The DESPEC Fast-Timing Project at FAIR: Sub-nanosecond Nuclear Timing

Spectroscopy with LaBr3 Scintillators

Paddy ReganDepartment of Physics

University of SurreyGuildford, UK

Email: p.regan@surrey.ac.uk

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.