1. EURICA Isomer and b--delayed g-ray Spectroscopy in the Vicinity of the 170Dy104 Valence Maximum & Future Studies at DESPEC.
Paddy Regan
Department of Physics,
University of Surrey. Guildford, GU2 7XH, UK
&
Radioactivity Group
National Physical Laboratory
Teddington TW11 0LW, UK
&

2. Outline Original Scientific Motivation: The Np.Nn valence maximum?
EURICA highlights and results
Sm / Gd Isomer spectroscopy (from Z~60 proposal by Ideguchi & Simpson)
Deformed (K-)Isomer spectroscopy of 164Sm100 & 166Gd100 .
Effects of b6 deformation and possible deformed shell closure for N=100 (Patel, Podolyak et al., from Ideguchi / Simpson proposal experiment);
4-qp Kp=11- Isomer in 160Sm – the lightest 4qp K-isomer to date.
Tb/Dy/Ho/Er Spectroscopy around A~170 (Watanabi, Söderström, Walker, Regan et al., proposal) .
Isomer spectroscopy of 170Dy and b- decay of 170Tb. E(2+) and hindrance
Isomeric (Conversion) Spectroscopy beyond the mid-shell for 172Dy.
Isomer spectroscopy of 165-8Tb. Mapping the Nilsson orbitals.
b decay into 168Dy102 (and 170Dy) and related structure in e.g., 174Er.
Future directions of related research.
Fast-timing LaBr3 array for DESPEC (36 LaBr3 detectors)
Possible studies at both RIKEN (e.g., Zr and Dy neutron-rich regions and FAIR (Dy – Pb) ?

3. Experiment number: NP1112-RIBF88R1-01: Spokespersons: Hiroshi Watanabe, Par-Anders Soderstrom, Patrick H. Regan & Philip M. Walker
238U beam time 5-11 November 2014.
Original LoI for EURICA Physics (submitted
as part of MoU - July 2011);
Final proposal submitted to RIKEN
PAC in May 2012.

4. Some old history (2011): Following PreSPEC, application to take the CLUSTER detectors to RIKEN following RISING to form EURICA. Note, possible physics highlights included 170Dy, ~110Zr and others

5. One of the early physics cases for EURICA – see e. g
One of the early physics cases for EURICA – see e.g., EURICA Physics workshop, held at GSI Sept

6. 2+ 0+ Excitation energy (keV) PHR, Physics World, Nov. 2011, p37
Ground state
Configuration.
Spin/parity Ip=0+ ;
Ex = 0 keV

9. B(E2) values for low-lying even-even nuclei with Z =62 (Sm) – 74 (W).
Very ‘collective’ transitions (>100 Wu) with maximum B(E2) at mid-shell.
This correlates with the lowest E(2+) excitation energy values.

10. R(E(4+) / E(2+)) Systematics plot from Burcu Cakirli

11. A Fundamental Nuclear Structure Physics Question
A Fundamental Nuclear Structure Physics Question? ‘Simple’ nuclear correlation schemes appear to show a direct link between nuclear quadrupole (b2) deformation and the number of proton-neutron valence interactions [e.g., Casten & Zamfir, Phys. Rev. Lett. 70, 402 (1993)]. Are the most ‘collective’ nuclei at the valence maximum? 170Dy is a Valence Maximum Nucleus, having 50→ 66 →82 protons & 82 → 104 → 126 neutrons How does the nuclear structure evolve as the valence maximum nucleus is approached?

12. But…..
E(2+) excitation energies do not
appear to (always) minimize
at the N=104.
Er (Z=68) and Hf (Z=70) have
minimum E(2+) at N=104.
…BUT Dy (Z=66) isotopes localised
at N=98 then again at N=102?
The microscopic effects of
‘isotope specific residual
proton-neutron interactions’
between defined (Nilsson) orbitals
causes fluctuations in the final
deformation.
From M. Asai et al., Phys. Rev. C59, 3060 (1999)

13. Dracoulis, Walker & Kondev Rep. Prog. Phys. 79, 076301 (2016)
K-isomer –rich
region
around the
Z~66 ; N~104
valence
maximum.
Expect to be
able to use
Isomeric
decays to
populate
low-lying states.

14. 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

15. 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)

16. Structure and decay properties of K isomers
Kπ = 6+ isomer and γ-band levels
Decay from the Kπ = 6+ isomer
N=104
N=104
K=6+
5+γ
4+γ
3+γ
2+γ
The relatively low-lying γ band gives
a useful way of populating it via
the decay of the Kπ = 6+ isomer.
The decay from the Kπ = 6+ isomer
is much less hindered in comparison
with those in the heavier isotones.
Chance mixing with the nearly degenerate 6+ member of the γ band (Kπ = 2+)
Similar situation expected for 170Dy104 (and 168Gd104)
Significant test for the stability of K isomers at the valence product maximum

17. 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?

18. Big RIPS tests identify 170Dy isomer (reported June 2013 from Isotope/isomer search performed in Oct 2011) not with EURICA

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

20. 166Gd
164Sm

21. 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’

22. 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

23. Deformed sub-shell closure at N=100?Sm
L. Sapathy, S.K. Patra, Nucl. Phys. A722, C24 (2003)

26. 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).

27. ~170Dy beam time
scheduled
5-11 Nov. 2014

28. 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)

29. Previous state of the art: Use in-beam DIC to study neutron-rich Dy isotopes to 168Dy.

30. 166,168Dy yrast states populated with CLARA+PRISMA experiment, gated on binary BLFs
(Kr isotopes) to select Dy partners following the 82Se+170Er DIC / binary transfer reaction.

31. Tentative evidence for (the 4+ → 2+ in) 170Dy ?
Gated on BLF Eg=777 keV
2+ →0+ in 82Kr + show coincs
for Doppler corrected 170-nDy TLFs

32. Particle identification(PID)
Hydrogen Like Mass number/(Z-1)
Fully stripped Mass number/(Z)

33. 170Dy104

34. 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

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

38. 172Dy106 : Past the mid-shell

40. 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).

41. 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

42. 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

43. β decay scheme of 174Ho->174Er
Data analyzed by Jiajian LIU at Hong Kong University
T1/2=3.4(10)s
Half-life of 199keV 3.9(11)s is consistent with β decay half-life of 174Ho 3.4(10)s
199keV transition is above the 8- isomeric state (T1/2 = 4.0 s) of 174Er
By comparing neighboring N=106 isotones
Spin parity of new state 9- in 174Er is assigned
Experimental logft values 5.7(3) and 5.3(2) are larger than 4.9 in well deformed nuclei region [1]
β decay of 174Ho is allowed transition
Spin parity Jπ=8- or 9- of ground state in 174Ho is proposed
[1] Phys. Rev. C (1970)

45. 168Tb:Gamma Spectroscopy

46. 168Tb:Gamma Spectroscopy

47. 168Tb:Gamma Spectroscopy

48. Nilson proton configuration for
Possible deformed single and
multi-particle configurations
Nilson proton configuration for
Z=65
3/2[411], 7/2[523], 5/2[413] and
5/2[532]
A. K. Jain et al;Rev. Mod. Phys. , Vol. 62, No. 2, April 1990

49. Nilson neutron configuration for
Possible deformed single and
multi-particle configurations
Nilson neutron configuration for
N=103
5/2[512], 7/2[514], 1/2[521] and
7/2[633]
A. K. Jain et al;Rev. Mod. Phys. , Vol. 62, No. 2, April 1990

50. 168Tb:Gamma Spectroscopy

51. 165Tb:Gamma Spectroscopy

52. 165Tb:Gamma Spectroscopy

53. 167Tb:Gamma Spectroscopy

54. 167Tb:Gamma Spectroscopy

55. Future at GSI / FAIR

56. 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)

57. TRD for FATIMA for NUSTAR.

58. 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).

59. 188Ta →188W
190Ta
→190W
192Ta →192W

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

61. 1University of Surrey, UK; 2National Physical Laboratory, UK
H.Watanabe4,5, P.-A.Söderström3, P.M.Walker1, L.A.Gurgi1. Zs.Podolyák1, S.Nishimura3,T.A.Berry1, P.Doornenbal3, G.Lorusso1,2,3, T.Isobe3, H.Baba3, Z.Y.Xu6,7, H.Sakurai3,8, T.Sumikama3,9,W.N.Catford1, A.M.Bruce10, F.Browne10, G.J.Lane11, F.G.Kondev12, A.Odahara13, J.Wu3,14, H.L.Liu15, F.R.Xu14, Z.Korkulu3,16, P.Lee17, J.J.Liu6, V.H.Phong3,18, A.Yagi13, G.X.Zhang5, T.Alharbi19, R.J.Carroll1,
K.Y.Chae20, Zs.Dombradi16, A.Estrade7,21, N.Fukuda3, C.Griffin21, E.Ideguchi13,23, N.Inabe3,
H.Kanaoka13, I.Kojouharov24, T. Kubo3, S.Kubono3, N.Kurz24, I.Kuti16, S.Lalkovski1, E.J.Lee20,
C.S.Lee17, G.Lotay1, C.-B.Moon25, I.Nishizuka9, C.R.Nita10.26, Z.Patel1, O.J. Roberts27, H.Schaffner24, C.M.Shand1, H.Suzuki3, H.Takeda3, S.Terashima5, Zs.Vajta16, S.Yoshida13 & J.J. Valiente-Dòbon28
1University of Surrey, UK; 2National Physical Laboratory, UK
3RIKEN Nishina Center; 4International Research Center for Nuclei and Particles in the Cosmos,
5School of Physics and Nuclear Energy Engineering; 6University of Hong Kong,
7KU Leuven, Instituut voor Kern- en Stralings fysica; 8University of 9Tohoku;
10University of Brighton; 11Australian National University,
12Argonne National Laboratory; 13Osaka University;
14Peking University, 15Xi’an Jiaotong University ;
16Institute for Nuclear Research, 17Chung-Ang University,
18NU Hanoi University of Science, 19 Almajmaah University, Saudi Arabia ;
20Sungkyunkwan University, 21University of Edinburgh,
22Central Michigan University, 23Research Center for Nuclear Physics (RCNP), Osaka University,
24GSI Helmholtzzentrum für Schwerionenforschung GmbH, 25Hoseo University, 6(IFIN-HH), RO , 27University College ; 28Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro.