Nukes are definitely interesting. And you are both right and wrong about their radius. They vary greatly in yield and application.

TLDR --

If your goal is to blow the frick out of everything, then you typically deploy the weapon in an airburst, 1000m or higher. This emphasizes the blast radius and minimizes the nuclear fallout.

You get the best shockwave, you still emanate infrared and light everything on fire, and you still emanate gamma radiation.

Very little of that blast contaminates the dirt, and very little of the entire process becomes long-term radiological particles, or what is known as fallout OMG JUST LIKE THE GAME!

Okay now let's get nerdy.

Let's talk a little bit about radiation, because most people are r-slurs.

This applies to !ifrickinglovescience !physics !chemistry and !biology because of the nuclear weapon effects, and you pros can correct the details. And even you !engineering fans can park your trains or whatever you do for a living.

If you turn on your light switch, you are creating electromagnetic radiation, and once you turn it off, the radiation is done. That's pretty much what happens in a nuclear air burst. Things change when you use a nuke to hit the ground, or underground, like maybe as a bunker buster.

Likewise, when you split a nucleus, the mass defect from the difference in the resulting nuclei factors into the calculated energy release. This emanates in a few different types of EM frequencies, plus heat, plus the other shit that shakes out from the Standard Model particles. I think there's even a big old kinetic release from the electrostatic repulsion of the overall positive nucleon charge.

But if you make a nuke explode at ground level, or detonate one a few hundred feet below the ground, this changes everything.

This is where you generate massive amounts of physical matter that disperses long-term fallout over a very large range.

A couple of the underground nuclear tests in Nevada ended up bursting outward above ground level, which dispersed radiological particles all the way to the Great Lakes.

Pretty much most cases of thyroid cancer come from radioactive isotopes of iodine produced by nuclear testing. This is why you stock up and take iodine pills after a nuclear war.

What's the recent research on Nuclear Winter?

I've heard that Carl Sagan used to exaggerate the effects back in the 80s. The assumption is that nuclear blasts will cause massive fires pumping particles into the atmosphere.

https://climate.envsci.rutgers.edu/pdf/IndiaPakistanBullAtomSci.pdf

This was the paper they used for the hypothetical Pakistan/India clash

I'll believe this because nukes in Civilization never do as much damage as you want them to

I FULLY SUPPORT NUCLEAR WAR

The only South American country that will survive is Paraguay.

I will never forget you baby