ИСТИНА

The central issue of nuclear astrophysics is understanding the nucleosynthetic origin of elements. The majority of heavy elements is processed in stars by radiative neutron captures referred to as s–process and r–process, which are sufficiently slow and rapid, respectively, compared with intervening beta-–decay. The radiative neutron capture cross sections for short–lived radioactive nuclei are difficult to measure due to the fact that the measurements require both highly radioactive samples and intense neutron source. So the probe for describing g–decays of a neutron captured state assuming Brink hypothesis is photodisintegration near threshold. Additionally there are 35 neutron deficient p–nuclides from 74Se to 196Hg which could be produced not in neutron capture chains of s– or r–types but only by different combinations of (g,n), (g,p) or (g,alpha) reactions. Therefore, photodisintegration can be used to improve the prediction of radiative neutron capture cross sections by experimentally constraining the g–strength function entering the statistical model calculations. At last years there is growing interest to measurements of near threshold photoneutron reaction cross sections. Many of those were obtained using modern source of purely quasimonochromatic g–rays from Compton scattering of laser photons from relativistic electrons. New accurate data revealed very important pygmy dipole (PD) and M1– resonances built on top of low-energy tail of GDR. At the same time new data definitely confirmed the well-known problems of systematical disagreements of photonuclear data obtained in various experiments. One of them is that in absolute values of partial photoneutron reaction cross sections obtained using quasimonoenergetic annihilation photons at Saclay and Livermore and another is that in energy resolution of data obtained using annihilation photons and bremsstrahlung. New reliable partial photoneutron reaction cross section data for (g,n), (g,2n) and (g,3n) reactions on 116-124Sn, 181Ta, 208Pb were evaluated in the frame of experimentally–theoretical method proposed before. Near thresholds those were analyzed in details concern both absolute value and energy resolution problems. The role of PD and M1– resonances in indirect method of determining radiative neutron capture cross sections for unstable nuclei and other consequences for astrophysical problems were discussed.