Partition of the total excitation energy between complementary fragments

TL;DR

This paper compares two methods for partitioning total excitation energy between fission fragments, analyzing their effectiveness across multiple systems and deriving parameterizations to improve predictive modeling of prompt neutron emissions.

Contribution

It introduces a systematic comparison of classical and experimental-based TXE partition methods and develops parameterizations for residual temperature ratios applicable to various fissioning systems.

Findings

Limitations of the classical TXE partition method are demonstrated.

Residual temperature ratios RT(AH) are parameterized for different systems.

PbP model calculations validate the RT(AH) parameterizations and extend predictive capabilities.

Abstract

Two methods of the total excitation energy (TXE) partition between complementary fission fragments (FF) are compared: one based on the "classical" hypothesis of prompt neutron emission from fully accelerated FF with both fragments having the same residual nuclear temperature distribution,the second one on the systematic behavior of the experimental multiplicity ratio {\nu}H/({\nu}L+{\nu}H) as a function of the heavy fragment mass number AH,the complementary FF having different residual temperature distributions.These methods were applied on six fissioning systems: 233,235U(nth,f), 239Pu(nth,f), 237Np(n5.5MeV,f), 252Cf(SF), 248Cm(SF) and fragment excitation energies,level density parameters,fragment and fragment pair temperatures were compared.Limitations of the "classical" TXE partition method are shown.Residual temperature ratios RT=TL/TH versus AH,local and global parameterizations of RT(AH) for the neutron induced fissioning systems are obtained.Average values of quantities characterizing prompt neutron emission are discussed.A linear decrease of <RT> with the mass number of the fissioning nucleus and a linear decrease of the average C parameter with the fissility parameter is obtained.Point by Point (PbP) model calculations validate the RT(AH) parameterizations.The multi-parametric matrix {\nu}(A,TKE) as well as prompt neutron and gamma-ray emission quantities as a function of fragment mass,total average prompt neutron multiplicity and spectrum and prompt neutron multiplicity distribution P({\nu}) were calculated.The global RT(AH) parameterization extends the use of the PbP model to predict prompt neutron emission quantities for fissioning systems without experimental data.An explanation of the less pronounced sawtooth shape of {\nu}(A) and the increase of {\nu}(A) with incident neutron energy only for heavy fragments is given and exemplified by quantitative results of the PbP model.