Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Van Allen belt

  1. Jan 18, 2005 #1
    Hi im struggling to find relevent and up to date material on the make up of the belts.i understand the low/high energy particles bit.How more low than high.What im struggling to find is mSv doses,or rem readings,and what is the comparison between mSv and rem.i particularly want to know if there is any data showing the actual dosage inside and outside the belts.So far the only thing ive found is the explorer 1,2,3 missions which i cannot find any data to quantify an actual radiation field level at its min/max.Is solar activity a high dose say when you consider one had the intensity to fry someone(what would be the rate eg900rem) what shielding would be possible to counter it.My present understanding is only a few metres of lead would sufficiently stop all radiation.What i do have difficulty is if polyethelene sheilding cannot stop high energy particles penetrating the hull of a craft and injuring the occupants,when they are in fact 600miles away from the VA belts...just what the use a few mm of aluminum could sheild against.In fact what is the maximum dosage which would render the aluminum irrelevent.
     
  2. jcsd
  3. Jan 18, 2005 #2
    it depends on a few things. what type of radiation, the energy of the incoming radiation etc. There is a catch 22 concerning lead in that you get secondary electrons ejected due to interactions of the incoming radiation with the lead atoms. aluminium is a good shield against electrons, whereas lead is a good shield against high energy photons. hence both used in conjunction will more than likely be more effective than using one or the other.

    as for the dosage and van allen belt, use google and do a search. heres some links i came up with:

    http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970228a.html

    http://www-istp.gsfc.nasa.gov/Education/wradbelt.html

    just sift through all the moon landing hoax websites, as some of these may be innaccurate, so as to strengthen their case!
     
  4. Jan 18, 2005 #3

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Hi reaper, welcome to PF. Golly matt, don't send the poor guy to the hoax sites yet. If he hangs out around here for awhile he will better appreciate the humor there.
     
  5. Jan 18, 2005 #4
    Thanks for the replies up to now guys.I read the links however still no luck,i dont know wether there is a definitive answer.It all seems to be 'I think' 'presume' etc.I had hoped that some actual experiments had been done to get a mean radiation level.Obviously im not interested in low energy flux which cannot penetrate the skin,but i havent given up hope some of the scientific community here might be able to help.
    Without going off on a tangent im having difficulty weighing up the belts without any hard facts.They seems more conflicting reports to just how dangerous the biological effect is.NASA wasnt much help,neither wikepedia.Both contradicted each statement they make.Aluminum shields against everything accept high energy flux 'hello but isnt that the point' then they state that an effect none as Bremsstrahlung would actually make the intensity of the penetrating particles greater on the inside of the ship.Thus from 400rem we then could possibly have around 800+.
    There must be some data somewhere,or how are we ever going to get to Mars! and further(solar flares) as when the sun dies off i dont want my decendants trapped here lol
    cheers guys REAPS
     
  6. Jan 19, 2005 #5
    Well, as you may know the van Allen belt is a result of the Earth's magnetic field. When charged particles travel through a magnetic field they have a force exerted on them perpendicular to both their velocity and the direction of the magnetic field. This causes the charged particles to spirl towards the Earth's poles (this is why you only see the aural borelis(sp?) near the north and south poles, charged particles are attracted to the poles and react with Earth's atmosphere).

    Now to get to your question. The bulk of these particles include alpha and beta rays, rogue electrons, and ionized hydrogen (H+). Most of these particles are emitted from the sun and therefore traveling away from the sun, like a wind. Infact, along with the gas and plasma the sun gives off, they call this the "solar wind."

    Alpha rays: These particles aren't really "rays," they are bare helium nuclei (helium atoms that have lost their electrons hence becoming positively charged) traveling through space. They are complosed of two neutrons and two protons and have a charge of +2.

    Beta rays: Like alpha rays, these aren't really "rays" either. They are positrons. A positron is a subatomic particle and is the anti-matter counterpart to the electron. Unlike the electron a positron has a positive electric charge and magnetic properties but has the same mass. These are created in the sun via nuclear fusion.

    Hope that helps you! I can't think of any related sites off the top of my head though.
     
