Radioisotope handling. Radio-pharmacist with a vial of nitrogen-13 (N-13), a radioisotope of nitrogen. N-13 is used in some forms of diagnostic medical imaging, such as PET (positron emission tomography) scans. However, it is very unstable, with a half life of just under 10 minutes, and so has to be produced in the hospital just prior to a scan. The gamma radiation given off by the decaying isotope is harmful to living tissue and has to be handled very carefully.