Fission-Fragment Energy-Correlation Measurements for the Thermal-Neutron Fission ofPu239and

Abstract

Fission-fragment mass and energy distributions and mass-versus-energy correlations have been obtained for 239 Pu and 241 Pu thermal-neutron-induced fission. Silicon surface-barrier detectors were used in energycorrelation measurements; absolute fragment energies were obtained by means of a recently developed mass-dependent energy calibration. Average total fragment kinetic energies before neutron emission are found to be 177.7=1=1.8 MeV for ^Pu and 179.6=bl.8 MeV for 241 Pu. Detailed experimental results are given and compared with those of other experiments. Observed fine structure in the fragment mass distribution and in the average total fragment kinetic energy as a function of mass is correlated with the energetically preferred even-even nucleon configurations in the fragments. New determinations of the root-mean-square width of the total-kinetic-energy distribution as a function of fragment mass show structure which also appears to be correlated with the energetically preferred even-even fragment configurations. Fission neutron and gamma-ray data of other experiments are used with the new fragment kinetic energies presented here to examine the total energy balance for fission for the two cases studied. A comparison of the two mass distributions shows the heavy-fragment groups almost superimposed; the light-fragment groups are separated almost uniformly by 2 amu.

Microscopic Calculation of Fission Fragment Energies for the 239Pu(nth,f) Reaction

“…Similarly, in the bottom panel we show the TXE as a function of heavy-fragment mass. A line representing the empirical "maximum" TXE is taken from [13], and was estimated from the binding energies of the fragments, the average number of neutrons they emit and their average kinetic energies, and the energy emitted by gamma decay (estimated as one half the binding energy of the first neutron not emitted). Therefore, because of the assumptions and approximations used in its calculation, the empirical line is not to be taken as the true maximum energy, but more as a guide.…”

Fragment angular momenta in low and medium energy fission of242Pu

“…The second terms in the equation (5a and 5 b) represent the contribution from fissioning nucleus angular momentum into fragment angular momentum. We have used the kinetic energy data [14] for z41Pu(nt~,f) to obtain the semimajor axis (z) of the fragment using the prescription of Satya Prakash et al [15] and assuming the fragments having ellipsoidal shapes at the scission point. Though the kinetic energy value used pertains to the most probable fragments (Z) corresponding to mass 128 and may not be for Z=51, the error introduced due to this will not be large considering the overall error on the observed angular momenta.…”

Generalized Energy-Dependent Q Values for Fission

“…One might assume that since fission is more sym- [10,11] show that EFR(A H ) is minimized near symmetric fission. This is a general feature of EFR that has been observed a number of times [10][11][12]. It is a result of several effects.…”