Transcript PowerPoint プレゼンテーション - University of Tokyo

Laser-microwave double resonance method
in superfluid helium
for the measurement of nuclear moments
Takeshi Furukawa
Department of Physics, Graduate School of Science,
Osaka University
Collaborator
Y. Matsuo2, A. Hatakeyama3, T. Ito4, Y. Ota4,
Y.Fukuyama2, T. Kobayashi2, and T. Shimoda1
1Dept.
Phys., Osaka Univ., 2RIKEN, 3Inst. Phys., Univ. of Tokyo,
4Dept. Phys., Meiji Univ.
Contents
1) Problems in measuring the nuclear moment
・Low-yield, high-contamination, small-polarization of unstable nuclei
2) Double resonance method to cope with the problems
・Double resonance method in He II
Laser spectroscopy & optical detection
Optical pumping in He II
(
3) Present status of the development
・Long atomic spin relaxation time in He II
・Hyperfine transition spectrum in He II
4) Summary and future prospect
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 the nuclear moment
ex) b-NMR method
detector
Polarized RI nucleus
detector
stopper
Measure the
hyperfine structure
Determination of
nuclear moments
Signals from RI
Merit in Optical Detection
low yield, high contamination
Laser spectroscopic method is suitable for unstable nuclei.
Laser Induced Fluorescence (LIF) photon
The impurity atoms can not absorb
the pumping laser.
Laser
Insensitive detection
to the impurity atoms.
Good S/N ratio
RI beam
Useful to measure
Pumping the RI atoms repeatedly.
the unstable nuclei
Detecting the LIF photons repeatedly.
Double resonance method
LIF intensity
(J=1, I=3/2
case)method.
We plan to measureHyperfine
the h.f.s Structure
with the double
resonance
expected spectrum
F=5/2
5/2A+5/4B
F=3/2
J=1, I=3/2
F=1/2
A=m<B>/IJ
5/2A
3/2A
3/2A-9/4B
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
microwave frequency
Optical
performed
nX
Measure the constant
A, Bpumping
of isotope mis
X and
Polarized atoms : Can not
laseratoms.
light.
only polarized
alkali-like
m absorb circularly
eQ
AmX ImX
=
mnX
AnX InX
mX
mX
eQnX
LIF Intensity ∝ 1 - P
z
=
BmX
BnX
Optical pumping in He II
In He II: possible to polarize various atoms with optical pumping
Optical spectrum of atoms is dynamically broadened
due to the influence of the surrounding He atoms.
Possible to optically pump the atoms
with complicated level structure
using a single laser beam
Mg 3s3p 3P2,1,0
Problem:
3s4s 3S1 Transition
How fast spin relaxes in He II ?
In vacuum
Many lasers needed.
In He II
Only one laser beam
induce to polarization.
Spin polarization in He II
Long spin relaxation time are expected in He II !
Relative polarization
How long the relaxation time ?
We have measured T1 of Cs atoms in He II
Spin relaxation of Cs atoms
Low temperature
Small polarizability
Spin-less atom
Achieved polarization : ~90 % in Cs
He II is suitable to use with our method.
Optical pumping of the atoms
other than alkalis is now in progress.
relaxing time
T. Furukawa et al., submitted to Phys. Rev. Lett.
Hyperfine structure of 133Cs
Check the feasibility in He II
Double Resonance spectrum of Cs atoms in He II
Hyperfine structure of
mF=+4
Details
of
133Cs
hyperfine
transition
+3
133Cs atom
+2
mF=+4~-4
+1
0
F=4
-1
9 levels+
F=4
-2
With σ pumping
-3
-4
ν+
Hyperfine
splitting
energy
2
6s
S1/2
With
σ- pumping
νν = (ν + Eνh.f.s
) /2= A・F = 4A
0
+
-
(A ∝ μI)
-3
F=3
-2
F=3
-1
0
mF=-3~+3
7 levels
+1
+2
mF=+3
Measurement Result of
Hyperfine Splitting
Preliminarily result
νσ+=9.257705(9) GHz
νσ-=9.243484(4) GHz
ν0 = (νσ+ + νσ-)/2 = 9.2505945(98) GHz
∴ A = ν0 / F = 2.3126486(25)
( in vacuum: 2.298157943 GHz )
~0.65% larger !!!
Pressure effect in He II
A = ν0 / F = 2.3126486(25)
( in vacuum: 2.298157943 GHz )
A=mI<H>/IJ
~0.65% larger !!!
