Victor T. Voronchev

Kinetic analysis of γ-ray-generating reactions for fuel ion and energetic particle diagnostics of D-T fusion plasma

In D–T fusion plasma seeded with a small amount of 6 Li, monochromatic 0.429-, 0.478- and 0.981-MeV γ rays are produced in the 6 Li+D and 6 Li+T nuclear reactions. In the present paper we investiga...

On the relation between forward and reverse nuclear reactions in an astrophysical plasma

In the standard relation between forward and reverse nuclear reactions in plasmas, the reverse reaction rate parameter σv obeys the law of temperature-dependent suppression by a factor of exp (− Q/T). This exponential law, originally obtained for thermal processes, has widely been used in studies of reaction kinetics in an ionized matter. In high-temperature plasmas, however, both thermal and suprathermal nuclear reactions can simultaneously occur. Astrophysical multicomponent plasma systems, in which catalytic processes generating fast particles can effectively proceed, provide favorable conditions for the suprathermal reactions to appear. On the example of one of such systems—the early universe plasma—we demonstrate that the relation between forward and reverse reactions may cease to follow the exponential law. This occurs when the plasma cools down and the suppression factor exp (− Q/T) essentially decreases thermal σv for reverse reactions. These reverse processes, however, can still be maintained by suprathermal particles—products of exoergic reactions in the plasma. Such competing nonthermal mechanism changes the conventional behavior of reverse processes so that the forward–reverse reaction relation departs from the standard formula. This phenomenon is obtained at some critical temperature Tcr for all reactions examined in the work: d(d, n)3He, d(d, p)t (for which Tcr 90–100 keV) and 3He(n, p)t, 7Be(n, p)7Li (for which Tcr 20 keV). The most significant effect is marked for the reverse n + 3He → d + d reaction. It is shown that at moderate temperatures of several keV to tens keV, fast neutrons can provide the rate of this reaction at an appreciable level typical of the thermal process at plasma temperatures as high as a few hundreds keV. The obtained phenomenon has universal nature and can manifest in other astrophysical plasma objects.

Non-thermal processes in standard big bang nucleosynthesis: II. Two-body disintegration of D, 7Li, 7Be nuclei by fast neutrons

Continuing the analysis of non-thermal effects in standard big bang nucleosynthesis (JCAP05(2008)010), we examine the role of suprathermal nuclear reactions induced in the early universe plasma by energetic nucleons of various origins. The processes of present interest are break-ups of D, 7Li, 7Be nuclei induced by 14-MeV neutrons generated in the plasma via the T(d, n)4He reaction. It is shown that this reaction forms the ensemble of fast neutrons whose fraction in the plasma neutron component is at the level of 0.01 %. In spite of the small percentage, such neutrons can effectively destroy the loosely bound D, 7Li, 7Be nuclei. It is found that at temperatures T9 < 0.8 the n-induced non-thermal break-ups of D and 7Li dominate over other reactions occurring in the n+D and n+7Li systems. However, the non-thermal neutronic effects prove to be insufficiently strong to modify the standard picture of nucleosynthesis. The D, 3He, 4He abundances are obtained to remain unchanged, and only a little effect is marked for primordial 7Li. The 0.01 % fraction of plasma neutrons (fast DT neutrons) reduces the 7Li abundance by 0.02 %.