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The DESPEC Fast-Timing Project at FAIR: Sub-nanosecond Nuclear Timing Spectroscopy with LaBr 3...
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Transcript of The DESPEC Fast-Timing Project at FAIR: Sub-nanosecond Nuclear Timing Spectroscopy with LaBr 3...
The DESPEC Fast-Timing Project at FAIR: Sub-nanosecond Nuclear Timing
Spectroscopy with LaBr3 Scintillators
Paddy ReganDepartment of Physics
University of SurreyGuildford, UK
Email: [email protected]
Talk Outline
• Nuclear structure physics research circa 2011.– The production and study of nuclei ‘far from stability’.
• Some (recent) history.– The (Stopped) RISING Collaboration at GSI.– Some physics from nuclear (isomer) decay spectroscopy
• The future.– DESPEC collaboration, with NuSTAR @ FAIR.
• The present Pre-DESPEC tests and some physics– Results of some LaBr3(Ce) detector array physics from
Bucharest.
‘BIG PHYSICS’ QUESTIONS ADDRESSED BY STOPPED RISING (isomer and beta-decays)• How robust are the magic numbers?
• What are the limits of nuclear existence?
• Does neutron excess modify structure ?
• How ‘good’ are nuclear physics quantum numbers, such as isospin, K and seniority?
K-electrons
L-electrons
T1/2 = 10.4 s205Au126
202Pt
T1/2Weiss(E3(94)) = 7.49 s
T1/2Weiss(M4(921)) = 10.6 s
K-electrons
L-electrons
T1/2=10.4 s
E(exp)(11/2-3/2+) = 912 keV
204Pt126
205Au126
N=82N=126
190Ta 190W+
N=Z
Projectile Fragmentation Reaction Process
Abrasion Ablation
Beam at Relativistic Energy ~0.5-1 GeV/A
Target NucleusFIREBALL Formation of a
compound nucleus
Reaction Products still travelling at Relativistic
Energies
Accelerator facility at GSI-Darmstadt
The Accelerators:UNILAC (injector) E=11.4 MeV/n
SIS 18Tm corr. U 1 GeV/nBeam Currents:
238U - 109 pps
FRS provides secondary radioactive ion beams:• fragmentation or fission of primary beams • high secondary beam energies: 100 – 700 MeV/u• fully stripped ions
Ion-by-ion identification with the FRS
TOF
E
Primary beam energies of ~ 0.5 →1 GeV per nucleon (i.e. ~200 GeV)
Cocktail of secondary, exotic fragments with ~ x00 MeV/u thru. FRS.
Separate and identify event-by-event. Chemically independent.
RISING
Rare Isotopic Spectroscopic
INvestigations @ GSI =
15 x Cluster germaniums for
(the most) exotic gamma-ray
spectroscopy
Passive Stopper measurements: -rays from isomer with T1/2 for 10 ns 1 ms.
Active Stopper measurements: particles, i.c. electrons, T1/2 ms →mins
2
8
20
28
(40)
50
V= SHO + l2.+ l.s.
82
1s1/2
1p3/2
1p1/2
2s1/2
3s1/2
1d5/2
1d3/2
2d3/2
2d5/2
1g7/2
1g9/2
1h11/2
1f7/2
1f5/2
2p3/2
2p1/2
2f7/2
1h9/2
1i13/2
Independent particle model of nucleus predicts some large energy gaps close for fully filled nuclear orbits. This leads to theconcept of Magic Numbers.
BUT, the energy ordering of the orbits depends on the solution to the Schrodinger Equationfor the nuclear mean-field.
If the mean field changes….the ordering of orbitals could changeand magic numbers might change /be washed out?
Predicted evolution of nuclear single particle states with increasing neutron ‘skin’
Evidence for nuclear shell structure.Energy systematics of 1st excited state in even-even nuclei:
E(2+).
large gaps in single-particle structure of nuclei…MAGIC NUMBERS = ENERGY GAPS
(changing) ordering of quantum states with neutron excess?
r-p
rocess a
bu
nd
an
ces
mass number, A
N=82
N=126
Any evidence for changed ordering of quantum states ?
Assumption of N=82 and N=126 shell quenching leads to animprovement in the global abundance fit in r-process calculations
r-p
roce
ss a
bu
nd
ance
s
mass number A
exp.pronounced shell gapshell structure quenched
A. Jungclaus et al., Phys. Rev. Lett. 99, 132501 (2007) RISING experiment
NOT for 130Cd82…but more information on excited states in evenmore neutron-rich nuclei is essential.
fragmentation/fission
~1GeV/u
fragmentseparator
350m
Facility for Antiproton and Ion Research (FAIR)
NUSTAR: SuperFRS and experiments on three (energy) branches…. > 800 collaborators
Low-energy branch / DESPEC
NuSTAR @FAIR will use Super FRagment Separator (SFRS) to select exotic nuclei of interest to final focal point at Low-Energy Branch for decay studies…
NUSTAR - The Project
The Collaboration
> 800 scientists
146 institutes
38 countries
DESPEC -, -, -, p-, n-decay spectroscopy
ELISE elastic, inelastic, and quasi-free e--A scattering
EXL light-ion scattering reactions in invere kinematics
HISPEC in-beam spectroscopy at low and intermediate energy
ILIMA masses and lifetimes of nuclei in ground and isomeric states
LASPEC Laser spectroscopy
MATS in-trap mass measurements and decay studies
R3B kinematically complete reactions at high beam energy
Super FRS RIB production, identification and spectroscopy
The Investment
82 M€ Super FRS
73 M€ Experiments
DESPEC = Decay Spectroscopy collaboration at FAIR
Members of the DESPEC CollaborationAarhus, Denmark , H. FynboBarcelona, Spain, Univ.Politécnica Cataluña, F. Calviño, B. Gómez HornillosBordeaux, France, B. Blank Bucharest, Romania, IFIN-HH, N.V. Zamfir, M. Ionescu-Bujor et al.Camerino, Italia, Univ. Camerino, D.L. Balabanski Daresbury. UK, CCLRC, J. Simpson, I.Lazarus, V.Pucknell and Daresbury engineersDarmstadt , Gremany, GSI, D. Ackerman, M. Górska, J. GerlKojouharov , C. Scheidenberger et al.Darmstad Uni. N. PietrallaEdinburgh , UK, Univ. Edinburgh, P.J. Woods, T. DavinsonGatchina, Russsia, PNPI, L. BatistGiessen, Germany, W. PlassGuelph, Canada, Univ of Guelph, P.GarrettJyväskylä , Finland, Univ. of Jyväskylä , J. Äystö, A. Jokinen, P. Jones, R. Julin, M. Leino, H. Penttilä., J. Uusitalo , C. ScholeyLeuven, Belgium, Univ. of Leuven, M. Huyse, G. Neyens, P. v.DuppenLiverpool, UK, Univ. of Liverpool, R. D. PageLund, Sweden, Univ. Lund, D. RudolphKöln, Germany, Univ. Köln, J. Jolie, P. ReiterKrakow, Poland, IFJ PAN, A. Maj et al.Madrid, Spain, CIEMAT, D. Cano-Ott, E. González, T. Martínez Madrid, IEM, A. JungclausMainz, Germany, Univ. Mainz, K.-L. Kratz Manchester, UK, Univ. Manchester, D. CullenMunchen, Germany, T. Faestermann, R. Krücken
Salamanca, Spain, B. QuintanaSofia, Bulgaria, G. Rainovski, S. Lalkovski, M. DanchevSwierk, Poland, SINS, E Ruchowska, S. Kaczarowski St. Petersburg, Russia, RI, I. IzosimovStockholm, Sweden, B. Cederwal, A. Johnson Strasbourg, France, IRES, G. DuchêneSurrey, UK, University of Surrey, W. Gelletly, Zs. Podolyak, P.H.Regan, P. Walker Tennessee, USA, ORNL, R. GrzywaczUppsala, Sweden, Uppsala University, H. Mach, J. NybergValencia, Spain, IFIC, CSIC-Univ. Valencia, B. Rubio, J.L.Taín. A. AlgoraWarsaw, Poland, University of Warsaw, W. Kurcewicz, M. Pfutzner
37 institutes
Prototype AIDA Enclosure
• Prototype mechanical design• Based on 8cm x 8cm DSSSD
evaluate prior to design for 24cm x 8cm DSSSD• Compatible with RISING, TAS, 4 neutron detector
• 12x 8cm x 8cm DSSSDs 24x AIDA FEE cards
• 3072 channels
• Design complete
• Mechanical assembly in progress
In –beam test on the FRS approved (S390)Hope to be scheduled in the 2nd half of 2011
Proposed DESPEC ‘Fast-Timing’ array scheme with 24 LaBr3 detectors 150mm from the centre of AIDA
DESPEC LaBr3 Detectors ‘Test’ Experiment(s)
18O(18O,pn)34P fusion-evaporation @36 MeV. 34P cross-section, ~ 5 – 10 mb
Target, 50mg/cm2 Ta218O enriched foil
18O. Beam from Bucharest Tandem (~20pnA).
Array 8 HPGe and 7 LaBr3(Ce) detectors
-3 (2”x2”) cylindrical-2 (1”x1.5”) conical-2 (1.5”x1.5”) cylindrical
Poster by Thamer Alharbi
Comparison of 152Eu and 56Co source spectra for a HPGe and 2”x2” LaBr3
T.Alharbi et al.,
Expected, E1/2 dependence of FWHM on gamma-ray energy.
T.Alharbi et al.,
Lifetime Measurement of I=4- Yrast State in 34P19 : (Some) Physics Motivation
•Breakdown of the N = 20 shell gap in neutron-rich nuclei linked to population of (deformed) intruder states associated with f7/2
orbit.
•Neutron-rich Ne, Na, Mg isotopes observed to have well-deformed ground states. Region termed “island of inversion”
2
8
20
28
1s1/2
1p3/2
1p1/2
1d5/2
2s1/2
1d3/2
1f7/2
2p3/2
•Studies of energy levels in N~20 nuclei help us understand the role of the f7/2 intruder orbital in the nuclear shell model description of such nuclei.
Scientific Motivation for ‘Fast-Timing’ Studies in 34P • 34P19 has I=4- state at E=2305
keV.
•Aim to measure a precision lifetime for 2305 keV state.
WHY?• A I=4-→ 2+ EM transition is allowed
to proceed by M2 or E3 multipole gamma-rays.
•M2 and E3 decays can proceed by
f7/2 → d3/2 => M2 multipole f7/2 → s1/2 => E3 multipole
• Lifetime and mixing ratio information gives direct values of M2 and E3 transition strength
• Direct test of shell model wfs…
.’’’
Z=15 = N=19
How is measuring the I=4-state
lifetime useful?
Transition probability (i.e., 1/mean lifetime as measured for state which decays by EM radiation)
(trivial) gamma-rayenergy dependence oftransition rate, goes as. E
2L+1 e.g., E5 for E2s
for example.
Nuclear structure information. The ‘reduced matrix element’ , B(L) tells us the overlapbetween the initial and final nuclear single-particle wavefunctions.
Measuring the lifetime and knowing the gamma-ray decay energies givesus the B(L) value directly.
Transition rates are slower (i.e., longer lifetimes) for higher order multipoles. Expect M2s to be slower than M1s of the same energy.
34P19 (Simple) Nuclear Shell Model Configurations
20
1d5/2
2s1/2
1d3/2
1f7/2
20
1d5/2
2s1/2
1d3/2
1f7/2
I = 2+ [2s1/2 x (1d3/2)-1] I = 4- [2s1/2 x 1f7/2]
•Theoretical predictions suggest 2+ state based primarily on [2s1/2 x (1d3/2)-1] configuration and 4- state based primarily on [2s1/2 x 1f7/2] configuration.
•M2 decay can go via f7/2 → d3/2 (j=l=2) transition.
15 protons 19 neutrons 15 protons 19 neutrons
34P19 (Simple) Nuclear Shell Model Configurations
20
1d5/2
2s1/2
1d3/2
1f7/2
20
1d5/2
2s1/2
1d3/2
1f7/2
I = 2+ [2s1/2 x (1d3/2)-1] I = 4- [2s1/2 x 1f7/2]
•Theoretical predictions suggest 2+ state based primarily on [2s1/2 x (1d3/2)-1] configuration and 4- state based primarily on [2s1/2 x 1f7/2] configuration.
•M2 decay can go via f7/2 → d3/2 (j=l=2) transition.
15 protons 19 neutrons 15 protons 19 neutrons
34P19 (Simple) Nuclear Shell Model Configurations
20
1d5/2
2s1/2
1d3/2
1f7/2
I = 2+ [2s1/2 x (1d3/2)-1]
•Theoretical predictions suggest 2+ state based primarily on [2s1/2 x (1d3/2)-1] configuration and 4- state based primarily on [2s1/2 x 1f7/2] configuration.
•M2 decay can go via f7/2 → d3/2 (j=l=2) transition.
M2 s.p. transition
20
1d5/2
2s1/2
1d3/2
1f7/2
20
1d5/2
2s1/2
1d3/2
1f7/2
I = 2+ [1d3/2 x (2s1/2)-1] I = 4- [2s1/2 x 1f7/2]
•Theoretical predictions suggest 2+ state based primarily on [2s1/2 x (1d3/2)-1] configuration with some small admixture of [1d3/2 x (1s1/2)-1]
•4- state based primarily on [2s1/2 x 1f7/2] configuration.
•E3 can proceed by f7/2 → s1/2 (j=l=3 transition).
•Admixtures in 2+ and 4- states allow mixed M2/E3 transition.
15 protons 19 neutrons 15 protons 19 neutrons
Total in-beam Ge spectrum from LaBr3-Ge matrix
Total in-beam LaBr3 spectrum from LaBr3-Ge matrix
429
1876
18O+18O fusion-evaporation reaction at 36 MeV.
Main evaporation channels p2n+33P and 3n+33S.~5-10% of cross-section into pn+34P
T1/2=2ns{1048}{429}
‘Prompt’ T~480ps
{429}{1876}
1048 keV gate
1876 keV gate
429 keV gate
P.J.Mason, T.Alharbi, PHR et al., to be published
T1/2<2ps
Summary
• Contemporary nuclear structure physics research focuses on nuclei with ‘extreme’ proton-to-neutron ratios.
• Gamma-ray spectroscopy remains a very powerful tool for detailed studies of nuclear structure, particularly for nuclear level scheme characterisation.
• A high-efficiency, modular, ‘fast-timing array’ of LaBr3 detectors is being designed and constructed for use by the DESPEC collaboration at the future FAIR facility.
• Test experiments using prototype LaBr3 arrays are already providing new physics insights into the single particle make up of excited states in exotic nuclei.