"Radioactive" is the wrong word, as there's no nuclear decay involved. The concern was X-rays. A CRT looks a lot like an X-ray tube, where you accelerate electr

"Radioactive" is the wrong word, as there's no nuclear decay involved. The concern was X-rays. A CRT looks a lot like an X-ray tube, where you accelerate electrons through 10^4 volts and smash them into a metal target, producing photons with 10^4 eV energy. These X-ray photons penetrate the body and cause tissue damage over time.