Pressurized by helium
Large <H> in He II
Because of compressed
electron orbit pressurized
with surrounding He atoms
H’H(> H)
No difference in isotopes ??
Next plan :
Check the difference of <H’> between
85,87Rb
Summary and Future prospect
Measurement Method for the nuclei near the drip-line
Double Resonance in He II
Problems
Meri
t photons repeatedly
・low-yield
・Detecting the LIF
・high-contamination ・Insensitive to the impurity atoms
・Long spin preservation, high polarization
・small-polarization
・High polarization, long spin reservation, and
precise resonance spectrum are confirmed in He II
Future prospect
Optical detection from low-yield RI atoms
Optical pumping of various atoms other than alkalis (Mg, Al, ..)
Measure the moments of various nuclei (22Al, 21Mg,...)
Additional OHP
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
Timing Chart of Measurement
linearly
Pumping laser
polarization
Counting
gate
circularly
Count1
LIF Intensity
∝NCs
LIF ratio :
linearly
Count2
Count3
∝NCs(1-PlaserPatom)
∝NCs
With microwave resonance
count2
 (1 Plaser  Patom )
(count1 count3) 2
Patom→small (with M.R.)
Ratio→Large
Experimental Setup
Hyperfine Splitting of 133Cs
Atomic level energy
W = WJ + A・K/2 + WB + gFμBBmF
K = F(F+1) - I(I+1) - J(J+1)
In 133Cs case ( |F, mf ＞: |4, +4＞ → |3, +3＞)….
ΔWσ+ = W(4, +4) - W(3, +3) = A・F + gJμBB×7/8
ΔWσ- = W(4, -4) - W(3, -3) = A・F - gJμBB×7/8
Timing Chart
原子供給on
50m
s
40 ms
EOM
Photon
50m
soff
2.5m
s on
count
Count1 Count2 Count3
gate
Gate
1ms
width :
0.5ms
1ms
LIF ratio : Count2 / { (Count1 + Count3) /2 }
Double Resonance Method
Need more effective measurement method!
Laser Double Resonance Method in He II
is suitable for the measurement.
Double resonance method
a sort of laser spectroscopy
Laser Induced
Fluorescence
（LIF）
Lenｓ
Optical filter
Lens
Bubble Model
Atoms in He II: repel the surrounding helium atoms
(by Pauli repulsion)
Deform
absorb the photon
Energy
Like as bubble
absorption
emission
emit the photon
Deform
Bubble radius
Energy levels in the ground state and excited state
as a function of bubble radius.
Physics motivation
22Al
: proton halo?
22Al
21Mg
35Ca
=
21Mg
+p
: Isospin symmetry?
21Mg-21F mirror pair in T = 3/2
: Z=20 magic?
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 )
Relaxation in the Dark Method
Timing chart
Measured LIF intensity
Measured LIF intensity
Spin Relaxation Mechanism
◯s-sta te e le ctro n (s) ( 2 S 1 /2 e le ctro n in Cs, Rb )
m a g n e tic in te ra ctio n (sp in -o rb it in te ra ctio n etc. . . )
e x ) Cs 2 S 1 /2 : 2 . 5 ×１０-24cm2
σ…≒10-19-26cm2
J> 1 e le ctro n (s) ( 3 P e le ctro n s in M g )
e le ctro sta tic in te ra ctio n
e x ) H g 3 P1 : 1 . 1 ×１０-15cm2
σ…≒10-14-15cm2
2
P1 /2 e le ctro n (s) ( 2 P1 /2 e le ctro n in Cs, Rb )
v irtu a l tra n sitio n to 2 P3 /2 & e le ctro sta tic in te ra ctio n
σ…≒10-16-17cm2
e x ) Tl 2 P1 /2 : 6 . 0 ×１０-19cm2
2
P1/2-2P3/2 ΔE ： 7793cm-1
Cs 2 P1 /2 : 2 . 1 ×１０-16cm2
554cm-1
M.R. Spectrum in He II
Check the feasibility in He II
Double Resonance spectrum of Cs atoms in He II
(Zeeman sublevel transition, Magnetic field : ~ 3 G)
Energy level of g.s Cs atom
Zeeman transition
6s1/2
...
F=4
Hyperfine
F=3 transition
Peak frequency:959.5(5) kHz
(preliminary)
Observing hyperfine resonance
same as that
Nuclear moments can be
determined precisely