Session FA: Frontiers of Gamma-Ray Spectroscopy

New Results from GRETINA at NSCL

The Gamma-Ray Energy TRAcking In-beam Nuclear Array GRETINA was installed in front of the S800 Magnetic Spectrograph for an in-flight gamma-ray spectroscopy campaign with fast beams of rare isotopes. In this type of experiments, rare-isotopes beams provided by the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory (NSLC) at Michigan State University are delivered onto a reaction target placed at the center of GRETINA. Reaction residues are detected in the spectrograph in coincidence with gamma rays in GRETINA. The high spatial resolution of GRETINA allows to perform accurate Doppler-shift reconstruction of the gamma-ray energies emitted by the reaction residues moving at velocities typically exceeding 30\% of the speed of light. GRETINA's tracking capability enables to acquire gamma-ray data of high spectral quality. During this one-year campaign, 24 experiments were performed using this powerful setup, covering topics in nuclear structure and nuclear astrophysics. This presentation will summarize the latest status of the physics' results obtained from this fruitful campaign.   

In beam gamma-ray spectroscopy of fast exotic beams at the RIBF

At the Radioactive Isotope Beam Factory stable primary beams are accelerated up to 345 MeV/nucleon and incident on a production target to produce secondary beam cocktails with the fragment separator BigRIPS ranging from the lightest nuclei up to the uranium region. For in-beam gamma-ray spectroscopy, the secondary beams impinge on a reaction target at energies between 100 and 300 MeV/nucleon. Reaction residues are detected with the ZeroDegree spectrometer and gamma-rays detected with the NaI(Tl) based DALI2 array. In my presentation I will give an overview of recent experiments performed at the RIBF employing this technique including the measurements inside and beyond the ``Island of Inversion'' as well as investigations around the doubly-magic nuclei 100Sn, 78Ni and 132Sn. Besides discussing selected results a description of the setup and an overview of in-beam gamma-ray spectroscopy physics program at the RIBF will given.   

Preliminary results from GRETINA at ATLAS

After a successful experimental campaign at the NSCL, the gamma-ray tracking array, GRETINA, has been relocated to the ATLAS facility at Argonne National Laboratory. During the fall of 2013, the detectors were installed on one of the two beam lines in area IV of the facility, where it shares the experimental hall with Gammasphere. In contrast to the NSCL campaign, where experiments were performed with fast beams, the GRETINA program at ATLAS utilizes low-energy accelerated beams with energies close to the Coulomb barrier. The experimental campaign is now underway. Experiments are utilizing stable beams as well as re-accelerated radioactive beams from CARIBU. Several of these experiments have been performed with CHICO II, a 4pi array of PPAC detectors, which surrounds the target and is utilized for multi-step Coulomb excitation measurements. In this talk, I will present preliminary results from some of the measurements performed with GRETINA at ATLAS and outline the experimental program going forward.   

Highlights of EURICA decay spectroscopy at RIBF

Gamma-ray spectroscopy following the $\beta $ decay is an effective tool for probing low-lying yrast and non-yrast states, from which key information on nuclear structure, such as shape transitions/coexistence and single-particle orbits, can be obtained. For the study of rare isotopes, especially when the nucleus of interest lies at the boundaries of availability for spectroscopic studies, isomeric decays are likely to be a more useful means than $\beta $ decays to populate excited levels. The combined $\beta $-$\gamma $ and isomeric-decay measurements at RIBF, which has the capability of providing the world's strongest RI beams, are at the forefront of exploration of exotic nuclei far from stability. Research opportunities for decay spectroscopy at RIBF can be expanded in the EURICA (\underline {EU}ROBALL-\underline {RI}KEN \underline {C}luster \underline {A}rray) project. The main body of EURICA consists of 12 Cluster-type HPGe detectors, surrounding a highly segmented silicon stopper system named WAS3ABi. In addition to the normal EURICA setup, 18 LaBr$_{\mathrm{3}}$ detectors and plastic scintillators are installed for the fast-timing measurement of $\gamma $ and $\beta $ rays, respectively. The aim of EURICA is to pin down currently controversial subjects in nuclear physics and nuclear astrophysics, such as the evolution of shell structures that can lead to the appearance or disappearance of the \textit{spherical} magic numbers, the effect of weak binding and pairing in largely diffused neutron densities, search for stable oblate, triaxial, and higher-order deformations at low excitation energy, and the decay properties of neutron-rich isotopes relevant to the r-process nucleosynthesis. A wide range of unstable nuclei on the Segre chart are within the scope of EURICA. In this presentation, the results of the EURICA experimental campaigns in 2012-2013 will be introduced, highlighting $\gamma $-ray spectroscopy of exotic nuclei in the vicinity of doubly magic $^{\mathrm{78}}$Ni and $^{\mathrm{100,132}}$Sn, and neutron-rich mid-shell $^{\mathrm{110}}$Zr and Z $\approx $ 60.