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An evaluation of the 232 Th neutron total and capture cross sections has been performed in the energy region between 4 keV and 140 keV. The evaluation results from a simultaneous analysis of capture, transmission, and selfindication measurement data, including the most recent capture cross-section data obtained at the GELINA facility of the Institute for Reference Materials and Measurements at Geel (B) and at the n-TOF facility at CERN (CH). The experimental data have been analysed in terms of average resonance parameters exploiting two independent theoretical approaches -the Characteristic Function model and the Hauser-Feshbach-Moldauer theory. The resulting parameters are consistent with the resolved resonance parameters deduced from the transmission measurements of Olsen et al. at the ORELA facility.

Abstract. The characteristic functions of the statisticalWigner's R-matrix for the case of one-channel scattering in competition with multichannel radiative capture have been drown. Different approximations and their relevance in neutron physics applications are discussed. PACS: 25.40.NyThe R-matrix theory of nuclear resonance reactions is a widely used mathematical method for treating the problem of neutron cross section parametrization. This method makes possible the description of resonance cross sections in relatively large energy interval using R-matrix:where E.e and 7;.c are real and energy independent parameters associated with the set of the resonances considered and the summation is performed over it [1][2][3][4].The rank of the R-matrix is equal to the number of reaction channels, excluding the radiation channels, which are accounted for by the imaginary term F./in the denominator. The non-resonant part of the R-matrix is usually included in the phase of the potential scattering and is omitted here [1][2][3].The reaction cross section is defined by the scattering matrix of the same rank [1,2]:where ~oc are the phases of the potential scattering and p is the diagonal matrix of the penetrability factors. The total cross section o-, the reaction cross section o-c and the radiative capture cross section o-.y for a given system of resonances with a fixed total angular momentum J and parity 7r are defined aswhere g(J) is a spin statistical factor [1][2][3][4]. It is possible to determine a complete set of resonance parameters in the R-matrix (Eq. (1)) in the resolved resonance region and this is the aim of the multilevel analysis of the resonance cross sections. But for the higher energies the experimental resolution is not sufficient for the identification of individual resonance levels and here the cross section analysis permits the determination of only average over many levels parameters strength functions ?2,/D,7~/D (D is the average level spacing for a given system J~).At the same time, besides the data on average cross sections and @c), a lot of experimental information on average transmission -

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Abstract. The investigation of resonance self-shielding effects in macroscopic medium is important for the physics of nuclear reactors and shielding. The degree of consistency of evaluated resonance cross sections data and the requirements to the accurate presentation of self-shielding effects can be estimated by using the simplest benchmark data for resonance averaged functions of neutron transmission and self-indication cross section at arbitrary filter thickness n. We report the developed (for nonfissile nuclei) methods for description of cross sections and their functionals in the unresolved resonance range that aim to estimate properly the self-shielding effects and reveal the resonance structure in averaging intervals (groups).

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The independent analysis of new experimental data for 232 Th cross sections in the unresolved region performed on the basis of the existing scheme and method of evaluation confirm the previously obtained average resonance parameters. The method of statistical modeling of the resonant cross-section structure in the unresolved resonance region, proposed and developed earlier by introducing the characteristic function of R-matrix elements distribution and the presentation of this by a ladder of fixed "resonances," is used for calculation of the self-shielding factors of 232 Th. The results are given in comparison with those of the code NJOY and experimental data.