T. Ohtsubo

Precision spectroscopy of pionic 1s states of Sn nuclei and evidence for partial restoration of chiral symmetry in the nuclear medium

Deeply bound 1s states of pi(-) in (115,119,123)Sn were preferentially observed using the Sn(d,3He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were precisely determined and were used to deduce the isovector parameter of the s-wave pion-nucleus potential to be b1=-(0.115+/-0.007)m(-1)(pi). The observed enhancement of |b(1)| over the free piN value (b(free)1/b1=0.78+/-0.05) indicates a reduction of the chiral order parameter, f*pi(rho)2/f2pi approximately 0.64, at the normal nuclear density, rho=rho(0).

Identification of 45 New Neutron-Rich Isotopes Produced by In-Flight Fission of a 238U Beam at 345 MeV/nucleon

A search for new isotopes using in-flight fission of a 345 MeV/nucleon 238 U beam has been carried out at the RI Beam Factory at the RIKEN Nishina Center. Fission fragments were analyzed and identi...

Measurements of the interaction cross sections for Ar and Cl isotopes

We have measured the interaction cross sections (σI) of 31–40Ar and 31–37Cl on carbon targets at energies of around 950 A MeV. The effective matter radii for these nuclei were deduced by a Glauber-model analysis. Combining our matter radii with measured charge radii for Ar isotopes, we could deduce the proton-skin thicknesses for the 32–40Ar isotopes, which were found to increase monotonically with decreasing neutron number. The larger radius of the proton drip-line nucleus 31Ar suggests an anomalous structure for this nucleus. In addition, using NaI(Tl) arrays surrounding the carbon target, we measured γ-rays emitted from excited states in these isotopes. In this way we could deduce the upper limits for the inelastic cross sections (σinela) on carbon targets at energies of around 950 A MeV.

Density distribution of 8B studied via reaction cross sections

Abstract Reaction cross sections ( σ R ) for 8 B on Be, C and Al targets were measured at energies of 40 A and 60 A MeV. The density distribution of 8 B was studied through a χ 2 -fitting procedure on the σ R including the high-energy data using the optical limit of Glauber theory with assumptions on the enhancement of the σ R at low energies. The result shows a long tail in the density distribution. Large one-proton removal cross sections were also observed to support the existence of a long proton tail consistent with its binding energy.

High-resolution measurement of the time-modulated orbital electron capture and of the β+ decay of hydrogen-like 142Pm60+ ions

Abstract The periodic time modulations, found recently in the two-body orbital electron capture (EC) decay of both, hydrogen-like 140Pr58+ and 142Pm60+ ions, with periods near to 7 s and amplitudes of about 20%, were re-investigated for the case of 142Pm60+ by using a 245 MHz resonator cavity with a much improved sensitivity and time resolution. We observed that the exponential EC decay is modulated with a period T = 7.11 ( 11 ) s , in accordance with a modulation period T = 7.12 ( 11 ) s as obtained from simultaneous observations with a capacitive pick-up, employed also in the previous experiments. The modulation amplitudes amount to a R = 0.107 ( 24 ) and a P = 0.134 ( 27 ) for the 245 MHz resonator and the capacitive pick-up, respectively. These new results corroborate for both detectors exactly our previous findings of modulation periods near to 7 s , though with distinctly smaller amplitudes. Also the three-body β + decays have been analyzed. For a supposed modulation period near to 7 s we found an amplitude a = 0.027 ( 27 ) , compatible with a = 0 and in agreement with the preliminary result a = 0.030 ( 30 ) of our previous experiment. These observations could point at weak interaction as origin of the observed 7 s -modulation of the EC decay. Furthermore, the data suggest that interference terms occur in the two-body EC decay, although the neutrinos are not directly observed.

