Independent Yields Of Fission Products Research Articles

The fission yield calculations with Langevin model, Hauser-Feshbach statistical decay, and beta decay

We performed the calculations of de-excitation of the primary fission fragments by the Hauser-Feshbach statistical decay followed by the β decay of de-excited fission products. We used the primary fission fragment mass distributions YP(A), total kinetic energy TKE(A), and its width σTKE(A) as input, which were calculated with the Langevin model using macroscopic-microscopic models of the potential energy surface. The prompt neutron multiplicity v̅ and the independent fission product yield (FPY) YI(Z, A, M) and cumulative FPY YC(Z, A, M) are calculated by the Hauser-Feshbach statistical decay and β decay calculations, respectively. The calculated v̅ was overestimated approximately 17% compared to the evaluated data. The decay heats from β and γ were in accordance with the experimental results. The β delayed neutrons yieild was also overestimated.

Prompt and Delayed Neutron Emissions and Fission Product Yield Calculations with Hauser-Feshbach Statistical Decay Theory and Summation Calculation Method

We demonstrate the neutron emission and fission product yield calculations using the Hauser–Feshbach Fission Fragment Decay (HF3D) model and β decay. The HF3D model calculates the statistical decay of more than 500 primary fission fragment pairs formed by the neutron induced fission of 235U. In order to calculate the prompt neutron and photon emissions, the primary fission fragment distributions, i.e. mass, charge, excitation energy, spin and parity are deterministically generated and numerically integrated for all fission fragments. The calculated prompt neutron multiplicities, independent fission product yield are fully consistent each other. We combine the β-decay and the summation calculations with the HF3D model calculation to obtain the cumulative fission product yield, decay heat and delayed neutron yield. The calculated fission observables are compared with available experimental data.

Atomistic model of xenon gas bubble re-solution rate due to thermal spike in uranium oxide

Atomistic simulations are performed to study the response of Xe gas bubbles in UO2 to ionizing fission products through the thermal spike approximation. A portion of the total electronic stopping power (Se) is taken as the thermal spike energy through a ratio variable ζ. The thermal spike energy causes extreme melting within the fission track cylindrical region. Molecular dynamics is employed to quantify the probability of a Xe gas atom to be re-solved (re-dissolved) back into the UO2 matrix. Subsequently, a re-solution model is developed and parametrized as a function of bubble radius (R), off-centered distance (r), and thermal spike energy (ζSe). The off-centered distance measures the shift of the thermal spike axis from the bubble center. To evaluate the re-solution model, independent fission product yield of U-235 fission due to thermal neutrons (0.0253 eV), taken from the JEFF-3.3 database, is used. The kinetic energy of the fission products is taken from the EXFOR database. Subsequently, the decay of Se over distance for each fission product is simulated. Finally, the evaluated re-solution rate (re-solution probability per second) is presented as a function of bubble radius for a range of ζ.

235U(n, f) Independent fission product yield and isomeric ratio calculated with the statistical Hauser–Feshbach theory

ABSTRACT We have developed a Hauser–Feshbach fission fragment decay model, HF3D, which can be applied to the statistical decay of more than 500 primary fission fragment pairs (1,000 nuclides) produced by the neutron induced fission of 235U. The HF3D model numerically integrates fission fragment yield and their initial excitation energy, spin and parity distributions for these 1,000 nuclides. The fission fragment yield Y(A) and the total kinetic energy are model inputs, and we estimate them from available experimental data for the 235U(nth,f) system. The model parameters in the statistical decay calculation are adjusted to reproduce some fission observables, such as the neutron emission multiplicity , its distribution P(ν), and the mass dependence (A). The calculated fission product yield (FPY) and isomeric ratio (IR) are compared with experimental data. The calculated independent FPY YI (A) at the thermal energy reproduces the experimental data well, while the calculated IRs tend to be lower than the Madland–England model prediction. The HF3D model is extended to higher incident neutron energies up to the second-chance fission threshold. We demonstrate for the first time that most of the IRs stay constant, although the production of isomeric state changes as the incident energy increases.

