Laser pumping of ionsin a cooler-buncher

The University ofManchester, UK

The University ofBirmingham, UK

At the JYFL accelerator facility, Finland

Collinear laser spectroscopy

Laser Ion source (cooler)

PMTGates

+40kV

+/-≈3kV

Platform

∙ Isotope shifts

∙ Hyperfine splitting

Magnetic moment<β2>Quadrupole moment

δ<r2>

δσ

Size

Shape

Diffuseness

• Fast and sensitive

δ<β22>

The JYFL IGISOL

● Fast extraction (~1ms)

● Chemically

non-selective

Reduced peak skewingReduced peak skewing

The RF cooler-buncher

z

V

z

He buffer gas End plate

Energy spread 100eV 1eV

Emittance = 3п.mm.mrad

Less spectral broadening

Better laser-ion overlap

Bunching and laser spectroscopy

Cou

nts

Cou

nts

0

30

100

2005.25 hours 48 minutes8000 ions/s 2000 ions/s

100V

zEnd

pla

te p

oten

tial Accumulate

Release

Before

After

PMT

15µs gate

Background eg. 200ms accumulation=20µs gate widthsuppression ~10

4

New results: multi QP isomers

Raghavan'89

Multi-QP states Reduced pairing• Less diffuse or more rigid

• Linked to origins of odd-even staggering?

Yttrium results

J = 0 J = 1 electronic transition

⇒ 3 peaks for each nuclide (maximum)

gives the centroid, μ and Q

One resonant photon per 2000 ions

Efficiency:-

• Shape change at N=59

• 98m is well deformed

Yttrium charge radii

Problem 1: Spin determination

Similarly with A=102 and A=100

98m

Problem 2: “Collapsed” ground states

Difficult to resolve underlying peaks and ordering

Spin ½

Spin 2

Spin ½ + isomer peak

Other yttrium transitions?

311nm J=0 → J=1 transition (2002) – 1 in 17000 efficiency

State selection in an ion cooler

Ti:Sa

363 nm pumping of yttrium

1 photon for every 6000 ions becomes 1 for every 3000 ions

(End of the beam line)

• Indifference to bunching

• Pumping saturates at 30mW

• Can use broadband lasers

98m 321.7nm predicted structure

Cerium Ti:Sa scan

Other pumping casesZr, Nb, Mo, Rh, Ta, W...

2 photon

M1/E2

Other possibilities: background suppression

Bro

adba

nd la

ser

pum

ping

ste

p Hig

h re

solu

tion

l

aser

ste

p

Hig

h re

solu

tion

l

aser

ste

p

Dec

ay d

etec

ted

by P

MT

Dec

ay d

etec

ted

by P

MT

Future work: polarisation

F=5/2

F=3/2

MF =-5/2 -3/2

-1/2

+1/2 +3/2 +5/2

-3/2

-1/2

+1/2 +3/2

In a strong magnetic field, the spins decouple leaving the nuclearspins polarised and allowing NMR experiments to be performed

Weak magnetic field ⇒ Zeeman splittingσ+ circularly polarised light ⇒ spin polarisation in state of maximum MF

Summary

• Method of controlling state population

• Choose transitions on basis of strengths, spins, splitting and charge state

• Cooler provides a focal point of slowly travelling ions

• Ti:Sa lasers provides wider range of wavelengthsand bandwidth or pulsing does not matter

• Necessary for yttrium; other cases being considered

• Aim to produce polarised beams out of the cooler for β-NMR work

Collaborators

The University of Manchester, UK

The University of Birmingham, UK

The JYFL accelerator laboratory, Jyväskylä, Finland

J. Billowes, P. Campbell, B.Cheal, B.A. Marsh, B.W. Tordoff

T. Eronen, J. Huikari, A. Jokinen, T. Kessler, I.D. Moore, A. NiemenenH. Pentillä, S. Rinta-Antila, J. Äystö

M.L. Bissell, D.H. Forest, G. Tungate