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

Radiotion decay

  1. May 2, 2003 #1
    Radioactive materials are considered to be relatively safe when their activity has fallen below 0.1% of their initial value.
    a How many half-lives does this take?

    a 0.1% = 0.001, and 1/2^n = 1/1000
    n = 10 or 10 half-lives

    how did they get n=10
     
  2. jcsd
  3. May 2, 2003 #2
    2-x = 0.001, so taking logarithm of both sides you get x = -log2(0.001) = 3log2(10)=3/log10(2)=3/0.301 = 9.97 = 10
     
    Last edited by a moderator: May 2, 2003
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook