Transcript ELISE @ GSI - Department

ELISe
A new facility for unprecedented
nuclear fission studies
CEA Bruyeres le Chatel – GSI Darmstadt – CEA Saclay
DEN – IPN Lyon – IPN Orsay – CENBG – CEA Saclay
SPhN
15th Nuclear Physics Workshop,
Kazimierz 2008
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The fission observables
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Fission x-section
n/g production (mult., energy)
FF yields
TKE, Angular distribution
/ E*, J
/ Fissioning system
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The observable measurement
• Most targets are radioactive
• Fission x-section
– Dramatic improvement in 50 years
• Neutron production
– Not much data, high precision/ applications
• FF isotopic yields
– Difficult measurements / low recoil velocity
– Scarce data, accuracy often limited
– Recent strong effort / inverse kinematics
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Fission@ELISe
• Innovative experimental tool (low and intermediate
energy fission)
– Fission fragment Yields (Z1, A1, Z2, A2) before b-decay, after nemission
– Neutron production (n, En)
– Branching ratio (Gf/Gtot)
• For lots of actinides and pre-actinides with reasonable
lifetime (min)
• As a function of the excitation energy
– Range: threshold < E* < 30 MeV
• Nobody could do that
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FAIR/ELISe facility
238U
acceleration : 1.A GeV
ELISe
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238U
Be
Fragmentation
Chosen nucleus
740 MeV/A
SIS 100
238U 1.A GeV
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The SuperFRS
• Select a specific nucleus
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Neptunium 232 to 238
Uranium 230 to 238
Protactinium 228 to 237
Thorium 225 to 235
Actinium 223 to 230
Radium 222 to 225
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• Time of Flight : 400ns
• Output : clean secondary beam (107/spill)
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Super FRS :
Chosen Actinide or
preactinide
e- acceleration (500MeV)
interaction Zone
Storage ring : 108 ions
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The interaction zone
Beam dimensions : 80 X 200 mm
1.5 GeV Centre of Mass
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e-ion interaction
• “pseudo-Bremstrahlung” :
– A virtual photon is transferred
– The electron is scattered
– Ion gains some excitation energy (GDR, GQR
mainly)
• Moderate total x-section : 50 mbarn
– Fission x-section ~ 5-30 mbarn
• High luminosity : 1028/cm2s
• Fission rate ~ 50-300 /s
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E* Measurement
Recoil e- detected
Kinetik energy measured
E* transfered
Resolution : 1 MeV
For every elect.-ion interaction : Z,A, E* (±1MeV)
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Excitation spectrum
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30 E* (MeV)
• “Low” excitation energy
• Structure effect studies
• nuclear reactor energy domain
• 236U E*=8MeV  n+235U with En=1.5MeV
– Same production
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Experimental set-up
Flight path :7m
TWIN MUSIC
FF1
FF2
≈ 50 cm
=> Z1, et Z2
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Data reduction
• Double IC (MUSIC) : Z1, Z2
• 3-fold position measurement gives r
• ion Optics :
Br = p / q
= k.A.v.g / Z
q = -Ze
• ToF gives v et g
We obtain A1 et A2
The neutron wall: n, et En
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Fission width estimate
• Simpler experiment / fission barrier
– Count the fission event #
– Count the inelastic event #
– Ratio gives the fission width / E*
• Lower Actinide Ekin = 100 MeV
– 100 keV E* resolution
– Higher angles
• Only one detector needed
– MUSIC has to count the fission fragments
– Larger/dedicated detector
– Almost 100% efficiency
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Conclusions
• Fission@ELISE will produce a huge volume of
innovative data
– Isotopic yields for FF,
– Multiplicity and neutron spectra,
– Fission probability
• Major interest for nuclear reactor simulation
• Astrophysics interest
• Fundamental physics data
– Shell effects (Proton/neutron disentangled)
– Odd-even effect
– Kinetic energy (scission configuration)
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The interaction zone
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