Fast timing measurements at the focal plane of the Solenogam  -e - spectrometer (and some other ideas…) Greg Lane

15 MV tandem linac post-accelerator (6MV equivalent, campaign mode of operation) 10 beam lines Highly flexible beam pulsing (ns to seconds) “Super-e” “Hyperion” “CAESAR” “Solenogam”

CAESAR Array 9 HPGe coaxial  -ray detectors (between 25 and 70%) 2 LEPS detectors Close geometry, thick target/isomer focus, leverage beam pulsing Isomers: high-K, shape coexistence, trans-lead shell model HIAS 2015 International conference in Canberra to celebrate George’s contributions to nuclear structure 14-18th September E0 workshop on 11-12th

Isomer studies in trans-lead shell model nuclei published ✔✔ ✔ ✔✔ ✔✔✔ ✔✔ ✔✔ ✔✔✔✔ ✔✔✔✔✔✔✔ ✔✔✔ ✔✔✔✔ ✔✔ ✔✔ ✔✔✔✔ ✔ ✔ ✔ to be published Long-lived states allow selection of out-of-beam decays and make comprehensive, high-spin level schemes possible. Testing ground for nuclear shell model

208 Pb 209 Pb 210 Pb 211 Pb 209 Bi 210 Bi 211 Bi 210 Po 211 Po 211 At 207 Pb 207 Tl 208 Tl 206 Tl 208 Bi 206 Pb 206 Hg 212 At 213 At 210 At 212 Po 208 Pb - central to our understanding of the nuclear shell model

Octupole states 3 - state is collective vibrational excitation Important throughout nuclei near 208 Pb. Vibration  deformation in the light actinides Pb 2.614

Enhanced E3 transitions  i13/2  f7/2 | 13/2> | 7/2>  f7/2  3 -  i13/2  3 - j15/2 g9/2 | 15/2> | 9/2> g9/2  3 - j15/2  3 - B(E3) ~ 30 W.u. Signature for the presence of certain wavefunction components Probe of underlying octupole collectivity (e.g. astatine nuclei) Enhanced, but still often long isomers (100ns -> 100  s) E3 Byrne et al, Phys Rev Lett 80 (1998) 2077

Recent work on 210 Fr – Vincent Margerin (MPhil) 5 proton particles and 3 neutron holes – calculational limits for shell model? Unusually low E3 strengths?

Advantage of flexible pulsed beam – clean in any time range 1 microsecond on / 9 microseconds off First 4.5  s Second 4.5  s Subtracted  Clean  Suitable for LaBr 3 gating

Recent work on 210 Fr – Vincent Margerin (MPhil) 2ns isomer also identified Remember the 686ns isomer

Intermediate lifetime exposed below the long isomer Centroids of time differences between various pairs of gamma-rays in HPGe detectors => isolate the state lifetime. Huge effort characterising prompt reponse and time walk – successful, but still a nightmare! Include LaBr3 (ala ROSPHERE) and this becomes trivial. We have plans for six LaBr 3 ’s. Huge number of short-lived isomers will become accessible providing new challenges for the shell model. (Non-yrast, more complex states)

Solenogam Concept Existing gas-filled solenoid recoil separator – SOLITAIRE  -ray and e - spectroscopy at the focal plane – Solenogam Separation in time and space – increased sensitivity

Locus of trajectories for 187 Pb residues at 37 MeV Target Focal Plane Stopper B Diaphragm Majority of beam projectiles and fission fragments hit stoppers placed along axis Majority of 187 Pb residues pass and reach the focal plane Monte Carlo Modeling Of Ion Trajectories

DeviceLengtht flight, v/c ~ 2%t flight, v/c ~ 4% RITU (Jyväskylä)4.8 m800 ns400 ns FMA (Argonne)8.2 m1370 ns685 ns SOLITAIRE 1.7 m 280 ns 140 ns Disadvantages Advantages Compact  Sensitivity to short lifetimes Relatively high transport efficiency ~40 to 80% Si(Li) for high-resolution electron spectroscopy No mass separation Relatively poor scattered beam rejection

Solenogam 6.5 T solenoid

Shape Coexistence – detailed spectroscopy 186 Pb example – rotational bands and three 0+ states Unique signatures of three shapes? “A triplet of differently shaped spin-zero states in the atomic nucleus, 186 Pb”, A.N. Andreyev et al, Nature 405 (2000) 430. Different wells have different orbital near Fermi surface and hence isomers of unique spin and parity, defining the shape. Use the isomers! Transport isomers to focal plane and measure properties of the quantum states characteristic of each well –Gamma-ray energies  excited state energies –Excited state lifetimes  decay rates –Conversion electrons  transition multipolarities  shape changes

Many “shears” bands in odd-Pb nuclei and much controversy concerning the band-head spins. Most are unmeasured.

Enhancements planned for Solenogam Move to 8T solenoid (a permanent home) Fast plastic beta counter for beta-gamma coincidences Moving tape system for background reduction Incorporate six LaBr 3 detectors into focal plane Gamma-electron time-correlated spectroscopy of isomer and ground-state decays in a background-free environment Decays expose possibility of probing short lifetimes below Shell model studies in neutron-deficient cases where there is fission competition Collectivity in low-lying states in shape coexisting nuclei Possible measurements of absolute E0 transition strengths

Summary We will be incorporating LaBr 3 detectors into CAESAR and Solenogam over the course of Some unique capabilities. Can be optimised for studies of short isomers fed either in decay or fed by longer-lived isomers. The Australian summer is in the northern hemisphere winter. Andrew and I are the PAC… Get in touch …. and bring some more LaBr 3 detectors!

Determination of spins and parities Lack of spin alignment below isomers and/or low statistics due to fission competition and low recoil transmission –traditional angular correlation and distribution techniques are very difficult. Solution - Conversion electrons –transition multipolarities –shape changes (E0’s) Not easy to measure! Most current systems are more optimised for alpha-spectroscopy.

Where is the Australian National University? ANU

208 Pb 209 Pb 210 Pb 209 Bi 210 Bi 210 Po 207 Pb 207 Tl 208 Tl 206 Tl 208 Bi 206 Hg 206 Pb Two Body Interactions                   Calculation Kuo / Herling (70) Warburton / Brown (91) Zwarts/Glaudemans (85) Alexa (97) Covello (99) Empirical Blomqvist (75) Lonnroth (81) Bayer (99)

208 Pb 209 Pb 209 Bi 207 Pb 207 Tl  h 9/ 2  f 7/ 2  i 13/ 2 p -1 1/ 2 f -1 5/ 2 p -1 3/ 2 i -1 13/ 2   d -1 3/ 2  h -1 11/ 2  d -1 5/ 2    Empirical Levels g 9/ 2 i 11/ 2 j 15/ 2  s -1 1/ 2

Triple shape coexistence in 188 Pb prolate rotor spherical ground state Dracoulis et al PRC 69 (2004) Gammasphere

Triple shape coexistence in 188 Pb 11 - isomer oblate 12 + isomer spherical isomeric states

1.2  s, K  =8 - isomer (N=106)