Charge Distribution Of Fission Products Research Articles

Transformations of actinides fission product yields due to post-scission emission of nuclear particles: 232Th

The “many ensembles” method was proposed to investigate the influence of nuclear particles’ post-scission emission on mass and charge distributions of fission products. The post-scission approximation was used: each of these ensembles consists of the fission fragments after emission of chains of different lengths, both the beta (β±) particles and neutrons. The theory allows one to find the most probable two-fragment clusters of fission products and study their evolution after the post-scission emission of nuclear particles. The isotope 232Th was chosen as an example, the fission fragments of which have been intensively studied experimentally. It is shown that the post-scission emission of nuclear particles eventually leads to the convergence of the asymmetric peaks, which looks like enhanced symmetric fission mode over the asymmetric mode for fission product yields. A comparison of the theoretical results and experimental data for the 232Th fission fragments indicates their satisfactory matching.

A new evaluation of fission product yields for the neutron induced fission of U-233 and Th-232

Worldwide R&D efforts in establishing the reactor technology with the Thorium-Uranium (Th-U) fuel cycle have significantly grown in the recent past. The study of fission product yields has a major impact on the understanding of the fissioning process and plays a vital role in the development, design and safety analysis of advanced nuclear energy systems. A new evaluation of fission product yields based on a new database of measurements up to 2013 will allow more reliable and accurate model calculations of the Th-U fuel cycle. This work is undertaken to study the mass and charge distributions of fission products for the fuel nuclei U-233 and Th-232 induced by thermal, fast, and about 14MeV neutrons. First, the available experimental data is analyzed systematically and evaluated. Second, it is necessary to predict the unmeasured fission yields and their errors by the systematics, due to the lack of experimental data. The mass distributions are well described by a superposition of 5 Gaussian functions, which is called the Multi-Gaussian model. The charge distributions are calculated on the basis of ZP model. Their parameters are derived based on evaluated data. Finally, the fission product yield library related with the Th-U fuel cycle is well established. The evaluated data is improved compared to the major international evaluated libraries, including ENDF/B-VII.1, JENDL-4.0 and JEFF-3.2.

Most probable charge of fission products in 24 MeV proton induced fission of238U

The charge distributions of fission products in 24 MeV proton-induced fission of {sup 238}U were measured by the use of an ion-guide isotope separator on line. The most probable charge (Z{sub p}) of the charge distribution was discussed in view of the charge polarization in the fission process. It was found that Z{sub p} mainly lies on the proton-rich side in the light mass region and on the proton-deficient side in the heavy mass region compared with the postulate of the unchanged charge distribution. The charge polarization was examined with respect to production Q values. {copyright} {ital 1998} {ital The American Physical Society}

Transport efficiency of fission products in IGISOL

Two types of double-room target chambers were constructed for effective stopping of fission fragments in ion-guide isotope separator on-line (IGISOL). It was found that the efficiencies for the double-room chambers are about three and four times larger than that for the standard one. The yield/μC decreases with an increase of the beam intensity. The decreasing trends for both chambers quite resemble each other. This fact suggests that the plasma effect remains even in the double-room chambers. Using the charge distribution of fission products obtained by IGISOL, the yield of RI beam was estimated for the proton-induced fission of 238U.

A new experimental method to measure the charge distributions of fission products

A ΔE− E telescope has been used associated with an X-ray detector to measure the nuclear charge distribution of 252Cf (s.f). Although the nuclear charge resolution of the ΔE− E detector is not sufficient to resolve nuclear charges around 40–42, the unfolding procedure allows an analysis of the elemental yields as a function of the kinetic energy of the fragments.

The ionic charge distribution of fission products and the influence of internal conversion on highly preionized heavy ions

At the mass spectrometer LOHENGRIN of the Institut Laue-Langevin the ionic charge state distributions of235U(n th,f)-fission products separated according to their mass, nuclear charge and kinetic energy were determined. The mean values and the widths of the ionic charge state distributions are compared with semiempirical predictions. Deviations between the experimental data and the estimation of Nicolaev and Dmitriev are found. Furthermore, the influence of the internal conversion process on the ionic charge state distribution of highly ionized fission products was established. Internal conversion is observed mainly for odd-odd nuclei and nuclei with 59 neutrons. The Auger cascade following the internal conversion process shifts the ionic charge state distribution by about 3 charge units. The yield of conversion electrons per fragment was determined in the mass range 85≦A≦103.

Charge distribution of fission products in the reaction 209Bi( 12C, fission)

The yields of about twenty five fission products in the system 209Bi( 12C, fission) have been measured by γ-ray analysis without chemical separation, at excitation energies of 40, 53 and 66 MeV in the 221Ac ∗ compound nucleus. The data were used to calculate the most probable charge Z p for each mass number. On the assumption that Z p varies monotonically with A, simple functions were tested and two were found to account adequately for the data. These functions were used to calculate the mean number of emitted neutrons ( ν ) at each energy. ν increases with energy at a rate of about 0.054 neutrons MeV −1. The nature of the charge distribution in the primary fragments is discussed briefly.

Nuclear charge distribution of fission products fromU235(nth),fof the masses 79 to 100

Passing mass separated recoil fission particles through a $\ensuremath{\Delta}E \mathrm{Si}$-surface barrier detector the nuclear charge distributions of fission products were measured in the mass chains 79 to 100. The average nuclear charge as well as the second, third, and fourth moment of the nuclear charge distribution reveal odd-even and shell effects.NUCLEAR REACTION, FISSION $^{235}\mathrm{U}({n}_{\mathrm{th}},f)$, measured nuclear charge distribution of $A=79$ to $A=100$, deduced element and isotone yields, proton and neutron odd-even effect.

Nuclear charge distribution of mass-separated isobars from thermal-neutron-induced fission of 235U

The nuclear charge distribution of fission products with mass numbers A = 90, 91, 94, 99, 100, 101 and 104 provided by the mass separator “Lohengrin” was measured. Adjacent elements in the group of the light fission products could be separated by their different energy loss in a carbon absorber. The Z-yields were found to be strongly dependent on the kinetic energy of the fission products. The widths of the nuclear charge distributions are very small, in general, and strongly dependent on A as well as on the kinetic energy. The influence of the neutron evaporation and odd-even effects are clearly detected. An asymmetric nuclear charge distribution was found for A = 104 indicating the suppression of fission fragments with Z = 43. The average nuclear charges of the fission products at their average kinetic energy are in good agreement with the results from measurements of the number of β-decays and K X-ray measurements. The average nuclear charge of the isobar A = 132 was measured at its average kinetic energy with a calibrated secondary electron detector to be Z = 51.14 ± 0.15 which is in very good agreement with the radiochemical results. Thus previous physical measurements indicating a large independent yield for the doubly magic nucleus 132Sn could not be confirmed.

Nuclear Charge Distributions in the Isobars 92 to 100 Resulting from Thermal Neutron Fission of Uranium-235

The nuclear charge distribution of fission products from $^{235}\mathrm{U}({n}_{\mathrm{th}}, f)$ is determined for the isobaric chains 92 to 100. The results were obtained from the energy loss of monoisobaric and monoenergetic fission products in a $\ensuremath{\Delta}E$ Si surface-barrier detector. The odd-even effect is found also in the mass chains reported here for the first time, revealing an approximately sinusoidal variation of the charge distribution width with mass.