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

I Element isotopes question

  1. Jun 12, 2017 #1

    something I've always had some confusion with is the vast number of radioactive isotopes that form from fission and subsequent decay of the fissioned nuclei.
    first of all does anyone have a link or something to a good high resolution picture of a chemical elements periodic table kind of table but which would show all additional possible isotopes for every element besides their stable version.

    Also the way i understand this is that the atomic number is the number of protons each element has so they are sorted in the periodic table one after another with respect to how many protons each have, but the total weight of any given element is its proton number plus its neutron number since they have roughly the same weight.
    So if we then have U238 and it absorbs a neutron and turns into Pu239 which is an isotope of Pu why instead it doesn't simply turn into say U239? Surely an element that does not exist.
    Also if I gather correctly I see that U238 turning into Pu239 has also changed its proton number from 92 to 94, how does this happened? It absorbed a neutron so where do the two extra protons came from? I read that two beta decays happen inbetween the U238 turning fully into the pU239 and in the midst of that it is for a short time Np239.
    Also I see that some heavier elements and all elements after Np have their atomic mass in brackets, why is that? Is it because their precise atomic mass is not known or because some of them are only artificial elements or they have no stable isotopes or what?

    Also is Np239 which is an isotope that forms after U238absorbs a neutron somehow different from the resultant Pu239? since I see they have the same atomic mass, is it then their proton to neutron ratio that is different why eventually they are given different names to represent them as different elements or isotopes?

    thank you
  2. jcsd
  3. Jun 12, 2017 #2


    User Avatar
    2017 Award

    Staff: Mentor

    Nuclide charts?
    It turns into U-239. U-239 quickly decays to Np-239 which quickly decays to Pu-239.
    It means they only exist artificially. "Natural composition" doesn't make sense for them.
    It is a different nuclide from a different element. Why do we give different names to hydrogen and helium? Because they are different elements. Same concept.
  4. Jun 12, 2017 #3


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

  5. Jun 12, 2017 #4
    Good lord the whole nuclide chart seems huge , maybe some three times if not more in count than the periodic table with stable elements

    Well ok it turns from U to Np and then to Pu239 , but how is then the intermediate Np and resultant Pu different from the original if they all have a mass number of 239 including the U238 after its neutron capture?
    I assume that the Np which forms after the first U239 beta decay has a different proton vs neutron ratio othetwise how else could it be a different element right?
  6. Jun 12, 2017 #5


    User Avatar
    2017 Award

    Staff: Mentor

    They are completely different elements. I don't understand what is unclear.
    The chemical properties depend only on the type of element, for example (with exceptions that are irrelevant here).

    Yes, the neptunium nucleus has one more proton than uranium. That's why it is called neptunium and not uranium. Neptunium has 93 protons. Np-239 has 146 neutrons.
    U-239 has 92 protons and 147 neutrons.
  7. Jun 12, 2017 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    U239 becomes Np239 when one of the neutrons changes to a proton during the emission of the Beta particle (essentially an high speed electron).
    Then the Np239 undergoes another beta decay with one of its neutrons becoming a proton to make Pu239
  8. Jun 13, 2017 #7
    Thanks the answer about the proton number difference was what i logically suspected and the reason i asked

    Also thanks Janus for answering about the first beta decay turning the neutron into an additional proton as rhat would have been my follow up question
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted