Impacts number and Impact energy

Hi everyone,
I'm try to simulae a tumbling mill and I want to estract some data such as the impacts number and the impact energy of the particles;
any idea about how to do it? Since the impact would be anaelastic I could use a compute command to obtain ke/atom, erotate/sphere/atom and pe/atom obtaining in this way N values (N number of particles) of total energy (that would be a per-atom quantity); I'd like to compare this value with the same parameter but in the next time step in order to obtain the difference that would be the energy lost during the impact. Unfortunately, all I'm able to do is to dump this value and I'm not able to process it..
Thank you for your help