Erratum to: “Measuring independent yields of fission products using a penning trap”

Erratum to: “Measuring independent yields of fission products using a penning trap”

Measuring independent yields of fission products using a penning trap

A new method for determining independent fission products is used in an experiment at the Accelerator Laboratory of the University of Jyvaskyla. The method combines the chemical universality of the ion guide technique and the unique properties of the Penning trap. A beam of charged particles is formed by stopping fission products in gaseous helium. The Penning trap is employed as a highly accurate filter to identify particles by their mass. The yields of fission products are determined by the ion count downstream of the trap. The setup’s mass resolving power is on the order of 105 with a radio frequency excitation time of 400 ms. Such high mass resolution occasionally allows us not only to separate nuclides but to separate the isomeric and ground states of nuclei as well. Independent yields of fission products are measured in the fission reaction of the 232Th isotope by protons with an energy of 25 MeV. A short description of the method ae nd soexperimental data are supplememnted by the results fro theoretical calculations.

A Multiparameter Nuclear-fission Experiment: Can All be Obtained at Once?

Abstract A large variety of experimental works has been done since the discovery of nuclear fission, aimed at studying different aspects of the phenomenon. Yet our comprehension of the fission process is not complete. This is, among others, due to a certain lack in multi-parameter experimental data. An example here is the correlation between fractional independent yields of fission products and neutron and gamma-ray multiplicities. Fragment-gamma-neutron measurements, especially if correlated with fission- fragment kinetic energies, give the complete set of observables and are therefore of interest from the point of view of modeling and understanding of the fission process. A two-arm spectrometer of fission products (STEFF) has been recently built at the Manchester University. In addition to the identification of masses from complementary fission products, by the double energy/double velocity measurement, the spectrometer is capable of delivering information on their nuclear charges, on the event-by-event basis. The spectrometer also comprises an array of NaI and may house a further array of neutron detectors. In such configuration, STEFF has been used at the ILL neutron guide at the benchmark experiment 235U(nth, f). Details on the experiment will be presented, results on the identification of atomic numbers in the light group of fission products will be demonstrated and the perspectives discussed.

Independent yields of neutron-rich nuclei in charged-particle induced fission

Yields of fission products have been studied at the recently upgraded IGISOL facility in Jyväskylä using 50 MeV H 2 + beam ( E p = 25 MeV) and thin natTh and natU targets. The independent yields of fission products in the mass regions A = 99−112 (elements Y, Nb and Tc) and A = 127−134 (elements Sn, Sb and Te) have been obtained. Comparisons of the experimental isotopic distributions with theoretical ones are presented. Enhancement of the production rate of the doubly magic 132Sn is observed in the experimental yield curve.

Isotopic product distributions in the near symmetric mass region in proton induced fission of 238U.

We have studied fission product yields using 19.8 MeV proton induced fission of a thin $^{238}\mathrm{U}$ target and the on-line mass separator IGISOL. The nonselectivity of the separation method used with respect to Z has allowed accurate determination of the yields of symmetric fission for the first time. The cumulative yields for the elements from Z=40 (Zr) up to Z=47 (Ag) have been determined from the beta- and gamma-radioactivity measurements. The independent fission product yield distributions for elements Tc, Ru, and Rh are obtained from the experimental data. An improved theoretical model for calculating mass and independent yields is described and applied. It is found that the charge splitting for the primary fragments differs from that obtained with the unchanged charge division model at moderate excitation energies of compound nuclei. A comparison of the calculated and experimental fission product yields shows that the model presented can be applied for predictions of cross sections for very neutron-rich nuclei in the light particle induced fission.

Correlation between fractional independent yields and neutron-to-proton ratio of fission products in low energy fission

Fractional independent yields of fission products in the thermal neutron-induced fission of233U,235U,239Pu,241Pu and in the spontaneous fission of252Cf have been correlated with the neutron-to-proton ratio of the fission products. The yields of the products from a fissioning system, when plotted as a function of neutron-to-proton (N/Z) ratio of fission preducts, fall on two Gaussian distribution corresponding to light and heavy fission products. The centroids of the distribution or the most probable value of neutron-to-proton ratio is found to be very close to theN/Z of the fissioning nucleus. From the most probable value ofN/Z the various parameters of charge distribution e.g. most probable massAp, most probable chargeZp, the mass dispersionσAand the charge dispersionσZhave been obtained and are in good agreement with the experimental values ofApandZp.

