1. Beta and isomer delayed spectroscopy of neutron-rich Dy to Os Nuclei: Mapping shape evolution and Quadrupole collectivity at large neutron excess.
Paddy Regan
Department of Physics,
University of Surrey. Guildford, GU2 7XH, UK
&
Radioactivity Group
National Physical Laboratory
Teddington TW11 0LW, UK
&

2. Decay spectroscopy. How quickly something decays…. …
Decay spectroscopy. How quickly something decays…. …..tells you what’s going on inside….
2008
1979
1988
1985

3. 2+ 0+ Excitation energy (keV) PHR, Physics World, Nov. 2011, p37
Ground state
Configuration.
Spin/parity Ip=0+ ;
Ex = 0 keV

5. Deformed region: Neutron-rich A～170 nuclei
K quantum number and collective rotation: K isomers R I
Change
direction
Spin selection … Yes
K-selection … Sort of !
K hindered
transitions
Weisskopf hindrance
Reduced hindrance
The degree of K forbiddenness
The identification and characterization of K-isomers provides information on
Intrinsic orbits near the Fermi surface
Pairing energies
The degree of axial symmetry

6. Deformed region: Neutron-rich A～170 nuclei
Kπ = 6+ isomers in N = 104 isotones
822 ns ?
104
F.R. Xu et al.,
PLB 435 (1998) 257
G.D. Dracoulis et al.,
PLB 635 (2006) 200
P.H. Regan et al.,
PRC 65 (2002)

7. Deformed region: Neutron-rich A～170 nuclei
Kπ = 8- isomers in N = 106 isotones and E1 decays
106
5.8 s ?
F.R. Xu et al.,
PLB 435 (1998) 257
E1 reduced hindrances
G.D. Dracoulis et al., PLB 635 (2006) 200
fν~100 from systematics
assume Eγ = 150 keV
T1/2 ~ 6.5 s
G.D. Dracoulis et al.,
PRC 79 (2009) (R)
⇒ compete with β decay?

8. While we were waiting for ~170Dy … N=100, 164Sm, 166Gd.

9. 166Gd
164Sm

10. Deformation (inferred from E(2+) and E(4+) states) appears to reduce again after
‘local’ increase at N=100; possible evidence for localised N=100 ‘deformed shell closure’

11. The role of the hexacontatetrapole (β6)deformation
Highest β6 predicted for ~164Sm (P. Moller et al.) Sm
β6 Kπ=6- -> 5-
~150 keV effect
Calc. by Honliang Liu

12. WAS3ABI & EURICA
WAS3ABI: Wide-range Active Silicon-Strip Stopper Array for Beta and Ion detection
Double-sided Silicon Strip Detectors
60 x 1 mm strips in x direction
40 x 1 mm strips in y direction
EURICA: Euroball RIKEN Cluster Array
for (ion correlated) gamma-ray measurements.
84 HPGe in 12 x 7 element CLUSTER dets.
18 LaBr3(Ce).

13. Decay spectroscopy of neutron-rich rare-earth isotopes around double mid-shell (report on RIBF beam-time, Nov. 2014)
H. Watanabe, P.-A. Söderström, P.H. Regan, P. Walker
Beihang/RIKEN/Surrey
Main goals:
Search for isomers in the 10 ns to 10 s range
b-delayed g-ray spectra around mid-shell
b-decay half-lives and the rare-earth peak
345 MeV/u U primary beam at 11 pnA
Purified by BigRIPS and ZeroDegree
Implanted in the WASABI active stopper
Gamma rays detected by EURICA
Outcome from three days of beam-time:
More than five new isomers in key nuclei
15 new beta-delayed gamma spectra
15 new half-lives
Capability to measure very long-lived isomers confirmed online with 174mEr (5.8 s)

14. 170Dy104

15. Under review at
Physics Letters
B (2016)
g-gated 170Dy
isomer decay
b-gated
170Tb decay
170Dy spectroscopy for first time by combining:
b--delayed tagging on 170Tb105 (T1/2 ~ 1 s) mother nucleus
and
(ii) isomer spectroscopy of 170Dy (T1/2~1 ms) Kp=(6+) isomer

18. Decay and mixing with
Kp=2+ ‘gamma’ band
and Kp=6+ isomeric decay
‘reduces’ the
Reduced hindrance
Compared to Np.Nn
Systematics for 170Dy.

19. 172Dy106 : Past the mid-shell

21. First 172Dy level scheme constructed by
(a) Isomer spectroscopy (by gating on
conversion of 0.7s isomer in 172Dy (using
WASABI; 172Dy gs half life measured to be ~3 s)
(b) b- delayed spectroscopy by gating on 172Tb
Mother nucleus (spectrum (k) on left).

