Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session HD: Mini Symposium on GRETINA Results |
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Chair: Alexandra Gade, Michigan State University Room: Grand Ballroom IV |
Friday, October 25, 2013 8:30AM - 9:06AM |
HD.00001: GRETINA: Status and Future Plans Invited Speaker: Augusto O. Macchiavelli GRETINA \footnote {S. Paschalis, I.Y.Lee, et al. NIM A709 (2013) 44-55 } is a first implementation of a gamma-ray spectrometer which is capable of tracking gamma-rays through its active detector volume. This new technology is based on segmenting the outer contact of large-volume HPGe crystals to allow the location of the individual scattering sites in the detector by analyzing both net and induced signals. The characteristics of the Compton and pair-production processes are then used to group and sequence the interactions points and determine the scattering path of the original gamma-rays. This ability to track gamma-rays accurately is crucial in building high-efficiency, closely packed HPGe arrays. GRETINA consists of seven, four-crystal modules (6x6 segments). Each crystal is individually encapsulated with all four crystals sharing a common cryostat. The irregular, tapered hexagonal crystals pack into a spherical shell with the seven modules spanning $1\pi$ solid angle. GRETINA was constructed and commissioned at LBNL and just completed its first physics campaign at NSCL/MSU. In this talk, I will discuss some technical aspects and the performance of the array and present an overview of the experimental program carried out at NSCL. Future plans for GRETINA as well as its evolution into GRETA, a full $4\pi$ coverage array, will also be discussed. [Preview Abstract] |
Friday, October 25, 2013 9:06AM - 9:18AM |
HD.00002: Performance of GRETINA for in-beam spectroscopy at NSCL Dirk Weisshaar, Vincent Bader, Travis Baugher, Daniel Bazin, Jill Berryman, Alexandra Gade, Christoph Langer, Antoine Lemasson, Eric Lunderberg, Shumpei Noji, Francesco Recchia, Ragnar Stroberg, Christopher Walz, Kathrin Wimmer, Chris M. Campbell, Heather L. Crawford, Mario Cromaz, Paul Fallon, I-Yang Lee, Augusto Macchiavelli, Andreas Wiens, Mike P. Carpenter, Shaofei Zhu, David Radford, Mike Scott In early summer 2012, the Gamma-Ray Energy TRAcking In-beam Nuclear Array GRETINA was installed in front of the S800 Magnetic Spectrograph for 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) 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 for accurate Doppler-shift reconstruction, while GRETINA's tracking capability provides gamma-ray data of high spectral quality. The performance of this powerful setup will be summarized. [Preview Abstract] |
Friday, October 25, 2013 9:18AM - 9:30AM |
HD.00003: Precise Measurement of the $2_1^+$ Level Lifetime in $^{12}$Be E.A. McCutchan, A.A. Sonzogni, T.D. Johnson, C.J. Lister, P. Chowdhury, E. Merchan, V.S. Prasher, H. Iwasaki, D. Weisshaar, A. Gade, V.M. Bader, S. Beceiro Novo, C. Loelius, E.M. Lunderberg, C. Morse, F. Recchia, K. Whitmore For many years, it has been suggested that $^{12}$Be exhibits a breakdown of the N=8 shell gap. This reflects the tension between the propensity for alpha-clustering in beryllium, with $^{12}$Be appearing as a 2-alpha dumb bell bound by a cloud of four poorly bound neutrons, and a more conventional Shell Model picture with the N=8 neutrons filling the p-shell and holding the nucleus to a near spherical shape. To provide a better understanding of the extent of the breakdown of the N=8 shell gap, the lifetime of the first $2^+$ state in $^{12}$Be was measured using intermediate-energy inelastic scattering of a $^{12}$Be beam combined with the Doppler Shift attenuation method. Gamma rays emitted at the target position were measured with GRETINA in coincidence with reaction residues detected in the S800 spectrometer at NSCL. Three different targets were measured, allowing for consistency checks and a better understanding of systematic effects. Preliminary results on the B(E2) transition strength from the first $2^+$ state will be presented. [Preview Abstract] |
