Spectrum Averaged Cross Sections Research Articles

Experimental evaluation of fission spectrum averaged cross sections of 93Nb(n, n′) 93mNb and 199Hg(n, n′) 199mHg reactions

The fission spectrum averaged cross section of the 93Nb(n, n′) 93mNb reaction has been performed to obtain (125 ± 28) mb. The value is about 15% larger than that calculated from the Hegedüs cross section data. For the 199Hg(n, n′) 199mHg reaction, (252 ± 20) mb has been obtained.

Fission spectrum averaged cross section for the 232Th(n, f) reaction

Fission spectrum averaged cross sections for the 232Th(n, f) reaction were measured relative to the average cross section of 102 mb for the 58Ni(n, p) 58Co reaction, (1) at the beam port E-3 of the Kyoto University Reactor (KUR) where the fast neutron spectrum had previously been confirmed to be equivalent to that of fission neutrons, and (2) with a fission plate installed at the thermal neutron facility of KUR. In the first experiment, a fission chamber composed of a thorium film and a silicon detector was used and the measured value was 77.4 ± 3.7 mb. Anisotropic effect in the fragment angular distributions was investigated by a Monte Carlo calculation. In the second experiment with the fission plate, induced-activities of 140Ba in the thorium foil were measured with a Ge(Li) detector, and the result was 78.1 ± 3.9 mb. These data are in good agreement with each other. Most of the average cross sections calculated by several researchers are generally around 70 mb, which is smaller by about 10% than the results of the integral measurements. The Fabry's value is about 7% larger than those of the author's.

Fission Spectrum Averaged Cross Sections of Some Threshold Reactions Measured with Fast Reactor “YAYOI”

Abstract Fission spectrum averaged cross sections of twenty one threshold reactions were measured in the core center of YAYOI which was a fast neutron source reactor. Fast neutron spectrum in the core was experimentally determined by using a set of activation foils and micro-fission counters, prior to the cross section measurement. It was found that the shape of the fast neutron spectrum was approximately the same as that of fission neutrons above about 2MeV. This fact was also supported by theoretical calculation. Since this neutron field has scarce thermal and epithermal neutrons, measurement of nuclei produced by threshold reactions is not affected by (n, γ) reactions which are induced by thermal and epithermal neutrons. Moreover, considerably high fast neutron flux (about 5 x 1011n/cm2·sec) enables to measure cross sections of small values. The results in general agreed with the previous values obtained in a reactor core or with a fission plate within an experimental error, while they were systematically smaller by about 10% than those recommended by Fabry. The measured values are also compared with the results calculated by Pearlstein based on a statistical model.

Fission Spectrum Averaged Cross Sections of Some Threshold Reactions Measured with Fast Reactor "YAYOI"

Abstract Fission spectrum averaged cross sections of twenty one threshold reactions were measured in the core center of YAYOI which was a fast neutron source reactor. Fast neutron spectrum in the core was experimentally determined by using a set of activation foils and micro-fission counters, prior to the cross section measurement. It was found that the shape of the fast neutron spectrum was approximately the same as that of fission neutrons above about 2MeV. This fact was also supported by theoretical calculation. Since this neutron field has scarce thermal and epithermal neutrons, measurement of nuclei produced by threshold reactions is not affected by (n, γ) reactions which are induced by thermal and epithermal neutrons. Moreover, considerably high fast neutron flux (about 5 x 1011n/cm2·sec) enables to measure cross sections of small values. The results in general agreed with the previous values obtained in a reactor core or with a fission plate within an experimental error, while they were systematica...

The calculation of displacement rates in stainless steel under neutron and electron irradiations

The calculation of displacement rates in neutron and electron irradiations is reviewed. Comparisons are made of neutron displacement cross sections calculated using several secondary displacement models. Included are comparisons of some spectrum-averaged cross sections for EBR-II and FFTF spectra. The status of electron displacement cross sections is reviewed. An exercise is performed to deduce neutron and electron displacement cross sections consistent with an assumed direction dependent damage energy threshold. It is suggested that neutron-electron damage correlations should be based on free defect cross sections rather than displacement cross sections.

Measurement of Average Cross Section for233U(n, 2n)232U Reaction

Isotopically pure /sup 233/U samples, with only 3 x 10/sup -3/ ppm /sup 232/U content, were prepared by thermal neutron irradiation of thoria and subsequent chemical processing. The /sup 233/U sample thus obtained was reirradiated with a fisaion neutron spectrum in the core of the Kyoto University Reactor (KUR), and measurements were made of the fission spectrum average cross section for the /sup 233/U(n 2n)/sup 232/U reaction. A value of 4.08 plus or minus 0.30 mb was obtained for this cross section, in agreement with the renormalized value of Halperin et al., ithin the limits of experimental error. In order to asaess the energy-dependent cross section from the value of this integral measurement, the /sup 233/U(n,2n) cross section was calculated assuming a Maxwellian-type fisaion spectrum and adopting the energydependent evaluated cross sections of ENDF/B-III and other authors. The values of the cross section thus determined were found to be about 32 to 91% larger than the measured cross section given above. The result of Pearlstein's calculation of the /sup 233/ U(n,2n) cross section by the statistical model, again assuming the Maxwellian distribution, is smaller than the measured crosss section by about 19%. (auth)

Measurement of Average Cross Section for 233U(n, 2n)232U Reaction

Isotopically pure 233U samples, with only 3 × l0−3 ppm232U content, were prepared by thermal neutron irradiation of thoria and subsequent chemical processing. The 233U sample thus obtained was reirradiated with a fission neutron spectrum in the core of the Kyoto University Reactor (KUR), and measurements were made of the fission spectrum average cross section for the 233U(n, 2n) 232U reaction. A value of 4.08±0.30 mb was obtained for this cross section, in agreement with the renormalized value of Halperin et al. within the limits of experimental error. In order to assess the energy dependent cross section from the value of this integral measurement, the 233U (n, 2n) cross section was calculated assuming a Maxwellian-type fission spectrum and adopting the energy dependent evaluated cross sections of ENDF/B-III and other authors. The values of the cross section thus determined were found to be about 32 to 91% larger than the measured cross section given above. The result of Pearlstein's calculation of the 2...

Spectrum-Averaged Cross Sections Deduced from Burnup Data and Their Application to Methods Verification

The determination of ratios of spectrum-averaged cross sections from isotopic concentrations is described along with their application to verification of analytical reactor design tools. The determ...

Theoretical spectrum-threshold detector data correlation in EBR-II

An experimental and computer program to further examine the neutron environment in the Experimental Breeder Reactor-II (EBR-II) has been completed. Monte Carlo and S 4 Transport methods were used to determine the neutron spectrum at various positions in the EBR-II core and blanket regions. Response functions for the threshold detectors 58Ni (n, p) 58Co and 54Fe (n, p) 54Mn were determined for each position and the corresponding predicted induced activities are compared with experimental results. Based on combinations of calculated neutron spectra, experimental detector responses, and cross section end points an empirical differential cross section was determined for the 46Ti (n, p) 46Sc threshold reaction. Spectrum averaged cross sections for the three threshold reactions which have been determined at various positions in this facility suggest that significant errors in fast neutron fluences will result if the usual fission spectrum averaged cross sections are used.

Fission spectrum averaged cross sections of threshold reactions of threshold reactions

Measurements of some (n, p) and (n, α) reaction cross sections have been made in a 235U fission neutron spectrum. The neutron spectrum used was that obtained from a neutron converter. The measured values are compared with the results from other workers.