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International audience; Background: Superdeformed (SD) bands are suggested by theory around Ca40 and in lighter alpha-conjugate nuclei such as Mg24, Si28, and S32. Such predictions originate from a number of theoretical models including mean-field models and antisymmetrized molecular dynamics (AMD) calculations. While SD bands have been identified in Ca40 and its near neighbors, evidence of their existence in the lighter, midshell nuclei is circumstantial at best. The key evidence of superdeformation would be the observation of transitions with high B(E2) transition strengths connecting states in a rotational sequence. This is challenging information to obtain since the bands lie at a high excitation energy and competition from out-of-band decay is dominant.Purpose: The purpose of the present study is to establish a new methodology to circumvent the difficulties in identifying and quantifying in-band transitions through directly populating candidate states in the SD band in Si28 through inelastic alpha scattering, selecting such states with a spectrometer, and measuring their gamma-ray decay with a large array of high-purity germanium detectors, allowing direct access to electromagnetic transition strengths.Methods: Excited states in Si28 were populated in the Si28(α,α′) reaction using a 130-MeV He4 beam from the K140 AVF cyclotron at the Research Center for Nuclear Physics. Outgoing alpha particles were analyzed using the Grand Raiden spectrometer positioned at an angle of 9.1∘ to favor the population of states with J≈4. Coincident gamma rays were detected with the CAGRA array of 12 HPGe clover detectors augmented by a set of four large LaBr3 detectors.Results: Data analysis showed that it was possible to identify additional low-energy transitions in competition with high-energy decays from excited states in Si28 in the vicinity of 10 MeV. However, while the candidate 4+ SD state at 10.944 MeV was populated, a 1148-keV transition to the candidate 2+ SD state at 9.796 MeV was not observed, and only an upper limit for its transition strength of B(E2)<43 W.u. could be established. This contradicts AMD predictions of ≈200 W.u. for such a transition.Conclusion: The present study strongly rejects the hypothesis that the candidate set of states identified in Si28 represents an SD band, which demonstrates the potential of the methodology devised here.

We searched for the $\alpha$ condensed state in $^{13}$C by measuring the $\alpha$ inelastic scattering at $E_{\alpha} = 388$ MeV at forward angles including 0 degrees. We performed the distorted-wave Born-approximation calculation with the single-folding potential and the multipole decomposition analysis to determine the isoscalar transition strengths in $^{13}$C. We found a bump structure around $E_x = 12.5$ MeV due to the isoscalar monopole ($IS0$) transition. A peak-fit analysis suggested that this bump consisted of several $1/2^-$ states. We propose that this bump is due to the mirror state of the 13.5 MeV-state in $^{13}$N, which dominantly decays to the $\alpha$ condensed state in $^{12}$C. It was speculated that the $1/2^-$ states around $E_x = 12.5$ MeV were candidates for the $\alpha$ condensed state, but the $3\alpha + n$ orthogonality condition model suggests that the $\alpha$ condensed state is unlikely to emerge as the negative parity states. We also found two $1/2^+$ or $3/2^+$ states at $E_x = 14.5$ and 16.1 MeV excited with the isoscalar dipole ($IS1$) strengths. We suggest that the 16.1-MeV state is a possible candidate for the $\alpha$ condensed state predicted by the cluster-model calculations on the basis of the good correspondence between the experimental and calculated level structures. However, the theoretical $IS1$ transition strength for this state is significantly smaller than the measured value. Further experimental information is strongly desired to establish the $\alpha$ condensed state in $^{13}$C., Comment: 24 pages, 12 figures, published in PTEP

Background: Mg 24 is a strongly deformed nucleus in the ground state. Deformation effects can be observed in the structure of the isoscalar giant monopole and quadrupole resonances. Mg 24 is also a nucleus that is well known to present different types of cluster-oscillation modes. Both giant resonances and cluster states are strongly populated by isoscalar transitions. Purpose: To extract the E 0 , E 1 , and E 2 transition strengths via Li 6 scattering. The Li 6 probe is a powerful tool for investigating the isoscalar nuclear response with a very favorable ratio of resonance-to-continuum background. Method: Double-differential cross sections of Li 6 inelastic scattering, at the beam energy of 100 MeV/u, were measured in the excitation-energy range 10 – 40 MeV and scattering angles 0 − 3 ∘ . A multipole-decomposition analysis was performed for extracting the isoscalar E 0 , E 1 , and E 2 strength distributions. Results: The extracted multipole strengths were compared with predictions from consistent quasiparticle random phase approximation calculations. The theoretical predictions are in fair agreement with the experimental data. The E 0 strength was also compared with results from antisymmetrized molecular dynamics calculations found in the literature. A few peaks in the experimental data might be associated with clustering in Mg 24 . Conclusions: Ground-state deformation effects were observed in the isoscalar giant monopole resonance (ISGMR) and isoscalar giant quadrupole resonance (ISGQR) distributions. The ISGMR strength is split in two peaks around 19 and 28 MeV. The ISGQR exhibits a pronounced peak at 20 MeV with a broadening at the low-energy region, similar to predictions from microscopic calculations. Signatures of excitation of cluster states were observed in the E 0 response. Further studies including particle-decay measurements will be required to confirm the nature of the observed peaks.