Friday, October 25, 2013 9:30AM - 9:42AM |
HD.00004: $^{17}$C Lifetime Measurements with the TRIPLEX Plunger and GRETINA Duane Smalley, H. Iwasaki, K. Whitmore, C. Morse, C. Loelius, A. Gade, D. Weisshaar, D. Bazin, C. Langer, F. Recchia, J. Berryman, V. Bader, S.R. Stroberg, C. Campbell, P. Fallon, A. Macchiavelli, K. Wimmer, A. Lemasson, J. Parker As nuclei approach the drip-line exotic features such as deformation and collectivity begin to manifest. Experimental observation of these features provide valuable inputs to test the validity of current theoretical models. Excited state lifetime measurements can be linked directly to the reduced transition probability allowing the inference of structure information. Recent lifetime measurements of the neutron rich $^{17}$C have been performed using the gamma-ray tracking array GRETINA and the newly designed TRIPLEX plunger at the NSCL. The TRIPLEX plunger allows multiple lifetimes, ranging from 1ps to 1ns, to be measured with a single setting. This provides a robust model independent methodology for determining excited state lifetimes through in-beam gamma-ray spectroscopy. Initial results of the lifetime measurements and the data analysis will be presented. [Preview Abstract] |
Friday, October 25, 2013 9:42AM - 9:54AM |
HD.00005: Lifetime Measurement of Low-lying States in $^{19}$C Kenneth Whitmore, Hironori Iwasaki, Duane Smalley, Chris Morse, Charles Loelius, Vincent Bader, Daniel Bazin, Jill Berryman, Alexandra Gade, Christoph Langer, Francesco Recchia, Ragnar Stroberg, Dirk Weisshaar, Antoine Lemasson, Chris Campbell, Paul Fallon, I-Yang Lee, Augusto Macchiavelli, Kathrin Wimmer, John Parker Halo nuclei are unique phenomena occurring along the neutron dripline in which the wave function of the valence neutron extends far beyond the nuclear core. $^{19}$C is known to be a one-neutron halo with a ground-state spin and parity of 1/2$^{+}$. Previous experiments have observed two gamma transitions at 197 keV and 72 keV, suggesting two excited states below the neutron separation energy of 580(90) keV. However, lifetime information is missing, and a level scheme has not been firmly established. A more recent experiment has called into question the bound nature of the second excited state. Lifetimes of the excited states of $^{19}$C have been measured at the NSCL using the lineshape technique. Gamma rays emitted in-flight were detected by GRETINA in coincidence with particles in the S800 spectrometer. Results on the lifetime of the 197 keV transition as well as evidence for the 72 keV transition will be discussed. [Preview Abstract] |
Friday, October 25, 2013 9:54AM - 10:06AM |
HD.00006: Detection of High-Energy Gamma Rays with GRETINA Edana Merchan, Mario Cromaz, C.M. Campbell, Heather Crawford, Torben Lauritsen, Amel Korichi Recent experiments performed with the new tracking device GRETINA has given valuable insight on the properties of nuclei over a wide area of the nuclear chart. This new type of array has the ability of measure high gamma multiplicity reactions, fast-moving ions emissions and high energy gamma events, the later one is the problem addressed here. It is well known that the pair production cross section become important for gamma rays with energies of several MeV as the photo-electric cross section decreases. Identifying events that undergo pair production and reconstruct their full energy is one of the goals of the tracking algorithm used in the data analysis. The selection of pair production events is realized by considering the positions and relative distance of the interaction points within the detector. A study using GEANT4 simulations has been carried out to improve the pair-production selection efficiency in the tracking algorithm. The new analysis algorithm is being tested with a data set of $^{24}$Mg(p,n)$^{24}$Al, which decays back to $^{24}$Mg via $\beta$ decay, collected with the GRETINA array at LBNL, where $\gamma$-rays of more than 7~MeV in the $^{24}$Mg de-excitation process have been detected. [Preview Abstract] |
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