Coulomb dissociation studies as a tool of nuclear astrophysics

Abstract

The Coulomb field of heavy nuclei provides an intense source of quasi-real photons acting on passing nuclear particles. This fact has many applications in studies of problems of nuclear structure and particle physics. In 1984 Coulomb dissociation of fast projectiles was proposed as a novel method to investigate radiative capture processes (time-reversed to photodisintegration). This was a new access to a specific class of radiative capture reactions at low energies, relevant for nuclear astrophysics, and it can overcome various limitations of direct measurements. Since then, various dedicated experiments in this field have been performed and many interesting results have been obtained. The status of this approach is critically reviewed and future directions of experimental and theoretical investigations suggested. After sketching the theoretical basis and the basic experimental requirements, some examples are scrutinized. Emphasis is put on a general discussion of the favourable experimental conditions, of related theoretical problems of the analysis and possible pitfalls of the approach. Various astrophysically relevant cases of current and future applications are discussed.

AstrophysicalS(E)factor of theN15(Cognata1, Romano2, Spitaleri3 et al. 2007Phys. Rev. C

“…[3], because the fluorine abundances observed in giants can constrain AGB star models [2]. In this context it has been shown that a key isotope for 19 F production in AGB stars is 15 N and a crucial role is played by the 15 N(p, α) 12 C reaction, removing both proton and 15 N nuclei from 19 F production chain in the AGB intershell environment. The available reaction rates have at least an 8% uncertainty in the fluorine surface abundance [2], due to a factor 2 difference between NACRE [4] and CF88 [5] reaction rates usually employed in calculations.…”

“…For charged-particle-induced reactions, such as 15 N(p, α) 12 C, the Coulomb barrier, E C.B. , (about 2 MeV in the present case), is much higher than the energies of interest ( 100 keV), thus implying that the reaction takes place via a tunneling effect with an exponential decrease of the cross section, σ (E) ∼ exp(−2πη) (where η is the Sommerfeld parameter).…”

Breakup of 8B and the 7Be(p, γ)8B reaction

“…The double differential cross-section for the Coulomb excitation of a projectile from its ground state to the continuum, with a definite multipolarity of order πλ is given by [5,6,7] …”

“…Refs. [5,6]) the measured cross-sections of this reaction to those of the radiative capture reaction b + x → a + γ. Thus, the astrophysical S-factors of the radiative capture processes can be determined from the study of break-up reactions under these conditions.…”

“…This makes the rate of the reaction 7 Be(p, γ) 8 B the most poorly known quantity in the entire nucleosynthesis chain leading to the formation of 8 B [4]. It may be noted that the rate of the 7 Be(p,γ) 8 B reaction is usually given in terms of the zero-energy astrophysical S-factor, S 17 (0).The Coulomb dissociation (CD) method provides an alternative indirect way to determine the cross sections for the radiative capture reactions at low energies [5,6,7,8,9]. In this procedure it is assumed that the break-up reaction a+Z → (b+x)+Z proceeds entirely via the electromagnetic interaction; the two nuclei a and Z do not interact strongly.…”