Thorium Spectroscopy
Tanja E. Mehlstäubler
Center for Quantum Engineering and Space Time Research
Leibniz Universität Hannover
Physikalisch-Technische Bundesanstalt, Braunschweig
Department of Time & Frequency
Physics with Trapped Charged Particles – Les Houches, 19 January 2012
Outline ͻ Why is nuclear laser spectroscopy difficult? ͻdŚĞůŽǁ-‐ĞŶĞƌŐLJŝƐŽŵĞƌŝĐƐƚĂƚĞŝŶdŚ-‐229 ͻdŚ-‐229 as a precise optical nuclear clock • Application search for D
Visible light not matched to energy scales in nucleus Energy scales: Photon in optical range: !Z | 2 eV
Nucleus: bound nucleon 'x | 5 10 15 m
2
!
ǁŝƚŚ 'x 'p ! o
0,83 MeV
2
2('x) m p
(rest energy of proton: 938 MeV) Atomic shell: bound electron ǁŝƚŚ 'x | 10 10 m
'x 'p
!2
! o
2('x) 2 me
(rest energy of electron: 0,51 MeV) 3,8 eV
Electric field scales inside atom / nucleus E
e-‐ Shell: Nucleus: r 10 10 m
r
5 10
15
m
ES
1. 4 1011 V/m
EN
5.8 1019 V/m
q
4SH 0 r 2
ůĞĐƚƌŝĐĨŝĞůĚŽĨĞůĞĐƚƌŽŵĂŐŶĞƚŝĐǁĂǀĞŽĨŝŶƚĞŶƐŝƚLJI: I
1
H 0 cEL2
2
EL
ES o I
2.5 1015 W/cm 2
EL
EN o I
4.5 1032 W/cm 2
Maximum intensity of short-‐pulse laser Intensity Limit: ŐĂŝŶďĂŶĚǁŝĚƚŚ ƉŚŽƚŽŶĞŶĞƌŐLJϭͬ;ŵŝŶ͘ǁĂŝƐƚͿ I max | N Ph hQ 'v
N Ph
|
Q2
c2
area of ampl. medium
transition cross section
| 1012
I max | 10 24 W/cm 2
e-‐ shell-‐field strength: reachable nuclear electr. field strength: far beyond Mourou et al., Phys. Today 51, 22 (1998)
EƵĐůĞƵƐŝƐŶŽƐƵŝƚĂďůĞĂŶƚĞŶŶĂĨŽƌǀŝƐŝďůĞůŝŐŚƚ >ŝĨĞƚŝŵĞĨŽƌƌĂĚŝĂƚŝǀĞĚĞĐĂLJǀŝĂĞůĞĐƚƌŝĐ multipole-‐radiation of order l: (antenna length = 5 ×10-‐15 m) 1
W E (l )
P
r
v Z ( ) 2l
O
!Z
W E (1) | 100 s
r
O
| 10 8
at 1 eV
(Jackson, Classical Electrodynamics)
Long-‐ůŝǀĞĚĞdžĐŝƚĞĚƐƚĂƚĞƐ͗ŝƐŽŵĞƌƐ e.g. Ta-‐180: natural isomer, ĚĞĐĂLJƐǀŝĂϴƌĂĚŝĂƚŝŽŶ;l =8) at 75.3 keV, half time > 1015 a ! Nuclear spectroscopy still holds record in resolution Mößbauer-‐spectrum of 93.3 keV resonance of Zn-‐67 Q 'QQ x
Potzel et al., J. Phys., Colloq. 37, 691 (1976) EƵĐůĞŝǁŝƚŚŝƐŽŵĞƌŝĐƐƚĂƚĞƐĂƚůŽǁĞŶĞƌŐŝĞƐ dĐ-‐99 Hg-‐201 W-‐183 U-‐235 dŚ-‐229 2150 eV 1561 eV 544 eV 73 eV 7.8 eV Energies on the order of excitation energy of electronic shell Outline ͻ Why is nuclear laser spectroscopy difficult? ͻ dŚĞůŽǁ-‐ĞŶĞƌŐLJŝƐŽŵĞƌŝĐƐƚĂƚĞŝŶdŚ-‐229 ͻdŚ-‐229 as a precise optical nuclear clock • Application search for D
229Th:
- from 233U D-decay
- half-life 7880 years
actinides
Nuclear structure of thorium-‐229 since 1970s!
