Zhi-Yu Sun

Neutron-proton asymmetry dependence of spectroscopic factors in Ar isotopes

Spectroscopic factors have been extracted for proton-rich 34Ar and neutron-rich 46Ar using the (p, d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton-rich nucleus 34Ar compared to that of 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements.

Fragmentation cross sections and binding energies of neutron-rich nuclei

An exponential dependence of the fragmentation cross section on the average binding energy is observed and reproduced with a statistical model. The observed functional dependence is robust and allows the extraction of binding energies from measured cross sections. From the systematics of Cu isotope cross sections, the binding energies of {sup 76,77,78,79}Cu have been extracted. They are 636.94{+-}0.4,647.1{+-}0.4,651.6{+-}0.4, and 657.8{+-}0.5 MeV, respectively. Specifically, the uncertainty of the binding energy of {sup 75}Cu is reduced from 980 keV, as listed in the 2003 mass table of Audi, Wapstra, and Thibault to 400 keV. The predicted cross sections of two near drip-line nuclei, {sup 39}Na and {sup 40}Mg from the fragmentation of {sup 48}Ca are discussed.

PRESENT STATUS OF HIRFL IN LANZHOU

HIRFL has been upgraded for basic research on nuclear physics, atomic physics, irradiative material and biology from beginning of this decade. So far, the main performances of HIRFL have improved in the beam species from light ion to uranium and the maximum beam intensities reaching ~10μA from SFC, 1.5 μA from SSC. Therefore, some experiments have been performed during this period, especially, on new isotope synthesis and unstable nuclear physics. The new upgrading project Cooling Storage Ring (CSR) is under commissioning by ~2p μA carbon beam stripping injection. About 109 C ion have stored inside CSRm, and part of them have been cooling down by the electron cooler. The acceleration of CSRm also has been test successful. Some future experiment are under development.

Projectile fragmentation of Kr86 at 64 MeV/nucleon

We measured fragmentation cross sections produced using the primary beam of 86 Kr at 64 MeV/nucleon on 9 Be and 181 Ta targets. The cross sections were obtained by integrating the momentum distributions of isotopes with 25 ≤ Z < 36 measured using the RIPS fragment separator at RIKEN. The cross-section ratios obtained with the 181 Ta and 9 Be targets depend on the fragment masses, contrary to the simple geometrical models. We compared the extracted cross sections to EPAX; an empirical parametrization of fragmentation cross sections. Predictions from current EPAX parametrization severely overestimate the production cross sections of very neutron-rich isotopes. Attempts to obtain another set of EPAX parameters specific to the reaction studied here to extrapolate the neutron-rich nuclei more accurately have not been very successful, suggesting that accurate predictions of production cross sections of nuclei far from the valley of stability require information of nuclear properties that are not present in EPAX.

The plastic scintillator detector for DAMPE

Abstract The DArk Matter Particle Explorer (DAMPE) is a general purpose satellite-borne high energy γ − ray and cosmic ray detector. Among the scientific objectives of DAMPE are the search for the origin of cosmic rays and an understanding of the Dark Matter particles. As one of the four detectors in DAMPE, the Plastic Scintillator Detector (PSD) plays an important role in the particle charge measurement and the photons/electrons discrimination. It can identify the atomic number Z/charge states of relativistic ions from H to Fe and the detection efficiency for Zxa0=xa01 particles can reach 0.9999. The PSD has been working reliably since the successfully launching of DAMPE on December 17, 2015. In this paper, the design, assembly, qualification tests of the PSD and some of the performance measured on the ground are presented in detail.

First application of combined isochronous and Schottky mass spectrometry: Half-lives of fully-ionized49Cr24+ and 53Fe26+ atoms

Lifetime measurements of β-decaying highly charged ions have been performed in the experimental storage ring (CSRe) by applying the isochronous Schottky mass spectrometry. The fully ionized Cr49 and Fe53 ions were produced in projectile fragmentation of Ni58 primary beam and were stored in the CSRe tuned into the isochronous ion-optical mode. The new resonant Schottky detector was applied to monitor the intensities of stored uncooled Cr24+49 and Fe26+53 ions. The extracted half-lives T1/2(Cr24+49)=44.0(27) min and T1/2(Fe26+53)=8.47(19) min are in excellent agreement with the literature half-life values corrected for the disabled electron capture branchings. This is an important proof-of-principle step towards realizing the simultaneous mass and lifetime measurements on exotic nuclei at the future storage ring facilities.

Plastic scintillation detectors for precision Time-of-Flight measurements of relativistic heavy ions

Plastic scintillation detectors for Time-of-Flight (TOF) measurements are almost essential for event-by-event identification of relativistic rare isotopes. In this work, a pair of plastic scintillation detectors of dimensions 50 × 50 × 3t mm3 and 80 × 100 × 3t mm3 have been set up at the External Target Facility (ETF), Institute of Modern Physics (IMP). Their time, energy and position responses are measured with the 18O primary beam at 400 MeV/nucleon. After off-line corrections for walk effect and position, the time resolutions of the two detectors are determined to be 27 ps (σ) and 36 ps (σ), respectively. Both detectors have nearly the same energy resolution of 3.1% (σ) and position resolution of about 3.4 mm (σ). The detectors have been used successfully in nuclear reaction cross section measurements, and will be be employed for upgrading the RIBLL2 beam line at IMP as well as for the high energy branch at HIAF.

Constraints on the density dependence of the symmetry energy

Collisions involving 112Sn and 124Sn nuclei have been calculated with the ImQMD transport model in order to place constraints on the density dependences of the nuclear symmetry energy. Consistent constraints on the symmetry energy at sub-saturation density have been obtained by comparing these transport calculations to measurements of isospin diffusion and to the ratios of neutron and proton spectra. New isospin diffusion results from E/A = 35 MeV are also presented.

Charge measurement of cosmic ray nuclei with the plastic scintillator detector of DAMPE

One of the main purposes of the DArk Matter Particle Explorer (DAMPE) is to measure the cosmic ray nuclei up to several tens of TeV or beyond, whose origin and propagation remains a hot topic in astrophysics. The Plastic Scintillator Detector (PSD) on top of DAMPE is designed to measure the charges of cosmic ray nuclei from H to Fe and serves as a veto detector for discriminating gamma-rays from charged particles. We propose in this paper a charge reconstruction procedure to optimize the PSD performance in charge measurement. Essentials of our approach, including track finding, alignment of PSD, light attenuation correction, quenching and equalization correction are described detailedly in this paper after a brief description of the structure and operational principle of the PSD. Our results show that the PSD works very well and almost all the elements in cosmic rays from H to Fe are clearly identified in the charge spectrum

Temperature dependence of the plastic scintillator detector for DAMPE

The Plastic Scintillator Detector (PSD) is one of the main sub-detectors in the DArk Matter Particle Explorer (DAMPE) project. It will be operated over a large temperature range from −10 to 30 °C, so the temperature effect of the whole detection system should be studied in detail. The temperature dependence of the PSD system is mainly contributed by the three parts: the plastic scintillator bar, the photomultiplier tube (PMT), and the Front End Electronics (FEE). These three parts have been studied in detail and the contribution of each part has been obtained and discussed. The temperature coefficient of the PMT is −0.320(±0.033)%/°C, and the coefficient of the plastic scintillator bar is −0.036(±0.038)%/°C. This result means that after subtracting the FEE pedestal, the variation of the signal amplitude of the PMT-scintillator system due to temperature mainly comes from the PMT, and the plastic scintillator bar is not sensitive to temperature over the operating range. Since the temperature effect cannot be ignored, the temperature dependence of the whole PSD has been also studied and a correction has been made to minimize this effect. The correction result shows that the effect of temperature on the signal amplitude of the PSD system can be suppressed.