Speaker
Clarisse Tur
(Michigan State University / NSCL)
Description
The rate of the triple alpha process, which plays a central role in the production of
12C in stars, is known with an accuracy of about 12%. Variations within the +/-12%
errors can cause significant changes in the determination of the mass of the iron
core in core-collapse supernovae (type II) and the composition of the material later
ejected in the interstellar medium, as well as a factor of two change in the surface
abundance of 12C in light ABG stars. The present triple alpha experiment aims
therefore at reducing the uncertainty on the knowledge of this rate to about 6% by
measuring more accurately than has been done in the past the pair branch for the
7.654 MeV state in 12C. This state is excited by inelastic proton scattering, taking
advantage of a strong resonance at an excitation energy of 10.6 MeV and a scattering
angle of 135 degrees in the lab. The protons are produced by using the Tandem
accelerator at Western Michigan University. A reduction in the gamma ray background
is achieved by a coincidence requirement between a thin scintillator tube and the
large block of plastic scintillator surrounding it. The pair branch is then given by
the ratio of the number of electron-positron pairs detected in the plastic
scintillators in coincidence with the protons scattered at 135 degrees to the total
number of such scattered protons. The experimental status will be presented.
Author
Clarisse Tur
(Michigan State University / NSCL)
Co-authors
Prof.
Alan Wuosmaa
(Western Michigan University)
Prof.
Sam Austin
(Michigan State University / NSCL)
