When people talk about the aftermath of a nuclear war, they envision the area to be a place where people cannot live for 100s or thousands of years. But people live in Hiroshima and Nagasaki today. Why is this? was it just an issue of the bombs used on Japan being alot weaker than the bombs made today?
I would venture to say that when people are talking about land uninhabitabe for 100k + years, they’re talking about the cataclysmic exchange we all feared about during the Cold War (lots of bombs, lots of targets, lots of fallout and radiation).
But then again, the yield of the weapons today has exploded [sub]pun intended[/sub]. IIRC, the Hiroshima bomb was only about 20 kilotons, whereas what we currently mount (the W-78) onto a Minuteman III missile up here is Montana is closer to 360 kT (and you can squeeze three of those MIRVs on a Minuteman III). The Soviets also tested a few of their own, I think in the 4 megaton range. :eek:
This here is a good link to get you started on a timeline of development of “the bomb”.
Tripler
Bombs away!
Many people have incorrect or distorted ideas about the effects of nuclear weapons. As a rule of thumb, radiation levels from fallout decline rapidly, proportional to t**(-1.2). If the radiation level is 1000 REM/hr at one hour after detonation, it will be 100 REM/hr at seven hours after detonation, 10 REM/hr at 49 hours after detonation, etc.
A typical modern nuclear weapon is about 10-20x the yield of a Hiroshima size bomb. The problem is that there are so many nuclear weapons. In the event of an all-out nuclear war, every major city could be targeted with multiple nuclear weapons.
Fallout shelters work if you can survive the immediate effects of an attack.
Cecil discusses much this issue in this old column.
Basically, the notion that bombed areas would be uninhabitable for long periods afterwards largely derives from a newspaper scare in August 1945. Initial classified wartime estimates had envisaged that sites might remain seriously radioactive for a few days - as in the Frisch-Peierls memorandum - but what produced the big story was an interview with Dr Harold Jacobson of Columbia University (who I presume is the “American science writer” Cecil refers to). While some of the ensuing damage control by the US military was pure spin, it’s true that Jacobson’s predictions were, in the immediately specific instance, completely wrong. The memory of his predictions, however, lingered.
The main issue is not the size of the bombs, it’s how you use them. Scenarios can always be argued over, but, at least for wiping out large numbers of civilians, the way to go is air bursts. Those tend not to kill via the residual radiation.
Ground blasts do leave far more serious long-term effects, though again not to the extent popularly imagined.
I am certainly no scientist, but my understanding is that the original Hiroshima/Nagasaki bombs were fairly inefficient “gun-type” designs. You have two hemispheres of plutonium or uranium and when brought together, they form a critical mass.
Later on, you start getting into thermonuclear bombs. These use conventional explosives, milled to exacting specifications, to crush the “ball” of uranium or plutonium into a supercritical mass. However, there’s at least one (and probably two) additional stages which add yield. These other stages take the weapon into a “fission-fission-fusion” bomb, whereby the initial CE crushes the ball, which begins to fission. This emits x-rays which are reflected inside the case and eventually cause a second fission reaction within the “spark plug” of the secondary fuel. The “spark plug” leads to a fusion reaction within the secondary fuel. Big boom. IIRC, tritium and possibly a couple of other things can be added to boost yield again. My recollection is that the second fission stage was responsible for creating lots and lots of fallout.
So, I think the development of H-bombs with their second-stage fission reaction, led to the fears of nuclear winter and places being desolate for thousands of years. That in combination with the fear of huge amounts of bombs hitting at once.
I’m sure someone with a scientific background (mine’s humanities) will correct me, but that’s how I got my mind around it.
The bomb dropped on Hiroshima, “little boy”, was a uranium gun type bomb. The bomb that fell on Nagasaki was a plutonium device called “fat man”.
The hydrogen bomb is fairly well explained by Wikipedia:
http://en.wikipedia.org/wiki/Teller-Ulam_design
The thing that causes lots of fallout is the “tamper”, a sleeve of uranium that surrounds the fusion fuel. When the Soviets detonated the biggest bomb in history, they replaced this tamper with lead, reducing the yield by about 50% and reducing fallout by a large amount.
Biggest bomb ever:
http://en.wikipedia.org/wiki/Tsar_Bomba