Astrophysical factor for the radiative capture reaction α+d→6Li+γ

Abstract

We consider the radiative capture process u+d-+ Li+ y at energies, E,~3 00 keV, that are relevant for astrophysical processes. Due to the peripheral character of the reaction, the overall normalization of the astrophysical factor S24 is entirely governed by one quantity, the asymptotic normalization coefficient Col for Li-+ u+ d. Using the recently well established value for this constant Co& = 2.3~0.12 fm ", we calculated S24 taking into account both E1 and E2 contributions. Our recommended value for S24 is 2.57 MeV nb at the most effective energy for the capture reaction in astrophysical processes, E, = 70 keV, which gives a reaction rate 0.036 cm mole ' s ' at the temperature 0.8X 10 K. We found a significant energy dependence of S24 at astrophysical energies. At energies of less than 110 keV, the E1 component dominates over the E2 component. At E, =70 keV, the E1 contribution to the total transition is about 58%%uo.

Reexamination of the astrophysicalSfactor for theα+d→6Li

“…It has been long ago recognized that the α + d → 6 Li + γ process at astrophysical energies is entirely peripheral reaction in the two-body potential model [17]. Evidently, the potential model itself is a limitation and it would be nice to check peripherality of this reaction within a many-body ab initio approach similar to what has been done recently for the 3 He + 4 He → 7 Be + γ in [22].…”

“…The cut-off radius R c is introduced to reflect a peripheral character of the process. It has been shown in [17] that the matrix element shows a very small sensitivity for R c ≤ 4.5 fm, i.e. until distances, which exceed the 6 Li radius.…”

“…Since such ab initio many-body calculations are not yet available we have to live with a more simple two-body potential model. The matrix element for the α + d → 6 Li + γ direct radiative capture in the long-wave approximation is given by [17] …”

“…The analysis of the data was performed under assumption that the reaction mechanism is contributed purely by the Coulomb breakup. However, the extracted data, which can be considered as an upper limit of the astrophysical factor, at low energies turned out to be constant what contradicted to all the calculations showing significant drop [17]. Recently in [21] a new attempt has been done to get the astrophysical factor S 24 (E) at astrophysically relevant energies from the 208 Pb( 6 Li (150A MeV), α d) 208 Pb breakup reaction.…”

“…The ANC plays a very important role in nuclear astrophysics because many astrophysical radiative capture processes are peripheral and their overall normalization is governed by the tail of the overlap function, i.e. by the ANC [15][16][17][18]. Among the important astrophysical processes, where the ANC plays a crucial role, is the primordial radiative capture process α + d → 6 Li + γ, which is the only process that produces 6 Li in the big bang model.…”