Nilsson state
classification
dǁŽĐůŽƐĞ-‐lying band-‐heads: ground state and isomer K. Gulda et al., Nuclear Physics A 703, 45 (2002)
Some History dŚĞŽŶůLJŬŶŽǁŶŝƐŽŵĞƌǁŝƚŚĂŶĞdžĐŝƚĂƚŝŽŶĞŶĞƌŐLJŝŶƚŚĞŽƉƚŝĐĂůƌĂŶŐĞ and in the range of outer shell electronic transitions. ͻ Studied by C.W. Reich et al. at INL since the 1970s, ĞƐƚĂďůŝƐŚĞĚƚŚĞůŽǁĞŶĞƌŐLJŝƐŽŵĞƌ͕ from J-‐spectroscopy: 3.5 ± 1.0 eV, published in 1994 ͻ dŚĞŽƌĞƚŝĐĂůǁŽƌŬďLJ͘s͘dŬĂůLJĂ͕&͘&͘<ĂƌƉĞƐŚŝŶ͕ĂŶĚŽƚŚĞƌƐ isomer lifetime, coupling to electronic excitations (W ΕĨĞǁϭϬϬϬƐ) ͻ &ĂůƐĞĚĞƚĞĐƚŝŽŶƐŽĨŽƉƚŝĐĂůĞŵŝƐƐŝŽŶŝŶƚŚĞh-‐233 decay chain in 1997/98 ͻ Proposal of nuclear laser spectroscopy and nuclear clock ͘WĞŝŬĂŶĚŚƌ͘dĂŵŵ͕ƉƵďůŝƐŚĞĚŝŶϮϬϬϯ ͻ Unsuccessful search for optical nuclear excitation or decay ͻ More precise energy measurement from J-‐spectroscopy at LLNL: 7.6 ± 0.5 eV, published in 2007 ͻ 2011: still no direct detection of the optical transition; ĞdžƉĞƌŝŵĞŶƚĂůĞĨĨŽƌƚƐŝŶƐĞǀĞƌĂů ŐƌŽƵƉƐǁŽƌůĚǁŝĚĞ DĞĂƐƵƌĞŵĞŶƚŽĨƚŚĞĞŶĞƌŐLJŽĨƚŚĞdŚ-‐229 isomer ĞĐŬĞƚĂů͘;>>E>Ϳ͕WŚLJƐ͘ZĞǀ͘>Ğƚƚ͘98, 142501 (2007) J-‐ƐƉĞĐƚƌŽƐĐŽƉLJŽĨƚǁŽĚĞĐĂLJĐĂƐĐĂĚĞƐ from the 71.82-‐keV-‐ůĞǀĞů Isomer energy: Difference of the doublet splittings: 7.6 ± 0.5 eV (corr.: 7.8 ± 0.5 eV, LLNL-‐Proc-‐415170) Ϯϵ<ĞsůŝŶĞƐ ϰϮ<ĞsůŝŶĞƐ 'ƌŽƵŶĚƐƚĂƚĞїŝƐŽŵĞƌ͗ƚƌĂŶƐŝƚŝŽŶŝŶƚŚĞǀĂĐƵƵŵ-‐UV at about 160 nm ǁĂǀĞůĞŶŐƚŚ ͻ Why is nuclear laser spectroscopy difficult? ͻdŚĞůŽǁ-‐ĞŶĞƌŐLJŝƐŽŵĞƌŝĐƐƚĂƚĞŝŶdŚ-‐229 ͻ dŚ-‐229 as a precise optical nuclear clock • Application search for D
A high-‐precision nuclear clock EƵĐůĞĂƌŵŽŵĞŶƚƐĂƌĞƐŵĂůů͘&ŝĞůĚŝŶĚƵĐĞĚƐLJƐƚĞŵĂƚŝĐĨƌĞƋƵĞŶĐLJƐŚŝĨƚƐ can be smaller than in an (electronic) atomic clock. e.g. Zeeman shifts… µN = 5 x 10-‐27 :ͬd µB = 9 x 10-‐24 :ͬd 3 + [631] _ 2 229mdŚ/ƐŽŵĞƌ P=-‐0.08 PN YуϮ·∙10-‐28 e·∙m2 ' E=7.8 eV M1 transition WуϭϬϬϬ s 5 + _ [633] 2 P=0.4 PN Q=3.1·∙10-‐28 e·∙m2 229dŚ'ƌŽƵŶĚ^ƚĂƚĞ A high-‐precision nuclear clock Frequency shifts that only depend on |n,L,S,J> are
common in both levels and do not change the transition frequency
For structureless point-like nucleus
ground and excited state shifts are identical
Campbell et al., arXiv:1110.2490v1 (2011)
Peik et al., EPL 61, 181 (2003)
ŶĂůŽŐŽŶ͗ŽďƐĞƌǀĂƚŝŽŶŽĨƋƵĂŶƚƵŵũƵŵƉƐŝŶƐŝŶŐůĞŝŽŶ Cycling transition for detection Dehmelt et al. 1986 Clock transition to ŵĞƚĂƐƚĂďůĞůĞǀĞů WŽƐƐŝďůĞƌĞĂůŝnjĂƚŝŽŶƐŽĨdŚ-‐229 nuclear clocks: ͻ Laser-‐ĐŽŽůĞĚdŚ3+ in an ion trap ͻ dŚŝŽŶƐĂƐĚŽƉĂŶƚŝŶĂƚƌĂŶƐƉĂƌĞŶƚĐƌLJƐƚĂů;ůŝŬĞĂ&2͕>ŝ&ĞƚĐ͘Ϳ Experimental problem: dƌĂŶƐŝƚŝŽŶĞŶĞƌŐLJŬŶŽǁŶŽŶůLJƚŽуϭϬйƵŶĐĞƌƚĂŝŶƚLJ͕ not a system for high resolution spectroscopy yet. džƉĞƌŝŵĞŶƚĂůƉƌŽũĞĐƚƐ͗ Wd͗ ƚƌĂƉƉĞĚdŚ+ ŝŽŶƐ͖dŚ-‐doped crystals 'ĞŽƌŐŝĂdĞĐŚ͗ ƚƌĂƉƉĞĚdŚ3+ ions UCLA / LANL: dŚ-‐doped crystals dhsŝĞŶŶĂ͗ dŚ-‐doped crystals :LJǀćƐŬLJůćͬDĂŝŶnj ZĞƐŽŶĂŶĐĞŝŽŶŝnjĂƚŝŽŶƐƉĞĐƚƌŽƐĐŽƉLJŽĨdŚƌĞĐŽŝůŶƵĐůĞŝ …. EƵĐůĞĂƌĐůŽĐŬǁŝƚŚůĂƐĞƌĐŽŽůĞĚ229dŚ3+ dŚ3+ ƉŽƐƐĞƐƐĞƐĂŵƵĐŚŵŽƌĞƐŝŵƉůĞůĞǀĞůƐĐŚĞŵĞ ;ƐŝŶŐůĞǀĂůĞŶĐĞĞ-‐) can be laser-‐cooled using diode lasers & ĚĞƚĞĐƚĞĚǀŝĂƌĞƐŽŶĂŶĐĞĨůƵŽƌĞƐĐĞŶĐĞŝŶƚŚĞƌĞĚŽƌE/Z electronic and nuclear resonances are separated in energy dƌĂƉƉŝŶŐĂŶĚůĂƐĞƌĐŽŽůŝŶŐŽĨdŚ3+ Loading via laser ablation with ns pulsed Nd:YAG (tripled)
Trap L = 188 mm r = 3.3 mm, taylored for efficient
loading of ablation plume
Trapping and cooling 103 – 104 Th3+ ions (Th-229 & Th-232)
(enhanced loading efficiency with initial buffer gas cooling)
Campbell et al., Phys. Rev.Lett 106, 223001 (2011)
dƌĂƉƉŝŶŐĂŶĚůĂƐĞƌĐŽŽůŝŶŐŽĨdŚ3+ Low lying energy levels in 229Th3+ :
cooling on 1088 nm line to
tens of K
cooling to tens of mK on lambda
scheme
sympathetic cooling on even
isotope (no HF!)
