M. Mihara

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.

Magnetic moment of proton drip-line nucleus 9C

Abstract The magnetic moment of the proton drip-line nucleus 9 C (I π = 3 2 − , T 1 2 =126 ms ) has been measured for the first time, using the β-NMR detection technique with polarized radioactive beams. The measured value for the magnetic moment is |μ( 9 C )| = 1.3914±0.0005 μ N . The deduced spin expectation value 〈σ〉 of 1.44 is unusually larger than any other ones of even-odd nuclei.

Probing effect of tensor interactions in 16O via (p, d) reaction

Abstract We have measured the 16O(p, d) reaction using 198-, 295- and 392-MeV proton beams to search for a direct evidence on an effect of the tensor interactions in light nucleus. Differential cross sections of the one-neutron transfer reaction populating the ground states and several low-lying excited states in 15O were measured. Comparing the ratios of the cross sections for each excited state to the one for the ground state over a wide range of momentum transfer, we found a marked enhancement of the ratio for the positive-parity state(s). The observation is consistent with large components of high-momentum neutrons in the initial ground-state configurations due to the tensor interactions.

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.

QUADRUPOLE MOMENT OF THE PROTON DRIP-LINE NUCLIDE 13O

Abstract The quadrupole moment of the proton drip-line nuclide 13O(Iπ=3/2−,T=3/2,T1/2=8.6 ms) has been determined for the first time by detecting its β-NQR signal following the production of polarized 13O through the projectile fragmentation process in the 16O + Be collision. The quadrupole moment has been determined to be |Q(13O)|=11.0±1.3 mb. The present result together with the quadrupole moment of its mirror partner 13B is compared with the theoretical values obtained by the shell model code, OXBASH, and by the Hartree-Fock calculation with its single proton separation energy taken into account.

Lattice locations of 8Li in Cu

The dipolar broadening of the NMR on short-lived β-emitter 8Li implanted in single crystal Cu has been observed as a function of crystal orientation at several temperatures. From the orientation angle dependence of the line width, it was found that the main component of the 8Li occupies substitutional site, while about 30% of 8Li occupies octahedral interstitial site at temperatures below 300 K.

Proton Irradiation Experiment for X-ray Charge-Coupled Devices of the Monitor of All-Sky X-ray Image Mission Onboard the International Space Station: II. Degradation of Dark Current and Identification of Electron Trap Level

We have investigated the radiation damage effects on a charge-coupled device (CCD) to be used for the Japanese X-ray mission, the monitor of all-sky X-ray image (MAXI), onboard the international space station (ISS). A temperature dependence of the dark current as a function of incremental dose is studied. We found that the protons having energy of >292 keV seriously increased the dark current of the devices. In order to improve the radiation tolerance of the devices, we have developed various device architectures to minimize the radiation damage in orbit. Among them, nitride oxide enables us to reduce the dark current significantly and therefore we adopted nitride oxide for the flight devices. We also compared the dark current of a device in operation and that out of operation during the proton irradiation. The dark current of the device in operation became twofold that out of operation, and we thus determined that devices would be turned off during the passage of the radiation belt. The temperature dependence of the dark current enables us to determine the electron trap level that generates the dark current. We fitted dark current as a function of temperature by the thoretical models and found that the dark current increase after proton irradiations is caused by, at least, two kinds of electron trap levels. The shallow trap level (Ec-Et 210 K. On the other hand, another trap level is located roughly at the center of the silicon bandgap which might be associated with divacancies or P–V traps. We finally investigated the spatial distribution of the low-energy protons in the orbit of the ISS. Their density has a peak around l ~20° and b ~-55° independent of the altitude. The peak value is roughly two orders of magnitude higher than that at the South Atlantic Anomaly.

Hyperfine interaction of13O and23Mg implanted in Pt

The spin relaxation timeT1 for short-lived beta emitters13O and23Mg implanted in Pt have been measured for the first time;T1T13O) = 2.90 ±0.65 Ks andT1T(23Mg) = 1665 ±140 Ks. The Knight shift for13O in Pt was measured at 300 K to beK(13O) = +(4.23 ±0.14) × 10−3. In the case of13O, the Knight shift is unusually large and the relaxation time is unusually fast compared with other interstitial impurities in Pt. A KKR band-structure calculation reproduces the present large Knight shift fairly well.

Quadrupole moments of neutron-deficient 20,21Na

Abstract The electric-quadrupole coupling constant of the ground states of the proton drip line nucleus 20Na ( I π = 2 + , T 1 / 2 = 447.9 ms ) and the neutron-deficient nucleus 21Na ( I π = 3 / 2 + , T 1 / 2 = 22.49 s ) in a hexagonal ZnO single crystal were precisely measured to be | e q Q / h | = 690 ± 12 kHz and 939 ± 14 kHz , respectively, using the multi-frequency β-ray detecting nuclear magnetic resonance technique under presence of an electric-quadrupole interaction. An electric-quadrupole coupling constant of 27Na in the ZnO crystal was also measured to be | e q Q / h | = 48.4 ± 3.8 kHz . The electric-quadrupole moments were extracted as | Q ( Na 20 ) | = 10.3 ± 0.8 e fm 2 and | Q ( Na 21 ) | = 14.0 ± 1.1 e fm 2 , using the electric-coupling constant of 27Na and the known quadrupole moment of this nucleus as references. The present results are well explained by shell-model calculations in the full sd-shell model space.

A Possible Nuclear Spin Dewar. Hyperfine Interactions of Short-Lived β Emitter 8Li and 12B in TiO2

It was confirmed by detecting the β-NMR of 12B (Iπ=1+, T1/2=20.2 ms) in a TiO2 (rutile) crystal that the nuclear spin polarization of 12B was totally maintained in the crystal as produced through a nuclear reaction before implantation. Two locations, site 1 and site 2, were found with the relative populations 9 and 1, respectively, and the electric field gradients (EFGs) at those sites were obtained to be q(site 1)=+(37.1±0.5)1015 V/cm2, η(site 1)<0.03, q(site 2)=+(185±5)1015 V/cm2 and η(site 2)=0.62±0.02. We also found that about 30% of the initial polarization of 8Li (Iπ=2+, T1/2=838 ms) was maintained in the crystal. Since the polarizations of other β emitting nuclei, 12,16N, 13,19O, and 41Sc were also totally maintained in the crystal, the crystal can be a “Spin Dewar” in which many short-lived nuclides can be implanted with their polarizations totally maintained during their lifetimes for the studies not only on the electronic structure of impurities in it but also on the nuclear properties.