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

Background Radiation

  1. Dec 10, 2003 #1
    What's the nutshell story on background radiation? It sounds like there is a small level of nuclear radiation coming from the soil just about everywhere. Is this the case? What is it coming from? Are there trace amounts of radioactive elements pretty much all over the place?
  2. jcsd
  3. Dec 10, 2003 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yup. Snoop around on "crustal abundance."
  4. Dec 10, 2003 #3
    OK. I've been to two sites. Too much to wade through.

    Anyone interested in expounding on background radiation?
  5. Dec 10, 2003 #4


    User Avatar

    Staff: Mentor

    Probably need to refine that google search. Try "background radiation exposure environement." The fist site is the http://www.ocrwm.doe.gov/factsheets/doeymp0337.shtml [Broken]
    THIS site has a small chart saying what you get from certain things such as a plane trip across the country (5mrem) and a chest xray (10mrem).

    I looked for what environmentalist websites say on the subject, but only found a handful of dead links. Its not surprising to me though since its existence tends to counter arguements against things like nuclear power. (check out the mkaku forum for how a poster named "theroyprocess" ignores any mention of background radiation)
    Last edited by a moderator: May 1, 2017
  6. Dec 10, 2003 #5
    Thanks Russ, that level of info is more what I'm looking for.

    I did actually search "crustal abundance + background radiation" and came up with sites that were more technical than I could grasp overall.

    There was much mention of "radionuclides". This, I get the feeling, is different than there being alot of uranium or plutonium specks scattered everywhere.

    Your quotes mentioned radon as the primary source of BR from the soil, which is something the sites I found didn't do.

    I'm curious as to what causes it to leave the ground when it does?
    Even though it's a gas, it's got a heavier nucleus than gold.

  7. Dec 10, 2003 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There used to be an experiment which high school physics teachers did to teach gas diffusion. A gas jar full of H2S was opened at the front of the class, and students asked to put their hands up when they first smelled the 'rotten eggs'. Radon can move from its place of creation by gas diffusion.

    Besides that, gases in soil move in response to pressure differences ('the wind'), which is partly how water vapour (for example) moves upwards through the soil, drying it out. Radon is 'just another gas'.

    There are plenty of naturally occuring radionuclides besides thorium and the various isotopes of uranium (and their daughter decay products, including radon?).

    You've heard of 'carbon dating'? The technique is based on 14C, which is produced by cosmic rays interacting with nitrogen atoms in the air. The radioactive carbon (it has a half-life of ~5,700 years) becomes part of living things, through photosynthesis in plants (which get eaten, etc) ... yes, you are radioactive! Here's a link:

    40K (potassium) is another naturally occuring radionuclide, and yes, those bananas which are 'high in potassium' are also radioactive.
  8. Dec 11, 2003 #7
    This is a surprise! Alchemy?
    Meaning plants tend to prefer to take in the radionuclide over the conventional element?
  9. Dec 11, 2003 #8


    User Avatar

    Staff: Mentor

    No, that just means that since some potassium is radioactive, the more potassium you eat, the more radioactive potassium you eat.
  10. Dec 11, 2003 #9


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yes zooby, essentially all nuclear reactions are alchemy.

    When a cosmic ray collides with an oxygen or nitrogen nucleus (say) in the air, a cascade of secondary particles is produced. Some of the secondaries are neutrons. A neutron with the right energy may interact with a 14N to produce 14C:

    n + 14N -> 14C + 1H

    More details:
    http://en2.wikipedia.org/wiki/Radiocarbon_dating [Broken]

    Here's a proposed Polish high school project on cosmic rays; very nice.:smile:

    It includes the following sentence: "At the separate detector level (4 separate pieces of information per mini array) the secondary cosmic ray particle flux can be constantly measured. The intensity is about 170 counts per second for 1m2 detector (corresponding to 6 penetrating and ionising particles passing per second per human head or 1 particle per hand)."
    Last edited by a moderator: May 1, 2017
  11. Dec 11, 2003 #10
    Thanks, Nereid. I can follow this explanation. Prior to this I just had the vague notion that carbon-14 was something that was just hanging around. It is a surprise to find out it is constantly being created, and in this fascinating way.

    Yes, great project. The high schools I attended were too light on science to get into anything this cool.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook