Romualdo de Souza

1
Ternary Fission and Neck Fragmentation
Romualdo de Souza
2
(No Transcript)
3
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
neutrons
Spontaneous Fission
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
??L (deg.)
Neck (equatorial)emission gt97
Romualdo de Souza
5
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
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 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/A50 MeV E ? 140 MeV ?max ? 33 ?
12C 232Th E/A22 MeV E ? 230 MeV
?max ? 120 ? gt ?RLDM ? 70 ?
Romualdo de Souza
7
3He 232Th at Elab/A90 MeV
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

• 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
Target

• Measurement of IMFs at backward angles
  eliminates pre-equilibrium component

30 cm
95.0?
PPAC/MWPC
Experimental Setup of 4He 232Th E/A50 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 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/A50 MeV E ? 140 MeV ?max ? 33 ?
12C 232Th E/A22 MeV E ? 230 MeV
?max ? 120 ? gt ?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
Target

• Measurement of IMFs at backward angles
  eliminates pre-equilibrium component

30 cm
95.0?
PPAC/MWPC
Experimental Setup of 4He 232Th E/A50 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
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