Ternary Fission and Neck Fragmentation Romualdo de Souza

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

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

Neck fragments are focused relative to the scission axis. 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 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/A=50 MeV E*  140 MeV max  33  12C + 232Th E/A=22 MeV E*  230 MeV max  120  > RLDM  70  Romualdo de Souza

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

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

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/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

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

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