Indirect techniques in nuclear astrophysics. Asymptotic Normalization Coefficient and Trojan Horse

Owing to the presence of the Coulomb barrier at astrophysically relevant kinetic energies it is very difficult, or sometimes impossible, to measure astrophysical reaction rates in the laboratory. That is why different indirect techniques are being used along with direct measurements. Here we address two important indirect techniques, the asymptotic normalization coefficient (ANC) and the Trojan Horse (TH) methods. We discuss the application of the ANC technique for calculation of the astrophysical processes in the presence of subthreshold bound states, in particular, two different mechanisms are discussed: direct capture to the subthreshold state and capture to the low-lying bound states through the subthreshold state, which plays the role of the subthreshold resonance. The ANC technique can also be used to determine the interference sign of the resonant and nonresonant (direct) terms of the reaction amplitude. The TH method is unique indirect technique allowing one to measure astrophysical rearrangement reactions down to astrophysically relevant energies. We explain why there is no Coulomb barrier in the sub-process amplitudes extracted from the TH reaction. The expressions for the TH amplitude for direct and resonant cases are presented.Comment: Invited talk on the Conference "Nuclear Physics in Astrophysics II", Debrecen, Hungary, 16-20 May, 200

Narrow \chem{\alpha+ {}^{28}Si} elastic-scattering states at high excitation in \chem{^{32}S}

The excitation function and angular distributions of elastic $\alpha$-particle scattering on \chem{^{28}Si} have been measured in the laboratory energy range 6–28 MeV using a backscattering technique on a thick target, yielding a continuous energy distribution. More than 200 narrow states are observed, with widths in the range $\sim 30$–100 keV at excitation energies $E^* =13$–32 MeV. Angular distributions at backward angles were measured, and angular momentum values of more than 83 states have been deduced. The analysis gives spin-parities $J^\pi$, $\alpha$-partial widths $\Gamma_\alpha$ and reduced widths of the narrow high-lying resonant states in \chem{^{32}S}. The experimentally observed states display both the negative- and the positive-parity rotational-like sequences with seemingly no parity splitting, a finding which is at variance with most potential-model predictions. The deduced effective moment of inertia indicates a more extended structure than the ground-state configuration. The observed strength of each $\ell$-value is analyzed in terms of an underlying split doorway state of Lorentzian form, which yields an interpretation as fragmented rotational $\alpha + \mathrm{^{28}Si}$ states

Study of the A+13C interaction at heavy ION acceleration DC-60

In astrophysics, nuclear reactions play a great role in understanding the formation of our universe.The reaction 13C(α,n)16O is considered to be the main source of neutrons for the s process at low temperatures in low mass stars in the asymptotic giant branch. Many problems exist in analyzing this reaction using conventional experimental methods; therefore, we aimed to obtain and analyze data from the a +13C resonance elastic scattering reaction at small angles and low energies using Thick Target Inverse Kinematic method (TTIK) at heavy ion accelerator DC-60

Study of the A+13C interaction at heavy ION acceleration DC-60

In astrophysics, nuclear reactions play a great role in understanding the formation of our universe.The reaction 13C(α,n)16O is considered to be the main source of neutrons for the s process at low temperatures in low mass stars in the asymptotic giant branch. Many problems exist in analyzing this reaction using conventional experimental methods; therefore, we aimed to obtain and analyze data from the a +13C resonance elastic scattering reaction at small angles and low energies using Thick Target Inverse Kinematic method (TTIK) at heavy ion accelerator DC-60