Answer:
Due to emission of radiation by Radioisotopes.
Step-by-step explanation:
Radioisotopes substitute for non-radioactive isotopes of elements in experiments because the radioactive isotopes releases radiation which can be seen on a specific device while non-radioactive isotopes emitted no radiation and we can not see the pathway of the reaction which occurs inside the plant body so that's why radioisotopes are used in place for non-radioactive isotopes in the experiment for detection.