H. Miyatake

New aspect of intermediate energy heavy ion reactions. Large spin polarization of fragments

Abstract The spin polarization, P , of 12 B ejectiles has been measured for projectile fragmentation reactions induced by a 40.6 MeV/u 14 N beam. Large values of P were observed, showing a characteristic dependence on the outgoing momentum including a sign change occurring at a momentum corresponding to the beam velocity. This behavior corresponds well with simple kinematical arguments based on projectile fragmentation models.

RIKEN isotope separator on-line GARIS/IGISOL

Abstract This paper describes the fabrication and the characteristics of an isotope separator on-line (ISOL) which was constructed at the RIKEN Ring Cyclotron Facility. The ISOL consists of a gas-filled recoil separator and an ion-guide isotope separator on-line. Because of this combination the ISOL enables us to study short-lived isotopes of almost all elements.

Systematic behavior of ejectile spin polarization in the projectile fragmentation reaction

Abstract Ejectile spin polarization P in intermediate-energy projectile fragmentation has been measured for different targets and incident energies using the RIPS fragment separator at RIKEN. The observed P as a function of the fragment momentum shows a systematic change when the atomic number of the target or the incident energy is varied. Most remarkably, P does not vanish at the momentum corresponding to the beam velocity, indicating an important effect which has not been considered in the previously proposed model.

Measurement of the magnetic moments of 14B and 15B using projectile fragmentation spin polarization

Abstract By making use of the phenomenon of ejectile spin polarization in the projectile fragmentation reaction as a tool to produce polarized radioactive nuclei, the magnetic moments of 14B and 15B have been determined by the β-NMR measurement, to be μ( 14 B ) = (1.185±0.005) μn and μ( 15 B ) = (2.659±0.015) μn where μn is the nuclear magneton. The comparison of the results with shell model calculations suggests that the single-particle energy of the neutron s 1 2 orbit shifts downwards considerably compared with the d 5 2 orbit in 14B, and also indicates the importance of Jπ = 2+ configurations of neutrons in the sd shell. Thus, it is demonstrated that the measurement of magnetic moments provides useful information on the nuclear structure in the newly accessible region of light-mass unstable nuclei.

β-spectroscopy of 11Li and 14Be —With a β-n-γ triple coincidence method

Abstract Experimental studies of β-decay measurements of the neutron drip line nuclei 11Li and 14Be are presented. β-decay schemes of these nuclei are determined by measuring β-rays, delayed neutrons and γ-rays in triple coincidence. The decay schemes of both 11Li and 14Be associated with single neutron emission are unambiguously determined. New levels in their daughter nuclei, 11Be and 14B, are found. In addition, the deduced level scheme of 14B indicates the lowering of 2s 1 2 single neutron orbital with respect to 1p 1 2 orbital in the N=9 isotones. Such behavior is known to exist in N=7.

Design study of the secondary-beam line at RCNP

Abstract A beam line for use with the new RCNP ring cyclotron ( K = 400) has been designed to separate unstable nuclei produced in high energy heavy-ion reactions. The separation principle takes advantage of A - and Z -dependence of the energy loss of ions in matter (energy degrader), and enables us to obtain the reaction products in the form of a secondary beam. Ion-optical consideration has been made for the separator by treating the degrader as one of the ion-optical elements. By this new treatment it has been made possible to optimize the optics of the system according to experimental requirements. The methods (i) to achieve an achromatic focusing of the secondary beams and (ii) to obtain beams with small energy spread are discussed. The effects of energy straggling in the degrader are shown to be the principal factor to limit the isotopic resolution of the separator. Ion-optical calculations have been performed for the secondary-beam line taking into account the transfer matrix elements up to third order. The design specifications are described and the expected profiles of the secondary beams are presented.

New α-decaying neutron deficient isotopes197Rn and200Fr

New neutron-deficient isotopes,197Rn,197mRn, and200Fr have been produced and identified on the basis of genetic correlations in the166Er(36Ar,5n)197Rn (Elab=186, 200 MeV), and169Tm(36Ar,5n)200Fr (Elab=186 MeV) reactions. The evaporation residues were separated from the beam by using a gas-filled recoil separator and implanted onto a position-sensitive solid-state detector. The α-decay energies (half-lives) of197Rn,197mRn and200Fr have been determined to be 7261±30 keV (51−15+35 ms), 7370±30 keV (18−5+9ms), and 7500±3O keV, (570−140+270 ms), respectively.

Polarization in projectile fragmentation andg-factor measurements for neutron-rich nuclei

A method to produce beams of polarized unstable nuclei was developed, which fully exploits the advantageous features of the projectile fragmentation reaction. The method was applied tog-factor measurements of several neutron-rich nuclei. We present experimental results so far obtained and discuss capabilities and limitations the present polarization method has.

High resolution study of24Mg(p, d)23Mg for the Ne-E problem

Nuclear levels of23Mg near and above the proton threshold were investigated with high resolution. A new level has been identified at 7.643 MeV (66 keV above the proton threshold) with a possible Jπ=(3/2, 5/2)+. Some other spin-parity and excitation-energy assignments are also made. These results enable the reaction rate estimate of22Na(p,γ)23Mg with much smaller uncertainties, which is critical for the Ne-E problem in nuclear astrophysics.

Level structure of 21Mg and the 20Na(p, γ)21Mg stellar reaction rate

Abstract The nuclear level structure of 21Mg has been studied by the 24Mg(3He, 6He)21Mg reaction at 74 MeV. Angular distributions of the three-nucleon transfer reaction (3He, 6He) are measured for the first time, and successfully analyzed with exact finite-range distorted-wave-Born-approximation calculations, giving clear transferred angular momentum assignments. More than 20 states have been identified with excitation energy and spin-parity determinations, including a possible s-wave resonance just above the proton threshold. One of the s-wave resonances assumed in the previous stellar reaction rate estimates is found to be a bound state. The stellar reaction rate of the 20Na(p, γ)21Mg process is estimated using the experimental data. The results predict the ignition of the proton radiative-capture process at T = 1×108K under typical nova conditions (hydrogen density, XHϱ = 5×105 g/cm3). This temperature happens to be in agreement with the previous theoretical estimates, but the new reaction rate is a few orders of magnitude smaller than the previous predictions for T ⋍ 2–10×10 8 K . The results also suggest that the nucleosynthesis flow of the rapid-proton process will run up to 21Mg immediately after breakout from the hot-CNO cycle.