This review paper concerns the research devoted to the study of the properties of dipole excitations in nuclei. The main focus is on questions related to isospin effects in these types of excitations. Particular attention is given to the experimental and theoretical efforts made to understand the nature and the specific structure of the low-lying dipole states known as the Pygmy Dipole Resonance (PDR). The main experimental methods employed in the study of the PDR are reviewed as well as the most interesting theoretical aspects. The main features of the experiments and of theoretical models are reported with special emphasis on the reaction cross sections populating the dipole states. Results are organized for nuclei according to different mass regions. The knowledge of the isovector dipole response as well as its low energy part is important in order to deduce the nuclear polarizability as accurate as possible. This issue is discussed in this paper together with the connection with the neutron skin and the nuclear equation of state. The important role played by the dipole response to deduce other physical quantities of general interest is discussed in the last two chapters. One concerns the level density and the other the isospin mixing in nuclei at finite temperature and its relation with beta decay.

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.

Radiative neutron capture reactions play an important role in nuclear astrophysics. In some cases direct neutron capture reaction studies are not possible and neutron transfer reactions have been suggested as a surrogate approach. We have performed a detailed study of the $^{25}\mathrm{Mg}(d,p)^{26}\mathrm{Mg}$ reaction at a beam energy of 56 MeV as a surrogate reaction to the radiative neutron capture reaction $^{25}\mathrm{Mg}(n,\ensuremath{\gamma})^{26}\mathrm{Mg}$. A large number of neutron bound and unbound states between 10.6 and 12.1 MeV excitation energy in $^{26}\mathrm{Mg}$ were observed. Angular distribution analysis provided information about the orbital momentum transfer populating these levels. The comparison with resonances observed in the $^{25}\mathrm{Mg}(n,\ensuremath{\gamma})^{26}\mathrm{Mg}$ reaction indicate that different levels in $^{26}\mathrm{Mg}$ are being populated through the two reaction mechanisms, causing substantial discrepancies in the reaction-rate prediction. This result demonstrates that neutron transfer reaction studies may not necessarily lead to reliable predictions for neutron capture reaction rates.

We present a precise measurement of the cross section, proton and $\rm ^3He$ analyzing powers, and spin correlation coefficient $C_{y,y}$ for $p$-$\rm ^3He$ elastic scattering near 65 MeV, and a comparison with rigorous four-nucleon scattering calculations based on realistic nuclear potentials and a model with $\Delta$-isobar excitation. Clear discrepancies are seen in some of the measured observables in the regime around the cross section minimum. Theoretical predictions using scaling relations between the calculated cross section and the $\rm ^3 He$ binding energy are not successful in reproducing the data. Large sensitivity to the $NN$ potentials and rather small $\Delta$-isobar effects in the calculated cross section are noticed as different features from those in the deuteron-proton elastic scattering. The results obtained above indicate that $p$-$\rm ^3He$ scattering at intermediate energies is an excellent tool to explore nuclear interactions not accessible by three-nucleon scattering., Comment: 22 pages, 6 figures

Background: Inelastic proton scattering at energies of a few hundred MeV and very-forward angles including $0^\circ$ has been established as a tool to study electric-dipole strength distributions in nuclei. The present work reports a systematic investigation of the chain of stable even-mass Nd isotopes representing a transition from spherical to quadrupole-deformed nuclei. Purpose: Extraction of the equivalent photo-absorption cross sections and analysis of their fine structure in the energy region of the IsoVector Giant Dipole Resonance (IVGDR). Method: Proton inelastic scattering reactions of 200 MeV protons were measured at iThemba LABS in Cape Town, South Africa. The scattering products were momentum-analysed by the K600 magnetic spectrometer positioned at $\theta_{\mathrm{Lab}}=0^\circ$. Using dispersion-matching techniques, energy resolutions of $\Delta E \approx 40 - 50$ keV were obtained. After subtraction of background and contributions from other multipoles, the spectra were converted to photo-absorption cross sections using the equivalent virtual-photon method. Results: Wavelet-analysis techniques are used to extract characteristic energy scales of the fine structure of the IVGDR from the experimental data. Comparisons with the Quasiparticle-Phonon Model (QPM) and Skyrme Separable Random Phase Approximation (SSRPA) predictions provide insight into the role of different giant resonance damping mechanisms. Conclusions: Fine structure is observed even for the most deformed nuclei studied. Fragmentation of the one particle-one hole ($1p1h$) strength seems to be the main source of fine structure in both spherical and deformed nuclei. Some impact of the spreading due to coupling of the two particle-two hole ($2p2h$) states to the $1p1h$ doorway states is seen in the spherical/transitional nuclei, where calculations beyond the $1p1h$ level are available.

