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 p.regan@surrey.ac.uk & paddy.regan@npl.co.uk

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) ?

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.

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

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. 2011.

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

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.

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

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?

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)

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.

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

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) 037302

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

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) 061303(R) ⇒ compete with β decay?

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

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

166Gd 164Sm

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’

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

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

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).

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

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)

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

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.

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

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

170Dy104

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

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

172Dy106 : Past the mid-shell

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).

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

Dy Preliminary Candidates for Kπ = 2+ and 2- states 168 66 102 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

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 1 2060(1970)

168Tb:Gamma Spectroscopy

168Tb:Gamma Spectroscopy

168Tb:Gamma Spectroscopy

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

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

168Tb:Gamma Spectroscopy

165Tb:Gamma Spectroscopy

165Tb:Gamma Spectroscopy

167Tb:Gamma Spectroscopy

167Tb:Gamma Spectroscopy

Future at GSI / FAIR

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)

TRD for FATIMA for NUSTAR.

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).

188Ta →188W 190Ta →190W 192Ta →192W

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

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-077125, 27University College ; 28Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro.