cool
The term for implanting radioactive materials into tissues for treatment is called brachytherapy.
unstable, radioactive
The phrase, "fall out," is a military term; an order from a superior, to troops in formation at attention. It is also a term in nuclear warfare referring to the radioactive dust created by a nuclear explosion.
The generic term would be "irradiated", which is also used to mean illuminated but can be identified by its context. This is similar to the use of "contaminated" to mean radioactive.
"The radioactive decay of certain unstable isotopes is used to calculate the age of objects."
no
I suppose you must mean uranium, it is slightly radioactive.
brain scan
Radioactive decay is the process in which unstable nuclei release radiation in the form of alpha particles, beta particles, or gamma rays.
If it is related to Nuclear studies, then the answer would be fusion.
Radioactive elements.
its nuclei can split apart