That all depends on the yield, detonation site, and other important factors. ....
Thank you very much!
Are people a little or more than a little irrational about radiation exposure in various forms?
I suppose we are, but I also think it cuts both ways. I will always be skeptical of the "don't be a wimp about radiation" school of thought. We Terran organisms are adapted to a certain degree of environmental ionizing radiation, a certain level of stuff gets ingested and we have exterior exposure to a certain level, from local radiation spikes and cosmic rays. Clearly both of these fluctuate a fair amount.
But some mass extinctions were really narrow passages, involving extermination of really high percentages of all organisms, leaving just rag tag and very few survivors to repopulate the planet on longer terms. A few thousand years is practically nothing in terms of evolutionary time, which is probably a lot faster than geological time especially when it is a matter of surviving lineages radiating into vacated niches. But we are talking about the survival of our species, and the degree to which high tech modern industrial civilization in some form can survive and recover, and for either of those, it matters a lot how much agricultural land yielding crops with acceptably low concentrations of radioactive isotopes people must ingest to eat the food remains--as dialog here points out, ruining such land is precisely a war planning goal on both sides of a major superpower exchange, and not necessarily just the land within the borders of the ostensible combatants either, as neutrals sitting out the exchange could be invaded and exploited to sustain one side or the other post-exchange. The logic of a major superpower all out war to the end leads to systematic ruining of the best assets known, the only limit being the capacity of each side to do damage to the other, which both tended to simply increase without limit.
Although nuclear weapons are absolutely expensive, they are actually quite efficient in terms of bang for buck; the major expenditure limits on both sides of the Cold War related more to "conventional" systems; both superpowers were strongly tempted to spend on WMD in the hope of economizing on the expensive conventional systems they judged they would need for equivalent strategic power.
I think it is a pretty bold claim to say Chernobyl involved greater contamination than a mid-80s nuclear weapons exchange would, perhaps you have some means of backing it up?
But consider this:
1) during a nuclear war between peer superpowers, each side is going to be trying to do as much damage to the other side's ability to strike at them as possible. To a great extent this involves the wholesale massacre of the other nation, since any industrial potential whatsoever can be weaponized in time. Such destruction is best accomplished by relatively clean airbursts, doing maximum area blast damage and starting firestorms; the fireball is way up in the air. {Edit--as our author points out, another consideration is precisely aimed at concentrating the degree of fallout ruining enemy ability to recover by ruining established city sites and agricultural land with deliberate ground strikes exactly to raise fallout levels; this only underscores my point here, reducing airburst utility to tactical situations}. But a major part involves striking at the enemy's hardened assets--missile silos, command bunkers, possible fortified underground industrial installations, storage bunkers, etc. For that you need groundbursts, to bring heavy hard blows to bear on hardened structures.
Chernobyl bore some passing resemblance to a ground burst, insofar as the RBMK design involved bricks of graphite interspersed with fissionable material units. As I understand it, a runaway fission chain reaction flareup produced a surge of heat that could be characterized as a small fission explosion, but this was sufficient to crack the containment; hydrogen liberated from the coolant water then burned in a chemical explosion blowing the roof off the core, and that exposed quite hot graphite moderator to the air, where it burned intensely. The moderator itself had picked up some fission daughter products and I guess the carbon itself or other elements in the structure had been neutron-activated, and the heat of the flames picked up fissionable unit dust, itself liberally dosed with daughter products and decay products as well as uranium, and it all went up as soot and combustion gases. So that has some semblance to a ground burst. But limited; the quite miscellaneous mix of materials to be transmuted right there at the fireball in a ground burst is going to produce more of a witches brew I think and the action of the intense heat release is going to draw it all up into the sky quite vigorously.
2) you (
@Dunois )seem to be thinking solely of daughter isotopes and perhaps acknowledging some neutron-activated stuff from ground bursts, but a major part of nuclear fallout is actually the unfissioned portion of the fissionable material itself. Now were I in the nuclear weapons design biz, I certainly would want to make my warheads so they fissioned as much of the fissionable material as possible, to get maximum bang from the considerable bucks involved; everything points to that kind of efficiency. But I don't think it is actually that easy to achieve. Certainly early generation fission bombs managed to induce a fission chain reaction in only a portion of the weapons grade material comprising their fissionable cores. Presumably the art of nuclear chemistry has improved and nowadays (and nowadays probably not a lot better than in 1984) the percentage of material fissioned is much much higher, perhaps better than 90 percent.
