K. Sugimoto

Measurement of interaction cross sections using isotope beams of Be and B and isospin dependence of the nuclear radii

Abstract Interaction radii for 11,12,14 Be and 8,12,13,14,15 B have been determined by the measurement of interaction cross sections at 790 MeV/nucleon. Effective root-mean-square (RMS) radii of nucleon distribution of these nuclei have been deduced using a Glauber-model calculation. Isospin dependence of nuclear radii are presented for isobars of mass numbers from 6 to 12, and compared with theoretical predictions by the droplet model and by a Hartree-Fock (HF) model. The HF model with the Skyrme-III potential, which includes a strong density-dependent force, reproduce the observed isospin dependence.

Revelation of thick neutron skins in nuclei

Abstract Thick neutron skins (∼ 0.9 fm) have been verified for the first time in 6He and 8He nuclei from a combined analysis of the interaction and the fragmentation cross sections of 4,6,8He incident reactions at 800A MeV. A relativistic mean field (RMF) model was applied to 6He and 8He nuclei and shown to reproduce the neutron skin thicknesses very well. It is also shown that the RMF model predicts a gross linear dependence of the neutron skin thickness on the difference between the proton and the neutron Fermi energy in a wide range of nuclei. Possible observations of thick neutron skins in other nuclei, in particular in Na isotopes, are also discussed.

Electromagnetic dissociation and soft giant dipole resonance of the neutron-dripline nucleus 11Li

Abstract The electromagnetic dissociation (EMD) cross sections of light neutron-dripline projectile 11Li have been inferred from the target dependence of the interaction cross section, σ1, and the two-neutron-removal cross section, σ−2n, at an incident energy of 0.8 GeV/nucleon. The EMD cross sections of 11Li projectiles on a lead target were found to be quite large; σ I EMD ( 11 Li + Pb )=1.72 ±0.65 b and σ −2 n EMD ( 11 Li + Pb )=0.89 ±0.10 b , which are approximately 80 times larger than those of 12C projectiles after scaling the cross section by Zproj2. The large EMD cross section is related to the possible existence of a soft mode of the giant dipole resonance at low excitation energy in the extremely neutron-rich nuclei.

Determination of the density distribution and the correlation of halo neutrons in 11Li

Interaction cross sections (σ1) and transverse momentum Pt distributions of 9Li fragments in 11Li reactions were measured 1467 using p and d targets at 800A MeV, and Be and C targets at 400A MeV. The density distribution of the 11Li nucleus has been determined for the first time from these σIs. It is confirmed that only a distribution with a long tail (halo) consistently reproduces the observed data. From a combined analysis of Pt distributions of 9Li and of neutrons, the momentum correlation of the two halo neutrons was extracted. It suggests that these neutrons have a strong tendency to move in the same direction.

Interaction cross sections and radii of the mass number A=17 isobar (17N, 17F, and 17Ne)

Abstract Interaction cross sections of mass number A=17 isobar (717N10,917F8, and 1017Ne7) have been measured at around 700 MeV/nucleon. Effective root-mean-square (RMS) radii of the nucleon distribution of these nuclei have been deduced using Glauber-model calculation. A strong isospin dependence of the radii has been observed in the A=17 isobar, which shows an increase of the radii on the proton rich side from 17F to 17Ne. The radius of 17Ne is also found to be larger than that of its mirror nucleus 17N. The increase of the radius in 17Ne suggests its anomalous structure. One of the possibilities is that an inversion of the s and d orbitals occurs in this nucleus. The role of the centrifugal barrier in the formation of a halo is also discussed.

