1. Ternary Fission and Neck Fragmentation
Romualdo de Souza

3. There are 3 probes of nuclear dynamics in fission:
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:
Total kinetic energy of fission fragments
Pre-scission emission of neutrons
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

4. Ternary fission can be used as a probe of the scission configuration
Spontaneous Fission
neutrons
Excited Compound Nucleus
Possible Emission of an IMF
neck
nth, ,12C
232Th
Fission fragments
Polar Emission 0.3%
Theobald et al.
E (MeV)
252Cf
Net Force
Scission axis
Neck (equatorial)emission >97%
L (deg.)
Romualdo de Souza

5. Neck fragments are focused relative to the scission axis.
Cosper et al. [ S.W. Cosper, J. Cerny, and R.C. Gatti, Phys. Rev (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

6. Experiments on IMF/Cluster Production in Hot Ternary Fission
Intermediate Mass Fragments (IMF): 3  Z  20
3He + 232Th Elab/A = 90 MeV (IUCF) D.E. Fields et al., PRL (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 MeV
E*  140 MeV
max  33 
12C + 232Th E/A=22 MeV
E*  230 MeV max  120  > RLDM  70 
Romualdo de Souza

7. 3He + 232Th at Elab/A=90 MeV Detector orthogonal to scission axis!
D.E. Fields et al Phys. Rev. Lett. 69, 3713 (1992)
Detector orthogonal to scission axis!
Focused angular distribution (due to cancellation of Coulomb forces along scission axis)
Other three Detectors are non-orthogonal to scission axis!
Low kinetic energies (due to emission from an extended system)
Ternary Fission
Romualdo de Souza

8. Experimental Setup of 4He + 232Th E/A=50 MeV
5cm x 5cm 300 m quadrant Si design
axial IC design
18-20 torr CF4 in IC
3cm CsI(Tl) with PD readout
100.0
PPAC/MWPC
143.2
55
E Threshold  0.7 MeV/u
4-pack
160.8
Beam
Measurement of IMFs at backward angles eliminates pre-equilibrium component
Target
30 cm
95.0
PPAC/MWPC
Experimental Setup of 4He + 232Th E/A=50 MeV
Romualdo de Souza

9. Experiments on IMF/Cluster Production in Hot Ternary Fission
Intermediate Mass Fragments (IMF): 3  Z  20
3He + 232Th Elab/A = 90 MeV (IUCF) D.E. Fields et al., PRL (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 MeV
E*  140 MeV
max  33 
12C + 232Th E/A=22 MeV
E*  230 MeV max  120  > RLDM  70 
100.0
PPAC/MWPC
55
143.2
Ion Chamber-Si-CsI(Tl)/PD telescopes
4-pack
160.8
E Threshold  0.7 MeV/u
Beam
Measurement of IMFs at backward angles eliminates pre-equilibrium component
Target
30 cm
95.0
PPAC/MWPC
Experimental Setup of 4He + 232Th E/A=50 MeV
Romualdo de Souza

10. Identification of FF by hybrid PPAC/MWPC
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)
Romualdo de Souza

11. KE spectra orthogonal to the scission axis are bimodal
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)
Romualdo de Souza