He and Ne ages of large presolar silicon carbide grains: Solving the
  recoil problem
  Knowledge about the age of presolar grains provides important insights into
Galactic chemical evolution and the dynamics of grain formation and destruction
processes in the Galaxy. Determination from the abundance of cosmic ray
interaction products is straightforward, but in the past has suffered from
uncertainties in correcting for recoil losses of spallation products. The
problem is less serious in a class of large (tens of micrometer) grains. We
describe the correction procedure and summarise results for He and Ne ages of
presolar SiC "Jumbo" grains that range from close to zero to ~850 Myr, with the
majority being less than 200 Myr. We also discuss the possibility of extending
our approach to the majority of smaller SiC grains and explore possible
contributions from trapping of cosmic rays.