  7. Jan 19, 2005 #6
  8. Jan 19, 2005 #7

    DB

    User Avatar

    This I did not know. So within the outer Belt of Earth for example, Beta e+ (positrons) are caught in the magnetic field sent from the sun? Why positrons and not electrons?
     
  9. Jan 19, 2005 #8

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Good question. Beta radiation includes both positrons and electrons. Nuclei with an excess of neutrons decay by converting a neutron into a proton, electron and antineutrino. Nuclei deficient in neutrons decay by converting a proton into a neutron, positron and neutrino.

    Getting back to the original question, the van allen belts are not particularly hazardous to space travel. Even in highest radiation flux regions, an astronaut could survive several months before receiving a lethal dose. Of course they spend nowhere near that much time in the belts and flight paths are chosen to pass through low intensity regions. Solar flares, on the other hand, are the greatest threat according to NASA. The risk in traveling to the moon is minimal since large flares are infrequent and can be anticipated over a short period of time. On a trip to mars, the risk would be very real. The astronauts can, however, be protected to a significant extent by providing a shielded retreat for them to hole up and ride out a solar storm.
     
    Last edited: Jan 19, 2005
  10. Jan 19, 2005 #9

    DB

    User Avatar

    Thanks Chronos. I have an assumtion and I dont know if its right. I've read that a neutron can't last on it's own for more than a few milli-seconds, then it coverts into a proton (I think it's due to the quarks). Since a proton has a bit smaller mass than a neutron, is the loss in mass converted into an electron an anti-neutrino?
     
  11. Jan 19, 2005 #10

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Yes. A free neutron has a half life of about 10 minutes. It decays into a proton, electron and an electron antineutrino.
     
  12. Jan 19, 2005 #11

    DB

    User Avatar

    o 10 minutes? I thought it was less. Thanks
     
  13. Jan 20, 2005 #12
    I dont mean to be impolite Chronos,you seem to have a good understanding.As this paragraph is a cut n paste from another site,and not your own thoughts.I would like to say its this explanation which has made me attempt to find hard data.
    If i may one explanation the several months stay in high rad flux assertion is contradicted alot depending on site for the following reasons.The most important is solar flares.Unfortunately there is no method i could find that would allow scientists to predict them.Nasa has made this claim yet apollo 16's trip to the moon coincided with one of the largest solar flares in modern history,and with intensity 900+rem(i say this figure because experiments show the big flares are at least this)and astronauts having an eight day jaunt while all this is happening with sheilding that would be inadaquate even if they were holed up.From my research i have found that rad intensity of 900rem would have the biological effect of certain fatality within a short period of days,has this has not been the case,we are left with a choice that to me is ridiculus.
    I fail to see any scientific benefit gained from giving the crazies hoax sites credence,that is why im trying to get as much actual data as possible.
     
  14. Jan 20, 2005 #13
    Just to expand on this thought process a little. I would have to disagree about the statement about solar flares being the most dangerous. For the Mars mission, flares can theoretically be shielded against with a radiation shelter. Sunspot activity can be used (albeit very crudely) to predict solar flares. When one is detected the crew can retire to a radiation shelter. On a long duration mission, like a Mars mission, the largest contribution to the radiation dose will be from Galactic Cosmic Rays (GCR). The GCR is a constant background of radiation. Since it is always present, a simple radiation shelter cannot be used. This is the reason people are working on different spacecraft configurations and shielding strategies. See for instance NASA CP-3360 "Shielding Strategies for Human Space Exploration," NASA RP-1257 "Transport Methods and Interactions for Space Radiation," and NASA/TM-2004-212995 "MESTRN: A Deterministic Meson-Muon Transport Code for Space Radiation" which can be found on http://techreports.larc.nasa.gov/ltrs/
    Cheers
     
  15. Jan 20, 2005 #14

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Interesting, you have a link? I'm not in the habit of pasting quotes without crediting the source.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Van Allen belt
  1. Kuiper belt (Replies: 9)

  2. Third Van Allen belt (Replies: 3)

  3. Van Allen Radiation (Replies: 3)

Loading...