International Nuclear Physics Conference 2007 - Jun. 4 -
Hyperfine structure of 85,87Rb and
133Cs atoms in superfluid helium
Development of new laser spectroscopy project
using superfluid helium stopper
Takeshi Furukawa
Nishina-Center, RIKEN
Collaborator
Y. Matsuo1, A. Hatakeyama2, T. Ito3, K. Fujikake3
T. Kobayashi1, and T. Shimoda4
1Nishina-Center,
RIKEN,
2Dept. Appl. Phys., Tokyo Univ. of Agr. Tech.,
3Dept. Phys., Meiji Univ.
4Dept. Phys., Osaka Univ.
International Nuclear Physics Conference 2007 - Jun. 4 -
Contents
1) Our New laser spectroscopy project
・Double resonance method in He II
Laser spectroscopy & optical detection
Optical pumping in He II
(
2) Measurement data in the development
・Long atomic spin relaxation time in He II
・hyperfine resonance spectrum of 85,87Rb and 133Cs in He II
・determination of nuclear magnetic dipole moment
・hyperfine anomaly in He II
3) Summary and future prospect
International Nuclear Physics Conference 2007 - Jun. 4 -
Overview of Our Method
Development : laser spectroscopy for short-lived RI atoms
OROCHI project
(tentative)
Optical RI-atom Observation in Condensed Helium
He II liquid
RI atom
purpose
Systematical measurement of
unknown hyperfine structures
in exotic RI atoms
Laser
RI beam
Laser induced fluorescence (LIF)
effective stopping & trapping of RI atoms
wavelength separator
& photon detector
using superfluid helium as a stopper & trap
from “DRAEMON” vol. 22, by FUJIKO, F. Fujio
International Nuclear Physics Conference 2007 - Jun. 4 -
Nuclear Laser Spectroscopy
Contaminated atoms: no absorbing laser light
→ observe only objective atoms !!
Laser induced fluorescence (LIF) photon
He II
absorb & emit photons cyclically
→ detect much photons/atom
Laser
(typically ~ 105-108 photons /sec)
→ good statistic !!
Scattered laser photon
absorption spectra in He II : largely broadened & blue-shifted.
RI beam
wavelength : λatoms   laser
suppress the detection of scattered laser light
feasible to achieve optical pumping of various atomic species
i.e.) In, Tl, ….
International Nuclear Physics Conference 2007 - Jun. 4 -
Double Resonance Method
Purpose: measure the hyperfine structure of RI atom
LIF intensity
expected spectrum
microwave frequency
Polarized atoms : Can not absorb circularly polarized laser light.
LIF Intensity ∝ 1 - Pz
International Nuclear Physics Conference 2007 - Jun. 4 -
Spin relaxation in He II
To polarize the atoms : spin relaxation time is important
long spin relaxation time in He II has been measured.
feasible to achieve optical pumping
133Cs
atoms in He II
extremely longer than optical pumping time
T. Furukawa et al., Phys. Rev. Lett. 96, 095301 (2006)
International Nuclear Physics Conference 2007 - Jun. 4 -
Experimental Setup
Measurement of the hyperfine splitting in Cs, Rb atoms
CsI
Cs
Cs
International Nuclear Physics Conference 2007 - Jun. 4 -
Double resonance peak in He II
Hyperfine resonance measurement ：stable 133Cs, 85,87Rb
measured spectrum using double resonance method
ν133Cs= 9.2580915 (4) GHz
ν85Rb= 3.05802 (10) GHz
A85Rb = 1.01702(2) GHz
A133Cs = 2.312 76(2) GHz
（Preliminary）
（Preliminary）
ν87Rb= 6.87652 (10) GHz
A87Rb = 3.43517(4) GHz
（Preliminary）
International Nuclear Physics Conference 2007 - Jun. 4 -
Hyperfine Structure in He II
Hyperfine coupling constant A
He II (GHz)
133Cs
DA/A (%)
H (> H)
H’
2.31276 (2) 2.2981579 0.635 (1)
85
Rb
Vacuum (GHz)
Pressurized by helium
87
0.505 (2)
3.43517 (4) 3.4173413 0.522 (1)
1.01702 (2)
1.0119109
Calcuration from hyperfine coupling constant
mI85Rb (mN)
85D87
This work (from AHeII)
1.357 84 (1) mN
0.331 7 (7) %
literature value
1.353 351 5 mN
0.348 7 (3)%
difference
0.331 7 (7) %
4.8 (2) %
In He II
electron
nuclei
Enable to obtain the nuclear information efficiently!!
