Fission Cross Section Of 235U Research Articles

Simultaneous evaluation of fission and capture cross sections and their covariances for heavy nuclei

Abstract The fission cross sections of 235U, 238U, 239Pu, 240Pu, and 241Pu, and the capture cross sections of 197Au and 238U have been simultaneously evaluated for JENDL-3 in the energy range from 50 keV to 20 MeV. A generalized least squares method has been applied to estimate their cross sections and associated covariances from experimental data of absolute and ratio measurements. The experimental covariances were estimated from the partial errors for each measurement. The partial errors were categorized to a few groups which have specific correlation factors. The correlation only in neutron energies was taken into account. The presently evaluated fission cross sections of 235U and 239Pu are a few percent lower than those of JENDL-2 below 1 MeV.

Measurement of proton induced fission cross-section of 235U at sub-coulomb barrier energies

Abstract It has been observed that in heavy ion induced fission the sub-coulomb cross section does not decrease with energy as rapidly as expected. In order to study the situation prevailing in proton induced fission, measurements of fission cross-sections for protons on 235 U were carried out using plastic track detectors in a close geometry for Ep= 2 to 4 MeV. Care was taken to measure the background tracks due to neutron induced fission at each energy. The results show a much lower fall off of cross-section with energy than is indicated by an optical model prediction. At 2.5 MeV the fission cross-section is several orders of magnitude higher than the predicted reaction cross-section. An interpretation of the results as fission following coulomb excitation is suggested which requires the existence of a third well in the potential energy surface for 235 U.

Fields of ionizing radiations on the Tokamak-10 fusion unit

I. WRENDA 83/84. World request list for nuclear data. Nuclear data section. Vienna: IAEA (1983). 2. A. A. Goverdovskii, A. K. Gordyushin, B. D. Kuz'minov, et al., "Measurement of the fission cross sections of heavy nuclei by the method of pulse synchronization," in: Neutron Physics, Part 4 [in Russian], TsNIIatominform, Moscow (1984), p. 115. 3. A. A. Goverdovsky, A. K. Gordjushin, B. D. Kuzminov, et al., "The 236U and 2SSU to 235U fission cross section ratios in the neutron energy range 5-11 MeV," in: Proc. Int. Spec. Meeting on Transactinium Isotopes Nuclear Data, Uppsala (1984). 4. A. A. Goverdovskii, A. K. Gordyushin, B. D. Kuz'minov, et al., "Measurement of the fission cross section ratios of 236U and 2SSU by the method of isotopic admixtures," Problems of Atomic Science and Engineering, Ser. Nuclear Constnats 3 (57) [in Russian], (1984), pp. 13-15. 5. A. A. Goverdovskii, A. K. Gordyushin, B. D. Kuz'minov, et al., "Measurement of the ratio of the neutron-induced fission cross sections of 2STNp and 2~SU in the energy range 4-11 MeV," At. ~nerg., 58, 137-139 (1985). 6. J. Behrens and G. Carlson, "Measurements of the neutron-induced cross sections of 2S~U, 236U, and 2ssU to 2SSU from 0.i to 30 MeV," Nucl. Sci. Eng., 63, 250-267 (1977). 7. J. Meadows, "Neutron-induced fission cross section ratios of 2a4U, 2S6U and 23SU," Nucl. Sci. Eng., 65, 171 (1978). 8. C. Nordborg et al., "Fission cross section ratios of ~S2Th, 226U, and 2S5U," in: Proc. Int. Conf. on Nuclear Data, Vol. I, Harwell (1979), p. 910. 9. H. Knitter and C. Budtz-J~rgensen, "Barrier heights of plutonium isotopes from (n, n'f)," in: Proc. Int. Conf. on Nuclear Data for Science and Technology, Vol. i, Antwerpen, Sept. 6-10 (1982), pp. 744-747. I0. ENDF/B V Third Ed. BNL (1979), 23SU (MAT 1395). Ii. S. Bj#rnholm and J. Lynn, "The double-humped fission barrier," Rev. Mod. Phys., 52, 725 (1980).

Method for Calculating Thermal Neutron Spectrum in BWR Lattice

A new method for calculating space-dependent thermal neutron spectrum in a BWR lattice has been developed primarily aiming at its application to a lattice design code. Since the method has been constructed from combination of the cell-by-cell THERMOS calculation with leakage boundary condition and the coarse-mesh diffusion calculation for the cell leakage coupling, it is considerably economical as compared with various other transport theory approaches. Validation of the method has been made through comparisons with Monte Carlo calculations for a typical 8x8 BWR lattice. The discrepancies with the reference Monte Carlo calculations are mostly in the ranges of ±1.7 and ±3.0% for the rod-by-rod 235U fission cross section and the absorption rate distribution, respectively. The accuracy is acceptable and ensures the validity of various simplifications and assumptions involved in the present method. The present method is expected to be applicable to the BWR lattice analysis over the practical range of design p...

