[Xichekolas]

You just need to lay a few down the west side and wait for radioactive winds to take care of everyone else, but yeah, you have a point. I think most people vastly overestimate the blast radius of nuclear weapons.

A 1 megaton nuclear bomb detonated near the surface has a blast radius of about 1.7 miles. Pretty much nothing is left within this circle. Meaningful lethal damage only continues out to about 2.7 miles.

A 1.7 mile radius translates to roughly 9 mi^2. A 2.7 mile radius is roughly 23 mi^2. To carpet bomb New Hampshire, you'd need a lot of nukes. About 988 of them in fact.

Now 25 megatons is more interesting... you'd need about 68 of those to ensure <2% survival rate, or 25 of them if you are satisfied with <50% survival rate.

Of course, with good placement and strong winds, you could effectively kill 99% with only about 12-15 one megaton bombs. All that radioactive dust from the mushroom cloud comes down somewhere, and with a 15mph wind, that means a lethal dose within 90 miles of ground zero,

Source: http://www.nationalterroralert.com/nuclear/

[electromagnetic]

Even with the UK's very limited nuclear arsenal (compared to the US and Russia) it would be capable of wiping out the whole population of the US using its American-sold MIRV's.

One nuclear launch can easily land well over a dozen nukes with considerable tonnage.

The real question is what's more cost effective 1000 1-megaton nukes or 70 25-megatons? 1000 megaton total vs 1750 megaton total.