for lowest temperatures
229Th3+
Laser cooled ion crystals:
232Th3+
Campbell et al., Phys. Rev.Lett 106, 223001 (2011)
Ground state in 299dŚ3+ for clock spectroscopy? Clock transition from ground state (5F5/2):
With laser cooled and trapped ion
fractional frequency inaccuray
as low as
10-19
should be possible!
Campbell et al., arXiv:1110.2490v1 (2011)
or metastable S-state:
Peik et al., EPL 61, 181 (2003)
Doped solid-‐ƐƚĂƚĞĐƌLJƐƚĂůƐǁŝƚŚdŚ+ Th+
Doped solid-‐ƐƚĂƚĞĐƌLJƐƚĂůƐǁŝƚŚdŚ+ Optical Mössbauer Spectroscopy >ĂƐĞƌĞdžĐŝƚĂƚŝŽŶŽĨdŚ-‐ions in a solid їĐŽŵƉĂĐƚŽƉƚŝĐĂůĨƌĞƋƵĞŶĐLJƐƚĂŶĚĂƌĚ! ,ŽƐƚĐƌLJƐƚĂůŵƵƐƚďĞͬŚĂǀĞ͗ -‐ ůĂƌŐĞďĂŶĚŐĂƉїƚƌĂŶƐƉĂƌĞŶƚ -‐ no impurities / color centers -‐ symmetric -‐ diamagnetic WŽƐƐŝďůĞĐĂŶĚŝĚĂƚĞƐ͗Ă&2͕>ŝ&͕ĞƚĐ͙ Crystal doped with 1 nucleus per O3: 1014 ions per cm3
- simple fluorescence detection is possible
- initial broadband excitation experiment with synchrotron light Th4+
Doped solid-‐ƐƚĂƚĞĐƌLJƐƚĂůƐǁŝƚŚdŚn+ Optical Mössbauer Spectroscopy >ĂƐĞƌĞdžĐŝƚĂƚŝŽŶŽĨdŚ-‐ions in a solid їĐŽŵƉĂĐƚŽƉƚŝĐĂůĨƌĞƋƵĞŶĐLJƐƚĂŶĚĂƌĚ! Th4+
First experiments at ALS in Berkeley:
-‐ ^LJŶĐŚƌŽƚƌŽŶƉƌŽǀŝĚĞƐƚƵŶĂďůĞůŝŐŚƚ;ϱ-‐ϯϬĞsͿŽĨůŝŶĞǁŝĚƚŚϬ͘ϭϳϱĞs -‐ >ŝ&ĐƌLJƐƚĂůĚŽƉĞĚǁŝƚŚ232dŚ -‐ Measured fluorescence background from D-‐decay їŶĂƌƌŽǁĚŽǁŶƌĞƐŽŶĂŶĐĞ 0.1 nm! ¥
Rellergert et al., Phys. Rev. Lett. 104, 200802 (2010)
¥
&ŝĞůĚƐŚŝĨƚƐŝŶƐŝĚĞĐƌLJƐƚĂů ŽŵŝŶĂŶƚĐƌLJƐƚĂůĨŝĞůĚƐŚŝĨƚ͗ůĞĐƚƌŝĐƋƵĂĚƌƵƉŽůĞƐŚŝĨƚ Ğ͘Ő͘ĨŝĞůĚŐƌĂĚŝĞŶƚŝŶdŚ4 (tetragonal): Vzz = 5×1021 V/m2 ĺdŚ-‐ϮϮϵŶƵĐůĞĂƌŐƌŽƵŶĚƐƚĂƚĞƋƵĂĚƌƵƉŽůĞƐŚŝĨƚуϭ',nj! їuse cubic crystal symmetry dĞŵƉĞƌĂƚƵƌĞĚĞƉĞŶĚĞŶĐĞŽĨůŝŶĞǁŝĚƚŚĂŶĚĨƌĞƋƵĞŶĐLJƐŚŝĨƚƐ͗ ͻ ƌĞůĂƚŝǀŝƐƚŝĐŽƉƉůĞƌƐŚŝĨƚ͗ϭϬ-‐15 ͬ< ͻ electric crystal field shifts may be » 10-‐15 ͬ< (e.g. contact interaction nucleus / e-‐ cloud) ĺ)RUKLJKSUHFLVLRQEH\RQG-15
