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

.

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