Examining the exotic structure of the proton-rich nucleus {sup 23}Al

The longitudinal momentum distribution (P{sub //}) of fragments after one-proton removal from {sup 23}Al and reaction cross sections ({sigma}{sub R}) for {sup 23,24}Al on a carbon target at 74A MeV have been measured. The {sup 23,24}Al ions were produced through projectile fragmentation of 135A MeV {sup 28}Si primary beam using the RIPS fragment separator at RIKEN. P{sub parallel} is measured by a direct time-of-flight (TOF) technique, while {sigma}{sub R} is determined using a transmission method. An enhancement in {sigma}{sub R} is observed for {sup 23}Al compared with {sup 24}Al. The P{sub parallel} for {sup 22}Mg fragments from {sup 23}Al breakup has been obtained for the first time. FWHM of the distributions has been determined to be 232 {+-} 28 MeV/c. The experimental data are discussed by using the Few-Body Glauber model. Analysis of P{sub //} demonstrates a dominant d-wave configuration for the valence proton in ground state of {sup 23}Al, indicating that {sup 23}Al is not a proton halo nucleus.

Direct observation of long-lived isomers in 212Bi.

Long-lived isomers in (212)Bi have been studied following (238)U projectile fragmentation at 670 MeV per nucleon. The fragmentation products were injected as highly charged ions into a storage ring, giving access to masses and half-lives. While the excitation energy of the first isomer of (212)Bi was confirmed, the second isomer was observed at 1478(30) keV, in contrast to the previously accepted value of >1910 keV. It was also found to have an extended Lorentz-corrected in-ring half-life >30 min, compared to 7.0(3) min for the neutral atom. Both the energy and half-life differences can be understood as being due a substantial, though previously unrecognized, internal decay branch for neutral atoms. Earlier shell-model calculations are now found to give good agreement with the isomer excitation energy. Furthermore, these and new calculations predict the existence of states at slightly higher energy that could facilitate isomer deexcitation studies.

Present and Future Experiments with Stored Exotic Nuclei at Relativistic Energies

Recent progress is presented from experiments on masses and lifetimes of bare and few‐electron exotic nuclei at GSI. Relativistic rare isotopes produced via projectile fragmentation and fission were separated in flight by the fragment separator FRS and injected into the storage ring ESR. This worldwide unique experimental technique gives access to all fragments with half‐lives down to the microsecond range. The great research potential is also demonstrated by the discovery of new isotopes along with simultaneous measurements of mass and lifetime. Representative results from time‐resolved Schottky mass spectrometry are compared with modern theoretical predictions. The measured isospin dependence of pairing‐gap energies is not reproduced by conventional mass models. The first direct observation of bound‐state beta decay has been achieved. Single particle decay measurements and the continuous recording of both stored mother and daughter nuclei open up a new era for spectroscopy. The combination of stochastic...

Magnetic moments of proton drip-line nuclei13O and9C

The magnetic moments of the proton drip-line nuclei13O(Iπ = 3/2−,T1/2 = 8.6 ms) and 9C(Iπ = 3/2−,T1/2 = 126 ms) have been determined for the first time through the combined techniques of polarized radioactive nuclear beams andβ-NMR detection. The observed magnetic moments are ¦μ(13O)¦ = 1.3891 ±0.0003μN and ¦μ(9C)¦ = 1.3914 ±0.0005μN. Spin expectation values 〈σ〉 are deduced to be 0.76 and 1.44 for13O and9C, respectively. While the 〈σ〉 of13O is consistent with the systematics from isospinT= 1/2 mirror pairs, the 〈σ〉 of9C is unusually large, even far larger than the single particle value, 〈σ〉 = 1.

LARGE-SCALE MASS MEASUREMENTS OF SHORT-LIVED NUCLIDES WITH THE ISOCHRONOUS MASS SPECTROMETRY AT GSI

Precise mass measurements of short-lived exotic nuclei are very important for the understanding of basic nuclear structure physics and astrophysical nucleosynthesis in nature, as well as for the test and the development of theoretical nuclear mass models. At GSI, the Isochronous Mass Spectrometry (IMS) dedicated to mass measurements of short-lived nuclides was developed. In this contribution, the IMS technique is briefly reviewed. Recently, the first large-scale measurement on the 238U fission fragment was done successfully. The measured mass values are in excellent agreement with the recent Penning trap data, however, they show a systematical deviation from the values in the latest atomic mass evaluation. Some representative results from this experiment will be presented, including their impact on nuclear structure physics and astrophysical r-process nucleosynthesis.