Neutron Scattering Cross Sections for Natural Carbon in the Energy Range 2-133 keV

Natural carbon is well known as reactor structure material and at the same time as one of the most important neutron scattering standards, especially at energies less than 2 MeV, where the neutron total and neutron scattering cross sections are essentially identical. The best neutron total cross section experimental data for natural carbon in the range 1-500 keV have uncertainties of 1-4%. However, the difference between these data and those based on R-matrix analysis and used in the ENDF libraries is evident, especially in the energy range 1-60 keV. Experimental data for total scattering neutron cross sections for this element in the energy range 1-200 keV are scanty. The use of the technique of neutron filtered beams developed at the Kyiv Research Reactor makes it possible to reduce the uncertainty of the experimental data and to measure the neutron scattering cross sections on natural carbon in the energy range 2-149 keV with accuracies of 3-6%. Investigations of the neutron scattering cross section on carbon were carried out using 5 filters with energies 2, 3.5, 24, 54 and 133 keV. The neutron scattering cross sections were measured using a detector system covering nearly 2{pi}. The detector consisting of {sup 3}He counters (58 units), was located just above the carbon samples. The {sup 3}He counters (CHM-37, 7 atm, diameter =18 mm, L=50 cm) are placed in five layers (12 or 11 in each layer). To determine the neutron scattering cross section on carbon the relative method of measurement was used. The isotope {sup 208}Pb was used as the standard. The normalization factor, which is a function of detector efficiency, thickness of the carbon samples, thickness of the {sup 208}Pb sample, geometry, etc., for each sample and for each filter energy has been obtained through Monte Carlo calculations by means of the MCNP4C code. The results of measurements of the neutron scattering cross sections at reactor neutron filtered beams with energies in the range 2-133 keV on carbon samples together with the known experimental data from database EXFOR/CSISRS and ENDF libraries are presented

Investigation of the scattering cross sections of neutrons on carbon nuclei at the reactor filtered beams

Natural carbon is well known as reactor structure material and at the same time as one of the most important neutron scattering standards, especially at energies less than 2 MeV, where the neutron total and neutron scattering cross sections are essentially identical. The best neutron total cross section experimental data for natural carbon in the range 1 - 500 keV has uncertainties of 1 - 4 %. However, the difference between these data and those based on R-matrix analysis and used in the ENDF libraries is evident; especially in the energy range 1 - 60 keV. Experimental data for total scattering neutron cross sections for this element in the energy range 1 - 200 keV are scanty. The use of the technique of neutron filtered beams developed at the Kyiv Research Reactor makes it possible to reduce the uncertainty of the experimental data and to measure the neutron scattering cross sections on natural carbon in the energy range 2 - 149 keV with accuracies of 3 - 6 %. Investigations of the neutron scattering cross section on carbon were carried out using 5 filters with energies 2, 3.5, 24, 54 and 133 keV. The neutron scattering cross sections were measured using a detector system covering nearly 2π. The detector consisting of 3 He counters (58 units), was located just above the carbon samples. The 3 He counters (CHM-37, 7 atm, diameter = 18 mm, L = 50 cm) are placed in five layers (12 or 11 in each layer). To determine the neutron scattering cross section on carbon the relative method of measurement was used. The isotope 208Pb was used as the standard. The normalization factor, which is a function of detector efficiency, thickness of the carbon samples, thickness of the 208Pb sample, geometry, etc., for each sample and for each filter energy has been obtained through Monte Carlo calculations by means of the MCNP4C code. The results of measurements of the neutron scattering cross sections at reactor neutron filtered beams with energies in the range 2 - 133 keV on carbon samples together with the known experimental data from database EXFOR/CSISRS and ENDF libraries are presented

Neutron spectra and fluxes in horizontal channels of research reactor WWR-M while conversion on low-enriched fuel

Neutron fluxes and spectra in the horizontal experimental channels of reactor WWR-M of the Institute for Nuclear Research, National Academy of Sciences of Ukraine (Kyiv) have been calculated using neutron transport Monte Carlo model with fuel enriched in 235U both to 36 and 19.7 %. It is shown that at the very beginning operating with low-enriched fuel, when the reactor core is 28 % filled with "fresh" fuel assemblies, and the remaining cells are filled with beryllium displacers, there is a significant change in the parameters of neutron beams. However, after the reactor will begin to operate at its usual mode, that will be after completing all or most part of the core with fuel assemblies partially burnt out, spectra and fluxes in channels will restore most of their previous values. Some differences are mainly due to changes in composition of the core – the removal of two voluminous vertical water channels located within the core. The work can be helpful to experimenter

Modeling of the neutron experiments at research reactor WWR-M in the Institute for Nuclear Research, National Academy of Sciences of Ukraine

Ideology of simulation of neutron experiments using Monte Carlo method for optimization of experimental conditions and analysis of measurement results is set out. Potentialities are shown and recommendations are worked out relative to use of simulation both on the stage of planning experiment and while correcting the results of measuring for ill-wresting factors

Determination of spectrum hardness as a parameter of neutron field at WWR-M research reactor

New method for determination of spectrum hardness in thermal neutron reactors is proposed. Adequacy of received data to the real values of spectrum hardness had been confirmed by comparison with experimental data which were determined from cadmium relation measured at WWR-M research reactor

Influence of neutron energy on formation of radioisotopes during the irradiation of targets in reactor

Method of calculation of nuclear transformations in irradiated targets is realized for selection of optimal conditions for accumulation of radioisotopes in reactor, taking into account contributions of different energy neutrons (thermal, resonance and fast). Wide potentialities of program complex MCNP-4C based on the method of statistical testing (Monte Carlo method) were used. Positive in proposed method is that all calculations starting from spectra and fluxes of neutrons in reactor and completing by quantity of accumulating nuclei carry out within the framework of the same methodological approach. It was shown by the example of radioactive 98Mo production in Mo98Mo(n, γ)99Mo reaction that for achievement of maximal yield of target radionuclide. it is necessary to irradiate start targets of Molybdenum in hard spectrum with essential contribution of resonance neutrons

Calculational investigations and analysis of characteristics of research reactor WWR-M as a source of neutrons for solution of scientific and applied tasks

Calculational studies and analysis of the neutron fields of WR-M research reactor of the Institute for Nuclear Research, National Academy of Sciences of Ukraine, as a basic nuclear facility for performing the fundamental and applied investigations and for experimentalindustrial production of radioisotope products for various spheres of application are carried out. The calculations are carried out by the method of statistic tests (Monte Carlo) applying the computer program MCNP-4C. The data on the spectra and the neutron flux density values at the 10 MW reactor power for all technological facilities designed for the works with neutrons: 19 vertical experimental channels for irradiation of specimens and 10 horizontal channels for beams extraction from the reactor are obtained. The effect of the neutron traps (water cavities) mounted in the core on the characteristics of the extracted from the reactor beams is demonstrated. Recommendations associated with optimization of the reactor core are adduced for amplification of its capabilities as a neutron source in experimental researches

A set of technological devises for replacing collimators in horizontal channels of reactor

Devices of original construction for replacing collimators are described in this paper. Special attention has been focused on technology of moving off “outdated” collimators that have been stuck inside a channel. Carried out set of devices has been used effectively in experiments at the reactor of the Institute for Nuclear Research of NAS of Ukraine and may be used at other reactors