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Thread: Van Allen belt

  1. #1
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    Van Allen belt

    The Van Allen belt is suppossed to protect us from radiation but I'm confused by this.
    First Xrays and Gamma rays pass straight through and are stop by the atmosphere.
    Second charged particles (like Alpha and Beta particles) are swept round into the north and south pole where they again are stop by the atmosphere. Polar explorers are simply not killed by radiation.
    So what would happen if their was no VA belt (which I believe happens whenever the earths magnetic field reverses).

    Also as these particles cannot penetrate a spaceships hull, why are they dangerous to the crew? (I'm not saying they're not I just don't know why).

  2. #2
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    Re: Van Allen belt

    Welcome to the Board, Igor Trip!

    Here's a link to a decent webpage on the Van Allen Belts. I'm not an expert on this sort of thing but I'll try to help - the Board doesn't get a lot of traffic on the weekends so it might be as long as a couple of days before we hear from an expert.
    Quote Originally Posted by Igor Trip
    First Xrays and Gamma rays pass straight through and are stop by the atmosphere.
    The Belts appear to protect us from charged particles from the solar wind (such as elctrons and protons), not specific types of radiation. The magnetic field of the Earth traps the particles. I'm not sure if a magnetic field can affect radiation such as gamma rays.
    Second charged particles (like Alpha and Beta particles) are swept round into the north and south pole where they again are stop by the atmosphere. Polar explores are simply not killed by radiation.
    Because the atmosphere stopped it, the charged particles hit the atmosphere and create the auroras at the poles.
    So what would happen if their was no VA belt (which I believe happens whenever the earths magnetic field reverses).
    Hmmm, don't know that one.
    Also as these particles cannot penetrate a spaceships hull, why are they dangerous to the crew? (I'm not saying they're not I just don't know why).
    Apparantly, from the website, they can. I recall reading posts at the Apollo Hoax forum that this was a concern of NASA when planning manned flights through the belts. IIRC the 'zone' where there is a lot of radiation is not very wide and a ship can get through it quickly so there is not a lot of exposure to radiation.

  3. #3
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    My understanding is that it's the magnetic field which protects us from the solar wind - a stream of mainly electrons and protons from the Sun - by deflecting them around the planet. But some of the particles become trapped in two donut-shaped rings, the Van Allen Belts. Other than helping to produce aurorae (by periodically spilling ions into the atmosphere), I didn't think the belts had any beneficent effects. I don't think we'd be any worse off without them.

  4. #4
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    The Van Allen Belts simply are a region in space where the charged particles coming from the sun are "escorted" around the earth by our planet's magnetic field. That means, the charged particles that hit the earth are passed around it in a relatively small "belt", therefore the concentration of this particles is quite high.
    (Hope this makes sense )
    EM waves are not affected by a magnetic field.

  5. #5
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    Van Allen belt

    Just read this in Bill Brysons "A short history of nearly everything" page 194.

    "Space is full of dangerous cosmic rays which, in the absence of magnetic protection, would tear through our bodies, leaving much of our DNA in useless shreds."

    Is this Bad Astronomy?

  6. #6
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    Re: Van Allen belt

    Quote Originally Posted by Igor Trip
    Just read this in Bill Brysons "A short history of nearly everything" page 194.

    "Space is full of dangerous cosmic rays which, in the absence of magnetic protection, would tear through our bodies, leaving much of our DNA in useless shreds."
    Here is a page that describes cosmic rays (last paragraph). It says that cosmic rays are from particles, in which case most are deflected by Earth's magnetic field (forming the Van Allen Belts). So that much appears to be true. As for the DNA effects of gamma and X-rays I have no idea.

  7. #7
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    Re: Van Allen belt

    Quote Originally Posted by Igor Trip
    The Van Allen belt is suppossed to protect us from radiation but I'm confused by this.
    First Xrays and Gamma rays pass straight through and are stop by the atmosphere.
    Second charged particles (like Alpha and Beta particles) are swept round into the north and south pole where they again are stop by the atmosphere. Polar explorers are simply not killed by radiation.
    So what would happen if their was no VA belt (which I believe happens whenever the earths magnetic field reverses).

    Also as these particles cannot penetrate a spaceships hull, why are they dangerous to the crew? (I'm not saying they're not I just don't know why).
    A concept that should be kept in mind when thinking about this issue is that of 'flux'. Flux can generally be described as the number of particles/photons that strike a given area in a given time. Because the Van Allen belts are effectively magnetically 'channelling' the charged particles of the solar wind, the flux is very high there (sort of a bit like how the gunk in your fuel gets trapped and accumulates at the fuel filter).

    Now, let's say that your spaceship is 99.99% efficient at shielding you from any given charged particle. Out in open space, the flux is usually low enough that this level of protection is OK. However in a high flux area like the VA belts, or during a significant solar flare, that 0.001% inefficiency of your shielding may still be enough to cause problems, given the vast numbers of particles.

    A useful analogy might be this: you're out on a walk and the weather is a bit overcast, so you take a raincoat. Sure enough, it is raining gently, but the raincoat keeps you comfortably dry. However, after a while the rain becomes torrential and the raincoat is not completely efficient at keeping out the moisture. So you try to minimise the amount of time that you are in that torrential rain.

    Likewise, the Apollo missions minimised the time that they had to traverse the VA belts, in order to minimise the high flux radiation to which their spacecraft was subjected.

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