Measurement of the fission cross section of238U and235U nuclei by 14 MeV neutrons

Measurement of the fission cross section of238U and235U nuclei by 14 MeV neutrons

Measurement of the ratio of the fission cross sections of238U and235U for neutron energies in the range 5.4?10.4 MeV

Measurement of the ratio of the fission cross sections of238U and235U for neutron energies in the range 5.4?10.4 MeV

Measurement of the thermal-neutron-induced fission cross-section of 238U

The thermal-neutron-induced fission cross-section of 238U was measured at an intense and very clean thermal-neutron beam of the Grenoble high-flux reactor. The best 238U sample material used contained only 12 ppb of 235U. The fission fragments were detected with surface barrier detectors. Relative to a thermal fission cross-section of 587.6 barn for 235U, a value of (11 ± 2) μbarn was obtained for the 238U fission cross-section. By comparing this result with 238U(n, f) measurements in the resonance region, the existence of a negative resonance or resonances in 239U is demonstrated.

Measured activation cross sections below 10 MeV for the 51V(n, p) 51Ti and 51V(n, α) 48Sc reactions

The activation method is used to measure cross sections for the 51V(n, p) 51Ti reaction from E n = 2.856 to 9.267 MeV and for the 51V(n, α) 48Sc reaction from 5.515 to 9.567 MeV. Both measurements utilize ENDF/B-V evaluated neutron-induced fission cross sections of 238U as a standard. The experimental results from this work are compared with corresponding ENDF/B-V evaluated cross sections for V and substantial differences are evident. The most significant difference is a tendency for the measured values to exceed evaluated ones by as much as 50% in the vicinity of 8 MeV.

Measurement of the Cross Section for the 7Li(n,n’t)4He Reaction in the 7- to 9-MeV Energy Range

Cross sections for the 7Li(n,n’t)4He reaction have been measured in the 7- to 9-MeV energy range. The tritium produced in encapsulated lithium metal samples by fast neutron bombardment was extracted and the activity measured using liquid scintillation counting techniques. The neutron fluence was measured with an ion chamber containing a 238U deposit. This deposit was calibrated by comparing it with standard 235U deposits. As a result, the error in the (n,n’t) cross section is insensitive to the 238U fission cross-section error but does depend directly on the error in the 235U fission cross section. The experimental results show that the 7Li(n,n’t)4He cross section is very insensitive to neutron energy in the 7- to 9-MeV range, and the value 372 mb (±3.8%) was obtained for the average cross section in this region.

Fission cross sections of medium-weight and heavy nuclei induced by 1 GeV protons

Coincidence studies performed in 4π geometry with silicon detectors and parallel plate avalanche counters have been used to measure total fission cross sections of238U,232Th,209Bi,208Pb,197Au,natYb,natHo,natTb,natSm,natTe,natAg andnatNi nuclei induced by 1 GeV protons. The experimental results agree qualitatively with cascade-evaporation calculations.

Determination of the details of the resonance structure of both the total cross section and the fission cross section of235U and239Pu for 2 eV-20-keV neutrons

It follows from Fig. 4 and 5 that the spread in the calculations of the factors of resonance self-shielding is extremely large. Our data for235U and239Pu are in regard to the factors ft systematically below the calculated values at energies above 1 keV. The experimental values are much larger than the values calculated with BNAB for the factors ff of239Pu.

A CAMAC experiment for the precise measurement of the cross section in fast neutron induced fission

A computer coupled measurement system in the CAMAC standard for the precise measurement of the fission cross section in neutron induced fission has been developed. Using the time correlated associated particle method in connection with the T(d, n) 4He reaction the fission cross section of 235U could be determined with an accuracy of ±1%.

Fission cross sections of235U and238U to neutrons with an energy of 14.7 MeV

Fission cross sections of235U and238U to neutrons with an energy of 14.7 MeV

Sensitivity analyses for the secondary intermediate-energy standard neutron field at the NISUS facility

Calculations are made to investigate sensitivities of the central NISUS spectrum and reaction-rate ratios to uncertainties in the macroscopic configuration. These uncertainties include density (of graphite, borone carbide and natural uranium), impurity (moisture and 10B in graphite), abundance ( 10B natural abundance) and tolerance (in Al cladding and B 4C shell). The sensitivities to the variations in the fission cross section of 235U and 238U are also studied. In these calculations the ANISN one-dimensional transport code is used with a 37 group data set derived from the UKAEA Nuclear Data Library by the GALAXY processing code. The effects of uncertainties are studied in detail and a comparison is made between the NISUS and MOL-ΣΣ standard neutron fields.

Absolute Neutron Fission Cross Sections of 235U, 238U, and 239Pu at 13.9 and 14.6 MeV

AbstractMeasurements of the absolute neutron fission cross sections of 235U, 238U, and 239Pu have been made at 13.9 and 14.6 MeV with a double 4π ionization chamber. The associated particle method with the time-of-flight technique was used. Our final values of σnf(235U), σnf(238U), σnf(239Pu), σnf(238U)/σnf(235U), and σnf(239Pu)/σnf(235U) are compared to previous data.

