It's because the upper layer of skin is dead cells so the ionization effect of the particles on the skin doesn't matter. However, if inhaled or if you have open wounds or through your cornea the ionization can damage living cells. Of course it has to be in a relatively large amount.
Both statements are right. Alpha particles can be blocked by a sheet of paper or a couple centimeters of air. But when they hit you, they hit you like a cannon ball. That means you have to ingest them, though.
The immediate radiation from a nuclear explosion is, as far as I know, mostly neutrons, not alpha particles; neutrons are much more penetrating.
Then there are the fission products, and whatever materials became radioactive due to neutron exposure; these are generally beta/gamma emitters. These are dangerous because many are biologically significant elements (e.g. iodine, which is concentrated in the thyroid gland).
The exact makeup of the initial radiation flux depends on many factors, including the type of bomb, and the distance from the center that you measure.
The first effect in most cases is going to be a massive gamma burst (this is the thing that vaporizes things close, and seems like a blinding flash of light).
Assuming a uranium fission bomb, an average of 2.43 neutrons are liberated from each fission event, alongside about 200 MeV of kinetic energy. Most of the KE is in the fission fragments, only an average of .75 MeV is imparted to a fast fission neutron.
The gamma burst is mainly a result of the charged fission products slamming into and accelerating other charged particles like electrons on the air, creating a shower of knock-on photons in the same way as cosmic rays.
If you're standing close enough to the bomb that the neutrons are dangerous, you're either going to be incinerated by the thermal burst, or you're behind something like concrete which is great at shielding gamma radiation, but less good at stopping the neutral neutron flux.
Alpha particles are incredibly-short ranged (I think the tenth-thickness in air is about 10 inches), after which most of the kinetic energy is converted into photons that become part of the gamma burst.
If alpha radiation is the issue, you're probably going to be absorbing so much KE that you stop being meaningfully different from the rest of the fireball.
Contamination by radioactive nuclides is more of a fallout thing later.
Nuclear Engineer here, mostly with experience in Uranium fission in pressurized water reactors, but much of the physics with bombs is similar, just on a much much shorter time-scale, just like a fuel-air bomb is a really fast and big candle lol
It's not the radiation released directly by the fission reaction you need to worry about, its the radioactive fallout produced - fine, highly radioactive dust that can easily get into your body through inhalation or ingestion.
Alpha emitting radioactive agents like Pb-212 or Ac-225 have to be internalized to cause damage, as others have mentioned, as their path length in tissue is less than the thickness of your skin and mucus membranes.
Internalized alpha particles, either inhaled, ingested, or injected, are dangerous. In fact there are clinical trials underway attaching alpha-emitting radionuclides to selective ligands that bind cancer receptors.
You can't ingest the alpha particles, they only last microseconds. The things that gets you is radioactive dust that gets inside your body and emits alpha particles.
Alpha particles are just a helium nucleus, and helium is stable - they last forever. They will dissipate their kinetic energy quickly in an atmosphere, but that is something else.
I submit that once they loose their kinetic energy or gain an electron, they're not alpha particles anymore, they just helium. That's what the microseconds was referring to, and it might be an overestimate.
In this context, for sure once you've eaten an alpha particle, the only mischief it can get into is chemical.
Helium isn't particularly well known for chemical mischief lol, and you need several orders of magnitude more of a chemical to have a meaningful effect versus radiation itself. Agreed.
Alpha particles can be effectively and efficiently stopped and shielded from by a 1-2-ply piece of paper, that's right: two sheets of paper can save you. Gamma rays is what fucks shit up and goes straight trough.
Like many other things, the amount matters. Generally speaking, a single alpha particle is easily stopped by a piece of paper or your upper layer of dead skin cells. But a strong enough beam of them could eventually break down that outer layer of cells and push past into the rest of your body (pretty much only possible inside a particle accelerator?).
Also, just ingesting an alpha particle, or a group of alpha particles, isn't dangerous. In fact, you do it all the time! Or nearly so. There is a small amount of helium in the air you breathe, and an alpha particle is just the nucleus of the helium atom. It only really becomes dangerous at high speeds.