Background: There is renewed interest in electric dipole strength distributions for a variety of reasons including the extraction of the dipole polarizability related to properties of the symmetry energy and a measure for the neutron skin thickness, understanding the structure of low-energy E1 strength in nuclei with neutron excess, and establishing the systematics of the isovector giant dipole resonance (IVGDR). Inelastic proton scattering at energies of a few hundred MeV and very forward angles including 0∘ has been established as a tool for the study of electric and magnetic dipole strength distributions in nuclei. Purpose: The present work aims at a systematic investigation of the electric and magnetic dipole strength distributions in the chain of stable even-mass tin isotopes. Methods: Inelastic proton scattering experiments were performed at the Research Center for Nuclear Physics, Osaka, with a 295-MeV beam covering laboratory angles 0∘–6∘ and excitation energies 6–22 MeV. Cross sections due to E1 and M1 excitations were extracted with a multipole decomposition analysis (MDA) and then converted to reduced transition probabilities with the “virtual photon method” for E1 and the “unit cross section method” for M1 excitations, respectively. Including a theory-aided correction for the high-excitation-energy region not covered experimentally, the electric dipole polarizability was determined from the E1 strength distributions. Results: Total photoabsorption cross sections derived from the E1 and M1 strength distributions show significant differences compared to those from previous (γ,xn) experiments in the energy region of the IVGDR. The widths of the IVGDR deduced from the present data with a Lorentz parametrization show an approximately constant value of about 4.5 MeV in contrast to the large variations between isotopes observed in previous work. The IVGDR centroid energies are in good correspondence to expectations from empirical systematics of their mass dependence. Furthermore, a study of the dependence of the IVGDR energies on bulk matter properties is presented. The E1 strengths below neutron threshold show fair agreement with results from (γ,γ′) experiments on Sn112,116,120,124 in the energy region between 6 and 7 MeV, where also isoscalar E1 strength was found for Sn124. At higher excitation energies, large differences are observed, pointing to a different nature of the excited states with small ground-state branching ratios. The isovector spin-M1 strengths exhibit a broad distribution between 6 and 12 MeV in all studied nuclei. Conclusions: The present results contribute to the solution of a variety of nuclear structure problems including the systematics of the energy and width of the IVGDR, the structure of low-energy E1 strength in nuclei, new constraints to energy density functionals (EDFs) aiming at a systematic description of the dipole polarizability across the nuclear chart, from which properties of the symmetry energy can be derived, and the systematics of the isovector spin-M1 strength in heavy nuclei.

We have measured the differential cross-sections and analyzing powers for ($p,2p$) reactions at an incident energy of 392 MeV on $^{12}$C, $^{16}$O, $^{40}$Ca, and $^{208}$Pb nuclei, leading to discrete states of the residual nuclei. The data are compared with two kinds of distorted-wave impulse approximation (DWIA) calculations, a standard calculation using a global optical potential and a calculation using wave functions generated in a relativistic Hartree model. The spectroscopic factors deduced from these two calculations agree with those determined in ($e,e'p$) studies mostly within 15% in the case of the lighter three target nuclei. However, those for the $^{208}$Pb target are overestimated compared with the ($e,e'p$) results. In the heavy target case, the DWIA results are very sensitive to the radius parameter of the bound-state potential and thus a careful treatment is required. Regarding the analyzing powers of the present measurement, we confirmed that the $j$-dependence is sufficient for practical spectroscopic use.

We conducted the coincidence measurement of $\alpha$ particles inelastically scattered from ${}^{20}$Ne at $0^{\circ}$ and decay charged particles in order to search for the alpha-particle condensed state. We compared the measured excitation-energy spectrum and decay branching ratio with the statistical-decay-model calculations, and found that the newly observed states at $E_x$ = 23.6, 21.8, and 21.2 MeV in ${}^{20}$Ne are strongly coupled to a candidate for the 4$\alpha$ condensed state in ${}^{16}$O. This result presents the first strong evidence that these states are the candidates for the 5$\alpha$ condensed state., Comment: 6 pages, 5 figures. The part of the analysis is updated, and some discussions are added

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.

