Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session C3: Invited Session: Novel Detection in Low-Energy Nuclear Physics |
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Sponsoring Units: DNP Chair: Sean Liddick, Michigan State University Room: Plaza E |
Saturday, April 13, 2013 1:30PM - 2:06PM |
C3.00001: Nuclear Spectroscopy with HELIOS Invited Speaker: Calem Hoffman Direct reaction studies have been instrumental in achieving our current understanding of nuclear structure through the measurement of angular distributions, the extraction of spectroscopic factors, and the determination of single-particle centroids. Traditionally, these experiments were carried out using a beam of light particles impinging on a heavy stable target. Over the last decade this important technique has been used with short-lived radioactive ion beams requiring these types of reactions to be carried out in inverse kinematics. There are numerous challenges to this approach, not least is the typical Q-value resolution being up to an order of magnitude worse than traditional measurements due mainly to the so-called kinematic compression. The Helical Orbit Spectrometer (HELIOS) is a detection system developed for the specific purpose of improving the Q value resolution for inverse direct reaction measurements, while also maintaining flexibility and high efficiency. The novel feature of HELIOS is use of a 3 Tesla solenoid inside which the reactions take place. This allows for light particles of interest to be measured at fixed longitudinal distances from the target as opposed to fixed laboratory angles. The subtle mapping from laboratory angle to longitudinal position removes the aforementioned kinematic compression effect improving the Q-value resolution by as much as a factor of five without out sacrificing detection efficiency. In addition, HELIOS provides a natural way to identify particles of interest, independent of energy, through their measured cyclotron period. The design and implementation of HELIOS at the Argonne Tandem Linear Accelerator System (ATLAS) on the site of Argonne National Laboratory will be presented. The device has been extremely successful as numerous early measurements have been conducted spanning masses $A=11$ to $136$, using varying reactions such as ($d,p$), ($d,^{3}$He), and ($^{6}$LI,$d$), as well as a range of beam energies. Physics highlights from these works will be discussed along with future prospects and developments, including the viability of HELIOS in conjunction with the exotic neutron-rich beams to be provided by the ATLAS Californium Rare Isotope Breeder Upgrade project (CARIBU). [Preview Abstract] |
Saturday, April 13, 2013 2:06PM - 2:42PM |
C3.00002: Active Target-Time Projection Chambers for Reactions Induced by Rare Isotope Beams: Physics and Technology Invited Speaker: Wolfgang Mittig Weakly bound nuclear systems can be considered to represent a good testing-ground of our understanding of non-perturbative quantum systems. Great progress in experimental sensitivity has been attained by increase in rare isotope beam intensities and by the development of new high efficiency detectors. It is now possible to study reactions leading to bound and unbound states in systems with very unbalanced neutron to proton ratios. Application of Active Target-Time Projection Chambers to this domain of physics will be illustrated by experiments performed with existing detectors. The NSCL is developing an Active Target-Time Projection Chamber (AT-TPC) to be used to study reactions induced by rare isotope beams at the National Superconducting Cyclotron Facility (NSCL) and at the future Facility for Rare Isotope Beams (FRIB). The AT-TPC counter gas acts as both a target and detector, allowing investigations of fusion, isobaric analog states, cluster structure of light nuclei and transfer reactions to be conducted without significant loss in resolution due to the thickness of the target. The high efficiency and low threshold of the AT-TPC will allow investigations of fission barriers and giant resonances with fast fragmentation rare isotope beams. This detector type needs typically a large number of electronic channels (order of magnitude 10,000) and a high speed DAQ. A reduced size prototype detector with prototype electronics has been realized and used in several experiments. A short description of other detectors of this type under development will be given. [Preview Abstract] |
Saturday, April 13, 2013 2:42PM - 3:18PM |
C3.00003: First Results from GRETINA at the S800 Spectrometer Invited Speaker: Heather Crawford The next-generation gamma-ray tracking array GRETINA has begun its first physics campaign at the National Superconducting Cyclotron Laboratory (NSCL). GRETINA, a first implementation of the future 4$\pi$ GRETA device, consists of 28 highly segmented Ge detectors, covering 1$\pi$ of the solid angle. The array makes use of the concepts of signal decomposition to localize the interaction of gamma-rays within the detector volumes, and gamma-ray tracking to identify the first hit position within the array. Combined, these techniques provide both an accurate position (within 2mm) for Doppler reconstruction, and rejection of Compton scattering events to reduce background and improve spectral quality. Completed in March 2011, GRETINA was successfully built and commissioned at LBNL, before moving to NSCL in the Spring of 2012. A physics campaign encompassing a wide range of topics in nuclear structure, nuclear reactions and astrophysics is currently underway at NSCL, using GRETINA coupled to the S800 spectrograph. The combination of these powerful devices, a cutting-edge gamma-ray spectrometer and a high-resolution, large acceptance spectrograph, allows spectroscopic studies of the most exotic nuclear systems, moving toward both the proton and neutron driplines. We will report on first results from the campaign of GRETINA at the S800, and present preliminary data from experiments studying nuclei across the chart of the nuclides. [Preview Abstract] |
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