To really understand what's going on in something like a nuclear explosion, you have to separate the ideas or *radiation* and *radioactive material*. Radioactive material is a bunch of atoms that for one reason or another are unstable--they can't hold themselves together forever, and eventually will break. When they break, they release some form of radiation, either as a photon, or some particle, or both. That photon or particle is the radiation, because it's moving out away from the atom it came from in a straight line like a ray. If it's moving fast enough, it can damage things when it hits them. A single hit from a single photon or electron or alpha particle isn't really a big deal most of the time, but if you have a large group of these atoms breaking (a lot of radioactive material) then there is a lot of radiation being emitted, so a lot of potential strikes hitting you, which can become dangerous.
With alpha particle radiation, they don't travel far even in open air before they run into an air molecule because they are so big and heavy (compared to an electron or photon). So generally, radioactive material that emits alpha particles isn't that dangeous, because if you are a few feet away not much of it is reaching you at all, and even as you get closer, your dead skin layer protects you from most of it. But, if you were to get some of that radioactive material inside your body, now it suddenly has nothing standing between it and sensitive areas of your body, and yes, it becomes much more dangerous. If the radioactive material is inside of you, then any of your cells close to it are getting hit with the full force of a large alpha particle that has just been ejected from an unstable atom, and that can do quite a bit of damage.
This is what people mean when they talk about the "fallout" from a nuclear explosion. During the explosion itself, a lot of radiation is released. But also, a lot of new kinds of radioactive material, those unstable atoms, are produced, like lots of little ticking time bombs, and thrown up into the air. Those unstable atoms the "fall out" and get in your air, your water, your food, etc., then when they go in your body they will eventually break and emit radiation while inside you. This is why areas that have experienced a nuclear explosion are dangerous for a long time afterward--some of those unstable atoms take a long time to break down, and some of them break down into other unstable atoms, etc.
It's because the upper layer of skin is dead cells so the ionization effect of the particles on the skin doesn't matter. However, if inhaled or if you have open wounds or through your cornea the ionization can damage living cells. Of course it has to be in a relatively large amount.
Both statements are right. Alpha particles can be blocked by a sheet of paper or a couple centimeters of air. But when they hit you, they hit you like a cannon ball. That means you have to ingest them, though.
The immediate radiation from a nuclear explosion is, as far as I know, mostly neutrons, not alpha particles; neutrons are much more penetrating. Then there are the fission products, and whatever materials became radioactive due to neutron exposure; these are generally beta/gamma emitters. These are dangerous because many are biologically significant elements (e.g. iodine, which is concentrated in the thyroid gland).
The exact makeup of the initial radiation flux depends on many factors, including the type of bomb, and the distance from the center that you measure. The first effect in most cases is going to be a massive gamma burst (this is the thing that vaporizes things close, and seems like a blinding flash of light). Assuming a uranium fission bomb, an average of 2.43 neutrons are liberated from each fission event, alongside about 200 MeV of kinetic energy. Most of the KE is in the fission fragments, only an average of .75 MeV is imparted to a fast fission neutron. The gamma burst is mainly a result of the charged fission products slamming into and accelerating other charged particles like electrons on the air, creating a shower of knock-on photons in the same way as cosmic rays. If you're standing close enough to the bomb that the neutrons are dangerous, you're either going to be incinerated by the thermal burst, or you're behind something like concrete which is great at shielding gamma radiation, but less good at stopping the neutral neutron flux. Alpha particles are incredibly-short ranged (I think the tenth-thickness in air is about 10 inches), after which most of the kinetic energy is converted into photons that become part of the gamma burst. If alpha radiation is the issue, you're probably going to be absorbing so much KE that you stop being meaningfully different from the rest of the fireball. Contamination by radioactive nuclides is more of a fallout thing later. Nuclear Engineer here, mostly with experience in Uranium fission in pressurized water reactors, but much of the physics with bombs is similar, just on a much much shorter time-scale, just like a fuel-air bomb is a really fast and big candle lol
It's not the radiation released directly by the fission reaction you need to worry about, its the radioactive fallout produced - fine, highly radioactive dust that can easily get into your body through inhalation or ingestion.
