The DESPEC Fast-Timing Project at FAIR: Sub-nanosecond Nuclear Timing Spectroscopy with LaBr 3 Scintillators Paddy Regan Department of Physics University of Surrey Guildford, UK

Talk Outline Nuclear structure physics research circa –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 FAIR. The present Pre-DESPEC tests and some physics –Results of some LaBr 3 (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 s 205 Au Pt T 1/2 Weiss (E3 (94) ) = 7.49 s T 1/2 Weiss (M4 (921) ) = 10.6 s K-electrons L-electrons T 1/2 =10.4 s E  (exp) (11/2 -  3/2 + ) = 912 keV 204 Pt Au 126 N=82 N= Ta  190 W+  N=Z

Projectile Fragmentation Reaction Process Abrasion Ablation Beam at Relativistic Energy ~0.5-1 GeV/A Target Nucleus FIREBALLFormation 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/n Beam Currents: 238 U 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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 GSI = 15 x Cluster germaniums for (the most) exotic gamma-ray spectroscopy

Passive Stopper measurements:  -rays from isomer with T 1/2 for 10 ns  1 ms. Active Stopper measurements:  particles, i.c. electrons, T 1/2 ms → mins

(40) 50 V= SHO + l 2.+ l.s. 82 1s 1/2 1p 3/2 1p 1/2 2s 1/2 3s 1/2 1d 5/2 1d 3/2 2d 3/2 2d 5/2 1g 7/2 1g 9/2 1h 11/2 1f 7/2 1f 5/2 2p 3/2 2p 1/2 2f 7/2 1h 9/2 1i 13/2 Independent particle model of nucleus predicts some large energy gaps close for fully filled nuclear orbits. This leads to the concept of Magic Numbers. BUT, the energy ordering of the orbits depends on the solution to the Schrodinger Equation for the nuclear mean-field. If the mean field changes….the ordering of orbitals could change and 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 1 st 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-process abundances 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 an improvement in the global abundance fit in r-process calculations r-process abundances mass number A exp. pronounced shell gap shell structure quenched A. Jungclaus et al., Phys. Rev. Lett. 99, (2007) RISING experiment NOT for 130 Cd 82 … but more information on excited states in even more neutron-rich nuclei is essential.

fragmentation/fission ~1GeV/u fragment separator 350m Facility for Antiproton and Ion Research (FAIR) NUSTAR: SuperFRS and experiments on three (energy) branches…. > 800 collaborators Low-energy branch / DESPEC

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 Collaboration Aarhus, Denmark, H. Fynbo Barcelona, Spain, Univ.Politécnica Cataluña, F. Calviño, B. Gómez Hornillos Bordeaux, 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 engineers Darmstadt, Gremany, GSI, D. Ackerman, M. Górska, J. Gerl Kojouharov, C. Scheidenberger et al. Darmstad Uni. N. Pietralla Edinburgh, UK, Univ. Edinburgh, P.J. Woods, T. Davinson Gatchina, Russsia, PNPI, L. Batist Giessen, Germany, W. Plass Guelph, Canada, Univ of Guelph, P.Garrett Jyväskylä, Finland, Univ. of Jyväskylä, J. Äystö, A. Jokinen, P. Jones, R. Julin, M. Leino, H. Penttilä., J. Uusitalo, C. Scholey Leuven, Belgium, Univ. of Leuven, M. Huyse, G. Neyens, P. v.Duppen Liverpool, UK, Univ. of Liverpool, R. D. Page Lund, Sweden, Univ. Lund, D. Rudolph Köln, Germany, Univ. Köln, J. Jolie, P. Reiter Krakow, Poland, IFJ PAN, A. Maj et al. Madrid, Spain, CIEMAT, D. Cano-Ott, E. González, T. Martínez Madrid, IEM, A. Jungclaus Mainz, Germany, Univ. Mainz, K.-L. Kratz Manchester, UK, Univ. Manchester, D. Cullen Munchen, Germany, T. Faestermann, R. Krücken Salamanca, Spain, B. Quintana Sofia, Bulgaria, G. Rainovski, S. Lalkovski, M. Danchev Swierk, Poland, SINS, E Ruchowska, S. Kaczarowski St. Petersburg, Russia, RI, I. Izosimov Stockholm, Sweden, B. Cederwal, A. Johnson Strasbourg, France, IRES, G. Duchêne Surrey, UK, University of Surrey, W. Gelletly, Zs. Podolyak, P.H.Regan, P. Walker Tennessee, USA, ORNL, R. Grzywacz Uppsala, Sweden, Uppsala University, H. Mach, J. Nyberg Valencia, Spain, IFIC, CSIC-Univ. Valencia, B. Rubio, J.L.Taín. A. Algora Warsaw, 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 2 nd half of 2011

Proposed DESPEC ‘Fast-Timing’ array scheme with 24 LaBr 3 detectors 150mm from the centre of AIDA

DESPEC LaBr 3 Detectors ‘Test’ Experiment(s) 18 O( 18 O,pn) 34 P MeV. 34 P cross-section,  ~ 5 – 10 mb Target, 50mg/cm 2 Ta 2 18 O enriched foil 18 O. Beam from Bucharest Tandem (~20pnA). Array 8 HPGe and 7 LaBr 3 (Ce) detectors -3 (2”x2”) cylindrical -2 (1”x1.5”) conical -2 (1.5”x1.5”) cylindrical Poster by Thamer Alharbi

Comparison of 152 Eu and 56 Co source spectra for a HPGe and 2”x2” LaBr 3 T.Alharbi et al.,

Expected, E 1/2 dependence of FWHM on gamma-ray energy. T.Alharbi et al.,

Lifetime Measurement of I  =4 - Yrast State in 34 P 19 : (Some) Physics Motivation Breakdown of the N = 20 shell gap in neutron-rich nuclei linked to population of (deformed) intruder states associated with f 7/2 orbit. Neutron-rich Ne, Na, Mg isotopes observed to have well-deformed ground states. Region termed “island of inversion” s 1/2 1p 3/2 1p 1/2 1d 5/2 2s 1/2 1d 3/2 1f 7/2 2p 3/2 Studies of energy levels in N~20 nuclei help us understand the role of the f 7/2 intruder orbital in the nuclear shell model description of such nuclei.

Scientific Motivation for ‘Fast-Timing’ Studies in 34 P 34 P 19 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  f 7/2 → d 3/2 => M2 multipole  f 7/2 → s 1/2 => 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-ray energy dependence of transition rate, goes as. E  2L+1 e.g., E  5 for E2s for example. Nuclear structure information. The ‘reduced matrix element’, B( L) tells us the overlap between the initial and final nuclear single-particle wavefunctions.

Measuring the lifetime and knowing the gamma-ray decay energies gives us 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.

34 P 19 (Simple) Nuclear Shell Model Configurations 20 1d 5/2 2s 1/2 1d 3/2 1f 7/2  20 1d 5/2 2s 1/2 1d 3/2 1f 7/2  I  = 2 + [  2s 1/2 x ( 1d 3/2 ) -1 ]I  = 4 - [  2s 1/2 x 1f 7/2 ] Theoretical predictions suggest 2 + state based primarily on [  2s 1/2 x ( 1d 3/2 ) -1 ] configuration and 4 - state based primarily on [  2s 1/2 x 1f 7/2 ] configuration. M2 decay can go via f 7/2 → d 3/2 (  j=  l=2) transition. 15 protons 19 neutrons

34 P 19 (Simple) Nuclear Shell Model Configurations 20 1d 5/2 2s 1/2 1d 3/2 1f 7/2  20 1d 5/2 2s 1/2 1d 3/2 1f 7/2  I  = 2 + [  2s 1/2 x ( 1d 3/2 ) -1 ]I  = 4 - [  2s 1/2 x 1f 7/2 ] Theoretical predictions suggest 2 + state based primarily on [  2s 1/2 x ( 1d 3/2 ) -1 ] configuration and 4 - state based primarily on [  2s 1/2 x 1f 7/2 ] configuration. M2 decay can go via f 7/2 → d 3/2 (  j=  l=2) transition. 15 protons 19 neutrons

34 P 19 (Simple) Nuclear Shell Model Configurations 20 1d 5/2 2s 1/2 1d 3/2 1f 7/2  I  = 2 + [  2s 1/2 x ( 1d 3/2 ) -1 ] Theoretical predictions suggest 2 + state based primarily on [  2s 1/2 x ( 1d 3/2 ) -1 ] configuration and 4 - state based primarily on [  2s 1/2 x 1f 7/2 ] configuration. M2 decay can go via f 7/2 → d 3/2 (  j=  l=2) transition. M2 s.p. transition

20 1d 5/2 2s 1/2 1d 3/2 1f 7/2  20 1d 5/2 2s 1/2 1d 3/2 1f 7/2  I  = 2 + [  1d 3/2 x ( 2s 1/2 ) -1 ]I  = 4 - [  2s 1/2 x 1f 7/2 ] Theoretical predictions suggest 2 + state based primarily on [  2s 1/2 x ( 1d 3/2 ) -1 ] configuration with some small admixture of [  1d 3/2 x ( 1s 1/2 ) -1 ] 4 - state based primarily on [  2s 1/2 x 1f 7/2 ] configuration. E3 can proceed by f 7/2 → s 1/2 (  j=  l=3 transition). Admixtures in 2 + and 4 - states allow mixed M2/E3 transition. 15 protons 19 neutrons

Total in-beam Ge spectrum from LaBr 3 -Ge matrix Total in-beam LaBr 3 spectrum from LaBr 3 -Ge matrix O+ 18 O fusion-evaporation reaction at 36 MeV. Main evaporation channels p2n+ 33 P and 3n+ 33 S. ~5-10% of cross-section into pn+ 34 P

T 1/2 =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 T 1/2 <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 LaBr 3 detectors is being designed and constructed for use by the DESPEC collaboration at the future FAIR facility. Test experiments using prototype LaBr 3 arrays are already providing new physics insights into the single particle make up of excited states in exotic nuclei.