Experimental Measurement And Monte Carlo Correction Of Neutron Capture Cross-sections

Neutron's capture reaction is a important part of the neutron's nuclear reactions, also is a problem which is cared by nuclear organizations and elementary form theories. Quick neutron's capture cross-sections are important parameters of nuclear reaction theories, nuclear science engineering designing, theories of element compounding in orb.Europium, molybdenum and cobalt are the main composing element of the structure materials and packing materials in reactors. With the irradiation of the neutrons in the reactors, reaction ¹⁵¹EU (n,γ) ¹52m,g)Eu, ¹⁵³Eu(n,γ)¹⁵⁴Eu,⁹⁸Mo(n,γ)⁹⁹Mo, ⁵⁹Co(n,γ)⁶⁰Co will take place. The cross-sections of these reactions are belong to "the 16 cross-sections which are to be measured immediately" which was offered by the International Atomic Energy Agency(IAEA) in 1988. These reactions all could produce long-lived radioactive nucleus. Therefore, it's very significative to measure the cross-sections accurately of these reactions for estimation of used reactor materials to avoid radioactive waste.Moreover, arsenic is becoming a kind of main material in semiconductor industry in recent years. Because the semiconductor which is composed by arsenic and gallium could resist radiation in outer space strongly, it's often used in aerostats. Because there are a few neutrons, which and ⁷⁵As could take place ⁷⁵As(n,γ)⁷⁶As, in cosmic rays, it's very necessary to measure the cross-sections for academic designing and experimental researching.The experimental data of the cross-sections of Above-mentioned reactions are very few, and there are branchings from each other. Therefore, in order to acquire accurate experimental data, we using the activation technique, setting the cross-section of ¹⁹⁷Au as the standard cross-section, measured the cross-section of ⁷⁵As(n,γ)⁷⁶As, ⁹⁸Mo(n,γ)⁹⁹Mo , ⁵⁹Co(n,γ)⁶⁰Co , ¹⁵¹EU(n,γ)^152m,gEu, ¹⁵³Eu(n,γ)¹⁵⁴Eu reactions.We did the experiments on Van de Graaff accelerators. The neutrons between 29 to 230 keV were produced by the ⁷Li (p, n)⁷Be reaction, and 215 to 1100 keV by the T(p, n)³He reaction. The target was cooled by water or constringent air.In the experiments, the packed samples were put on different positions on a circular sample support to obtain neutrons of different energy. The variety of the neutron flux was watched by a long neutron counter. A sample which was same to others was placed at 1.8m from the target and irradiated simultaneously to determine the effect of background neutrons. The activities of the samples and the gold disks were measured with a calibrated high resolution HPGe detector.In this experiment, the neutrons have to get through the substrate material layer and the water layer on the head of the target after they emit from the membrane layer, so the energy spectrum of the neutrons can be broadened by the layers. The material of the target, the material of the target pipe and other materials also can change the energy spectrum or change the flight directions when the neutrons hit them because of the multiple scattering. The neutron flux rate will be changed along with incident depth because of the self-shielding effects when the neutrons enter the sample. The effects of multiple scattering and self-shielding can't be neglected and can't be removed by experimental method. They can be corrected by the Monte Carlo method commonly. Therefore, we used the MCNP code to correct the result of the experiments. We also calculated the change of the correctional gene along with the thickness of the cooling water and the thickness of the target pipe. The results would be the reference for confirming the size of the materials in future experiments.Finally, we compared our results with others'.