Absolute measurements of 235U and 239Pu fission cross-sections with photoneutron sources

the fission cross-sections of 235U and 239Pu for NaBe, LaBe, NaD and GaD photoneutrons have been measured absolutely. The neutron source strength was measured using a manganese bath to compare the photoneutron yield from the sources with the standard source NBS-II. Fission counts were accumulated with the source positioned symmetrically between two identical fission foils in an experiment package suspended in a low-albedo laboratory. Fission fragments passing through limited solid angle apertures were recorded on polyester track-etch films. The masses of the foil deposits were determined by microbalance weighings and confirmed by thermal neutron fission and alpha counting. After making a correction for the calculated energy distribution of the source neutrons, values of 1.471 ± 0.029, 1.274 ± 0.026, 1.162 ± 0.025 and 1.195 ± 0.026 barns were obtained for the 235U fission cross-section at the source median energies of 140, 265, 770 and 964 keV, respectively. Corresponding values of 1.469 ± 0.045, 1.515 ± 0.038, 1.670 ± 0.039 and 1.643 ± 0.038 barns were determined for 239Pu.

A statistical analysis of the neutron-induced fission and total cross-section of235U up to 36 keV

The relative fission cross-section of235U has been measured up to 200 keV with a nominal resolution of 1.0 ns/m. The data have been analysed in order to detect nonstatistical effects due to intermediate structure. The statistical tests which have been applied to this fission and similar total-cross-section data include calculation of the correlation serial coefficients, variance and Wald-Wolfwitz tests. The comparison of the results indicates the presence of intermediate-structure effects in fission cross-section which may be interpreted on the basis of the double-humped deformation potential. Under the assumption that the first not fully open channel is theKπ=2-, the energies of the outer barrier and of the shape isomer of this transition state are obtained.

Evaluation of Neutron Cross Sections of Plutonium-241

The neutron cross sections of 241Pu were evaluated in the energy range between 10−5 eV and 15MeV, and are stored in the Japanese Evaluated Nuclear Data Library Version-1 (JENDL-1). In the energy range below 100eV, the evaluated data contained in ENDE/B-IV and the resonance parameters recommended in BNL-325 were tentatively adopted. The unresolved resonance parameters were determined between 100 eV and 21.5 keV so as to reproduce the experimental data of the fission and capture cross sections. Above 21.5 keV, the fission cross section was evaluated on the basis of the experimental data, most of which were reported as the ratio to the fission cross section of 235U and then were normalized by the fission cross section of 235U adopted in JENDL-1. The capture cross section was obtained from the experimental data of a in the energy range up to 250 keV. The capture cross section above 250 keV and the elastic and inelastic scattering, (n, 2n) and (n, 3n) reaction cross sections above 21.5 keV were obtained on the basis of the theoretical calculations. The calculated cross sections are connected smoothly with those obtained from the unresolved resonance parameters at 21.5 keV. This suggests the self-consistency of the present evaluation.

A statistical analysis of the resonance neutron fission cross sections of 233U, 235U, and 241Pu

The low energy fission cross sections of 233U, 235U, and 241Pu have been compared to simulated cross sections in order to determine values for the mean level spacing and mean level width which are not biased by failure to observe the numerous weak levels. We have obtained the following values for the mean level spacing and the ratio of mean level width to mean level spacing for both spin states: 233U, D = 0.55 ± 0.06 eV, 〈Γ〉 D = 1.31 ± 0.23 ; 235U, D = 0.38 ± 0.04 eV, 〈Γ〉 D = 0.58 ± 0.11 ; and 241Pu, D = 0.89 ± 0.09 eV, 〈Γ〉 D = 0.56 ± 0.11 . We have also obtained 3.5 ± 1 3 for the ratio of total number of open fission channels for the 3 − to the 4 − states of 235U in the energy range 1.6–59 eV.

Evaluation of Neutron Cross Sections of Plutonium-241

The neutron cross sections of 241Pu were evaluated in the energy range between 10−5 eV and 15MeV, and are stored in the Japanese Evaluated Nuclear Data Library Version-1 (JENDL-1). In the energy range below 100eV, the evaluated data contained in ENDE/B-IV and the resonance parameters recommended in BNL-325 were tentatively adopted. The unresolved resonance parameters were determined between 100 eV and 21.5 keV so as to reproduce the experimental data of the fission and capture cross sections. Above 21.5 keV, the fission cross section was evaluated on the basis of the experimental data, most of which were reported as the ratio to the fission cross section of 235U and then were normalized by the fission cross section of 235U adopted in JENDL-1. The capture cross section was obtained from the experimental data of a in the energy range up to 250 keV. The capture cross section above 250 keV and the elastic and inelastic scattering, (n, 2n) and (n, 3n) reaction cross sections above 21.5 keV were obtained on the basis of the theoretical calculations. The calculated cross sections are connected smoothly with those obtained from the unresolved resonance parameters at 21.5 keV. This suggests the self-consistency of the present evaluation.