Aren’t Gamma rays, just directed streams of Neutrons?
A gamma ray is just a very high energy form of electromagnetic ray, or what’s more commonly known as “light.” At the low end are things like radio waves, then infra-red, visible light, ultra violet, microwaves, x-rays, and finally gamma rays. The higher the energy, the more penetrating it is, and more damage it does to things like living cells.
Gamma rays can literally tear apart the long-chain chemicals in your body, like DNA, proteins, and enzymes. X-Rays can too, with a much lower chance, and that’s why we’ve found that exposure can cause cancer. The DNA is damaged, and a cancerous cell results.
If we got hit by a nearby, powerful, gamma ray burst, like a supernova or a black hole/star absorption, it could literally sterilize the entire earth in fractions of a second.
As for a “stream of neutrons”, there really isn’t such a thing, since single neutrons decay into a proton and electron (i.e. Hydrogen) with a half-life of 14 hours. Even if the nearest star to Earth (after the sun for nitpickers) Proxima Centauri, lobbed a wedge of neutrons at us at half the speed of light, by the time it reached us here (3.8 years away and after a time-dilated 3 odd years) the amount of neutrons would be nearly immeasurably low, and the protons/electrons would impact on the top of the atmosphere as either ionized particles (auroras channeled to the poles by the magnetic fields of Earth) or “cosmic rays” that would smash into other particles high in the atmosphere resulting in a slight increase in the constant rain of background particles/radiation we get every day.