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 2015International 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

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Long-lived states allow selection of out-of-beam decays and make comprehensive, high-spin level schemes possible.

Testing ground for nuclear shell model

208Pb 209Pb 210Pb 211Pb

209Bi 210Bi 211Bi

210Po 211Po

211At

207Pb

207Tl 208Tl206Tl

208Bi

206Pb

206Hg

212At 213At210At

212Po

208Pb - central to our understanding of the nuclear shell

model

Octupole states

• 3- state is collective vibrational excitation

Important throughout nuclei near 208Pb.

Vibration deformation in the light actinides.

0+

3-

208Pb

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 -> 100s)

E3 E3

Byrne et al, Phys Rev Lett 80 (1998) 2077

Recent work on 210Fr – 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 4.5s

Second 4.5s

Subtracted

Clean

Suitable for LaBr3 gating

Recent work on 210Fr – 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 LaBr3’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 –

SolenogamSeparation in time and space – increased sensitivity

Locus of trajectories for 187Pb residues at 37 MeV

Target

Focal Plane

Stopper B

Diaphragm

Majority of beam projectiles and fission fragments hit stoppers placed along axis

Majority of 187Pb residues pass and reach the focal

plane

Monte Carlo Modeling Of Ion Trajectories

Device Length

tflight, v/c ~ 2% tflight, v/c ~ 4%

RITU (Jyväskylä)

4.8 m 800 ns 400 ns

FMA (Argonne) 8.2 m 1370 ns 685 ns

SOLITAIRESOLITAIRE 1.7 m1.7 m 280 ns280 ns 140 ns140 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

• 186Pb example – rotational bands and three 0+ states

• Unique signatures of three shapes?

“A triplet of differently shaped spin-zero states in the atomic nucleus, 186Pb”, 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 LaBr3 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 LaBr3 detectors into CAESAR and Solenogam over the course of 2015.

• 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 LaBr3 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

208Pb 209Pb 210Pb

209Bi 210Bi

210Po

207Pb

207Tl 208Tl206Tl

208Bi

206Hg

206Pb

Two Body Interactions

• CalculationKuo / Herling (70)

Warburton / Brown (91)

Zwarts/Glaudemans (85)

Alexa (97)

Covello (99)• EmpiricalBlomqvist (75)

Lonnroth (81)

Bayer (99)

208Pb 209Pb

209Bi

207Pb

207Tl

h9/ 2

f7/ 2

i13/ 2

p-11/ 2

f-15/ 2

p-13/ 2

i-113/ 2

d-13/ 2

h-111/ 2

d-15/ 2

Empirical Levels

g9/ 2

i11/ 2

j15/ 2

s-11/ 2

Triple shape coexistence in 188Pb

prolate

rotor

sphericalground state

Dracoulis et alPRC 69 (2004)

054318Gammasphere

Triple shape coexistence in 188Pb

11- isomer oblate

12+ isomer

spherical

isomericstates

1.2s, K=8- isomer (N=106)