International Nuclear Physics Conference 2007 - Jun. 4 -
for RI Beam Experiment
to confirm the feasibility of our project
measure the LIF photons from RI atoms
Wavelength plate
Wavelength plate
Laser Induced
Fluorescence
（LIF）
Lens
Optical filter
Lens
estimated lower limit of the beam intensity to measure：only 10 cps
International Nuclear Physics Conference 2007 - Jun. 4 -
Conclusion
We are now developing successfully…
OROCHI project
(tentative)
Optical RI-atom Observation in Condensed Helium
measure the hyperfine structure of exotic RI atoms
133Cs, 85,87Rb
hyperfine splitting in He II
・deduce nuclear moment with 1% accuracy
・deduce hyperfine anomaly with 5% accuracy
* Nuclear spin can be also determined with rf-resonance
~Next plan~
+ RI beam experiment (plan: in next year)
+ Optical pumping of various elements (In, Tl, Ca, ….)
Goal : measurement of In, Tl isotopes
International Nuclear Physics Conference 2007 - Jun. 4 -
ふろく
Additional OHP
Zeeman sublevels of 85,87Rb
85Rb
高さの比 ＝6636/22370 ＝0.297
同位体比＝27.85/72.15 = 0.386
→ｒｆパワーが違うため？
周波数比 ＝1815/2720 ≒ 2/3
理論比 ＝ gF=3/gF=2 ≒ 2/3
→未知の核種の核スピン同定が可能！
87Rb
Pressure effect in HeII
Hyperfine coupling constant
HeII (GHz)
vacuum (GHz) HeII/vacuum ratio
2.31276(2)
2.29815794 1.00635(1)
85
1.01702(2)
1.01191092 1.00505(2)
87
3.43517(4)
3.41734131 1.00522(1)
133Cs
Rb
A=mI<H>/I・J
Difference of <H> in He II
Compressed atom by surrounding helium
Affect to the orbital of valence eveltrons
VCs＞VRb
＜ 1% increase
ΔCs＞ΔRb
Pressurized by helium
H’H(> H)
Determination of 85Rb moment
Deduce
m
85 Rb
I
g
85Rb
moment with
85 Rb 85 Rb
I
I
87Rb
moment as reference
85 Rb
A
85 Rb 87 Rb
I
g I  87 Rb  1.35784(1) m N
A
( g I87 Rb I 87 Rb  2.751818(2)mN )
85 Rb
m
 1.357782(1)mN
Use A value in vacuum: I
literature value：
mI85 Rb  1.3533515
(8)mN
・possible to determine the moment with 1% accuracy
・difference (～0.3%) ← caused by hyperfine anomaly
electron
nuclei
Effect of the distribution of
nuclear magnetization
Hyperfine anomaly in He II
Considering hyperfine anomaly…
m
85 Rb
I
g
85 Rb 85 Rb
I
I
85 Rb
A
1
85 Rb 87 Rb
I
g I  87 Rb
A
(185D87 )
In HeII
85
D87HeII  0.3317(7)%
In vacuum
85
D87vacuum  0.3487%
)
hyperfine anomaly
～５％ difference
In vacuum
Due to the deformed electron distribution
by the pressure of surrounding He ??
In HeII
Hyperfine Interaction
Hyperfine Interaction
W(F, mF)= A・K/2
+ B・{3K(K+1)/4 –I(I+1)J(J+1)}/{2(2I-1)(2J-1)IJ}
[K=F(F+1)-I(I+1)-J(J+1)]
A=m<B>/IJ
B=eQ<V>
I:nuclear spin, J:electronic angular momentum,
m: nuclear magnetic dipole moment,
eQ: nuclear electric quadrupole moment,
<B>:magnetic field produced by the electrons
<V>:electric field gradient produced by the electros
Measure the constant A, B of isotope mX and nX
mmX AmX ImX
mnX = A I
nX nX
eQmX BmX
=
eQnX BnX
Effect of surrounding He atoms
① Blue-Shifted
absorption spectrum in He II
② Broadened
(
Bubble model
absorption
Energy
Deform
absorption
emission
emission
Deform
Bubble radius
Energy levels in the ground state and excited state
as a function of bubble radius.
