T-REX [ TAMU Re accelerated EX otics ]
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Transcript of T-REX [ TAMU Re accelerated EX otics ]
T-REX [ TAMU Reaccelerated EXotics]
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Barbecue Pit
Pastina formation in low density nucleonic matter S. Wuenschel1, H. Zheng1. K. Hagel1, B. Meyer2, M. Barbui1, E-J Kim1,3, G. Roepke4 and J. B. Natowitz1
Core-collapse supernovae
cluster formation Influences neutrino flux
K.Sumiyoshi et al.,Astrophys.J. 629, 922 (2005)
Density. electron fraction, andtemperature profileof a 15 solar mass supernova at 150 ms after core bounce as function of the radius.
K.Sumiyoshi,G. RoepkePRC 77,055804 (2008)
Mass fraction X of light clusters for a post-bounce supernova core
Neutron Star
208Pb
1.4 x 10 -17 km
~ 20 km
Clustering in the Skins of Leptodermous Systems
Manifestations of Clustering in Nuclei -----1.Light Alpha Structure of Light Nuclei
See Talks Hagel, Barbui
Figure 2. The alpha-particle cluster structure of the Hoyle-state in 12C, as predicted using Fermionic Molecular Dynamics (M. Chernykh, et al., Phys.Rev. Lett. 98, 032501 (2007)).
7.67 MeV
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2. Alpha Decay of Heavy Elements
Bender, NN2012 Proceedings
Calculated Qα
C Isotope Preformation probabilities222Ra 208Pb +14C
Has been observed
3. Larger Cluster decay
4. “Long Range Particle” Ëmission in Fission ----Ternary Fission
• Common “ternary fission” - the break up into two massive fragments with a third fragment emitted approximately perpendicular to the massive fragments*
• The mass of this third fragment varies, but the decay is strongly dominated by the emission of alpha particles ~ 10 - 20 MeV
Light Particle Accompanied or “Ternary” Fission
252 Cf - Thesis Heeg, T U Darmstadt
Ternary fission Yields
• Thesis data of U. Koester
• nth induced ternary fission of 242Pu
• TU Berlin 1999
System Yp = 0.389
• Some experimental facts about ternary fission– The probability of ternary fission relative to binary
fission is very small (~1/1000)
• Simultaneous, dual, neck fracturing[1]– Characterized by:
• Neck radius parameter• Viscosity/surface tension
• Barrier systematics for alpha decay[2]– Characterized by:
• Fragment emission barrier height
• Frequency of assault on barrier
• ternary fission has been treated in a variety of models
[2] G.K. Mehta, et al PRC 7, 373 (1973)
• Dynamic process of third fragment formation at neck rupture– Can also been treated
statistically– Third fragment forms
from interacting nucleons
• Evaporation of fragments from hot neck region[3]
• TDHF nucleon associations[4]• Non-equilibrium fragment
formation[5]
[3] G.V Valsky Yad.Fiz. 24, 270 (1976) ** [4] J.W. Negele et al. Phys. Rev. C 17, 1098(1978)[5] V.A Rubchenya Yad.Fiz. 35, 576 (1982) ** (** unable to obtain these references)
Our approach to ternary fission
• In hot nuclear systems we know fragment formation can be very successfully treated as coalescence of free nucleons into fragments.
• Consider: – Ternary fission as a warm system (T=1-1.5 MeV)– The low density region between the forming heavy
fragments as an unstable region containing nucleons
– n/p ratio depending on initial composition + some diffusion
[6] L. Qin Phys Rev Lett 108, 172701 (2012)
Formation of the equilibrium distribution
• Using NSEC provided by B. Meyers at Clemson• Calculates the equilibrium concentration of
fragments being formed from an infinite source, characterized by:– T (originally T<1MeV – extension provided to
higher T)– Density– Yp – proton fraction of source
Challenges
• NSEC code assumes– Infinite size source– Infinite time (always reaches equilibrium)
• Infinite size source provides infinite nucleons to coalesce into large fragments (according to binding energy)
• Infinite time removes effect of transient fissioning system
Nucleation• Nucleation codes ‘coalesce’ nucleons into
clusters but are kinetic approaches including terms making process time dependent– Equilibrium Yield is modified by complementary
erfc term dependent upon three primary variables Time, Rho , AC
Nucleation
• Ac is the critical cluster size– A<Ac – fragments do not grow– A>Ac – fragments continue to grow
• In function, serves as the dividing line below which equilibrium yield is not affected and above which the yield falls dramatically
Neutron Star
208Pb
1.4 x 10 -17 km
~ 20 km
Clustering in the Skins of Leptodermous Systems
Pastina formation in low density nucleonic matter – a mechanism for ternary fission S. Wuenschel1, H. Zheng1. K. Hagel1, B. Meyer2, M. Barbui1, E-J Kim1,3, G. Roepke4 and J. B. Natowitz1
THANK YOU
Ternary fission yields in the reaction 241Pu(nth,f) are calculated using a new model which assumes a nucleation-time moderated chemical equilibrium in the low density matter which constitutes the neck region of the scissioning system. The temperature, density, proton fraction and fission time required to fit the experimental data are derived and discussed. A reasonably good fit to the experimental data is obtained. This model provides a natural explanation for the observed yields of heavier isotopes relative to those of the lighter isotopes, the observation of low proton yields relative to 2H and 3H yields and the non-observation of 3He, all features which are shared by similar thermal neutron induced and spontaneously fissioning systems.
241Pu
Fit metric is short M: z<7
245Cm
Fit metric is short M: z<7
249Cf
Fit metric is short M: z<7
**NOTE: normalized at 14C
NSEC and Ternary Fission