Search

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.

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 ${E}_{\ensuremath{\alpha}}\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/\mathrm{u}$.

By using para-hydrogen and a mechanical press made of neodymium magnets, we have succeeded in making a 1-mm-thick and 30-mm-diameter solid hydrogen target (SHT), and have measured elastic scattering of protons with radioactive ion beams at 300 MeV/u. We also succeeded in making not only a 0.5-mm-thick and 10-mm-diameter SHT but also a 2-mm-thick and 30-mm-diameter SHT to study excited-state properties of nuclei via (p,p′) reactions, and quasi-free (p,pα) reactions at intermediate energies. The ortho–para converter and the simple mechanical press show possibilities for making SHTs which have various radii and thicknesses.

"Background-free" spectra of inelastic $\alpha$-particle scattering have been measured at a beam energy of 385 MeV in $^{90, 92}$Zr and $^{92}$Mo at extremely forward angles, including 0$^{\circ}$. The ISGMR strength distributions for the three nuclei coincide with each other, establishing clearly that nuclear incompressibility is not influenced by nuclear shell structure near $A\sim$90 as was claimed in recent measurements., Comment: 5 pages, 4 figures; accepted for publication in Phys. Lett. B

We have developed a large, thin solid hydrogen target (SHT) that is 30 mm in diameter and 1 mm thick for elastic scattering of protons from unstable nuclei. By using para-H 2 that has a high thermal conductivity at low temperatures, we could prevent sublimation at the target center due to radiation from the higher temperature surroundings. The uniform SHT was used during long-term scattering experiments and it maintained its shape and thickness.

A Gamow–Teller (GT) transition from the drip-line nucleus 14Be to 14B was studied via the ( p , n ) reaction in inverse kinematics using a secondary 14Be beam at 69 MeV/nucleon. The invariant mass method is employed to reconstruct the energy spectrum. A peak is observed at an excitation energy of 1.27(2) MeV in 14B, together with bumps at 2.08 and 4.06(5) MeV. The observed forward peaking of the state at 1.27 MeV and a good description for the differential cross section, obtained with a DWBA calculation provide support for the 1 + assignment to this state. By extrapolating the cross section to zero momentum transfer the GT-transition strength is deduced. The value is found to compare well with that reported in a β-delayed neutron emission study.

An experimental study for the unbound nucleus 13Be has been performed by means of the invariant mass method via the one-neutron removal reaction H 1 ( Be 14 , Be 12 + n ) . A resonance has been observed at 0.51(1) MeV in the relative energy ( E rel ) spectrum of the Be 12 + n system. The transverse momentum distribution of the Be 12 + n system as well as the resonance width of 0.45(3) MeV gives evidence for the p-wave nature of the resonance. A d-wave resonance has also been observed at 2.39(5) MeV in the E rel spectrum. The observation of the low-lying p-wave resonance indicates the disappearance of the N = 8 magicity in the vicinity of the neutron drip line region.

Proton knockout reactions on carbon isotopes p( 9–16 C,2p) 8–15 B at 250 MeV/A were performed for systematic information on weakly- to strongly-bound 1p valence protons and deeply-bound 1s inner-shell protons. Various information such as the s-hole distributions, excitation energy of the s-hole states, momentum widths for 1s and 1p orbits, and relative (p,2p) yields are obtained.

The neutron-rich carbon isotopes 19,17C have been investigated via proton inelastic scattering on a liquid hydrogen target at 70 MeV/nucleon. The invariant mass method in inverse kinematics was employed to reconstruct the energy spectrum, in which fast neutrons and charged fragments were detected in coincidence using a neutron hodoscope and a dipole magnet system. A peak has been observed with an excitation energy of 1.46(10) MeV in 19C, while three peaks with energies of 2.20(3), 3.05(3), and 6.13(9) MeV have been observed in 17C. Deduced cross sections are compared with microscopic DWBA calculations based on p-sd shell model wave functions and modern nucleon-nucleus optical potentials. Jpi assignments are made for the four observed states as well as the ground states of both nuclei., 20 pages

Collective motions of β unstable nuclei are interesting because of the uniqueness of shapes different from those of stable nuclei. Measurements of such mode of the giant resonances will supply fruitful of information unaccessible from the previous experiments. In order to access region of the sufficiently high excited energy with small momentum transfer for β unstable nuclei, we newly constructed a magnetic spectrometer for 0 degree scattered recoil particles in inverse kinematics. By means of the spectrometer we measured the H(38S,p′) reaction at forwarding angles including θ CM = 0 ° at E 38 S = 62 A MeV as the first challenge of this method. As an experimental result, a bump is confirmed at around E x = 17 MeV . Direct evidences for ISGMR of the β unstable nuclei have not yet been derived. It is hoped that the E0 strength co-exists in the observed bump.

First experimental evidence of the population of the first 2- state in 16C above the neutron threshold is obtained by neutron knockout from 17C on a hydrogen target. The invariant mass method combined with in-beam gamma-ray detection is used to locate the state at 5.45(1) MeV. Comparison of its populating cross section and parallel momentum distribution with a Glauber model calculation utilizing the shell-model spectroscopic factor confirms the core-neutron removal nature of this state. Additionally, a previously known unbound state at 6.11 MeV and a new state at 6.28(2) MeV are observed. The position of the first 2- state, which belongs to a member of the lowest-lying p-sd cross shell transition, is reasonably well described by the shell-model calculation using the WBT interaction., Comment: 15 pages, 3 figures

Proton knockout reactions on carbon isotopes, p(9–16C,2p)8‐15B, at 250MeV/A were performed for systematic information on weakly to strongly bound 1p valence protons and deeply bound 1s protons. Various information such as energy gap between 1s and 1p orbits, widths of momentum distributions for 1s and 1p orbits, relative (p,2p) yields are obtained.

Excited states in 12C nuclei play a very important role in the nucleosynthesis in the universe. 12C nuclei are synthesized by the triple α reaction. Normally this process proceeds via the 0+2 state (Hoyle state) at Ex = 7.65 MeV in 12C, however, at high temperature T > 109 the highly excited 3α resonant states such as the 3−1 state at Ex = 9.64 MeV and the 2+2 state at Ex = 9.84 MeV play a part of the triple α reaction. Unfortunately, the γ-decay probability of the 3p state has not been determined, therefore we planned to determine the 7- decay probability using the inverse kinematic reaction 1H(12C, 12Cp) without measuring γ-rays. The test experiment was carried out at the cyclotron facility in RCNP. The results of the test experiment are reported in the present paper.