′), 6,7Li(3He,t) and 6,7Li(7Li,7Be) reactions at the incident energies of 300, 450 and 455 MeV, respectively. New resonances were found for the first time at Ex=27.0±1.5 MeV in 6Li and at Ex=29.0±1.5 MeV in 7Li, both with widths (FWHM) of 12±2 MeV. In 6He, 6Be, 7He and 7Be resonances with widths of 12±2 MeV were observed via the charge exchange reactions at Ex=24.0±1.5, 23.5±1.5, 18.0±1.5, and 28.0±1.5 MeV, respectively. All of these resonances were assigned to be dipole resonances based on the measured angular distributions of differential cross sections. The resonance shapes were reproduced well with the resonance shape of the GDR of 4He reported in the (γ,n) reaction. The averaged ratios of the cross sections for these resonances in A=6 to those in A=7 for each isotope were estimated to be nealy unity, 1.2±0.3. The averaged value of the respective cross section ratios of these resonances to the GDR in their respective target nuclei was 0.44±0.08, which was consistent with the ratios of the cross sections of the GDR in 4He to those of the GDR in 6,7Li reported in the photo‐nuclear reactions. The excitation energies of these dipole resonances in A=6 and 7 nuclei relative to the separation energies of an α‐particle in 6Li and 7Li, respectively, agreed well with the excitation energy of the GDR in 4He (≈26 MeV). We conclude that the resonances observed in 6,7Li are the GDR of the α‐cluster and the resonances in 6,7He and 6,7Be are their analogs.

Tri‐nucleon molecular structures in 6He and 6Be were investigated by using the 6Li(7Li,7Be)6He reaction at 455 MeV and 6Li(3He,t)6Be reaction at 450 MeV, respectively. Binary decay into t+t from a broad state at Ex = 18.0 ± 1.0 MeV in 6He and into 3He+3He from one at Ex = 18.0 ± 1.2 MeV in 6Be, were observed by measuring tri‐nucleon cluster‐decays in coincidence with reaction‐particles. The branching ratios for binary decay were estimated to be about 0.7 for both 6He and 6Be. From the angular correlations of decay particles, these states are assigned to be P states.