Excitation Spectrum in He II
① Blue-Shifted
absorption spectrum in He II
② Broadened
(
by the pressure of surrounding He atoms
atomic spectra in He II
Intensity (arb.unit)
133Cs
emission：peak ~892 nm, width ~3 nm
(in vacuum: 894.347nm)
absorption：peak ~876 nm, width ~15 nm
absorption≠emission
Wavelength (nm)
Optical Merit in He II
① Blue-Shifted
absorption spectrum in He II
② Broadened
(
In vacuum
In He II
Laser
Need many
laser lights!
Detector
Excitation with
only single
laser light
wavelength: lLIF llaser
suppress the detection of
scattered laser light
Feasible to acheve optical pumping
Optical Pumping
Optical pumping method
（in the case of alkali atoms J=1/2）
atom
laser
B
P1/2
σ+
D1 Line
S1/2
σ+
X
After the polarizing of atoms…
Decrease LIF intensity
(Laser Induced Fluorescence, LIF)
m = -1/2
m = +1/2
LIF Intensity ∝ 1 - Pz
Optical Pumping of
Metastable Mg atoms
21
Mg atomic energy diagram
Observable resonance line
(Assume I = 5/2)
3s3p 3P2 F=9/2 ⇔ F=7/2
[h.f.s = (9/2)A + (27/40)B]
F=7/2 ⇔ F=5/2
[h.f.s = (7/2)A + (7/40) B]
( 3s3p 3P1 F=7/2 ⇔ F=5/2 )
Optical Pumping of Al atoms
3s23p 2P1/2,3/2 ⇔ 3s24s 2S1/2 transition
LIF intensity（a.u.）
27Alの原子準位図
・3s23p 2P1/2,3/2,mF>+3の準位
→円偏光(σ+)を吸収不可能
特定の磁気状態に原子状態が集中
＝ 偏極生成可能！！
350
355
360
365
370
Wavelength（nm）
2
問題点：基底状態(3s 3p 2P1/2,3/2)の偏極緩和時間
2P ：電子軌道が非対称→緩和しやすい
3/2
2P ：電子軌道が球対称→緩和しにくい
1/2
→2P1/2では偏極生成可能？
Relaxation in the Dark Method
Measure the relaxation time
→“Relaxation in the dark” method
detect the photons only from the “spin relaxed” atoms
Timing chart
Spin relaxation time in He II
Dark period後のLIF強度
偏極ゼロ時のLIF強度
Measured LIF intensity
Demerits in Optical Detection
Problems in laser spectroscopic study of RI atoms
・stopping & Trapping efficiency
・possible elements
B.G. count of stray light
In He II・・・
Introduced to condenced helium
→ observe all of the stopped atoms
high trapping efficiency
Laser
RI Beam
Stopped & trapped
Using the characteristic spectrum of
atoms in He II
→Subtract the problems
Interaction with surrounding He
Scientific Motivation
Unstable nuclei near the drip-line
・low-yield
・high-contamination
・small-polarization
)
Laser spectroscopy
& optical detection
of RI atoms
Optical pumping in He II
Difficult to measure !!!!
ex)b-NMR method
detector
Polarized RI nucleus
stopper
detector
Signals from RI
Measure the
hyperfine structure
Determination of
nuclear moments
Scientific Motivation
目標：短寿命不安定核の系統的核モーメント測定法開発
Nuclear moments
Nuclear structure
however…
Unstale nuclei near the drip-line
・low yield
・low purity
・small polarization
Difficult to measure!!
ex)b-NMR method
detector
Polarized RI nucleus
stopper
detector
Signals from RI
そこで…
『Laser spectroscopy of stopped RI atoms in HeII』
に着目
Conclusion
超流動ヘリウム中でのレーザー・マイクロ波二重共鳴法
安定核133Cs, 85,87Rbの超微細構造を測定
・核モーメントを１％以下の精度で決定可能
RF共鳴を用いれば核スピンも決定可能
理論的には電気四重極モーメントも同時に測定可能
・hyperfine anomaly効果も数％の精度で決定可能
真空中の値と～５％のズレ
→ 核内核子の密度分布に対する新しい情報？
～Next Plan～
・HeIIの影響について考察
・不安定核ビームを用いた測定
・Al, Mg原子の光ポンピング