Laser spectroscopy experiments on fission products
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Laser spectroscopy experiments on fission products
Principle : use the electronic cloud to probe the nuclear electromagnetic properties
Measured quantities : spin I, magnetic moment I, spectroscopic
quadrupole moment Qs, evolution of the mean square charge radius <r2>c
Introduction : hyperfine interaction
Physics case (part of)
Physics of medium mass nuclei produced by fission
Laser spectroscopy systems
Resonant Ionisation spectroscopy (RIS) : COMPLIS
Collinear Spectroscopy after beam cooling : future laser system at ALTO
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Hyperfine interaction
=300 nm
106 GHz
h4eV
6
0
10E h
IJ
H 0 NIA
B )0(JJ e QS
2Q0
Axial symmetry
JIF
191Ir
5
Two hyperfine interaction energy termsMeasurement
Nuclear quantities3)1)(2I(I
)1I(IK3
2
Nuclear structureinformation
QS
3K2-
A B
4
3
2 1
4GHz
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
AA'AA'Vol F
• Change of the nuclear charge density between isotopes :
VOLUME SHIFT
AA'iVol
AA'iM i
AA’
2cr
2 21
2
AA'
• Change of nuclear mass between isotopes:
AA'
A'-AMM iSiN
AA'iM
MASS SHIFT
Measurement Nuclear quantity
Nuclear droplet model
Isotope shift
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Ni Z=28
N=50
neutron rich nuclei produced by fission at ALTO (Orsay) and then at SPIRAL2 (GANIL)
Fission
Nuclear regions explored at ALTO
N=82
Sn Z=50
Doubly magic regions 78Ni and 132Sn
e-
238U
target source
30 keV
1+
50 MeV
Expected intensities = SPIRAL2 /100
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Production /s/µA
Stable
104 – 105
105 – 5 105
5 105 – 106
106 – 5 106
5 106 – 107
107 – 5 107
5 107 – 108
108 – 5 108
5 108 – 5 109
Expected yields at ALTO
Extrapolations from measured yields at PARRNe
Represented yields 104pps
minimum yield for the laser set-up we envisage
Z=28
Z=50
N=50
N=82
Kr
RbSr
CdIn
Sn
XeCsBa
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Z=56 Ba
N=82
Z=54
Xe
mid-shell effect
A “sample” of the physics motivations
The evolution of the charge distribution is very sensitive to the structural changes
<r2>c
N=60N=50
=0.4
=0.3
=0.2
=0.1
=0
Rb (Z=37) C. Thibault Nucl. Phys. A367, 1 (1981)
Sr (Z=38) F. Buchinger Phys. Rev. C 41, 2883 (1990)
Sherical shell gap
<r2>c when N
<r2>c very rapidly when N
Shape transition
The <r2>c variations reflect both the change in volume and departures from spherical symmetry, the origins of which can be :
-rigid deformation (rotor behaviour)
-Zero point quadrupolar vibrations (or more generally dynamical effects)
-Core polarization
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Origin : monopole part of the neutron-proton interaction importance of the radial part of the orbital wave functions
Illustration of the core polarization effect
n=2 n=3 n=4
N<50
N>50
2d5/2
1g9/2
2p1/2
2p3/2
1f5/2
50
2d5/2
1g9/2
2p1/2
2p3/2
1f5/2
50
40
38
40
38
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Illustration of the “dynamical” effects
Recent results from
the COMPLIS measurements
on tin
F. Le Blanc et al. to be published in Phys Lett B
Theoretical Data
NL3 : G.A Lalazissis et al., At. Data and Nucl. Data Tables 71 (1999)1.Gogny : M. Girod and S. Péru, Private comm. (2001)SLy4 and SLy7 : P. Bonche and J. Meyer, Private comm. (2002).
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Resonant ionization mass spectroscopy system :COMPLIS
Desorption
Excitation
Ionization
Excitation
Target
Ion detector (MCP)
Magnet
Incident beam at 60 kV Emergent beam at 59 kV
Ion source (stables)Magnet
INJECTOR
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
graphite YAGbeam
dtca
resolution
MHz250
a
Ionization volume
First stagebeamIonization
beams
Ground state
Ionization continuum
351,7 nm (UV)
323,29 nm (UV)
646,58 nm (rouge)
Ionization zonedesorbed atoms
Dye laserlambda-physik
2
tunablemonomodedye laser
« compulsé »
YAGpumping10 Hz
2
1 atome/100
totalefficiency
10-5-10-6
YAGpumping10 Hz
Characteristics of the COMPLIS set-up
ZOOM
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Principle of the fast beam collinear laser spectroscopy
E=mv vEnergy spread
velocity spread
The kinematic compression of the velocity distribution
results in a reduction of the residual doppler width
D=0vcResidual
doppler width
Velocity v
Velocity v+v
Laser source fixed frequency
Frequency in the rest frame of the atoms
The hyperfine structure is scanned by a beam energy scan
with U=10-4, ~50 MHz
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
COLLINEAR laser spectroscopy system
electrons
Ion source
Mass separator
Photomultiplier
Retardation system
Charge-exchange cell
Ellipsoïdalmirror
High resolution laser
Separated beam
RFQ cooler-buncher
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
A. Transport : 70 %B. Neutralization : 80 % C. Feeding probability of the selected metastable state : 30%D. Spatial overlap between laser beam and ion beam : 5 10- 3
E. Resonance efficiency : 100%F. De-excitation efficiency : 50%
G. Collection efficiency : : 5 %
H. Detection efficiency : 90 %
TOTAL : ~10-5
4
Efficiency
but : signal/noise ratio strongly increased by the use of the cooler buncher
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
A few details on the cooler…
Ion deceleration 10eV
F. Herfurth NIM A 469 (2001) 254(ISOLTRAP)
Pulsed cavity
UcavityUHV
Ions
UHVUcavity
transfert
Ekin=e.( UHV-Ucavity )
Buffer gas
Ions
grounded UHV
Longitudinal potential shape
Ions
trapping
ejection
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
•Ag (Z=47) : from A=111 to A=123 (or further from the stability line depending on the effective productions) complete the measurements on this isotopic chain on the right side of the valley of stability•Transition : Z.Phys. A274 (1975)79.
• Ge (Z=32) : from A=77 to A=83 N=50 crossing
•then, les Br, As and Ga towards Ni, Sb, I, ...
547.7 nm
206 nm
422.7 nm
303.9 nm
First measurements at ALTO
N=50
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TAS Workshop LPC Caen, March 30-31, 2004 D. Verney
Coût et main d’œuvreCoût et main d’œuvre
Lentilles d’accélérationralentissement
Cellule àéchange de charge
Miroirellipsoïdal
Laser hauterésolution
1. Ligne de faisceau, éléments d’optique ionique et pompage : 50 k€
2. Cellule à échange de charge : LAC ou Mainz
3. Détection : 10 k€
4. Lasers et optique : 200 k€
5. Acquisition et commande : 40 k€
6. Total : 300 k€
Durée du montage et de la mise au point : 2 ans à 2 chercheurs plein temps plus aide service technique (construire l’acquisition et réaliser la ligne de faisceau)
F. Le Blanc IPN