Towards laser spectroscopy of 229 Th · 3. Search for the Isomer by Photons (visible – UV) POSITIVE RESULTS a. 3.5 eV, see 2.5 eV and 3.5 eV peaks, Irwin and Kim, Phys. Rev. Lett

EURONS laser and EURONS laser and traptrap collaborationcollaboration meetingmeeting, , SaturdaySaturday AprilApril 14, 200714, 2007

Towards laser spectroscopy

of 229Th

Towards laser spectroscopy

of 229Th

Iain Moore

University of Jyväskylä

Iain Moore

University of Jyväskylä


OutlineOutline

� Evidence for the isomer

� Why such an interest?

� Our method of detecting the isomer

� A challenge to produce a beam


Table of Isotopes


1. Isomer Energy by Closed Cycle of γ-ray energies

a. Measured -1±4 eV, Reich and Helmer, Phys. Rev. Lett. 64 (1990) 271

b. Measured 3.5±1.0 eV, Helmer and Reich, Phys. Rev. C 49, (1994) 1845

c. Reanalysed existing data 5.5±1.0 eV, Guimarães-Filho and Helene, Phys. Rev. C 71,

(2005) 044303

2. Direct reaction work

Burke et al, Phys. Rev. C 42 (1990) R499

3. Search for the Isomer by Photons (visible – UV)

POSITIVE RESULTS

a. 3.5 eV, see 2.5 eV and 3.5 eV peaks, Irwin and Kim, Phys. Rev. Lett. 79 (1997) 990

b. 3.5 eV, see 3.5 eV but not 2.5 eV peaks, Richardson et al., Phys. Rev. Lett. 80 (1998) 3206

NEGATIVE RESULTS

a. Photons due to fluorescence of nitrogen, Utter et al., Phys. Rev. Lett. 82 (1999) 505

b. Shaw et al., Phys. Rev. Lett. 82 (1999) 1109

c. No photons, Moore et al., ANL Report (2004)

4. Growth of 229Th, Browne et al., Phys. Rev. C 64 (2001) 014311

5. Alpha decay of the isomer, Mitsugashira et al., J. Rad. and Nuc. Chem. 255 (2003) 63


I.D Moore et al., Physics Division Report PHY-10990-ME-2004

Shaw et al., Phys. Rev. Lett. 82 (1999) 1109

Very difficult to distinguish radiative photons from

background caused by contaminant daughters or from

the alpha decay of uranium.

The region within the parabolic curves

defined by the branching ratio and

half-life excludes the 229Thm at a

confidence level of 99.7%.

But what if the energy is incorrect?


7.6±0.5 eV

153 - 175 nm

E(229mTh) = ∆E29 – ∆E42

where ∆E29 = (29.39-29.18 keV) and∆E42 = (42.63 – 42.43 keV)


Why such an interest?Why such an interest?

� Nuclear excitation energies are typically in the 104 – 106 eV range,generally much larger than atomic level energies which has preventedthe study of atomic-nuclear couplings using atomic probes (lasers).

� Possible applications include a clock with unparalled precision forgeneral relativity tests and measuring the variability of physical constants

� A superb qubit for quantum computing

� Tests of the effect of the chemical environment on nuclear decay rates

� Novel ways to achieve stimulated nuclear excitation


Development of a low-energy thorium ion beam for

laser spectroscopy

Development of a low-energy thorium ion beam for

laser spectroscopy

232Th(n,γ)233Th → 233Pa → 233U (electroplated onto stainless steel strips)

5000 6000 7000 8000 90000

20

40

60

80

100

120

140

Recoil spectrum of 233U

Co

un

ts p

er 1

0000

sec

Energy (keV)

212Po

213Po217

At

216Po

221Fr

220Rn

212Bi

225Ac

224Ra

224Ra

Volume of ion guide = 1240 cm3, exit hole 2 mm diameter, tevac = 690 ms


Static electric field plate designStatic electric field plate design

Without a skimmer electrode the ions stickto the final electrode!

Related to task 5of laser JRA –incorporation ofelectric fields inion guide.


-5 0 5 10 15 20 25 30 35 40

0

5

10

15

20

25

30

35

Ion Guide Efficiency as a Function of Electron Emitter Current

Ion

Gu

ide

Eff

icie

ncy

(%

)

Electron Emitter Current (µµµµA)

0 cm

1 cm

2 cm

4 cm

6 cm

8 cm

Electron emitter field guidanceElectron emitter field guidance

Ion guide efficiency for221Fr (4.9 min) and 217At(32.3 ms) 6±0.5 %.

