Paddy Regan Department of Physics University of Surrey & National Physical Laboratory, UK

1. New decay and isomer physics studies with fast scintillation detection arrays at Coulomb Barrier separator focal planes Paddy Regan Department of Physics University of Surrey & National Physical Laboratory, UK p.regan@surrey.ac.uk

2. Nuclear structure information. The ‘reduced matrix element’ , B(lL) tells us the overlap between the initial and final nuclear single-particle wavefunctions. (trivial) gamma-ray energy dependence of transition rate, goes as. Eg2L+1 e.g., Eg5 for E2s for example. Transition probability (i.e., 1/mean lifetime as measured for state which decays by EM radiation) How is measuring the lifetime useful?

3. Annual Review of Nuclear Science (1968) 18 p265-290

4. FATIMA for DESPEC • FATIMA = FAst TIMing Array = A high efficiency, gamma-ray detection array for precision measurements of nuclear structure in the most exotic and rare nuclei. • Specs. • Good energy resolution. • Good detection efficiency • Excellent timing qualities (~100 picoseconds). • (2012) Bought 31 x LaBr3 1.5” x 2” crystals for array (expect 36 in total). • Can use to measure lifetimes of excited nuclear states; provide precision tests of shell model theories of nuclear structure. • UK contribution to DESPEC (Decay Spectroscopy) project within NUSTAR. • Part of ~ £8M UK STFC NUSTAR project grant (runs to 2015).

6. Brighton & Surrey groups purchased 31 1.5” x 2” LaBr3 detectors from St Gobain (Dec. 2012). Mounted into designed holders with Hamamatsu PMTs Jan 2013.

7. Tests with 152Eu source to measure lifetime of Ip=2+ 122 keV level in 152Sm. T1/2 = 1.4ns

10. Acqiris digitizer model DC252HF. Tests by Mohammad Nakhostin (U. Surrey) Source Anode Dynode PMT PMT Dynode Digitizer To PC for offline analysis Digital CFD for timing Trigger CR-RC, Trapezoidal filters for energy CFD 4 GS/s (250 ps sampling interval) 10 bit resolution, 1 Volt input dynamic range, 4 GHz Bandwidth

11. Sample energy spectrum, 137Cs

12. Time resolution vs pulse sampling rate Energy gate: 1100-1400 keV Still preliminary! Analog result

13. Digital time spectra for two different energy gates The width and peak location of time spectra move with energy

14. Energy resolution vs sampling rate

15. Ba x-rays from 137Cs & EC from 138La decay 137Cs source gives (initial) test energy resolution of ~3.5% at 662 keV. Note presence of internal radioactivity in detector. PMT HV range ~1300 V 1436 keV EC (2+→ 0+ in 138Ba) 789 keV + b- In 138Ce

16. 5+ 138La ec (66%) b- (34%) 2+ 2+ 788.7 1435.8 0+ 138Ce80 0+ 138Ba82 138La, T1/2=1.02x1011 years A.A.Sonzogni, NDS 98 (2003) 515

19. An experimental example:138Ce80

20. N=80 Isotones • N = 80 isotones above Z = 50 display 10+ seniority isomers from coupling of (h11/2)-2 • 6+ level decays also usually ‘hindered’ e.g., in 136Ba, T1/2 = 3.1(1)ns. • Thought to be due to change in configuration and seniority. isomer 10+ (h11/2)-2 only 8+ 6+ Primarily (g7/2)2 4+ 2+ Primarily (d5/2)2 0+

21. N=80 Isotones • Neighbouring N=80 nuclei, 138Ce and 140Nd expected to show similar 6+ → 4+ hindrance. • Competing transitions to negative parity states • E1 decays, forbidden in truncated shell model space.

22. Restricted basis SM calculations give reasonable comparison with experimental (near-yrast) states in 138Ce. What about transition rates?

