“EM Radiation” is a term often used by fraudulent companies because it is scarier than the common name: “light”. In high intensities, said radiation is harmful: extreme radio wavelengths can cause you to become an antenna, inducing enough voltage within you to kill you. Microwaves at high intensity cause heating, again, potentially harmful.
But, please note, the energy required to kill someone with any EM radiation is simply not worth the effort: literally every other weapons system is simpler and more effective. The one time when using it would be effective is when the target is too dangerous, such as a missile defense system, used against missiles travelling too fast with too little time to their targets. But, I digress.
The next frequency range is infra-red; heat. In high intensities, it can be damaging, but then again, you can just use the power source to electrocute the victim. Light, of course, is similarly ineffective. Ultraviolet too: unless you’re persistent enough to stay with the victim with your high-powered, ultra-intense blacklight until they get melanoma or just intend to give them a bad sunburn, move on. X-rays. The first potentially harmful form of EM radiation.
Eventually, a victim would get radiation poisoning, and X-rays are hard to shield against! But then realise the real question: just how will you produce the X-rays needed? Generally a radioactive source is needed, which is difficult to acquire.
And people are mostly transparent to X-rays. Only the rare particle ever interacts in such a thin medium as meat. Finally, gamma rays. The most intense, and thus harmful. They lead to radiation poisoning and are very hard to shield against. But this leads to their disadvantage: they rarely interact with humans. But with a powerful enough source…
But where do you get the source? The reactions that produce gamma rays occur quickly, which makes them less dangerous. Why? Because within days of the production of the source, the radiation level would be comparable to flying in a plane.
However, some of humanity’s most lethal weapons are partially fueled by gamma and X-rays: thermonuclear weapons. A significant portion of the lethal radiation affecting covered or distant victims, or those who managed to survive the initial explosion while being exposed to various types of radiation, originates from the high-energy gamma and X-rays, which leads to radiation poisoning.
Nevertheless, the radiation at the onset of the explosion is primarily generated by the heat: the Sun occupies approximately 1 square degree in the sky.
Now, envision 300 square degrees of sunlight in the sky. Picture yourself inside a toaster. Indeed. Combine that with severe sunburn and the radiation from your toaster. That is akin to a nuclear explosion.
Source:
https://en.wikipedia.org/wiki/Radiation
https://www.wikidata.org/wiki/Q18335