Quadrupole Effects in NMR Spectra on Short-Lived β-Radioactive Nuclei, 12B and 12N

Quadrupole effects in NMR on 12 B( T 1/2 =20 ms) and 12 N( T 1/2 =11 ms) have been investigated by using the polarized nuclei produced and implanted through nuclear reactions and the resultant asymmetric β decay. The implantation media were polycrystalline bcc metals (Nb, Mo, Ta and W), TiB 2 and ZrB 2 . To increase the observable effects in NMR, a frequency-modu-lated r.f. field was employed. The spectra in bcc metals show the characteristics of quadrupole interaction for nuclear spin \(I{=}1\hslash\), and the determined coupling constants depend largely on the periodic groups of the related elements. The spectra in the bcc metals together with those in the fcc metals (Al, Cu, Pt and Au) indicate that the major implanted sites are interstitial. From the results on TiB 2 and ZrB 2 and the known values on 11 B, the ratio of quadrupole moments is determined as | Q ( 12 B)/ Q ( 11 B)|=0.42±0.04, and the moment of 12 B is deduced to be | Q ( 12 B)|=0.017 1 ±0.001 6 b.

Magnetic Moment of F17 – Nuclear Magnetic Resonance by Polarization Following O16 (d, n) F17 Reaction –

The nuclear magnetic resonance of F 17 ( T 1/2 =66 sec) has been observed using the polarization of recoil nuclei produced by the reaction O 16 ( d , n ) F 17 and the β-decay anisotropy as the indicator of the polarization. The accomplishment of the experiment was essentially due to the persistence of the polarization by specific experimental methods, i.e. , the use of a strong magnetic field (\({\gtrsim}5\) kG) in the direction of polarization and the use of pure CaF 2 crystals as the stopping material of recoil ions. The observed asymmetry of β-counting was about 2% and a spin relaxation time T 1 comparable to the half-life of F 17 was observed. The value obtained of the magnetic moment of F 17 is µ=4.7224±0.0012 nm with the diamagnetic correction.

Interaction cross sections and radii of light nuclei

Abstract The interaction cross sections (σIs) with 15B, 9C, 10C, 15C, 13N, 13O, 14O and 15O beams have been measured at energies of around 730A·MeV. The effective root-mean-square (RMS) radii of the nucleon distribution of these nuclei have been deduced using a Glauber-model calculation. The global isotope and isospin dependences of the radii are shown in the p-shell region. The σIs are also compared with those obtained at intermediate energies in the region. Furthermore, we calculated the Coulomb-energy differences of the mirror pairs deduced from the RMS charge radii and compared them with those obtained from the mass for some mirror pairs. From the above systematics, an anomalous nuclear structure (a halo and/or a skin) is suggested for 14B and 15C, and the occurrence of an s-d inversion is emphasized for the 17Ne17N mirror pair.

Magnetic Moments of Short-Lived β-Radioactive Nuclei, 12B and 12N

The magnetic moments of 12 B( T 1/2 =20 ms) and 12 N( T 1/2 =11 ms) have been determined by an NMR method using the recoil polarization and the asymmetric β decay. The nuclear polarization was preserved by using a holding static magnetic field and a recoil stopper of metal foil. Several kinds of metal foils were employed. Relative shifts of the order of 10 -3 between the centers of NMR by different metals and the resonance widths comparable to the dipolar broadening were observed. The results obtained for the magnetic moments are µ( 12 B, 1 + )=+(1.003±0.001) nm and µ( 12 N, 1 + )=+(0.4571±0.0005) nm.

Interaction cross section and interaction radius of the 8B nucleus

Abstract The interaction cross section ( σ I ) was re-measured by a transmission-type measurement for 5 8 B 3 at 790 A ·MeV on a C target confirming the previously reported value. 8 B, although it has a very small proton separation energy 0.137 MeV, shows no remarkable enhancement of the σ I expected from a possible proton halo, as suggested from studies of the quadrupole moment and other recent data such as the reaction cross section at low energies. The root-mean-square (RMS) radius of the nucleon distribution has been deduced using the Glauber model. The relation between the halo tail and the separation energy is discussed on the mirror nuclei 8 B and 8 Li. It was also found that the previously reported narrow momentum distribution of 7 Be from the fragmentation of 8 B is well reproduced by the presently determined density distribution.