The Gamow–Teller strength distributions of $${^{116} \text {Sb}}$$116Sb and $${^{122} \text {Sb}}$$122Sb were measured with the $${^{116,122} \text {Sn} (^{3} \text {He},t) ^{116,122} \text {Sb}}$$116,122Sn(3He,t)116,122Sb charge-exchange reactions at $${140 \ \text {MeV/u}}$$140MeV/u. The measurements were carried out at the Research Center for Nuclear Physics (RCNP) at Osaka University in Osaka, Japan using the Grand Raiden spectrometer. The data were analysed by Multipole-Decomposition Analysis (MDA). The Gamow–Teller strengths summed up to $${28 \ \text {MeV}}$$28MeV are $${(38 \pm 7) \%}$$(38±7)% and $${(48 \pm 6) \%}$$(48±6)% of the Ikeda sum rule for $${^{116} \text {Sb}}$$116Sb and $${^{122} \text {Sb}}$$122Sb, respectively, if the quasi-free scattering (QFS) contribution is not subtracted. These percentages are $${(29 \pm 7) \%}$$(29±7)% and $${(35 \pm 5) \%}$$(35±5)%, respectively, if the QFS contribution is maximally subtracted. These results were compared to those from previous measurements of the same isotopes, to recent measurements of $${^{150} \text {Pm}}$$150Pm, and to a Quasi-particle Random-Phase Approximation (QRPA) calculation with Quasi-Particle Vibration Coupling (QPVC). The data suggest that the true QFS contribution is small for $${^{116} \text {Sb}}$$116Sb, but are inconclusive about whether the QFS contribution is small or significant for $${^{122} \text {Sb}}$$122Sb. Therefore, these data may provide an interesting test for the general quenching phenomenon of the Gamow–Teller Resonance (GTR). However, more research to reveal the nature of the QFS contribution is still needed on both the experimental and the theoretical side.

We measured the cross section and the proton analyzing power A_yAy for pp–^33He elastic scattering at the angles \theta = 26.9^{\circ}θ=26.9∘–170.1^{\circ}170.1∘ in the center of mass system with a 65 MeV polarized proton beam. We compared the data with the rigorous numerical calculations based on the various nucleon–nucleon potentials. For the cross section, clear discrepancy is seen at the angles where the cross section takes minimum. For the proton analyzing power A_yAy, the calculations have moderate agreements with the data. In this proceedings, we show only the experimental results.

Nuclear matrix elements (NMEs) for double beta decays (DBDs) are crucial for studying the neutrino mass and other neutrino properties beyond the standard electro-weak model by measuring neutrino-less DBDs. The spin-dipole (SD) J π = 2- NME is one of the major components associated with the DBD NME. The SD NME for 76Ge was derived for the first time by using the 74,76 Ge (3He, t) at RCNP Osaka. The obtained SD NME for the 76Ge → 76As ground-state transition is in natural units. This is smaller by a coefficient around k ≈ 0.2 with respect to the quasi-particle model NME. The impact of the reduced (quenched) SD NME on DBD neutrino studies is discussed.

We performed the measurement of the cross section and the proton analyzing power \(A_y\) for p–\(^3\)He elastic scattering with a 65 MeV polarized proton beam at Research Center for Nuclear Physics (RCNP), Osaka University. The proton analyzing power \(A_y\) data are compared with the theoretical calculations based on the nucleon–nucleon potential (INOY04).

The dipole polarizability of stable even-mass tin isotopes 112,114,116,118,120,124 was extracted from inelastic proton scattering experiments at 295 MeV under very forward angles performed at RCNP. Predictions from energy density functionals cannot account for the present data and the polarizability of 208Pb simultaneously. The evolution of the polarizabilities in neighboring isotopes indicates a kink at 120Sn while all model results show a nearly linear increase with mass number after inclusion of pairing corrections., Comment: 10 pages, 6 figures, submitted to Phys. Lett. B

Proton inelastic scattering experiments at energy E_p = 200 MeV and a spectrometer scattering angle of 0 degree were performed on 144,146,148,150Nd and 152Sm exciting the IsoVector Giant Dipole Resonance (IVGDR). Comparison with results from photo-absorption experiments reveals a shift of resonance maxima towards higher energies for vibrational and transitional nuclei. The extracted photo-absorption cross sections in the most deformed nuclei, 150Nd and 152Sm, exhibit a pronounced asymmetry rather than a distinct double-hump structure expected as a signature of K-splitting. This behaviour can be related to the proximity of these nuclei to the critical point of the phase shape transition from vibrators to rotors with a soft quadrupole deformation potential. Self-consistent random-phase approximation (RPA) calculations using the SLy6 Skyrme force provide a relevant description of the IVGDR shapes deduced from the present data, Comment: 8 pages, 4 figures

The triple alpha reaction is one of the most important reactions in the nuclear astrophysics. However, its reaction rate in high temperature environments at T 9 > 2 was still uncertain. One of the major origins of the uncertainty was that the radiative-decay probability of the 3 1 − state in 12C was unknown. In the present work, we have determined the radiative-decay probability of the 3 1 − state to be 1.3 − 1.1 + 1.2 × 10 − 6 by measuring the 1H(12C,12Cp) reaction for the first time, and derived the triple alpha reaction rate in high temperature environments from the measured radiative-decay probability. The present result suggests that the 3 1 − state noticeably enhances the triple alpha reaction rate although the contribution from the 3 1 − state had been assumed to be small.

