X-irradiate

In this connection it would be of interest to X-irradiate portions of whole blood labeled with C¹⁴ or N¹⁵ in the hemoglobin molecule.

Source: wiktionary

If you X-irradiate animals on the 6th postnatal day and then every two days to 14 or 16 postnatal days, then it can be shown histologically that you differentially eliminate the cells which are dividing at the different stages.

Source: wiktionary

Some people even use that as a method, but with higher doses: they X-irradiate the nuclei then fuse them, but for that you need selective markers.

Source: wiktionary