Hi! I have a project where I am supposed to model the s-process in a star in its Helium shell burning region, and i shall do this for a variation of neutron exposure, where neutron exposure are defined as: [tex] \tau = N* \Delta t [/tex] , t is time. N is number density of neutrons. So I in principle have calculated everything i need, but what is left is that i dont know the times for different mass of stars where they are in the AGB (asymptotic giant branch), it is in the AGB phase where stars have Helium shell burning outside a C and O burning core. So i must find the time duration of those phases. I have consulted three textbooks. One is Nuclear Physics of stars by Iliadis, one is Stellar structure and evolution by Prianlik, and one is Modern astrophysics by Caroll.