arXiv subjects

Victor T. Voronchev

Publications and source records attributed to Victor T. Voronchev.

4 recordsLinked to original sources

arXiv2025

Non-thermal processes in standard big bang nucleosynthesis: III. Reactions with slow nuclei and the overall effect

The present paper completes a series of our works on non-thermal nuclear processes in big bang nucleosynthesis (BBN) started in JCAP05(2008)010 (Part I) and 05(2009)001 (Part II). The processes are triggered by non-Maxwellian particles naturally born in the main BBN reactions. Half of these reactions generate fast particles k^+ (= n,p,t,3He,alpha). The other half, being radiative capture processes, produce slow nuclei k^- (= d,t,3He,7Li,7Be) which can undergo (k^-,n) reactions with neutrons having large cross sections. The particle production rate R_k, thermalization time tau_k, and effective number density n_k are determined. It is shown that the values of n_k at the Universe temperatures T > 65 keV can exceed the number densities of Maxwellian 7Li and 7Be ions. To clarify the overall non-Maxwellian effect on BBN, both types of the non-Maxwellian particles are taken into account in the reaction network. Particular attention is paid to two-step sequential processes like p(n,gamma)d^-(n,gamma)t, d(p,gamma)3He^-(n,p)t, t(alpha,gamma)7Li^-(n,gamma)8Li, 3He(alpha,gamma)7Be^-(n,p)7Li, d(t,alpha)n^+(A,n)a_1a_2, and d(3He,alpha)p^+(A,p)a_1a_2 with (A,a_1,a_2) = 7Li,t,alpha) and (7Be,3He,alpha. It is obtained that the non-Maxwellian particles can selectively affect the element abundances, e.g., improve the prediction on 7Li/H by ~1.5% and at the same time leave unchanged the 4He abundance. The main conclusion however is that these particles are unable to significantly change the standard picture of BBN in general, and provide a pathway toward a solution of the cosmological lithium problem in particular.

astro-ph.CO↗

arXiv2022

Peculiarity of the stellar CNO cycle with energetic particles

A peculiarity of the stellar CNO cycle caused by MeV alpha-particles and protons generated in exoergic nuclear processes is analyzed. The main parameters of these particles and suprathermal reactions induced by them in a stellar core are calculated. It is shown that these reactions can trigger an abnormal nuclear flow in the second branch of the stellar CNO cycle. A conjecture is made that the phenomenon is of a general nature and can manifest in various stars at non-exploding stages of their evolution. The influence of the abnormal flow on some CNO characteristics is demonstrated.

nucl-th↗

arXiv2016

Model description of non-Maxwellian nuclear processes in the solar interior

A consistent model for the description of non-Maxwellian nuclear processes in the solar core triggered by fast reaction-produced particles is formulated. It essentially extends an approach to study suprathermal solar reactions discussed previously [Phys. Rev. C 91, 028801 (2015)] and refines its predictions. The model is applied to examine in detail the slowing-down of 8.7-MeV alpha particles produced in the 7Li(p,alpha)alpha reaction of the pp chain, and to study suprathermal processes in the solar CNO cycle induced by them. The influence of electron degeneracy and electron screening on suprathermal reactions through in-flight reaction probability and fast particle emission rate is clarified. In particular, these effects account for a 20% increase of the 14N(alpha,p)17O reaction rate at R < 0.2Rsun. This new type of correction is important for the suprathermal reaction like 14N(alpha,p)17O as it is recognized to be capable of distorting the CNO cycle in the 95% region of the solar core. In this region, normal branching 14N <-- 17O --> 18F of nuclear flow transforms to abnormal sequential flow 14N --> 17O --> 18F, and the 14N(alpha,p)17O reaction rate exceeds the rate of 17O burn up through conventional 17O(p,alpha)14N and 17O(p,gamma)18F processes. It is shown that these factors can enhance the 17O abundance in the core as compared with standard estimates. For the steady state case, the abundance enhancement is estimated to be as high as ~ 100 in the outer core region. A conjecture is made that other CNO suprathermal (alpha,p) reactions may also alter abundances of CNO elements, including those generating solar neutrinos.

astro-ph.SR↗

arXiv2006

On the enhancement of nuclear reaction rates in high-temperature plasma

We argue that the Maxwellian approximation can essentially underestimate the rates of some nuclear reactions in hot plasma under conditions very close to thermal equilibrium. This phenomenon is demonstrated explicitly on the example of reactions in self-sustained DT fusion plasma with admixture of light elements X = Li, Be, C. A kinetic analysis shows that the reactivity enhancement results from non-Maxwellian knock-on perturbations of ion distributions caused by close collisions with energetic fusion products. It is found that although the fraction of the knock-on ions is small, these particles appreciably affect the D+X and T+X reaction rates. The phenomenon discussed is likely to have general nature and can play role in other laboratory and probably astrophysical plasma processes.

physics.plasm-ph↗