Properties of isomers measured by high resolution laser ...
Transcript of Properties of isomers measured by high resolution laser ...
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Properties of isomers measured by high resolution laser spectroscopy
Jon BillowesBirmingham – Manchester – Jyväskylä
laser/IGISOL collaboration
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1. Nuclear charge radii –measurement and interpretation
2. The 8- isomers in 176Yb, 178Hf
3. Isomers and ground states of yttrium
4. Measurements by laser resonance ionization
Properties of isomers measured by high resolution laser spectroscopy
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Isotope Shift and Hyperfine Structure
Isotope shift of atomic transition
176Hf 178Hf
Analysis yields the change in nuclear mean square charge radius
Nuclear size, static and dynamic deformations
Hyperfine structure of atomic transition
177Hf
Nuclear spin I
Magnetic moment µ
Quadrupole moment Qs
ppm shift
(Isotope shift found using centroids of hyperfine multiplet)
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+40 kV
Ion beam cooler
Light collection region(Laser resonance fluorescence)
Reduces energy-spread of ion beam (<1 eV)
Trap and accumulates ions – typically for 300 ms
Releases ions in a 15 µs bunch
The laser/IGISOL facility at Jyväskylä
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Sensitivity gains using the RFQ ion-cooler
8000 ions/sec
5.3 hours
2000 ions/sec
48 minutes
Photons from laser-excitation of radioactive 88ZrLaser frequency
200
100
30
0
BEFORE
AFTER
(Photon-ion coincidence method)
(bunched beam method)
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Isotope Shift
Isotope shift of atomic transition
176Hf 178Hf
Analysis yields the change in nuclear mean square charge radius
Nuclear size, static and dynamic deformations
ppm shift
Transition energy difference between isotopes A and A’
+ mass shift (zero for isomers)
Deformed nucleus Spherical nucleus
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Mean square charge radii
δ<r2 >
(fm
2 )Volume
Deformation
Pairing effects?
Odd-even staggering
Radii of multi-quasiparticle
isomers178Hf 16+
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The K=8 isomers in 178Hf and 176Yb
Structure of 2-neutron 8- state in 176Yb
Structure of 2-qp 8- state in 178Hf is
60%(2ν)+40%(2π)
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The 176Yb 8- isomer
Production: (d,pn) at 13 MeV, 5.5 µAFlux: 200 isomers/sec (total flux at A=176: 8,400 ions/sec)
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176, 176mYb laser resonance spectrum
Yb+
λ= 328.9 nm
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δ<r2>176,176mYb fm2
-0.0224(1)
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The 178Hf 8- isomer
λ= 301.3 nm
Hf+
Production: 176Yb ( α, 2n) at 25 MeV, 5μA
Isomer beam: 3,000 per second
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8- δ<r2>178,178m1 = -0.0384(1) fm2
16+ δ<r2>178,178m2 = -0.0873(20)fm2 (Boos et al.)
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16+
8-
23/2-
Negative isomer shifts in multi-quasiparticle isomers
8-
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Calculation by Bordeaux Group (Pilletet al, Nucl. Phys. A 697 (2002) 141.)
Without pairing effects, Isomer shift = +0.051 fm2
Including pairing Isomer shift = -0.033 fm2
(Experiment: -0.087(2) fm2)<r2> for proton states
36.097 fm2
28.888 fm2
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84 86 88 90 92 94 96 98 100 102 104A Zr
18.4
18.8
19.2
19.6
20.0
20.4
20.8
fm2
<β2>=0.4
<β2>=0.2
<β2>=0.3
<β2>=0.1
<β2>=0.0
Charge radii of Zr isotopes
40Zr
mea
n sq
uare
cha
rge
radi
us
Deformed nucleus
Spherical nucleus
Spherical droplet modelMyers & Schmidt, Nucl. Phys. A410 (1983) 61.