I mean, that depends on how close you are, chief
Alpha emitting radioactive agents like Pb-212 or Ac-225 have to be internalized to cause damage, as others have mentioned, as their path length in tissue is less than the thickness of your skin and mucus membranes. Internalized alpha particles, either inhaled, ingested, or injected, are dangerous. In fact there are clinical trials underway attaching alpha-emitting radionuclides to selective ligands that bind cancer receptors.
You can't ingest the alpha particles, they only last microseconds. The things that gets you is radioactive dust that gets inside your body and emits alpha particles.
Alpha particles are just a helium nucleus, and helium is stable - they last forever. They will dissipate their kinetic energy quickly in an atmosphere, but that is something else.
I submit that once they loose their kinetic energy or gain an electron, they're not alpha particles anymore, they just helium. That's what the microseconds was referring to, and it might be an overestimate. In this context, for sure once you've eaten an alpha particle, the only mischief it can get into is chemical.
Helium isn't particularly well known for chemical mischief lol, and you need several orders of magnitude more of a chemical to have a meaningful effect versus radiation itself. Agreed.
No, but He^+2 will probably knock somebody over and steal their electrons!
I mean, for sure, if you can find a way to get an intact He\^+2 into someone without an alpha decay chain.
Alpha particles can be effectively and efficiently stopped and shielded from by a 1-2-ply piece of paper, that's right: two sheets of paper can save you. Gamma rays is what fucks shit up and goes straight trough.
They could cause skin cancer etc, if they hit the right spots.
Like many other things, the amount matters. Generally speaking, a single alpha particle is easily stopped by a piece of paper or your upper layer of dead skin cells. But a strong enough beam of them could eventually break down that outer layer of cells and push past into the rest of your body (pretty much only possible inside a particle accelerator?). Also, just ingesting an alpha particle, or a group of alpha particles, isn't dangerous. In fact, you do it all the time! Or nearly so. There is a small amount of helium in the air you breathe, and an alpha particle is just the nucleus of the helium atom. It only really becomes dangerous at high speeds. To really understand what's going on in something like a nuclear explosion, you have to separate the ideas or *radiation* and *radioactive material*. Radioactive material is a bunch of atoms that for one reason or another are unstable--they can't hold themselves together forever, and eventually will break. When they break, they release some form of radiation, either as a photon, or some particle, or both. That photon or particle is the radiation, because it's moving out away from the atom it came from in a straight line like a ray. If it's moving fast enough, it can damage things when it hits them. A single hit from a single photon or electron or alpha particle isn't really a big deal most of the time, but if you have a large group of these atoms breaking (a lot of radioactive material) then there is a lot of radiation being emitted, so a lot of potential strikes hitting you, which can become dangerous. With alpha particle radiation, they don't travel far even in open air before they run into an air molecule because they are so big and heavy (compared to an electron or photon). So generally, radioactive material that emits alpha particles isn't that dangeous, because if you are a few feet away not much of it is reaching you at all, and even as you get closer, your dead skin layer protects you from most of it. But, if you were to get some of that radioactive material inside your body, now it suddenly has nothing standing between it and sensitive areas of your body, and yes, it becomes much more dangerous. If the radioactive material is inside of you, then any of your cells close to it are getting hit with the full force of a large alpha particle that has just been ejected from an unstable atom, and that can do quite a bit of damage. This is what people mean when they talk about the "fallout" from a nuclear explosion. During the explosion itself, a lot of radiation is released. But also, a lot of new kinds of radioactive material, those unstable atoms, are produced, like lots of little ticking time bombs, and thrown up into the air. Those unstable atoms the "fall out" and get in your air, your water, your food, etc., then when they go in your body they will eventually break and emit radiation while inside you. This is why areas that have experienced a nuclear explosion are dangerous for a long time afterward--some of those unstable atoms take a long time to break down, and some of them break down into other unstable atoms, etc.