1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can anyone explain to me how Deuterium slows down neutrons?

  1. Nov 2, 2012 #1
    Hey all,

    First off, am I correct in saying (generally) that Deuterium slows down neutrons? That's why nuclear reactors use it because its easier to catch neutrons that are going slower. ??

    Does this apply to all neutrons?

    Example, lets say I drank a nice tall glass of delicious Heavy Water :). When the Deuterium interacts with whatever it comes in contact with in my body, will it slow down the neutrons of it?

    Can someone explain to me how deuterium does slow down neutrons?

    Thanks everyone.
  2. jcsd
  3. Nov 2, 2012 #2


    User Avatar

    Staff: Mentor

    Your body doesn't have any free neutrons.
  4. Nov 2, 2012 #3
    Thank you
  5. Nov 2, 2012 #4
    I am trying to find a whole collection of possible solutions HOW deuterium could possibly slow down the circadian clock.
  6. Nov 2, 2012 #5


    User Avatar

    Staff: Mentor

    Say which what? Have you read something (reliable) that you can post a link to?
  7. Nov 2, 2012 #6
  8. Nov 2, 2012 #7
  9. Nov 2, 2012 #8
    It's pretty simple. The special thing about deuterium is that it does not absorb (thermal) neutrons (very much, compared to hydrogen), i.e. the thermal neutron absorption (also called capture) cross section for deuterium is 3E(-4) vs 2E(-1) for ordinary hydrogen H(1). So the only thing that the neutrons can do is scatter. See the table near the end of
    http://en.wikipedia.org/wiki/Neutron_cross_section . Note that Oxygen(16) also does not absorb much. So heavy water D2O scatters energetic thermal neutrons with little absorbing. It is the scattering of the hot neutrons off of the room temperature deuterium oxide (heavy water) "moderator" which slows them down. For reactors, the neutrons are then absorbed by Uranium, which then undergoes fission.

    So why are deuterium and oxygen such poor absorbers compared say with elements with an odd number of nucleons? It is because of the magic numbers 2 and 16 in their atomic weights. The reason is a combination of quantum mechanics and spherical dynamics, and on a deeper level Lie Groups (I think) and somewhat similar to why Helium (with two electrons this time and Argon with 18 electrons) are "noble" gases and are basically unreactive chemically. The big philosophical point is that in this instance, Pythagoras (550 BC) was pretty much completely correct, "All [elementary structure] [really] is [integer] number" on the deepest level. To me this is perpetually amazing. On the other hand, in retrospect what else could it have been?

    Pretty much all of the neutrons in your body are locked up inside the nuclei of atoms. Heavy water won't affect them at all. It is only the free neutrons released from radioactive transmutation of the elements (e.g. decay) that are affected.
    Last edited: Nov 2, 2012
  10. Nov 3, 2012 #9
    Oops, sorry, never mind the above. While true, I completely missed your circadian rhythm question.

    I do not know much about the enzymes involved in the mechanism of circadian rhythm but there are many known "kinetic isotope effects" involving enzymes in biology, some involving isotope substitution in the solvent, but most in the substrate. If we are looking at a pure heavy water effect in the solvent, I suppose alterations in hydrogen bonding might be one possible mechanism, or involvement of a water molecule in the active site of a particular enzyme. The altered mass of the heavy isotope compound is the reason for the difference, sometimes via tunneling. Vibrations also differ.

    Since 1992 very much indeed has been learn about circadian rhythm, esp. in drosophila. You might look for genetics of circadian rhythm. A quick search shows no real biochemistry experiments yet.
    Last edited: Nov 3, 2012
  11. Nov 4, 2012 #10


    User Avatar
    Staff Emeritus
    Science Advisor

  12. Nov 4, 2012 #11
    http://cbn.eldoc.ub.rug.nl/FILES/root/2000/PhysiolBehOklejewicz/2000PhysiolBehavOklejewicz.pdf [Broken]
    Last edited by a moderator: May 6, 2017
  13. Nov 4, 2012 #12


    User Avatar
    Staff Emeritus
    Science Advisor

    Well, how does the circadian clock work in the first place?
  14. Nov 4, 2012 #13


    User Avatar
    Science Advisor

    Circadian Rhythm.

    Protons and deuterons diffuse at very different rates. Heavy water and regular water diffuse at noticeably different rates. Since so many metabolic processes are regulated by diffusion, fact that heavy water can alter various biological cycles is not surprising.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook