K. Yue

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.

First Nuclear Reaction Experiment with Stored Radioactive 56Ni Beam and Internal Hydrogen and Helium Targets

The investigation of light-ion induced direct reactions using stored and cooled radioactive beams, interacting with internal targets of storage rings, can lead to substantial advantages over external target experiments, in particular for direct reaction experiments in inverse kinematics at very low momentum transfer, q. This new and challenging experimental technique enables high-resolution measurements down to very low q and provides a gain in luminosity from accumulation and recirculation of the stored beams. For performing first experiments of this kind a dedicated experimental setup housing several DSSD (Double-sided Silicon Strip Detector) and Si(Li) detectors for recoil particles, well suited for meeting the demanding UHV (Ultra High Vacuum) conditions of a storage ring, was recently designed, constructed and installed at the internal target of the ESR storage ring at GSI. From the interaction of a stored 56Ni beam with an internal H2 target, good quality differential cross section data for elastic proton scattering, measured with the aim to determine the radial shape of the nuclear matter distribution of 56Ni, were obtained. Preliminary results are presented. Being the first reaction experiment ever performed with a stored radioactive beam on a world-wide scale, this experiment can be considered as a breakthrough for nuclear structure and astrophysics studies, and, in addition, as a successful proof-of-principle of the new experimental concept. In addition, preliminary results from a feasibility study on inelastic α-scattering from 58Ni in inverse kinematics, where it was demonstrated that the Isoscalar Giant Monopole Resonance in 58Ni can be investigated by the present technique down to CM angles below 1 degree, are discussed. Such an experiment, performed in the future with the doubly magic 56Ni, would provide important information on the EOS of nuclear matter.

A large area plastic scintillation detector with 4-corner-readout

A 760 mm × 760 mm × 30 mm plastic scintillation detector viewed by photomultiplier tubes(PMTs)from four corners has been developed, and the detector has been tested with cosmic rays and γ rays. A positionindependent effective time Teff has been found, indicating this detector can be used as a TOF detector. The hit position can also be reconstructed by the time from the four corners. A TOF resolution of 236 ps and a position resolution of 48 mm have been achieved, and the detection efficiency has also been investigated.A 760 mm × 760 mm × 30 mm plastic scintillation detector viewed by photomultiplier tubes(PMTs)from four corners has been developed, and the detector has been tested with cosmic rays and γ rays. A positionindependent effective time Teff has been found, indicating this detector can be used as a TOF detector. The hit position can also be reconstructed by the time from the four corners. A TOF resolution of 236 ps and a position resolution of 48 mm have been achieved, and the detection efficiency has also been investigated.

Status of the analysis of the first EXL experiment at the ESR

M. von Schmid †1, J.C. Zamora1, S. Bagchi 2, S. B̈onig1, M. Csatĺos3, I. Dillmann4, C. Dimopoulou4, P. Egelhof 4, V. Eremin5, T. Furuno6, H. Geissel 4, R. Gernḧauser7, M.N. Harakeh2, A-L. Hartig1, S. Ilieva1, N. Kalantar-Nayestanaki 2, O. Kiselev4, H. Kollmus4, C. Kozhuharov 4, A. Krasznahorkay 3, T. Kröll1, M. Kuilman2, S. Litvinov4, Yu.A. Litvinov4, M. Mahjour-Shafiei 2,8, M. Mutterer4, D. Nagae9, M.A. Najafi2, C. Nociforo4, F. Nolden4, U. Popp4, C. Rigollet2, S. Roy2, C. Scheidenberger 4, M. Steck4, B. Streicher 2,4, L. Stuhl 3, M. Tḧurauf1, T. Uesaka10, H. Weick4, J.S. Winfield4, D. Winters4, P.J. Woods 11, T. Yamaguchi 12, K. Yue1,4,13, J. Zenihiro10 for the EXL collaboration‡1 1IKP, TU Darmstadt;2Univ. of Groningen, KVI-CART, Groningen; 3MTA-Atomki, Debrecen;4GSI, Darmstadt; 5PTI, St. Petersburg; 6Kyoto University; 7TU München; 8University of Tehran;9University of Tsukuba; 10RIKEN, Tokio; 11University of Edinburgh;12Saitama University;13IMP, Lanzhou

Experimental study of the {beta}-delayed neutron decay of {sup 21}N

The first spectroscopic study for the beta decay of N-21 is carried out based on beta-n, beta-gamma, and beta-n-gamma coincidence measurements. The neutron-rich N-21 nuclei are produced by the fragmentation of the E/A=68.8 MeV Mg-26 primary beam on a thick Be-9 target and are implanted into a thin plastic scintillator that also plays the role of beta detector. The time of flight of the emitted neutrons following the beta decay are measured by the surrounding neutron sphere and neutron wall arrays. In addition, four clover germanium detectors are used to detect the beta-delayed gamma rays. Thirteen new beta-delayed neutron groups are observed with a total branching ratio of 90.5 +/- 4.2%. The half-life for the beta decay of N-21 is determined to be 82.9 +/- 7.5 ms. The level scheme of O-21 is deduced up to about 9 MeV excitation energy. The experimental results for the beta decay of N-21 are compared to the shell-model calculations.