Romualdo de Souza
Ternary Fission and Neck Fragmentation
Romualdo de Souza
Ternary Fission
In studying the interplay of Thermodynamics and Dynamical effects, ternary fission is a superior choice over multifragmentation due to low excitation and large deformation.
There are 3 probes of nuclear dynamics in fission:
1) Total kinetic energy of fission fragments
2) Pre-scission emission of neutrons
3) Ternary fission
Ternary fission can provide information on both the magnitude as well as the tensorial properties (one body vs. two body) of nuclear dissipation.
N. Carjan, A. Sierk, and J.R. Nix, Nucl. Phys. A452, 381 (1986)
Romualdo de Souza
Ternary fission can be used as a probe of the scission configuration
nth, ,12C 232Th
Excited Compound Nucleus Possible
Emission of an IMF
neck
Net Force Scission axis
neutrons
Fission fragments
Spontaneous Fission
L (deg.)
E (
MeV
)
Neck (equatorial)emission >97%
Polar Emission 0.3%
252Cf
Theobald et al.
Romualdo de Souza
Cosper et al. [ S.W. Cosper, J. Cerny, and R.C. Gatti, Phys. Rev. 154 1193 (1967).]
• Neck fragments are focused relative to the scission axis.
• Neutron rich isotopes are favored
• Kinetic energy spectra are approximately gaussian.
• Heavier clusters observed: e.g. 10Be
Romualdo de Souza
Experiments on IMF/Cluster Production in Hot Ternary Fission
• 3He + 232Th Elab/A = 90 MeV (IUCF) D.E. Fields et al., PRL 69 3713 (1992)
• 4He + 232Th Elab/A = 50 MeV (IUCF) S.L. Chen et al., PRC 54 R2114 (1996)
• 12C + 232Th Elab/A = 22 MeV (MSU) R. Yanez et al., PRL 82, 3585 (1999)
• 12C + 232Th Elab/A = 16 MeV (ANL)
4He + 232Th E/A=50 MeVE* 140 MeVmax 33
12C + 232Th E/A=22 MeV
E* 230 MeV
max 120 > RLDM 70
Intermediate Mass Fragments (IMF): 3 Z 20
Romualdo de Souza
Focused angular distribution (due to cancellation of Coulomb forces along scission axis)
D.E. Fields et al Phys. Rev. Lett. 69, 3713 (1992)
Detector orthogonal to scission axis!
Other three Detectors are non-orthogonal to scission axis!
Ternary FissionLow kinetic energies (due to emission from an extended system)
3He + 232Th at Elab/A=90 MeV
Romualdo de Souza
Experimental Setup of 4He + 232Th E/A=50 MeV
95.0
BeamTarget
55
PPAC/MWPC
PPAC/MWPC
30 cm
4-pack160.8
143.2
100.0
• 5cm x 5cm 300 m quadrant Si design
• axial IC design
•18-20 torr CF4 in IC
• 3cm CsI(Tl) with PD readout
E Threshold 0.7 MeV/u
• Measurement of IMFs at backward angles eliminates pre-equilibrium component
Romualdo de Souza
Experimental Setup of 4He + 232Th E/A=50 MeV
95.0
BeamTarget
55
PPAC/MWPC
PPAC/MWPC
30 cm
4-pack160.8
143.2
100.0
E Threshold 0.7 MeV/u
• Measurement of IMFs at backward angles eliminates pre-equilibrium component
Experiments on IMF/Cluster Production in Hot Ternary Fission
• 3He + 232Th Elab/A = 90 MeV (IUCF) D.E. Fields et al., PRL 69 3713 (1992)
• 4He + 232Th Elab/A = 50 MeV (IUCF) S.L. Chen et al., PRC 54 R2114 (1996)
• 12C + 232Th Elab/A = 22 MeV (MSU) R. Yanez et al., PRL 82, 3585 (1999)
• 12C + 232Th Elab/A = 16 MeV (ANL)4He + 232Th E/A=50 MeVE* 140 MeVmax 33
12C + 232Th E/A=22 MeVE* 230 MeV
max 120 > RLDM 70
Intermediate Mass Fragments (IMF): 3 Z 20
Ion Chamber-Si-CsI(Tl)/PD telescopes
Romualdo de Souza
• Single wire resolution in X (0.8 )
• Slightly larger than single wire in Y
• Pulse Height separation of FF from alphas
• Time of flight relative to RF (fission mass asymmetry)
Identification of FF by hybrid PPAC/MWPC
Romualdo de Souza
0
200
400
600Be in4-pack
FF2
IMF FF1
FF2
IMF FF1
0
200
400
600C in4-pack
0 20 40 60 800
50
100
150
200 Be inDet. 5
CM Energy Spectra of Be and C12C + 232Th at E
LAB = 264 MeV
0 20 40 60 800
50
100
150
200C inDet. 5
ECM
(MeV)d
N/d
EC
M
Fragments Emitted in Carbon induced reactions show the same features as in the He induced reactions
KE spectra orthogonal to the scission axis are bimodal
Low energy component is focused orthogonal to scission axis
(Near scission/neck emission)
High energy component is “isotropic”
(early stage emission while system is still compact)