Nuclear-charge distribution near symmetry for thermal-neutron-induced fission of 235U.

Available data concerning nuclear-charge distribution for thermal-neutron-induced fission of $^{235}\mathrm{U}$ have been evaluated for the region near symmetry (104\ensuremath{\le}A\ensuremath{\le}129, 42\ensuremath{\le}Z\ensuremath{\le}50). Evaluated data or averages are listed and are interpreted by the use of empirical ${Z}_{P}$ and ${A}_{P}^{\mathcal{'}}$ models. The parameters and functions derived for the two models are presented and are compared with each other and with the data. Both models represent most data satisfactorily, and they permit the calculation of more reliable estimates of unmeasured independent-fission-product yields near symmetry than has been possible in the past. The two models show the same major trends, so the physical phenomena deduced from the trends are not model dependent. The independent yields of fission products with Z values of 50 and 42 are much larger than those of products with Z values of 43 through 49. The yields for products with Z values of 49 and 43 are larger than those of products with Z values of 44 through 48. These yield differences indicate that the stable filled, or nearly filled, 50-proton shell in the heavy fragment causes the fission probability to increase rapidly with mass number in the range from 120 to 130 between improbable symmetric and probable asymmetric fission. The lack of even-odd-proton and -neutron effects near symmetry indicates that excitation energies are higher for $^{236}\mathrm{U}$ nuclei undergoing symmetric fission than for those undergoing asymmetric fission.

A General Correlation for Independent Fission Product Yield Uncertainties

Measurements of independent fission product yields from thermal-neutron fission of 235U, 239Pu, 233U, and 241Pu have been compared with expected yields from a semiempirical analytical model. A general correlation between the experimental/theoretical ratio and the distance of the nuclide from Zp, the most probable charge in a fission product mass chain, has been constructed. This correlation can serve as a basis for assigning uncertainties to theoretical yield estimates.

Charge distribution, neutron evaporation, and energy distribution in higher energy binary fission

A computational procedure based on the order-disorder model for predicting independent yields of fission products in higher energy fission is described. A scheme for the distribution of extra excitation between the fragments has been evolved. The extra excitation energy is shown to be shared between the two impending fragments in proportion to the number of neutrons out of the balance number (as per the order-disorder model) going to either of the fragments. The calculational procedure essentially consists of making use of the scheme and obtaining the excitation energy of the fragments for higher energy fission from those for spontaneous fission. Data on neutrons evaporated nu-bar (Z/sub i/,N/sub j/) individual fragments for the higher energy fission are calculated from the excitation energy using the cascade evaporation scheme. The product isotopic distributions are calculated from nu-bar data. The product isotopic distributions thus calculated along with experimental product mass yield data give the independent yields of the products. The results obtained for fission of /sup 235/U by fission spectrum neutrons (fast) and 14.7 MeV (high energy) neutrons are discussed. A comparison of the predicted independent yields with experimental values shows good agreement. The total isotopic yield versus Z distribution for fast and highmore » energy neutron fission show a decrease in peak to valley ratio with increasing excitation energy of the compound nucleus. Less pronounced shell effects at N=50 and 82 appear than in the case of thermal fission. The isotopic isobaric and isotonic averages of nu-bar retain the sawtooth nature. The study confirms the experimental observation that Z/subp/ for higher energy fission lies between the values predicted by the unchanged charge density and excited charge density hypotheses. (AIP)« less

Independent fission-product yields and fast-neutron emission by fission products

A method is described for calculating the independent yields of fission products on the basis of the quantitative characteristics of the fast-neutron emission. The formulation and solution of the inverse problem are discussed for fission by neutrons at ∼14.5 MeV.