Why are Hiroshima and Nagasaki safe to live while Marie Curie’s notebook won’t be safe to handle for at least another millennium?
In: Physics
If you clean the notebook you ruin it. The cities get rained on and otherwise have nuclear material dissipate.
Radiation is energy that comes from certain types of particles.
Imagine finding a small pebble that is really, really hot. And the weird thing is that it stays hot, for like 1000 years. As long as you don’t touch the pebble, you won’t get hurt. But if you touch it, the heat can burn you. If you accidentally picked it up, you might get a little burnt but you would drop it. The radiation energy here is not all that dangerous as long as you don’t touch the pebble, because most forms of nuclear energy can be blocked by a small barrier. But imagine accidentally swallowing the pebble. That would burn you from the inside a lot! And you wouldn’t be able to get it out.
When you have a bomb or a nuclear accident, you end up with radioactive fallout. This is basically dust and molecules that acts like that hot pebble but smaller. The area remains dangerous because it is very easy to get that dust on or inside of you like breathing the air or drinking water with the dust in it. And also, it will get on everything. But eventually, the dust will get cleaned up, or buried, or dispersed in the ground or water or air until it is not at a harmful concentration anymore.
Marie Curies diary is still covered in this dust, and it’s all embedded in the pages and stuff. You could stand next to it and probably be okay, but you don’t want that dust to get transferred to you or to breathe it in.
When a bomb goes boom most of its materials is converted into energy. This is the blast and explosion that kills people. So simply put the nuclear materials dispersed into energy and not much is left. The stuff that was left was cleaned up after the wäre
With a nuclear weapon there are 3 main sources of radiation:
1. Prompt – This is the initial burst of radiation from the fission reaction itself. X-rays, gamma rays, neutrons etc. Just like the flash, they’re gone right after the weapon detonates
2. Neutron Activation – Certain materials when bombarded with high energy neutrons become radioactive. This is more an issue in reactors where materials are under constant neutron flux, but some of this will happen when the weapon goes off
3. Fallout – Literal pieces of the weapon itself. Essentially the vapour of what was left condenses on materials sucked into the dust cloud or precipitated in rain. Air bursts reduce this, but there can still be plenty. This tends to be the long lived dangerous material you have to be careful about. It gets on clothes, food, inhaled etc
OK, so two things to correct in your question premise here.
Marie Curie’s notebook (and body) aren’t remotely dangerous. They’ve just got some radium contamination on/in them. Museum rules aside, you don’t need any special training or gear to handle them, relative to some ordinary object like a leaky bottle of rat poison. Wear gloves, and don’t eat the paper.
And the notebooks will be just as contaminated 1000 years from now. Radium has a 1620 year half-life. So the contamination will be detectable for around 162,000 years.
Nuclear bombs are designed to convert as much of the radioactive material into energy as possible. As a result, they use very little radioactive material and the stuff they use ends up decaying pretty quickly, so it ends up being mostly safe a few years later.
Marie Curie on the other hand investigated a bunch of random radioactive materials, including many that decay really slowly. Normally this wouldn’t be a problem because slow decay = very little radiation/second, but she studied large quantities of them and they also turned into radioactive dust, so handling her stuff would get a bunch of radioactive dust onto you which would slowly release a bunch of radiation into you over a longer period of time.
An airburst = the radiation can mostly be blown/washed away by weather in a fairly short period of time.
Handling items extensively = those items become heavily irradiated, and it doesn’t just blow off. And also, those items aren’t washable without destroying them.
There is the physical aspect and the radiological aspect.
Physically, the bombs in Hiroshima and Nagasaki were airburst above the ground. Most of the radioactive material was launched into the air. Some went up into clouds and were spread over great distance, some settled out in dust particles over a few kilometers, and some rained down near the explosion. Natural weather (wind & rain) spread a lot of the radioactive materials over a large distance, diluting the concentration to less harmful levels.
Marie Curie studied radioactive elements for decades in a few small laboratories. Her work was ground breaking, and the negative health effects of radiation were not well understood, so strict radiation control measures were not used. This lead to a concentration of radioactive material in certain locations.
Radiologically, each element has a half life – the time it takes to release half of the radioactivity. Different elements have different half lives, from a few seconds to millions of years.
Elements that have a very short half life (such as less than a day) release a lot of radiation quickly and decay away to safe levels. If an element has a half life of 1 day, it will be 1/2 as radioactive tomorrow, 1/4 as radioactive the next day, then 1/8, 1/16, etc… after 20 days, it will be a million times less radioactive, so even a terribly high level would be safe after a month.
Elements that have a very long half life (like a million years or more) release radiation so slowly that it is not harmful unless you are in close proximity to a lot of it for a long time.
In the middle are nasty elements that can cause harm over several months to several centuries. One of the worst from the atomic bomb was Iodine-131, which has a half life of 8 days. A concentration that is 500 times too high would take 9 half lives to get to safe levels. That is 72 days – people would be exposed for months without knowing. Marie Curie studied Polonium (half life of 140 days) and Radium (1600 years). From a 500x concentration, Polonium would take 34 years to get to a safe level, and Radium would take 14,400 years.
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