But still, a substantial mass of the fissionable material will fail to fission at all, and simply be superheated into an ultrahot plasma, which as the core remnants expands cools down to a hot gas creating a shock wave, The surviving U-235 or plutonium will be mixed with quite a lot of other material, mostly nitrogen and oxygen in an air burst, or God knows what drawn up into a ground burst fireball; either way it will wind up forming compounds that will be rained out in a big swathe over the Earth's surface.
The thing is, plutonium is quite nasty and unlike the daughter product isotopes you are fixed on, it has a very long half life too.
And the heavy use of battlefield "tactical" weapons makes the percentage of unfissioned material higher I would think, since it is easier to design a big bomb for most efficient fissioning, versus a small bomb, where to make it go boom at all one might need to lavish on lots of extra fissionable material that won't actually fission. We can't just multiply megatonnage expended by a fixed fraction based on the most efficient weapons; the actual average fraction will be higher, and higher the more small yield strikes there are. "Dial-a-yield" works precisely by dialing down the efficiency a given bomb can theoretically achieve after all.
3) You are confusing the kind of radiation damage that attacks human bodies from the outside, versus what I think would do the damage post-exchange, which is far less vigorously decaying substances that last a long time and are taken up into the ecosystem, taken inside bodies, of plants and animals and any humans who eat any of these, or drink contaminated water. The isotopes do not have to be terribly intense in their net energy release to do a lot of damage when each decay event is happening right inside a living organism; every erg of their ionizing potential will result in ionization trails within the body, every micrometer of the paths of the decay particles destroying cells. In this, a long half life material like plutonium is what does the damage.
Chernobyl I believe was a uranium reactor; whereas I gather modern nuclear weapons tend to use plutonium. It is the release of much of this material as so much dust that I believe poses the major threat to global ecosystems.
It may well be that a full on mid-80s exchange between NATO and the WP would be just medium or even small on the scale of extinction events Earth has suffered already. But the question for human survival is, what percentage of arable land remains arable; where if anywhere will crops be able to grow that won't each be laced with such poisons to such a degree that lifespans are reduced to a handful of decades or less for humans who eat them. If those lifespans are down below the age of fertility, and fertility is reduced by heavy fallout loads, then our species will face possible extinction due to the survivors of the Exchange being unable to adequately reproduce.
4) if fear of radiation is "irrational," many actors in the development of nuclear energy have suffered the opposite extreme, consistently underestimating again and again how damaging ionizing radiation can be. It started with Mdme Dr Curie herself of course. Operation Crossroads, generally known as the Bikini tests, was meant to be three "shots", but only two were actually set off. Crossroads was in interservice rivalry terms the US Navy's attempt to rebut USAF charges that the Navy was obsolete. During the course of WWII, most USN ships had been heavily armored, against enemy aerial bombing attacks, and in fact after the Able and Baker shots, Navy predictions that various ships included in the test would hold up quite well quite remarkably near the A-bomb fireballs were borne out.
What doomed many of these test ships though was--fallout. The intensely dirty water that washed over decks in the Baker shot (Able was air-dropped and an air burst; Baker was a bomb set off in shallow water; Charlie was to have been a bomb deeply submerged) was so "hot" that the Navy had to acknowledge any damage control crews would have been fatally irradiated, and so the ships generally sank because such crews could not be introduced to the ships to prevent their sinking.
Now that of course refers to the sort of high intensity fallout that poses a threat from outside the body of course. The point here is to highlight that optimism about being able to discount the importance of radioactive materials. This is a chronic pattern of nuclear advocates and weapons designers; again and again the general risks of radioactive contamination have been underestimated, and actual experimentation has again and again been quite sobering.
Take the attitudes of Ted Taylor and Freeman Dyson to the development of the Orion space propulsion concept for instance. Both of them are on record in retrospect saying it was probably a good thing the program was abandoned for various reasons. Taylor for instance remarked that back in the late '50s and early '60s they were pretty confident that "cleaner" fusion releases would soon be a reality, not relying on primary fission, and he was later glad that was not the case since the main handle on nuclear weapons proliferation is control of ability to obtain or create weapons grade fissionables, whereas fusion bombs bypassing a fission trigger would be pretty much impossible to control. Dyson observed that their attitude that Orion launches would not seriously increase general fallout levels related to the fact that nuclear testing was growing exponentially, due fundamentally to the fact that one experiment tends to generate multiple new questions requiring more than one future test to resolve experimentally; if this trend were not arrested, then the additional releases from Orion launches would be a small addition to total fallout levels being created. But Dyson also agreed that actually the levels of fallout being generated by the actual testing going on were already reaching seriously alarming levels, and ongoing air testing would inevitably cross the line to serious health damage, so the test ban treaty was a Godsend; if that meant no Orion launches from Earth, so be it.
