Residual nuclei distribution

I calculate photonuclear yields of isotopes from different targets when they are irradiated by bremstrahlung photons. The number of primary electrons is 1E+9.In _sum.lis file there are such string

**** Residual nuclei distribution **** **** (nuclei / cmc / pr) ****

What here means / pr ? Per electron or per photon ?

It depends on what you have set as primary beam particle. If you started from the electron beam, it’s per electron. In case you started directly with photons, it’s per photon.
Note that / cmc (i.e. cm^-3) actually applies only if you have input the region volume in the RESNUCLEi card.