STUDAY OF NUCLEOSYNTHESIS USING keV NEUTRONS

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It is quite important to measure the cross section of the ^<14>N(n, p) ^<14>C reaction at the stellar neutron energy, 10 - 250 keV, to investigate the nucleosynthesis in stara. In order to measure the cross section we have developed the new type of a gas scintillation drift chamber, operating in the N_2 gas. After constructing the chamber we did the off-line test using the alpha source. Good resolutions of energy and time were obtained as expected. In the on-line test, the average cross section of 1.3 mbarn was obtained at the average of 40 keV.Although another ezperiment to get higher statistics is certainly important, the above preliminary result indicates that the N is likely to absord neutrons for the s-process especially in metal deficient stars.The experimental data of the ^<12>C(n, gamma) ^<13>C reaction have been analyzed and for the first time we obtained the accurate cross section in the neutron energies between 10 - 250 keV.From the present resunt it turned out that the carbon acts as a neutron poison in massive metal-deficient stars. The result may affect strongly the scinario of the nucleosynthesis in stars. Furthermore, it was shown for the first time that the cross section increases as the neutron energy increases. This is due to the contribution of the non-direct p-wave capture, which was deduced from the energy dependence of the cross section and the gamma -ray branching ratio from a capturing state.In the neutron capture reaction large amounts of samples are used, as the cross section is usually very small. Therefore it is important to correct properly the multiple scattering events in the thick sample. For the correction wedeveloped a Monte Garlo code and the validity of the code was tested by using paraffine samples with various thickness.