work at cryogenic temperature to
freeze out lattice fluctuations
Rellergert et al., Phys. Rev. Lett. 104, 200802 (2010) WĞŝŬĞƚĂů͕͘WƌŽĐ͘ϳƚŚ^LJŵƉ͘ŽŶ&ƌĞƋƵĞŶĐLJ^ƚĂŶĚĂƌĚƐĂŶĚDĞƚƌŽůŽŐLJ;Ăƌyŝǀ͗ϬϴϭϮ͘ϯϰϱϴͿ Search for nuclear resonance in 229dŚ+ -‐ Electron Bridge Processes ^ĞĂƌĐŚĨŽƌŶƵĐůĞĂƌĞdžĐŝƚĂƚŝŽŶǀŝĂĞůĞĐƚƌŽŶďƌŝĚŐĞƉƌŽĐĞƐƐ ͻ Ed;EƵĐůĞĂƌdžĐŝƚĂƚŝŽŶďLJůĞĐƚƌŽŶdƌĂŶƐŝƚŝŽŶͿ͗dƌĂŶƐĨĞƌŽĨĞdžĐŝƚĂƚŝŽŶ
from the electron shell to the nucleus ͻ Excitation of the shell in a 2-‐photon process їŶŽƚƵŶĂďůĞůĂƐĞƌĂƚϭϲϬŶŵƌĞƋƵŝƌĞĚ ͻ Excitation rate may be strongly enhanced at ƌĞƐŽŶĂŶĐĞďĞƚǁĞĞŶĞůĞĐƚƌŽŶŝĐĂŶĚŶƵĐůĞĂƌ ƚƌĂŶƐŝƚŝŽŶĨƌĞƋƵĞŶĐLJ ĺǀĞƌLJůŝŬĞůLJŝŶƚŚĞĚĞŶƐĞůĞǀĞůƐƚƌƵĐƚƵƌĞŽĨdŚ+ ͻ ĞƚĞĐƚŝŽŶŽĨƚŚĞŶƵĐůĞĂƌĞdžĐŝƚĂƚŝŽŶǀŝĂĨůƵŽƌĞƐĐĞŶĐĞŽƌĐŚĂŶŐĞŝŶ
hyperfine structure dǁŽ-‐photon electron bridge excitation rate &ĞLJŶŵĂŶĚŝĂŐƌĂŵ electrons E1 Zatomicresonance line at 402 nm Ztunable laser to search for nuclear resonance ZN Z Z
Dϭ,&^ nucleus Excitation rate as a function of nuclear resonance frequency (elect. levels from ab-‐initio calculations) їĞdžĐŝƚĂƚŝŽŶƌĂƚĞŽĨĂƚůĞĂƐƚ 10 s-‐1 ǁŝƚŚĐŽŶǀĞŶƚŝŽŶĂů laser parameters WŽƌƐĞǀĞƚĂů͕͘WŚLJƐ͘ZĞǀ͘>Ğƚƚ͘105, 182501 (2010) Laser spectroscopy of trapped Th+ ions at PTB
- Linear Paul trap for buffer gas cooled clouds of Th+ (N >105)
- Laser ablation loading (N2-Laser, now Nd:YAG laser)
- Fluorescence detection in several spectral channels
Laser spectroscopy of trapped Th+ ions
Decay channels for the
402 nm resonance line
- Laser excitation in Th+ leads to population of many metastable levels
- These are quenched by collisions or emptied with repumper lasers
Th+ Level Scheme
ͻ >ĞǀĞůƐŝŶƚŚĞsearch range only ŝŶĐŽŵƉůĞƚĞůLJŬŶŽǁŶ ͻ džƉŽŶĞŶƚŝĂůŝŶĐƌĞĂƐĞŽĨůĞǀĞů
density expected ±1V
3x
800 nm
402 nm