A new type of neutron detector, named Stack Structure Solid organic Scintillator (S 4 ), consisting of multi-layer plastic scintillators with capability to suppress low-energy γ rays under high-counting rate has been constructed and tested. To achieve n - γ discrimination, we exploit the difference in the ranges of the secondary charged particles produced by the interactions of neutrons and γ rays in the scintillator material. The thickness of a plastic scintillator layer was determined based on the results of Monte Carlo simulations using the Geant4 toolkit. With layer thicknesses of 5 mm, we have achieved a good separation between neutrons and γ rays at 5 MeV ee threshold setting. We have also determined the detection efficiencies using monoenergetic neutrons at two energies produced by the d + d → n + 3 He reaction. The results agree well with the Geant4 simulations implementing the Li e ge Intranuclear Cascade hadronic model (INCL++) and the high-precision model of low-energy neutron interactions (NeutronHP).

The isospin characters of low-energy dipole excitations in neutron-rich unstable nucleus 20O were investigated, for the first time in unstable nuclei. Two spectra obtained from a dominant isovector probe (View the MathML sourceO20+Au) and a dominant isoscalar probe (View the MathML sourceO20+α) were compared and analyzed by the distorted-wave Born approximation to extract independently the isovector and isoscalar dipole strengths. Two known 1−1− states with large isovector dipole strengths at energies of 5.36(5) MeV (View the MathML source11−) and 6.84(7) MeV (View the MathML source12−) were also excited by the isoscalar probe. These two states were found to have different isoscalar dipole strengths, 2.70(32)% (View the MathML source11−) and 0.67(12)% (View the MathML source12−), respectively, in exhaustion of the isoscalar dipole-energy-weighted sum rule. The difference in isoscalar strength indicated that they have different underlying structures. ispartof: Physics Letters B vol:768 pages:387-392 status: published

Quasi-monoenergetic high-energy neutron fields induced by 7 Li(p,n) reactions are used for the response evaluation of neutron-sensitive devices. The quasi-monoenergetic high-energy field consists of high-energy monoenergetic peak neutrons and unwanted continuum neutrons down to the low-energy region. A two-angle differential method has been developed to compensate for the effect of the continuum neutrons in the response measurements. In this study, the two-angle differential method was demonstrated for Bonner sphere detectors, which are typical examples of moderator-based neutron-sensitive detectors, to investigate the method's applicability and its dependence on detector characteristics. Experiments were performed under 96–387 MeV quasi-monoenergetic high-energy neutron fields at the Research Center for Nuclear Physics (RCNP), Osaka University. The measurement results for large high-density polyethylene (HDPE) sphere detectors agreed well with Monte Carlo calculations, which verified the adequacy of the two-angle differential method. By contrast, discrepancies were observed in the results for small HDPE sphere detectors and metal-induced sphere detectors. The former indicated that detectors that are particularly sensitive to low-energy neutrons may be affected by penetrating neutrons owing to the geometrical features of the RCNP facility. The latter discrepancy could be consistently explained by a problem in the evaluated cross-section data for the metals used in the calculation. Through those discussions, the adequacy of the two-angle differential method was experimentally verified, and practical suggestions were made pertaining to this method.

International audience; We measured the α-clustering strength at the surface of tin isotopes ^112,116,120,124Sn by using quasi-free \((p,p\alpha )\) reaction at RCNP. Formation of α clusters at the surface of tin isotopes was clearly evidenced from our results. Surface α-clustering in heavy nuclei provides a natural explanation for the origin of α particles in α decay, and may also impact the neutron-skin thickness which plays a critical role in constraining the nuclear symmetry energy.

Gamow-Teller (GT) transitions starting from the ${T}_{z}=+2$ nucleus $^{64}\mathrm{Zn}$ to the ${T}_{z}=+1$ nucleus $^{64}\mathrm{Ga}$ were studied in a ($p,n$)-type ($^{3}\mathrm{He},t$) charge-exchange reaction at a beam energy of 140 MeV/nucleon and scattering angles close to ${0}^{\ensuremath{\circ}}$. Here, ${T}_{z}$ is the $z$ component of the isospin $T$. The experiment was conducted at the Research Center for Nuclear Physics (RCNP) in Osaka, Japan. An energy resolution of $\ensuremath{\approx}34$ keV was achieved by applying beam matching techniques to the Grand Raiden magnetic spectrometer system. With our good resolution, we could observe GT strength fragmented in many states up to an excitation energy of $\ensuremath{\approx}11$ MeV. By performing angular distribution analysis, we could identify states in $^{64}\mathrm{Ga}$ excited by GT transitions. The reduced GT transition strengths [$B$(GT) values] were calculated assuming the proportionality between the cross sections and the $B$(GT) values. Shell-model calculations using the GXPF1J interaction reproduced the $B$(GT) strength distribution throughout the spectrum. States with isospin $T=3$ were identified by comparing the $^{64}\mathrm{Zn}\text{(}{}^{3}\text{He,}t{\text{)}}^{64}\text{Ga}$ spectrum with a $^{64}\mathrm{Zn}(d,^{2}\mathrm{He})^{64}\mathrm{Cu}$ spectrum. Relative excitation energies of the corresponding structures are in good agreement, supporting the robustness of isospin symmetry in the mass number $A=64$ nuclei.

