Nuclear temperature

In statistical mechanics the Boltzmann constant, /cB, with dimensions of energy per degree is included in expressions so that the temperatures can be given in degrees Kelvin. The numerical values of nuclear temperatures in Kelvin are very large, for example 109 K, so the product of /cB and T is usually quoted in energy units (MeV) and the Boltzmann factor is often not written explicitly. 

Example Problem In a certain nuclear reaction, a beam of lsO was combined with 233U nuclei to form a compound nucleus of 256Fm. The nuclei were produced with an excitation energy of 95 MeV. Calculate the nuclear temperature assuming that y = 1, and then the relative probability of neutron to fission decay of the excited system. 

The nuclear temperature-density phase diagram, indicating the nuclear landscape now available for reaction studies. The dotted trajectory shows the stepwise evolution of an energetic nuclear collision, in steps of about 1 x s (Adapted from Mueller and Serot 1995)... 

A model, based on the construction of a potential energy surface from a combination of liquid drop terms for protons and neutrons as a function of deformation and shell corrections, has been published by Wilkins, Steinberg, and Chasman (Wilkins et al. 1976). In the model, a specific excitation energy (nuclear temperature) is assumed at scission and the probability to reach this specific state is calculated. The general trends of mass-yield curves in the fission of very different nuclides from "Po to Fm and for different excitation energies of the fissioning nucleus from 0 MeV (spontaneous fission) to highly excited fission reactions are reproduced correctly. In particular, the transition from the symmetric fission of (the compound nuclei) Po to a triple-humped mass-yield curve for Ra to double-humped yield curves for and Cf and, finally, a partial return to symmetry for Fm is... 

The effect of. these variations On a number of characteristics of the diva f critical assembly have been calculate by a Monte Carlo code and are summarized in Table n. The effect of a 30% decrease in the, nuclear temperature used in the evaporation model also investigated. The results are eiqiressed as differences, in percent, between the values obtained from using the evaporation model at all energies at the Ugber temperature and the values bbtained by each of the other variations. 

Much of the nuclear temperature-monitoring> flow-monitoring and other instrumentation which are in the safety clrc ts will ve useful functions for process control. Auxiliary Instrumentation systems which will be provided for N Reactor which a-e not In the safety circuit are described below. 

The CPMD approach exploits in another way the separation of fast electronic and slow nuclear motions, as compared to BOMD. The KS orbitals are imbued with a fictitious time dependence, that is, y/i t)—> y/i t,t), and a dynamics for the orbitals is introduced that propagates an initially fully minimized set of orbitals to subsequent minima corresponding to each new nuclear configuration. This task is accomplished by designing the orbital dynamics in such a way that the orbitals are maintained at a fictitious temperature that is much smaller than the real nuclear temperature T but are still allowed to relax qitiddy in response to the nuclear motion. 

In the following discussion, the nuclear temperature dependence of T e will be considered to be negligible, because they are functions of... 

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