ͻ Why is nuclear laser spectroscopy difficult? ͻdŚĞůŽǁ-‐ĞŶĞƌŐLJŝƐŽŵĞƌŝĐƐƚĂƚĞŝŶdŚ-‐229 ͻdŚ-‐229 as a precise optical nuclear clock • Application search for D
Are fundamental constants really constant?
Equivalence Principle: fundamental constants need to be constant in time
=
=
Reinhold et al., PRL 96, 151101 (2006)
Murphy et al., Mon. Not. R. Astron. Soc. 345, 609 (2003)
Laboratory Tests
Sensitivity factor A of different
atomic transitions to a potential
drift of D
x
f
f
w ln f
wt
w ln Ry
w ln D
A
;
wt
wt
Al+/Hg+
A{
w ln F
w ln D
Hg+
Yb+
Present status:
Dzuba et al. PRL 82 (1999)
w ln D
(2.4 r 2.7) 10 17 yr 1
wt
w ln Ry
(0.0 r 3.2) 10 16 yr -1
wt
Laboratory Tests
Sensitivity factor A of different
atomic transitions to a potential
drift of D
A ~ 10,000
.
.
.
229Th
Dzuba et al. PRL 82 (1999)
!
x
f
f
w ln f
wt
w ln Ry
w ln D
A
;
wt
wt
A{
w ln F
w ln D
Th-229: most sensitive probe in a search for D
Scaling of the 229Th transition frequency Z in terms of D and quark masses:
V. Flambaum et al., Phys. Rev. Lett. 97, 092502 (2006)
105 enhancement in sensitivity results from near perfect
cancellation of O(MeV) contributions to nuclear level energies
But: it depends a lot on nuclear structure!
See for example:
Hayes et al., Phys. Rev. C 78, 024311 (2008)
Litvinova et al., Phys. Rev. C 79, 064303 (2009)
> 10 theory papers
2006 - 2009
(|A| } 103)
(|A| } 4×104)
Solution: measure isomer shift ('<r²>) and get better estimate for change in Coulomb energy!
J. C. Berengut et al., PRL 102, 210808 (2009)
To Do List for Thorium Trappers
ͻ locate transition at 160 10 nm ͻŵĞĂƐƵƌĞŝƐŽŵĞƌƐŚŝĨƚїƐĞŶƐŝƚŝǀŝƚLJŽŶD
ͻůŝĨĞƚŝŵĞŽĨŝƐŽŵĞƌŝĐƐƚĂƚĞ͍ • evaluate clock systematics Optical Clock
Groups
at PTB:
Ekkehard Peik
Christian Tamm
Piet Schmidt
Uwe Sterr
T.E.M.
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