The 18F(p,$\alpha$) reaction determines the rate of destruction of 18F in novae. It represents the key nuclear physics uncertainty in modelling the calculated flux of annihilation radiation emitted following the radioactive decay of 18F. The major uncertainties relate to states representing s-wave resonances in the compound system, 19Ne. We report a first study of the 19F(3He, t)19Ne reaction at intermediate energies and forward angles. This reaction has a simple, model-independent, mechanism that we use here to identify states near the proton threshold energy in 19Ne corresponding to $\Delta L=0$ transitions. In particular, we observe a $\Delta L=0$ state at 6.13 MeV which could significantly affect the 18F(p,$\alpha$) astrophysical S-factor at nova burning temperatures.

Inelastic proton scattering under extreme forward angles including $0^\circ$ and at energies of a few hundred MeV has been established as a new spectroscopic tool for the study of complete dipole strength distributions in nuclei. Such data allow an extraction of the electric dipole polarizability which provides important constraints parameters of the symmetry energy, which determine the neutron skin thickness and the equation of state (EOS) of neutron-rich matter. Also new insight into the much-debated nature of the pygmy dipole resonance (PDR) is obtained. Additionally, the isovector spin-M1 resonance can be studied in heavy nuclei, where only limited experimental information exists so far. Together with much improved results on the isoscalar spin-M1 strength distributions in $N = Z$ nuclei, these data shed new light on the phenomenon of quenching of the nuclear spin response. Using dispersion matching techniques, high energy resolution ($\Delta E/E \leq 10^{-4} \,\,$ full width at half maximum, FWHM) can be achieved in the experiments. In spherical-vibrational nuclei considerable fine structure is observed in the energy region of the isovector giant dipole resonance (IVGDR). A quantitative analysis of the fine structure with wavelet methods provides information on the role of different damping mechanisms contributing to the width of the IVGDR. Furthermore, level densities can be extracted from a fluctuation analysis at excitation energies well above neutron threshold, a region hardly accessible by other means. The combination of the gamma strength function (GSF) extracted from the E1 and M1 strength distributions with the independently derived level density permits novel tests of the Brink-Axel hypothesis underlying all calculations of statistical model reaction cross sections in astrophysical applications in the energy region of the PDR., Comment: 52 pages, 64 figures, review article submitted to Eur. Phys. J. A

The isospin character of p-n pairs at large relative momentum has been observed for the first time in the ^{16}O ground state. A strong population of the J,T=1,0 state and a very weak population of the J,T=0,1 state were observed in the neutron pickup domain of ^{16}O(p,pd) at 392 MeV. This strong isospin dependence at large momentum transfer is not reproduced by the distorted-wave impulse approximation calculations with known spectroscopic amplitudes. The results indicate the presence of high-momentum protons and neutrons induced by the tensor interactions in the ground state of ^{16}O.

International audience; α-clustering strength at the surface of tin isotopes ^112,116,120,124Sn was measured by using quasi-free (p, pα) reaction at RCNP. By measuring the scattered protons and α particles in coincidence, formation of α clusters at the surface of tin isotopes was clearly evidenced. Surface α-clustering in heavy nuclei provides a natural explanation for the origin of α particles in α decay, and may also impact the neutron-skin thickness which plays an important role in constraining the nuclear symmetry energy.

Our research goal is to measure the cross section of the 7Be(d, p) reaction to find a solution for the cosmological the 7Li problem, which is an overestimation of the primordial 7Li abundance in the standard Big-Bang nucleosynthesis (BBN) model. We developed a method to produce an unstable 7Be target to measure the reaction in normal kinematics in a high-resolution measurement. We performed an experiment to produce the 7Be target and also to measure the cross section of the 7Be(d, p)8Be reaction with the produced 7Be target at the tandem facility, Kobe University. A 2.36 MeV proton beam irradiated a Li target to transmute 7Li particles to 7Be particles via the 7Li(p, n)7Be reaction. We produced 2.6×1013 7Be particles in the target after two days’ proton irradiation. After the target production, the beam ion was changed to deuterons with energies of 0.6, 1.0, and 1.6 MeV to measure the 7Be(d, p) reaction. The outgoing protons were measured by two ΔE-E silicon telescopes placed at 30° and 45°. We report the preliminary results of this experiment, including the 7Be(d, p) cross section.

The angular distribution of 12 C + 12 C scattering at an incident energy of 100 A MeV has been measured. The elastic and inelastic scatterings in 12 C to the excitation energies of up to ∼ 45 MeV were measured simultaneously for the first time with the high-resolution Grand Raiden spectrometer at the Research Center for Nuclear Physics (RCNP). The angular distributions of the elastic scattering to the ground state ( 0 1 + ) and inelastic scattering to the 4.44 MeV ( 2 1 + ) excited state were precisely obtained in the angular range of 1.0°–7.5° with a step of 0.1°. Additionally, the angular distribution was obtained for the sum of the cross sections for excitation energies above the 4.44 MeV state up to 11 MeV, which includes the 7.65 MeV ( 0 2 + ), 9.64 MeV ( 3 1 − ), and 10.30 MeV ( 2 2 + ) states, in addition to probably the simultaneous excitation of the 4.44 MeV state in the projectile and the target nuclei. Those combined data provide a means to study the effects of channel coupling on the elastic cross section. The observed angular distributions are compared with theoretical calculations based on three double-folding models with complex G-matrix interactions, the CEG07b, MPa, and ESC models. The importance of three-body repulsive forces included in the CEG07b and MPa models will be discussed.

