T. Zheng

Production and decay properties of 272111 and its daughter nuclei

The production and decay of 272 111 has been investigated using a gas-filled recoil ion separator in irradiations of 209 Bi targets with 64 Ni beam at 320, 323 and 326 MeV. We have observed 14 α-decay chains in total, that can be assigned, on the basis of their time correlations, to subsequent decays from 272 111 produced in the 209 Bi( 64 Ni,1n) reaction. The present result is the first clear confirmation for the discovery of 272 111 and its α-decay products, 264 Bh and 268 Mt, reported previously by a GSI group. New information on their half-lives and decay energies as well as the excitation function is presented.

Systematic studies of scintillation detector with timing resolution of 10 ps for heavy ion beam

Abstract We have tested Time-Of-Flight detectors consisting of several combinations of scintillators and photomultiplier tubes for the identification of produced heavy ion beam. Timing resolution of 6.8 ps (RMS) is achieved with energy deposited of 150– 160 MeV in the plastic scintillator, where 40 Ar beam is used as a primary beam at the total energies of 3.8 GeV . Our systematic studies suggest the importance of maximizing the number of photoelectrons, where the timing resolution seems to be scaled by the pulse height according to the characteristic function of the photomultiplier tube. In addition, scintillator with faster timing property seems to be also essential for better timing resolution.

Study of the halo nucleus 6He through the direct nuclear reactions

Differential cross sections for quasi-elastic scattering, breakup reaction as well as 1n- and 2n-transfer reactions induced by 6He at 25 MeV/nucleon from a 9Be target are reported. The experimental data were analysed in the context of the coupled-channel calculations. The internal structure of 6He is discussed and further studies are proposed.

Efficiency calibration of a large-area neutron detector by using Am/Be neutron source

Neutron detection efficiency for a long wedge-shaped plastic scintillation detector was measured by using the Am/Be neutron source. The overall efficiency attains 23% at around 2 MeV and decreases to 15% at about 5 MeV. The experimental results are in agreement with the Monte Carlo simulation calculations.

Production and decay properties of

The production and decay of 272 111 has been investigated using a gas-filled recoil ion separator in irradiations of 209 Bi targets with 64 Ni beam at 320, 323 and 326 MeV. We have observed 14 α-decay chains in total, that can be assigned, on the basis of their time correlations, to subsequent decays from 272 111 produced in the 209 Bi( 64 Ni,1n) reaction. The present result is the first clear confirmation for the discovery of 272 111 and its α-decay products, 264 Bh and 268 Mt, reported previously by a GSI group. New information on their half-lives and decay energies as well as the excitation function is presented.

^{272}

Abstract One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at E decay = 50 ± 3 keV , corresponding to an excited state in 23O at 2.78 ± 0.11 MeV , as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d-wave neutron knockout, providing support for a J π assignment of 5 / 2 + . The associated spectroscopic factor was deduced to be C 2 S ( 0 d 5 / 2 ) = 4.1 ± 0.4 by comparing the measured cross section ( σ − 1 n exp = 61 ± 6 mb ) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0 d 5 / 2 orbital is in line with the N = 16 shell closure in 24O.

111 and its daughter nuclei

Measurement of one-, two- and three-neutron removal cross sections of 17C at 79 A MeV on a 12C target has been carried out using the fragment separator RIPS of RIKEN. The one-neutron removal cross sections were compared with the few-body Glauber calculations coupled with the spectroscopic factors from the shell model. A fair agreement between the calculation and the experimental data was found. The prediction of the relation between the reaction cross sections and one-neutron removal cross section can be well satisfied, which means that 17C could be described by a core plus valence neutron system. The two- and three-neutron removal cross sections of 17C are reported for the first time.

Neutron occupancy of the 0d5/2 orbital and the N = 16 shell closure in 24O

A gas-filled type of recoil separator for heavy element research was installed at an experimental hall of RIKEN Linear Accelerator facility to realize getting higher intensity of primary beam and long beam time. Performance of the separator was studied using target recoils and various nuclear reactions. The results show the high performance of the separator for heave element research. As an application of the GARIS, production and identification of an isotope of the 110th element 271[110] have been performed using the 208Pb(64Ni,1n)271[110] reaction. Three decay chains coincide well both in decay times and energies with the ones reported by the group of SHIP experiment at GSI, Germany. Our results provide a confirmation of the synthesis of an isotope 271[110] of element 110.

Neutron removal reactions of 17C

A knockout reaction experiment was carried out using a 6He beam at 82.3 MeV/u impinged on carbon and hydrogen targets. The recoil protons were detected in coincidence with the forward moving charged fragments and neutrons. It is demonstrated that through the correlation between the recoil protons and forward moving charged fragments, the core fragment knockout and valence nucleon knockout reaction mechanisms can be discriminated at energies around 100 MeV/u. The 5He ground-state resonance was reconstructed based on the selection of the valence nucleon knockout mechanism. The resonance parameters were obtained for both carbon and hydrogen targets, which are consistent with those previously reported in the literature. The importance of selecting appropriate reaction mechanisms is discussed based on reconstructions using events with larger transverse momentum transfer.

Status of heavy element research using a gas-filled recoil separator at RIKEN

Knockout reaction experiment for 8He at 82.3 MeV/u on Hydrogen target was carried out at the RIPS beam line in RIKEN. Recoil protons were detected in coincidence with the forward moving core fragments and neutrons. The quasi-free knockout mechanism is identified through the polar angle correlation and checked by various kinematics conditions. The absolute differential cross sections for 6He core cluster are obtained and compared with the simple Glauber model calculations. The extracted spectroscopic factor is close to unity and a shrinking of the cluster size is evidenced.