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Californium-242 nucleus 242/98 Cf decays via alpha decay

  1. Apr 26, 2009 #1
    Hey I'm new to this forum, just want to say hi! I'm not sure if this is the rite place to put this but sry if i posted in the wrong section >.<

    I'm actually working on an assignment in my natural science course and I'm stuck on this question cause i'm not sure how to use the variables in the equation.

    The californium-242 nucleus 242/98 Cf decays via alpha decay with half life of 210s
    A)what is its daughter nucleus?
    B) if we originally have 10 000 californium-242 nuclei, how many will remain as californium after one half-life? Explain
    C)if we originally have 10 000 californium-242 nuclei, how many will remain as californium after five half-life? Explain

    Ok so how I view this... I need to use the Decay Law equation to find the daughter nucleus rite? since its going through alpha decay.

    So equation would be N(t) = N e^(-λt)
    N(210) = N e^(-λ210)

    is N = 242?
    So... wuts e? and λ?
  2. jcsd
  3. Apr 26, 2009 #2
    Re: Decaying

    The decay law N(t) is the number of nuclei survived the decay. It decreased with time. N(0)-N(t) is the number of decayed nuclei. It increases with time. Lambda is 1/(210s), N=10 000, e=2.72 (do you know natural logarithms?).

  4. Apr 26, 2009 #3
    Re: Decaying

    Careful there. Half life != decay lifetime.

    In any case, the OP seems to need homework help, so it would be good for a moderator to move this there.
  5. Apr 26, 2009 #4


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    Welcome to PF!

    Hey kchkwan! Welcome to PF! :smile:
    e = 2.718281828459 …

    it's the base of the natural logarithms (ln), so if ey = x, then ln(x) = y …

    both ex and ln(x) should be on your calculator.

    And the half-life is ln(2)/λ = 0.69314/λ …

    see the https://www.physicsforums.com/library.php?do=view_item&itemid=193" entry for details :wink:
    Last edited by a moderator: Apr 24, 2017
  6. Apr 26, 2009 #5
    Re: Decaying

    You are right, I missed the logarithm. The tim's answer is correct.

  7. Apr 26, 2009 #6
    Re: Decaying

    Hiii thanks for the help everyone!

    but i'm only a first year student and i haven't really learned anything else other than that equation, so any of the log stuff i haven't learned yet. I'm just gonna try readin over this and see if i can get an answer lol


    EDIT* ok so my Equation is now this rite?

    N(210) = 242(2.72)^-(0.69)(210)
    = 25490.06???

    and thats 1 half life? O_O lol... im so lost on this question for some reason XD
    Last edited: Apr 26, 2009
  8. Apr 26, 2009 #7
    Re: Decaying

    i just figured out everything thanks!
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