Nuclei in the Cosmos - IX

Measuring 12C(alpha,gamma)16O with ERNA

27 Jun 2006, 18:00

15m

CERN, Geneva

Oral contribution Experiments in nuclear astrophysics 8 Experiments in nuclear astrophysics II

Speaker

Daniel Schuermann (Ruhr-Universitaet Bochum)

Description

The fusion of carbon and helium via ${}^{12}$C$(\alpha ,\gamma {)}^{16}$O in the helium burning phase of red giant stars is generally accepted to be a key reaction of nuclear astrophysics. Although there exist several direct and indirect measurements, the cross section in the Gamow peak is still not known sufficiently well. A new measurement of the ${}^{12}$C$(\alpha ,\gamma {)}^{16}$O reaction cross section has been done using the European Recoil separator for Nuclear Astrophysics ERNA. \par In ERNA the reaction is performed in inverse kinematics, i.e. guiding a ${}^{12}$C beam on a ${}^4$He gas target. In the recoil separator the high intensity beam is filtered from the oxygen recoil nuclei using velocity and momentum filters. ERNA also needs to provide the necessary acceptances in angle and energy needed to cover the kinematics governed by the gamma ray emission. At the end of the separator the recoil nuclei are freely (i.e. without coincidence conditions) detected in a $\mathrm{\Delta }$E-E ionisation chamber telescope. Assuming full acceptances for the choosen charge state one therefore measures the total cross section. Additional measurement of the coincident gamma rays will provide information on the different capture amplitudes.\par The key parameters of the recoil separator like acceptance of the recoil nuclei and suppression of the incoming beam are discussed. The results of the measurements of the total cross section of ${}^{12}$C$(\alpha ,\gamma {)}^{16}$O in an energy range of 1.9-5 MeV are presented and compared to R-Matrix calculations.

Presentation materials

Slides

ERNA_nic2006.ppt