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Radioactivity Question

  1. Oct 8, 2008 #1
    Hello everybody :)

    I've been wondering about how radiation is harmful for living beings... I know that the three kinds of radiation (α, β, γ). α radiation composed of helium nuclei (2 protons and 2 neutrons), β radiation is composed by the emission of electrons, caused by the conversion of neutrons into protons in an atom's nuclei, and gamma radiation emission occurs by itself (in form of packages called photons as long as I know) during radioactive decay, but also happen more frequently during emission of α and β particles. I've got a few questions..

    1. Let's put for example 212Rn, witch has an half life of 24 minutes, meaning that half of the 212Rn will loose 2 protons and 2 neutrons every 24 minutes, and will so form 208Po. It's obvious that 212Rn is highly radioactive, But why is 235U, for example, more harmful, even having a decay from billions of years?

    2. Witch radiation is more dangerous for living beings? α particles are MASSIVE compared to β, about 7220 times heavier, but have although very small penetration power and short range, due to its size, witch makes α particles ionize a large number of atoms during its travel, but ending at Ek=0 (excluding controlled acceleration of α particles) ; β particles are much smaller then α particles and do so travel longer distances, being able to cause ionization in long range but not necessarily in large scale; gamma radiation is an electromagnetic wave witch must transport more eV then necessary for causing an orbiting electron to release itself from the nuclei, ionizing the atom. This told, I can't really get a picture of witch kind of radiation can cause more damage under same circumstances and under natural velocity standards?

    3. now a strange question :P Why do uranium bars, witch are cooled in water chambers in nuclear reactors, burn the skin and also cause it to peel off like a piece of paper when we pick it up from a table? :)

    Thanks for taking the time of reading! Have a nice day!
     
  2. jcsd
  3. Oct 8, 2008 #2
    1. Let's put for example 212Rn, witch has an half life of 24 minutes, meaning that half of the 212Rn will loose 2 protons and 2 neutrons every 24 minutes, and will so form 208Po. It's obvious that 212Rn is highly radioactive, But why is 235U, for example, more harmful, even having a decay from billions of years?

    The U-235 is *not* more harmful.

    2. Witch radiation is more dangerous for living beings? α particles are MASSIVE compared to β, about 7220 times heavier, but have although very small penetration power and short range, due to its size, witch makes α particles ionize a large number of atoms during its travel, but ending at Ek=0 (excluding controlled acceleration of α particles) ; β particles are much smaller then α particles and do so travel longer distances, being able to cause ionization in long range but not necessarily in large scale; gamma radiation is an electromagnetic wave witch must transport more eV then necessary for causing an orbiting electron to release itself from the nuclei, ionizing the atom. This told, I can't really get a picture of witch kind of radiation can cause more damage under same circumstances and under natural velocity standards?

    Which is more dangerous depends on where it is - an alpha emitter outside your body is harmless (the particle is stopped by the air or your clothes or your outer (dead) skin cells. If you breathe it in and it gets lodged in your lungs, the particles will be stopped by your lung cells - that's bad.

    3. now a strange question :P Why do uranium bars, witch are cooled in water chambers in nuclear reactors, burn the skin and also cause it to peel off like a piece of paper when we pick it up from a table? :)

    Uranium bars won't burn your skin. "Spent" fuel from a rector would, but that is due to the highly radioactive fission products contained within the fuel.
     
  4. Oct 8, 2008 #3

    CompuChip

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    Note that alpha particles are much more massive but also much more energetic than beta particles (and similarly for gamma particles with respect to betas). So at, say, 1 cm outside your body, a beta particle is much more dangerous because it can actually penetrate your body (even if only the upper skin) and release its energy there. An alpha particle is completely harmless, because it can only travel a very short distance and will not even make it to your skin.

    On the other hand, if you put an alpha and beta emitter inside your body (for example, in your mouth, lungs or intestines by swallowing or breathing it) the alpha source is more dangerous, because the particles it emits have much more energy.

    Maybe you have ever seen the formula "H = w D", where H [Sv] is the equivalent dose, w is a weighing factor and D [Gy = J/kg] is the absorbed dose. D can be calculated just from properties of the particles and tissue (e.g.: "10^4 particles with an energy of 12 eV are emitted every second, and absorbed by 3 kg of tissue during 2 hours"). The equivalent dose also takes into account the effects I mentioned above. For alpha particles, w = 20 (iirc) and for beta and gamma, w = 1. Therefore, a dose of 1 Gy corresponds to an equivalent dose of 20 Sv if the particles are alpha, which is 20 times more dangerous than the same dose of beta (for which D = 1 Gy corresponds to H = 1 Sv).
     
  5. Oct 9, 2008 #4
    Oh! Ok, I knew I was wrong but didn't know why :)

    Now I understand why Uranium is more harmful than other elements found in nature, probably because of its high emission of gamma radiation witch travels very long distances and penetrate through eventually EVERYTHING (intensity reduction of gamma radiation decreases exponentially and so, never reaches 0. Please, correct me if I'm wrong! ^^), and so it doesn't need to transmute in order to generate high amounts of radiation. I didn't express correctly at explaining the kind of environment that I had in mind ^^ It was something like having a pile of Uranium (235 or 238) or having an non-radiation absorbing container with Radon or Francium or any other kind of high radioactive gas standing in the middle of a park or something ^^ Sorry for my mistake! ^^

    PS: It's for a little presentation that I want to do for physics :)

    Have a nice day!
     
  6. Oct 9, 2008 #5

    CompuChip

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    Note that in physics, "decreasing exponentially" means "decaying to zero in finite time/length". Depending on the application, e^(-100), e^(-10) or even e^(-2) may already constitute negligible (or, as one of my teachers used to put it: "zero, for all practical purposes").

    But indeed, that's the reason that gamma sources need to be shielded by large amounts of lead and other nice materials, while for alpha sources a layer of air suffices.
     
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