Narrow Results

In the framework of the modified potential cluster model (PCM), the possibility of describing the available experimental data for the total cross-sections for n¹¹B radiative capture at thermal and astrophysical energies were considered with taking into account the 21 keV and 430 keV resonances.

The total cross-sections of the radiative neutron capture processes on ⁹Be, ¹⁴C, ¹⁴N, ¹⁵N and ¹⁶O are described in the framework of the modified potential cluster model with the classification of orbital states according to Young tableaux. The continued interest in the study of these reactions is due, on the one hand, to the important role played by this process in the analysis of many fundamental properties of nuclei and nuclear reactions, and, on the other hand, to the wide use of the capture cross-section data in the various applications of nuclear physics and nuclear astrophysics, and, also, to the importance of the analysis of primordial nucleosynthesis in the Universe. This article is devoted to the description of results for the processes of the radiative neutron capture on certain light atomic nuclei at thermal and astrophysical energies. The considered capture reactions are not part of stellar thermonuclear cycles, but involve in the reaction chains of inhomogeneous Big Bang models.

We have studied the neutron-capture reactions ^10,11B(n, γ) and the role of the ¹¹B(n, γ) reaction in seeding r-process nucleosynthesis. The possibility of the description of the available experimental data for cross-sections of the neutron capture reaction on ¹⁰B at thermal and astrophysical energies, taking into account the resonance at 475 keV, was considered within the framework of the modified potential cluster model (MPCM) with forbidden states (FS) and accounting for the resonance behavior of the scattering phase shifts. In the framework of the same model, the possibility of describing the available experimental data for the total cross-sections of the neutron radiative capture on ¹¹B at thermal and astrophysical energies were considered with taking into account the 21 and 430 keV resonances. Description of the available experimental data on the total cross-sections and astrophysical S-factor of the radiative proton capture on ¹¹B to the GS of ¹²C was treated at astrophysical energies. The possibility of description of the experimental data for the astrophysical S-factor of the radiative proton capture on ¹⁴C to the GS of ¹⁵N at astrophysical energies, and the radiative proton capture on ¹⁵N at the energies from 50 to 1500 keV was considered in the framework of the MPCM with the classification of the orbital states according to Young tableaux. It was shown that, on the basis of the M1 and the E1 transitions from different states of the p¹⁵N scattering to the GS of ¹⁶O in the p¹⁵N channel, it is quite succeed to explain general behavior of the S-factor in the considered energy range in the presence of two resonances.

We have studied the neutron-capture reactions ⁸Li($n,\gamma {)}^9$Li and its role in the primordial nucleosynthesis. The $n{+}^8\mathrm{\text{Li}}{\to }^9\mathrm{\text{Li}}+\gamma$ reaction has a significant astrophysical interest because it includes one of the variants of chain of primordial nucleosynthesis processes of the Universe and thermonuclear reactions in type II supernovae. Furthermore, we consider the ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ reaction in the astrophysical energy range in the modified potential cluster model (MPCM) with splitting of orbital states according to Young tableaux and, in some cases, with forbidden states (FS). The reaction ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ plays an important role in primordial and stellar nucleosynthesis of light elements in the $p$ shell. Hydrogen burning in second-generation stars occurs via the proton–proton (pp) chain and CNO cycle, with the ${}^9\mathrm{\text{Be}}{(p,\gamma )}^{10}\mathrm{\text{B}}$ reaction serving as an intermediate link between these cycles. Furthermore, the possibility of describing available experimental data for the total reaction cross-sections of neutron radiative capture on ${}^{10}$Be at thermal and astrophysical energies has been shown. This reaction is a part of one of the variants of the chain of primordial nucleosynthesis of the Universe due to which the elements with a mass of $A>11\text{–}12$ may be formed. The results in the field of study of thermonuclear proton-capture reaction on ${}^{10}\mathrm{\text{B}}$ at ultralow, i.e., astrophysical energies will be presented further. The possibility of description of the experimental data for the astrophysical $S$-factor of the proton radiative capture on ${}^{16}$O to the ground state (GS) of ${}^{17}$F was considered in the frame of the MPCM with FS and classification of the states according to Young tableaux. It was shown that on the basis of the $E1$ transitions from the states of $p^{16}$O scattering to the GS of ${}^{17}$F in the $p^{16}$O channel generally succeed to explain the value of measured cross-sections at astrophysical energies.

We have studied the proton capture reaction ${}^3\mathrm{\text{H}}{(p,\gamma )}^4\mathrm{\text{He}}$. It plays a role in the nucleosynthesis of primordial elements in the early Universe leading to the prestellar formation of ${}^4\mathrm{\text{He}}$ nuclei. All results of our researches and more new data from works show that the contribution of the ${}^3\mathrm{\text{H}}{(p,\gamma )}^4\mathrm{\text{He}}$ capture reaction into the processes of primordial nucleosynthesis is relatively small. However, it makes sense to consider this process for making the picture complete for the formation of prestellar ${}^4\mathrm{\text{He}}$ and clearing of mechanisms of this reaction. Furthermore, we have considered the ${}^3\mathrm{\text{He}}{{(}^2\mathrm{\text{H}},\gamma )}^5\mathrm{\text{Li}}$ reaction in the low energy. This reaction also forms part of the nucleosynthesis chain of the processes occurring in the early stages of formation of stable stars. They are possible candidates for overcoming the well-known problem of the $A=5$ gap in the synthesis of light elements in the primordial Universe. Continuing the study, we have considered the radiative capture ${}^4\mathrm{\text{He}}{{(}^3\mathrm{\text{He}},\gamma )}^7\mathrm{\text{Be}}$ at superlow energies, which has a undeniable interest for nuclear astrophysics, since it takes part in the proton–proton fusion chain, and new experimental data on the astrophysical $S$-factors of this process at energies down to 90 and 23keV and data on the radiative capture reaction ${}^4\mathrm{\text{He}}{{(}^3\mathrm{\text{H}},\gamma )}^7\mathrm{\text{Li}}$ down to 50keV appeared recently. Moreover, radiative capture reactions ${}^4\mathrm{\text{He}}{{(}^3\mathrm{\text{He}},\gamma )}^7\mathrm{\text{Be}}$ and ${}^4\mathrm{\text{He}}{{(}^2\mathrm{\text{H}},\gamma )}^6\mathrm{\text{Li}}$ may have played a certain role in prestellar nucleosynthesis after the Big Bang, when the temperature of the Universe decreased to the value of $0.3T_9$.

Review of calculation results for astrophysical $S$-factor of the ${}^{14}$N${(p,\gamma )}^{15}$O capture reaction in the $p^{14}$N channel of ${}^{15}$O was presented. It was carried out in the frame of the modified potential cluster model (MPCM) taking into account resonances in the ${}^{15}$O spectrum up to 3.2MeV at energy of incident protons varying of 30keV to 5MeV. It is possible to describe experimental data for the astrophysical $S$-factors of the radiative proton capture on ${}^{14}$N to five excited states of ${}^{15}$O at excitation energies of 5.18MeV to 6.86MeV, only under assumption, that all five resonances are $D$ scattering waves. Quality new physical interpretation of the capture mechanism is discussed in this channel to the ground state of ${}^{15}$O. We assumed that the ground state of ${}^{15}$O is determined by the $p^{14}$N${}^{\ast }$ channel with excited ${}^{14}$N${}^{\ast }$ cluster, which immediately allowed us to correctly describe order of values of the experimental $S$-factor for capture to this state. Taking into account these results, the total $S$-factor of the proton capture on ${}^{14}$N and the reaction rates to the ground and five excited states of ${}^{15}$O were determined at temperatures of 0.01$T_9$ to 10$T_9$. The parametrization of the total reaction rate with a simple form is performed, which allows as to obtain ${\chi }^2$ equal to 0.06 with 5% errors of the calculated rate.