22. g vibrational Kp=2+ band is particularly
enhanced in 172Dy106 due to simultaneous
excitation of several 2qp configurations
close to the Fermi surface for N=106
which couple to give K=2 and induce
non-axially symmetric, collective motion

23. Dy Preliminary Candidates for Kπ = 2+ and 2- states 168 66 102 Dy
G.X. Zhang
Beihang Univ.
M. Asai et al., Phys. Rev. C 59, 3060 (1999)
4-; π3/2+[411]⊗ν5/2-[512]
Candidates for
Kπ = 2+ and 2-
states
M. Asai et al.,
PRC 59, 3060 (1999)
Preliminary

24. 168Tb:Gamma Spectroscopy

25. Future at GSI / FAIR

26. F. Browne, A. M. Bruce, T. Sumikama et al. , EURICA + FATIMA, Phys
F. Browne, A.M.Bruce, T. Sumikama et al., EURICA + FATIMA, Phys. Lett. B (2015)

27. TRD for FATIMA for NUSTAR.

28. FATIMA for DESPEC
FATIMA = FAst TIMing Array = State of the art array for precision measurements of nuclear structure in the most exotic and rare nuclei. 36 LaBr3(Ce) detectors.
Energy resolution better than 3% at 1 MeV.
Detection efficiency of ~ 5% Full-energy peak at 1 MeV.
Excellent timing qualities (sub 100 ps).
Use to measure lifetimes of excited nuclear states & provide precision tests of nuclear structure, uses a fully-digitised Data Acquisition System (CAEN 1 GHz digitizers).

29. Passive Stopper measurements: g-rays from isomer with T1/2 for 10 ns  1 ms.
Active Stopper measurements: b -particles, i.c. electrons, T1/2 ms →mins

30. RISING Active Stopper Measurements
Passive Stopper: g ray from isomer cascades with T1/2 ~ 10 ns  1 ms.
Active Stopper measurements: b-particles, internal conversion electrons.
T1/2 up to ~ minutes; associated with delayed g rays.
5 cm x 5 cm DSSSD (16 strips x 16 strips = 256 pixels) x 3 = 758 total pixels.
See P.H. Regan et al., Int. Jour. Mod. Phys. E17 (2008) 8 ;
R. Kumar NIM A598 (2009) 754

32. b--gated (fast-timing) W-Pt region at GSI/FAIR

33. 188Ta →188W
190Ta
→190W
192Ta →192W

34. New data points on R(4/2) for 190W and 1/E(2+) point to new
sub-shell closure signature around Z~74 in neutron-rich nuclei (N >114).
1/E(2+)

35. RISING with 208Pb primary
Beam and active stopper.
Gate on 194Re decays to
Populate states in 194Os
(including second 0+ state).

36. Mapping the deformation shape changes?
Experimental signatures?
E(2+) of yrast sequence and evolution with (N,Z), valence product ?
R(4/2) = E(4+)/E(2+) = evolution from 3.3 <–> 2.5 <- > 1.8?
E(2+2), excitation energy of ‘gamma’ band; low-lying 2+2 states consistence with axial softness.
E(0+2), excitation energy of ‘b’- bandhead, low-lying states consistent with (e.g.) prolate/oblate shape co-existence shape (e.g., around N=116,118, 190,2W and 192,4Os)
T1/2 for Ip=2+ (and perhaps higher spin states?) to get magnitude of Qt and b deformation parameter.
Decays and id of isomeric states to map (deformed) single-particle spectrum (prolate vs. oblate isomeric configurations for example?)

37. What the yrast Ip=2+ lifetime can give you ?

38. b--gated (fast-timing) W-Pt region at GSI/FAIR

39. What can we reach / get to now?

40. Sum of time differences between 143-keV and any higher lying feeding transition (assumes negligible half-life for intermediate states).
T1/2=0.87(12) ns

41. Some quick revision on extracting (nuclear excited state) lifetimes…
Assuming no background contribution, the experimentally measured, ‘delayed’ time distribution for a g-g-Dt measurement is given by:
P(t’-t0) is the (Gaussian) prompt response function and l=1/t, where t is the mean lifetime of the intermediate state.
See e.g., Z. Bay, Phys. Rev. 77 (1950) p419;
T.D. Newton, Phys. Rev. 78 (1950) p490;
J.M.Regis et al., EPJ Web of Conf. 93 (2015) 01014

42. Deconvolution and lineshapes?
If the instrument time response function R(t) is Gaussian of width s,
If the intermediate state decays with a mean lifetime t, then
The deconvolution integral for a single state lifetime is given by (ignoring the normalisation coefficients).
1-erf(x) is the complementary
error function of x.

44. Examples / Technical limits ?
For a fixed source, lifetimes of the order of > 1 ns are ‘easy’ using LaBr3 coincidences, if you have enough counts.
E.g. 152Eu source data using RoSPHERE.

45. Some comments on ‘at the edge’ timing measurements at FAIR.
Problem 1
Rare, weakly produced final nuclei, few counts at focal plane
Solution: clean by tagging and ion-beta-gating
Timing correlations using Fast LaBr3 detectors; also (in some cases) allows ordering of gammas in a cascade below beta or isomer.
Problem 2
Distributed source (across the focal plane) = spread in time of flight of gammas, focal plane distances could vary by ~ 10 cm (Dt = d/c ~330 ps spread for 10 cm).
Solution, clean position tagging at focal plane and event-by-event correction (demonstrated at Jyvaskyla by Cullen et al., for 138Gd).
Problem 3
Need a fast ‘start’ signal for the LaBr3(Ce).
Solution(s) LaBr3(Ce) - LaBr3(Ce) coincidences can be ‘self-timed’ wrt each other, but AIDA not fast enough for electron start for b-g coincs. Add in a fast plastic start detector (a la EURICA ?).

46. 192Os(18O,16O)194Os at IFIN-HH, Bucharest, T. Daniel, PhD thesis, U
192Os(18O,16O)194Os at IFIN-HH, Bucharest, T. Daniel, PhD thesis, U. Surrey
Use 192Os unsafe
Coulex channel as
test of analysis and Internal time/energy response calibration.

47. 194Os deformation by fast-timing

49. Current state of the art and predictions?