Gammasphere and its recent science highlights I-Yang Lee Lawrence Berkeley National Laboratory Outline Success of Gammasphere Science highlights High-spin studies Weak branching Auxiliary detectors Outlook of gamma-ray spectroscopy 7/27/2016 NS 2016 2 Success of Gammasphere
Continue to produce excellent science for 20 years New science ideas Sufficient beam time Dedicated management staff Maintenance and upgrades New auxiliary detectors Community involvement 7/27/2016 NS 2016 3 Gammasphere beam time at ATLAS 7/27/2016
Average = 72 days (1700 hr.) per year, 1/3 ATLAS time March 2014 June 2015 operating GRETINA 2016 as of June 30. NS 2016 4 Upgrade: Digital Gammasphere Same modules as GRETINA Digitizer module (LBNL) 10 channel 14 bit, 100MHz Energy
Leading edge timing Constant fraction timing Pulse shape 7/27/2016 Trigger, timing, and control module (ANL) NS 2016 1 master, 1 router / 8 digitizer Sync all clocks Fast multiplicity trigger 300 ns Slow trigger 2 msec Multiplicity, energy, hit pattern
5 Digital Gammasphere performance Increase counting rate from 10,000/s to 40,000/ s due to shorter shaping time Increase trigger rate due to shorter dead time: Singles rate from 40,000 to 500,000 /s g-g-g-g-gg-g-g-g-gg-g-g rate from 15,000 to 120,000 /s Improve reliability and serviceability same modern technology as GRETINA, share resources 7/27/2016 NS 2016
6 Science from Gammasphere Continue to produce excellent science for 20 years >80 Publications in 2011 2015, covering: Triaxial super deformed states High-K isomers Coulomb excitation of isomer Wobbling mode and Chiral doublet Octupole structure Neutron-rich nuclei studies from deep-inelastic reactions Band termination High-spin structure of sd shell nuclei 7/27/2016 NS 2016 7 Evolution
of structure a function of Along the Yrast Line 158Eras circa mid 90s 158 After another exptspin: at Daresbury Erwith EUROGAM 1 What happen above band termination, I>49 ? ? 7/27/2016 NS 2016 8
Collaborators on a 157, 158Er experiment in mid 2000s University of Liverpool A. Evans, E.S. Paul, P.J. Nolan, P.T.W Choy Daresbury Laboratory J. Simpson, D.E. Appelbe, D.T. Joss Florida State University A. Pipidis, M.A. Riley, D.B. Campbell LBNL P.Fallon, D.Ward, A.O.Macchiavelli, R.M.Clark, M.Cromaz, A.Grgen, I.Y. Lee Lund Institute of Technology I. Ragnarsson, F. Saric 7/27/2016 NS 2016 9 157, 158 Er experiment Gammasphere with 102 Ge detectors. A 215-MeV 48Ca beam from the 88 Inch
Cyclotron Two foils of 114Cd, of total thickness 1.1 mg/cm2. A total of 1.2 109 events, seven Comptonsuppressed Ge reconstructed into 6.5 1010 quadruples coincidence events 7/27/2016 NS 2016 10 Highly deformed triaxial bands Two highly 7/27/2016
NS 2016 deformed bands each in 157, 158 Er beyond termination 50-100 weaker than SD bands! 11 Along the Yrast Line 158Er 7/27/2016 NS 2016 12
Selected as the first ever Editors Suggestion in nuclear physi 7/27/2016 NS 2016 13 Measure of collectivity : DSAM experiment 215 MeV 48Ca beam from ATLAS 1 mg/cm2 114Cd target backed by a 13 mg/cm2 Au layer. 7/27/2016
NS 2016 14 158 Er TSD bands Qt values CNS calculations 158 Er (Wang et al., Phys. Lett. B 702, 127, 2011) B.G. Carlsson, I. Ragnarsson, PRC 74 (2006) 011302(R) Qt values too large for TSD1, But closer to TSD2 and TSD3
A.V. Afanasjev et al., PRC 86(2012) 031304R TSD3 (6271) has the right Qt But much higher spin. 7/27/2016 NS 2016 15 Evolution of Gamma-Ray Spectroscopy and 158Er (NRC/Nat. Acad. Sci. Decadal Report June 2012, p 49 Nuclear Physics: The Heart of Matter) 7/27/2016 NS 2016 16
Very weak branch: E5 decay in 137Ba M4 7/27/2016 E5, 378 keV NS 2016 19 Ci Ci 137Cs source Gammasphere, - 93 detectors at ANL Two fold coincidence
2nd order 2-photon decay E5 branch 17 The Compton problem 662 keV scattering 7/27/2016 NS 2016 18 Compton scattering Energy difference vs. two detector opening angle 53 - 130 Eg-g-g
Eg-g-g ' Eg-g-g 1 -g-g cos C 1 511 E Eg-g-g -g-g 2 Eg-g-g ' 12 2 C -g-g 180 7/27/2016 NS 2016 19 Energy difference spectrum E1 + E2 = 662 keV (378 - 284) = 94 keV 7/27/2016
NS 2016 Total peak counts: 526 20 Bottom Line E5 gamma branching ratio = 5.7 0.7 10-8; Weakest branch observed with Gammasphere so far. Transition strength, B(E5) = 0.34 0.04 W. u.,means transition has low collectivity and value is similar to other single particle 11/2- to 1/2+ transitions Second order two-Photon Decay: Original motivation for the experiment This cascade does not affect double photon
branch(10-6 vs. 10-8) 7/27/2016 NS 2016 21 The power of auxiliary Detectors FMA, Hercules evaporation residual Neutron shell - neutron 7/27/2016 Si-box + wall, ARRUBA charged particle Phoswichcharged particle NS 2016
MicroballCharged particle CHICO Heavy particle 22 Hercules and Gammasphere A high-efficiency evaporation-residue counter 64 thin fast-plastic scintillators 4 rings at 23 cm Cover angles 727 Rate/counter = 0.5 MHz Use time-of-flight to reject beam and fission products W. Reviol et al., Nucl. Instr. and Meth. A 541 (2005) 478. 7/27/2016 NS 2016
23 Hercules Mg + 198Pt 26 E =128 MeV Ekin(ER) 11 MeV ToF-ray gating PH residue gating (Hercules) e = 59(4) % Residue and -ray gating ray gating (Gammasphere) Gate: 513 keV 7/27/2016
NS 2016 24 Example of Hercules experiment 7/27/2016 Pb(18O,4n)221Th, E = 96 MeV from ATLAS Hercules + 98 Gammasphere modules ToF (ER)= 91 126 nsec 207 NS 2016 25 Simplex doublet
yrast S=-ray gating i S = P exp(i I) non-yrast S=+i Pb (18O,4n) 221Th 207 non-yrast S=-ray gating i E.g. 13/2+ vs. 13/2-ray gating Erel=250 keV Previous work: Dahlinger et al. NPA 484 (1988) 7/27/2016
Intensity difference: about factor of 5 NS 2016 Reviol et al., PRC 90, 044318 (2014) 26 Degeneracy plot: Erel= E(I, s=+i) - E(I, s=-i) yrast -ray gating non-ray gating yrast Th: parity doublet of two non-yrast structures 221 7/27/2016 NS 2016 27
Spin behavior Use the = sequence in even-A as reference: Th yrast band is as collective as 222-224 Th rotational 221 Th non-yrast band is less collective as 220Th phonon tidal wave 221 7/27/2016 NS 2016 28 Single particle structure 219
223 Th133 (i11/2)2(g9/2)5 K=5/2 Grodzins estimate for 221Th: 2=.11 7/27/2016 Related paper: Cwiok & Nazarewicz, NPA 529 (1991) NS 2016 29 Outlook of gamma-ray spectroscopy Gamma-ray spectroscopy, due to its excellent energy
resolution, will continue to be a unique tool in the experimental studies of the nuclear structure as we push the limits of mass (A), proton number (Z), neutron number(N), spin (I), and excitation energy (E*) Several large arrays will be needed in various facilities Plans to complete the 4p tracking arrays GRETA, AGATA. Continue the productive use of Compton suppressed arrays Gammasphere, Clover arrays etc. Start R&D for new ideas beyond tracking detector. 7/27/2016 NS 2016 30 2015 US Long Range Plan
7/27/2016 GRETA white paper http://greta.lbl.gov/ NS 2016 DOE announced CD0 in October 2015 31 GRETA: funding profile and schedule GRETA CD0 GRETA CD1 GRETA
CD2A/3A GRETA CD4 GRETA CD2B/3B Project Cost ($k) 2 2015 1 Total cost $52 M 1
FRIB Full Power 2025 NSCL FRIB CD4 2022 ANL FRIB Early Completion 2020 2025 32 g-g-g-ray array development ?
The resolving power is a measure of the ability to observe weak transitions. It is a function of efficiency, energy resolution, and P/T . 7/27/2016 NS 2016 33 Beyond tracking array Some possible directions Higher efficiency, P/T, and compactness Better energy resolution
Better time resolution High-Z materials (e.g., a shell of 1.6 cm W = 9 cm of Ge) Cryogenic bolometers (eV compared to keV for Ge) Faster scintillation detector and electronics. Sub-pico second time resolution will allow 7/27/2016 Lifetime measurements Decay sequence determination event-by-event Determine scattering sequence for gamma-ray tracking (1mm = 3 ps) NS 2016
34 Acknowledgements LAWRENCE BERKELEY NATIONAL LABORATORY A.O. Macchiavelli, C.M. Campbell, H. Crawford, M. Cromaz, R.M. Clark, P. Fallon ARGONNE NATIONAL LABORATORY Shaofei Zhu, M. Carpenter , R. Janssens, T. Lauritsen, D. Seweryniak FLORIDA STATE UNIVERSITY M. Riley et al. UNIVERSITY OF MASSACHUSETTS, LOWELL C. J. Lister et al. WASHINGTON UNIVERSITY, ST. LOUIS W. Reviol et al. Work supported under contract number DE-AC02-05CH11231 7/27/2016 NS 2016
Vice-President/Director of Publications Blue Bars Editor History Director of Publications 1962 & 1963 Blue Bars Editor Richard "Dick" Wolf Director of Publications 1964 Blue Bars Editor Norman D. VanderPlaats 1965 Blue Bars Editor Ed Butcher 1965 & 1966 Director of...
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