3. Isomers and ground states of yttrium
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b2b2
Qs=0
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Problem: charge radius increase inconsistent with deformation derived from B(E2; 0+ →2+)
40Zr
Lack of Qs data to investigate problem further…. but wealth of ground states and isomers with I > ½ in neighbouring 39Y chain
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I=0
I≠0 Prolate
J=0
J=1
Yttrium atomic structure
Hyperfine structure
I=0
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Example of spectra for neutron-rich yttrium isotopes
(production by proton-induced fission of uranium)
Shift to lower laser frequency indicates increase
in the nuclear rms radius
Measured moment Qs is the projection of Q0 on quantization axis:
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β 2=0.0
β 2=0.1
β 2=0.2
β 2=0.3
β 2=0.4
β 2=0.5
17.8
18.2
18.6
19.0
19.4
19.8
20.2
84 86 88 90 92 94 96 98 100 102 104Mass Number, A
<r2 >A /
fm2
Stable IsotopesRadioactivesIsomers
Yttrium charge radii Yttrium charge radii
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N
Spherical
I=1
I=3
I=2
I=1
I=3
I=2
100Y
102Y
Mean square charge radius
(fm2)
Mean square radius from isotope shift data
Mean square radius predicted from spherical droplet model corrected for deformation
deduced from measured quadrupole moment
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Neutron number
Spherical
Isotope shift data (ground states)
Droplet model + deformation from Qs
Isotope shift data (isomers)
Mean square charge radius
(fm2)
Charge radii of yttrium isotopes
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p1/2
g9/2
Ground state and two isomers in 97Y
I=27/2
(The smaller nucleus is shifted to higher frequency)
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9/2+ (πg9/2) Q0=-1.40(15) b δ<r2>97,97m1 = +0.122 fm2
27/2- (πg9/2)(νg7/2)(νh11/2) Q0 = -1.50(17) bδ<r2>97m1,97m2 = -0.098(1) fm2
Results for 97Y isomers
-Same effect in an oblate multi-quasiparticle state – the 3qp isomer is smaller than the 1qp isomer.
-Other isomers with same feature: 130Ba(8-), 202Pb(9-), 135Cs(19/2-)
-Appears to be a common feature for multi-quasiparticle states
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The collinear-beams resonance ionization method5 µs 10 ns
50 Hz repetition rate lasers
Atom bunch
50 Hz delivery rate, synchronized with
laser pulse
All atoms from the ion source have a chance to be ionized
Resonance located by ion counting (not photon counting)
Doppler-broadening free
Ionization limit
308 nm
532 nm
Off-line tests with
27Al
4. Measurements by laser resonance ionization
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Comparison with low-flux bunched beams
1.5 GHz
Photon counting (12 minutes)
Ion counting (4 minutes)
Sensitivity: 1 resonance ion per 30 atoms
within 1 µs time window
(compared with 1 photon per 50,000 atoms)
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Ti:Sapphire lasers
Nd:YAG100W, 10 kHz
Pulsed dye lasersCopper vapour laser 45W, 10kHz
cw dye laser
cw pump laser
Isotope separatorIon guide
Fast Universal Resonant laser IOn Source FURIOS
Fast Universal Resonant laser IOn Source FURIOS
In-source laser spectroscopy (Doppler broadened)
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LIST: Laser ion source trapMethod being developed by FURIOS collaboration at JYFL
Applications:
* Production of high isobaric purity isotope or isomer beams
* In-source laser spectroscopy
IGISOL
Pulsed laser beams
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Manchester: J Billowes, P Campbell, A Nieminen, B Cheal, K Flanagan, M Avgoulea, B A Marsh, B W Tordoff
Jyväskylä: J Äystö, H. Penttilä, A Jokinen, J Huikari, S Rinta-Antila
Birmingham: G Tungate, D H Forest, M D Gardner, M Bissell
AcknowledgementsMatthew Gardner – Yttrium analysis
Bradley Cheal – Yttrium analysis
Mark Bissell – 178Hf(8-) analysis
Kieran Flanagan – 176Yb(8-) analysis
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Present work: Tantalum gs & isomers
9- isomer (>1.2 x 1015 y)
180Ta
9-
1+ 0 (8h)75 keV
J=1
J=2J=1
264 GHz
Ta+ ion
296.
5nm
7/2+ ground state