International audience; A very first experiment in the field of nuclear structure at the Cyclotron Centre Bronowice (CCB) facility in Kraków, Poland has been performed recently. The medical cyclotron IBA Proteus C-235 located at CCB produces proton beams in the energy range of 70–230 MeV, that can be used for experimental purposes as well. In the reported measurement, the energy of scattered protons at the incident beam energy of 85 MeV and emitted γ rays from the excited 208Pb target were measured in coincidence. During the experiment excitations in the energy region of the Giant Quadrupole and Dipole Resonances, as well as the Pygmy Dipole States were observed. By applying different conditions on the data, spectra corresponding to γ decays of excited states to selected low-lying levels in 208Pb were obtained, allowing a look into the Brink–Axel hypothesis.

Background: Inelastic neutrino-nucleus scattering is important for understanding core-collapse supernovae and the detection of emitted neutrinos from such events in earth-based detectors. Direct measurement of the cross sections is difficult and has only been performed on a few nuclei. It is, therefore, important to develop indirect techniques from which the inelastic neutrino-nucleus scattering cross sections can be determined. Purpose: This paper presents a development of the (Li-6,Li-6*[T = 1, T-z = 0, 0(+), 3.56 MeV]) reaction at 100 MeV/u as a probe for isolating the isovector spin-transfer response in the inelastic channel (Delta S = 1, Delta T = 1, Delta T-z = 0) from which the Gamow-Teller transition strengths from nuclei of relevance for inelastic neutrino-nucleus scattering cross sections can be extracted. Method: By measuring the Li-6 ejectile in a magnetic spectrometer and selecting events in which the 3.56 MeV gamma ray from the decay of the Li-6*[3.56 MeV] state is detected, the isovector spin-transfer selectivity is obtained. High-purity germanium clover detectors served to detect the gamma rays. Doppler reconstruction was used to determine the gamma energy in the rest frame of Li-6. From the Li-6 and 3.56 MeV gamma-momentum vectors the excitation energy of the residual nucleus was determined. Results: In the study of the C-12(Li-6,Li-6*[3.56 MeV]) reaction, the isovector spin-transfer excitation-energy spectrum in the inelastic channel was successfully measured. The strong Gamow-Teller state in C-12 at 15.1 MeV was observed. Comparisons with the analog C-12(Li-6,He-6) reaction validate the method of extracting the Gamow-Teller strength. In measurements of the Mg-24, Nb-93(Li-6,Li-6*[3.56 MeV]) reactions, the 3.56 MeV gamma peak could not be isolated from the strong background in the gamma spectrum from the decay of the isoscalar excitations. It is argued that by using a gamma-ray tracking array instead of a clover array, it is feasible to extend the mass range over which the (Li-6,Li-6*) reaction can be used for extracting the isovector spin-transfer response up to mass numbers of similar to 25 and perhaps higher. Conclusions: It is demonstrated that the (Li-6,Li-6*[3.56 MeV]) reaction probe can be used to isolate the inelastic isovector spin-transfer response in nuclei. Application to nuclei with mass numbers of about 25 or more, however, will require a more efficient gamma-ray array with a better tracking capability.

The isoscalar giant monopole, dipole, and quadrupole strength distributions have been deduced in $^{90,92}\mathrm{Zr}$ and $^{92}\mathrm{Mo}$ from ``background-free'' spectra of inelastic $\ensuremath{\alpha}$-particle scattering at a beam energy of 385 MeV at extremely forward angles, including ${0}^{\ensuremath{\circ}}$. These strength distributions were extracted by a multipole-decomposition analysis based on the expected angular distributions of the respective multipoles. All these strength distributions for the three nuclei practically coincide with each other, affirming that giant resonances, being collective phenomena, are not influenced by nuclear shell structure near $A\ensuremath{\sim}90$, contrary to the claim in a recent measurement.