23. 130Te(12C,4n)138Ce @56 MeV

24. 138Ce80 T.Alharbi et al., Phys. Rev. C87 (2013) 014323

26. 138Ce80

27. 138Ce80

28. 138Ce – Lifetime of the 11+ State Using “delayed” HPGe gate T1/2 = 140(11)ps S.-J. Zhu et al. Chin.Phys.Lett. 16, 635 (1999)

30. 188W

31. 110 111 112 113 114 115 N 2 neutrons more than heaviest stable Tungsten (Z=74) isotope (186W). Populate 188W using 186W(7Li,ap)188W ‘incomplete fusion’ reaction. (Not really a fusion-evap reaction, but populates medium spin states). See e.g., Dracoulis et al., J. Phys. G23 (1997) 1191-1202

32. Half-life of the yrast 2+ state in 188W • Neutron-rich A ~ 190 nuclei, a long predicted prolate – oblate shape transition region. e.g. Bengtsson et al. PLB190 (1987) 1 • Unusual (energy) deviation at 190W compared to trend of other nuclides. • Measurement of B(E2;2+→0+) gives best measure of (evolution of) low-lying collectivity

33. Half-life of the yrast 2+ state in 188W • 16 mg/cm2186W target with thick Pb backing • 186W(7Li,p)188W. 31-, 33-MeV beam (Coul. Barr. ~ 29 MeV) • Estimated   0.1-1 mb • Strongest channels: 187Re (1-p transfer) 189Ir (fusion-evap)

34. Sum of time differences between • 143-keV (2->0) transition and any • higher lying feeding transition.

35. Time difference between 143 keV 2+→0+ and feeding transitions. T1/2=0.87(12) ns

36. 188W 188W 188W

37. Other Recent Uses of Fatima Detectors • 21 detectors went RIKEN for use in EURICA array from Nov. 2012 (see poster by Frank Browne). • 8 detectors used with EXOGAM@ILL from Feb. – March 2013 for use in 235U(n,f) experimental campaign.

39. 140 keV 2+→0+ in 104Zr Demonstrates that beta-gamma time differences can be used in projectile fragmentation/fission spectroscopy to measure, e.g., 2+ lifetimes in many, even-even, exotic nuclei, down to ~100 ps?

40. EXILL + FATIMAEXOGAM + FATIMA LaBr3 array at ILL Grenoble Ge-Ge-LaBr3-LaBr3 quadruple coincs between prompt gammas from fission fragments in 235U(n,f) reaction using thermal neutrons.. Massive data set, under analysis (led by Koln group)

41. PROMPT gammas Isomeric state Isomeric state Delayed Gammas Tagging Methods at Jyväskylä • JUROGAM, RITU, GREAT and the TDR. Trigger-less Data Acquisition System D.M. Cullen, Physics with Large Arrays of Novel Scintillators, Dublin, Jan 2014

42. Technique Isomeric state (~100ns – several µs) Delayed γ rays but in prompt coincidence with each other (ps lifetimes) Measure LaBr3 – LaBr3 coincidences with ~200ps intrinsic LaBr3 timing resolution. Extract lifetimes down to ~5ps (centroid shift). ~ 5ps ~ 50ps ~ 100ps Ground state D.M. Cullen, Physics with Large Arrays of Novel Scintillators, Dublin, Jan 2014

43. Possible array configuration at focal plane of RITU spectrometer at JYFL

44. An experimental challenge….

45. Some potential Physics Experiments at RITU: • Minimum half-life possible is ~ few 100 ns • (flight time through RITU, depends on v/c) • Maximum half-life possible is ~ few ms • (depending on tagging method and implant rate (beam current)). • N=74 K-Isomers e.g. 138Gd / 140Dy? to address the deformation of ground-state bands approaching the proton drip-line. Deformations used in hindrance calculations and also proton decay tunnelling calculations but not yet measured. • Deformation of states in neutron deficient Pb (188-194) under known isomers (11- isomers and K isomers). • States below the 14+ isomer in 94Pd giving information on n-p pairing. • ... D.M. Cullen, Physics with Large Arrays of Novel Scintillators, Dublin, Jan 2014

46. Acknowledgements • Zsolt Podolyák, Peter Mason, Thamer Alharbi, Christopher Townsley, Daniel Terver, Laila Gurgi, Mohammad Nakhostin (Surrey) • Alison Bruce, Oliver Roberts, Frank Browne (Brighton) • Dave Cullen et al. (Manchester) • Nicu Marginean et al., (Bucharest) • Funding for detectors and DAQ from STFC UK.