Both are in equilibrium in the sourcetherefore evacuation time of ion guide < 32.3 ms


Particle identification using JYFLTRAPParticle identification using JYFLTRAP

Purification trap only, M/∆M for 229Th+ = 23,500

Using the reaction Th+ + O2 → ThO+ + O (reaction coefficient k = 6.0×10-10)τ = 390(70) ms. This indicates an impurity level of 4.3×109 cm-3 in the RFQ.Using 0.1 mbar buffer gas pressure, this gives 1.6 ppm (expected from purityof He gas bottle used).

y = y0 + Aexp(x/τ)

A reduced extraction efficiency was observed for 229Th (0.06%). Missingefficiency arises from molecular formation inside the ion guide and anunknown neutral fraction (which will be addressed using FURIOS).


Design of a new ion guide (static electric fields)Design of a new ion guide (static electric fields)

New guide sent by McGill University (no simulations �). Built to haveDC electric field along the guide axis, and for in-situ baking. Testedunsuccessfully in January….


Lets add an RF carpet (+ simulations!)…….Lets add an RF carpet (+ simulations!)…….

Helium gas at 40 mbarRF 110V, 2.2 MHz

(no gas flow).

We can use our own SPIGsupply.

Expected testing in July




Towards the futureTowards the future

� Once the testing of the RF carpet has been completed with an α-recoil

source a collinear laser spectroscopy run will be attempted. Tests usinga discharge source of 232Th have been successful (and optical pumping!)

� Possible RIS schemes identified using Ti:Sapphire lasers to autoionizingstates (Johnson et al., Spectrochimica Acta, 47B (1992) 633)

� In discussion with Russians to acquire 229Th coated discharge electrodein order to study the HFS of the ground state (which will make theidentification of any isomer structure easier)


T. Eronen, T. Kessler, A. Nieminen,S. Rinta-Antila,

T. Sonoda & J. ÄystöJYFL, Jyväskylä, Finland

B. Tordoff, J. Billowes, P. Campbell

& B. Cheal

Manchester University, UK

J. Lee

McGill University, Montreal, Canada

A. Popov

PNPI, Gatchina, St-Petersburg, Russia

T. Eronen, T. Kessler, A. Nieminen,S. Rinta-Antila,

T. Sonoda & J. ÄystöJYFL, Jyväskylä, Finland

B. Tordoff, J. Billowes, P. Campbell

& B. Cheal

Manchester University, UK

J. Lee

McGill University, Montreal, Canada

A. Popov

PNPI, Gatchina, St-Petersburg, Russia

Thanks to the collaborators, past and presentThanks to the collaborators, past and present

THANKS FOR YOUR ATTENTION!


Phys. Rev. C. vol. 42, no. 2 (1990)

Experiments with deuterons on 230Th

show resonances associated with

excitations of the rotational band built

upon the low lying isomer (3/2+), in

agreement with the gamma ray cascade

measurements.

An analogous band in 231Th built on the

same Nilsson configuration has a visible

3/2+ resonance in the same experiment

with 232Th as the target.

Evidence for the Isomer –

Single Nucleon Transfer

Reactions

Evidence for the Isomer –

Single Nucleon Transfer

Reactions


Phys. Rev. C. vol. 42, no. 2 (1990)

Evidence for the Isomer – Single Nucleon Transfer ReactionsEvidence for the Isomer – Single Nucleon Transfer Reactions

Angular distributions of the

beam scattered off the target

infer the angular momentum

assignments of the excitation

level. The fits are DWBA

calculations of the l assignment

for stated Nilsson configurations.

Since the shapes are consistent

with the angular distributions for

the 231Th [631] band of the same

configuration and no large shape

change is observed between the

two nuclei, this is strong evidence

for the low lying isomer as the 229mTh [631] bandhead.


Static field plate design 2Static field plate design 2

Documents

Towards laser spectroscopy of 229 Th · 3. Search for the Isomer by Photons (visible – UV) POSITIVE RESULTS a. 3.5 eV, see 2.5 eV and 3.5 eV peaks, Irwin and Kim, Phys. Rev. Lett