Direct and sequential radiative three-body reaction rates at low temperatures

Abstract

We investigate the low-temperature reaction rates for radiative capture processes of three particles. We compare direct and sequential capture mechanisms and rates using realistic phenomenological parametrizations of the corresponding photodissociation cross sections. Energy conservation prohibits sequential capture for energies smaller than that of the intermediate two-body structure. A finite width or a finite temperature allows this capture mechanism. We study generic effects of positions and widths of two-and three-body resonances for very low temperatures. We focus on nuclear reactions relevant for astrophysics, and we illustrate with realistic estimates for the α-α-α and α-α-n radiative capture processes. The direct capture mechanism leads to reaction rates which for temperatures smaller than 0.1 GK can be several orders of magnitude larger than those of the NACRE compilation. PACS. 21.45.-v Few-body systems -25.40.Lw Radiative capture -26.20.-f Hydrostatic stellar nucleosynthesis

Astrophysical reaction rate forBe9formation within a three-body approach

“…Therefore, the photodissociation cross section of 9 Be shows a relatively broad peak at the energy of the resonance, very close to the three-body and twobody thresholds. This resonance is the main contribution to the α(αn, γ) 9 Be reaction rate, especially at the lowest temperatures where other j π contributions are negligible [6,14]. The experimental cross section shows also a rather narrow peak around 0.…”

“…In any case, the final reaction rate at low temperature depends mainly on the photodissociation cross section at the lowest energies (0-0.2MeV) and the total strength, so diferences in the height, shape, Ref. [49] (dashed line), [15] (dot dashed), [14] (dotted) and experimental data of Refs. [3] (triangles) and [6] (circles).…”

“…a + b + c → A + γ. The energy-averaged reaction rate for such process, R abc (ε) , is given as a function of the temperature T by the expression [14,19] …”

“…It has been found that the radiative capture reaction α(αn, γ) 9 Be is mainly governed by the 1/2 + contribution of electric dipolar transitions to the ground state [6,14].…”

“…The complete computation of three-body reactions in the whole energy range requires a narrow grid of continuum states right above the breakup threshold [14], which * jcasal@us.es is a difficult task. The asymptotic behavior of continuum states for systems with several charged particles is not known in general, and very involved procedures are needed to deal with this problem [16][17][18].…”