$${}^{5}$$He($${}^{3}$$He,$${}^{4}$$He)$${}^{4}$$He as a three-body reaction via a continuum resonance in the n+$${}^{4}$$He system

The $${}^{5}$$ 5 He($${}^{3}$$ 3 He,$${}^{4}$$ 4 He)$${}^{4}$$ 4 He reaction involving the unstable $${}^{5}$$ 5 He nucleus is a possible process in primordial nucleosynthesis to convert $${}^{3}$$ 3 He into $${}^{4}$$ 4 He in a neutron transfer reaction. Since experimental data for the reaction cross section are not available, a theoretical prediction is needed to estimate the relevance of this process in comparison to other reactions, e.g., $${}^{3}$$ 3 He($${}^{2}$$ 2 H,p)$${}^{4}$$ 4 He or $${}^{3}$$ 3 H($${}^{2}$$ 2 H,n)$${}^{4}$$ 4 He. In this work the cross section and the Maxwellian-averaged transition rate of the $${}^{5}$$ 5 He($${}^{3}$$ 3 He,$${}^{4}$$ 4 He)$${}^{4}$$ 4 He reaction are calculated using a post-form distorted-wave Born approximation in a simple cluster model. For that purpose the reaction is treated as a genuine process with three particles, $$\text{ n }+{}^{4}\text{ He }+{}^{3}\text{ He }$$ n + 4 He + 3 He , in the entrance channel proceeding through the $$3/2^{-}$$ 3 / 2 - resonance in the $$n-{}^{4}$$ n - 4 He scattering continuum.

Primordial nucleosynthesis constraints on high-z energy releases

ABSTRACT The cosmic microwave background (CMB) spectrum provides tight constraints on the thermal history of the universe up to z ∼ 2 × 106. At higher redshifts, thermalization processes become very efficient so that even large energy releases do not leave visible imprints in the CMB spectrum. In this paper, we show that the consistency between the accurate determinations of the specific entropy at primordial nucleosynthesis and at the electron–photon decoupling implies that no more than 7.8 per cent of the present-day CMB energy density could have been released in the post-nucleosynthesis era. As pointed out by previous studies, primordial nucleosynthesis complements model independent constraints provided by the CMB spectrum, extending them by two orders of magnitude in redshift.

The Study of the 6Li(p,γ)7Be Reaction at LUNA

The 6Li(p,γ)7Be reaction is mainly involved in two astrophysical scenarios: the primordial nucleosynthesis and 6Li consumption in pre-main and main sequence stars. A recent measurement of 6Li(p,γ)7Be reaction S-factor reported a resonance-like structure at Ecm = 195 keV, which has not been confirmed neither by other direct measurements nor by theoretical calculations. A new experiment was performed at the Laboratory for Underground Nuclear Astrophysics (LUNA). The extremely low background environment allowed to measure the 6Li(p,γ)7Be cross section down to low energies with unprecedented sensitivity leading to clarify the existence of the claimed resonance. Details on the experimental setup and the preliminary results of the ongoing analysis are reported in this work.