We systematically measured the differential cross sections of inelastic $\ensuremath{\alpha}$ scattering off self-conjugate $A=4n$ nuclei at two incident energies ${E}_{\ensuremath{\alpha}}=130\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and $386\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ at Research Center for Nuclear Physics, Osaka University. The measured cross sections were analyzed by the distorted-wave Born-approximation (DWBA) calculation using the single-folding potentials, which are obtained by folding macroscopic transition densities with the phenomenological $\ensuremath{\alpha}N$ interaction. The DWBA calculation with the density-dependent $\ensuremath{\alpha}N$ interaction systematically overestimates the cross sections for the $\mathrm{\ensuremath{\Delta}}L=0$ transitions. However, the DWBA calculation using the density-independent $\ensuremath{\alpha}N$ interaction reasonably well describes all the transitions with $\mathrm{\ensuremath{\Delta}}L=0$--4. We examined uncertainties in the present DWBA calculation stemming from the macroscopic transition densities, distorting potentials, phenomenological $\ensuremath{\alpha}N$ interaction, and coupled channel effects in $^{12}\mathrm{C}$. It was found that the DWBA calculation is not sensitive to details of the transition densities nor the distorting potentials, and the phenomenological density-independent $\ensuremath{\alpha}N$ interaction gives reasonable results. The coupled-channel effects are negligibly small for the ${2}_{1}^{+}$ and ${3}_{1}^{\ensuremath{-}}$ states in $^{12}\mathrm{C}$, but not for the ${0}_{2}^{+}$ state. However, the DWBA calculation using the density-independent interaction at ${E}_{\ensuremath{\alpha}}=386\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ is still reasonable even for the ${0}_{2}^{+}$ state. We concluded that the macroscopic DWBA calculations using the density-independent interaction are reliably applicable to the analysis of inelastic $\ensuremath{\alpha}$ scattering at ${E}_{\ensuremath{\alpha}}\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/\mathrm{u}$.

International audience; The dependence of the single-particle strength on the difference between proton and neutron separation energies is studied for oxygen isotopes in a wide range of isospins. The cross sections of the quasi-free (p, 2p) reaction on 14,16,18,22,24O were measured at intermediate energies. The measured cross sections are compared to predictions based on the distorted wave impulse approximation and shell-model psd valence-space spectroscopic factors. The reduction factors, which are the ratio of the experimental cross sections to the theoretical predictions, show no apparent dependence on the proton–neutron separation energy difference. The result is compatible with the result of the (e, e p) reaction on stable targets and with the predictions of recent ab initio calculations.

The electric dipole is an important property of heavy nuclei. Precise information on the electric dipole response provides information on the electric dipole polarisability which in turn allows to extract important constraints on neutron-skin thickness in heavy nuclei and parameters of the symmetry energy. The tin isotope chain is particularly suited for a systematic study of the dependence of the electric dipole response on neutron excess as it provides a wide mass range of accessible isotopes with little change of the underlying structure. Recently an inelastic proton scattering experiment under forward angles including 0º on 112,116,124Sn was performed at the Research Centre for Nuclear Physics (RCNP), Japan with a focus on the low-energy dipole strength and the polarisability. First results are presented here. Using data from an earlier proton scattering experiment on 120Sn the gamma strength function and level density are determined for this nucleus.

A survey of the fine structure of the Isovector Giant Dipole Resonance (IVGDR) was performed, using the recently commissioned zero-degree facility of the K600 magnetic spectrometer at iThemba LABS. Inelastic proton scattering at an incident energy of 200 MeV was measured on $^{27}$Al, $^{40}$Ca, $^{56}$Fe, $^{58}$Ni and $^{208}$Pb. A high energy resolution ($\rm{\Delta}\it{E} \simeq$ 40 keV FWHM) could be achieved after utilising faint-beam and dispersion-matching techniques. Considerable fine structure is observed in the energy region of the IVGDR and characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The comparison with Quasiparticle-Phonon Model (QPM) calculations provides insight into the relevance of different giant resonance decay mechanisms. Photoabsorption cross sections derived from the data assuming dominance of relativistic Coulomb excitation are in fair agreement with previous work using real photons., Comment: 15 pages, 15 figures

Isotopic and natural carbon foils made by thermal cracking method are used for various purposes in nuclear physics experiments. An apparatus equipped with an oil free vacuum pumping system has been constructed to produce such foils on a resistively heated metallic Ta filament by the thermal cracking method. Properties of the foils such as accessible thickness and area, uniformity, purity and yield in the foil preparation were investigated. We also investigated the following issue during the foil production; when the Ta filament temperature was decreased after the cracking process, the cracked layer sometimes broke into pieces from the filament. Eventually, we could successfully fabricate enriched isotopic 12C foils and natural carbon foils with thicknesses from 0.2 to 5 mg/cm2 and with a dimension of 20 × 20 mm2 or even larger.

International audience; We performed experiments to study the low-energy part of the E1 response (Pygmy Dipole Resonance) in $^{90,94}$Zr nuclei, by measuring the (p,p’γ) and (α,α’γ) inelastic scattering reactions at energies Ebeam,p = 80 MeV and Ebeam,α = 130 MeV respectively. The inelastically scattered particles were measured by employing the high-resolution spectrometer Grand Raiden. The gamma-rays emitted following the de-excitation of the Zr target nuclei were detected using both the clover type HPGe detectors of the CAGRA array and the large volume LaBr3:Ce scintillation detectors from the HECTOR+ array. Some preliminary results are presented here.