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!

Radioactive Decay to a Non-radioactive Isotope

  1. Jan 6, 2015 #1
    1. The problem statement, all variables and given/known data
    Magnesium (Z = 12) has isotopes that range from Mg–20
    to Mg–31. Only Mg–24, Mg–25, and Mg–26 are not
    radioactive. What mode of radioactive decay would
    convert Mg–20, Mg–21, Mg–22, and Mg–23 into stable
    isotopes most quickly?
    (A) electron emission
    (B) alpha particle emission
    (C) gamma emission
    (D) positron emission

    2. Relevant equations

    3. The attempt at a solution
    I assume they want you to convert the unstable isotopes to the non-radioactive isotopes (because they tell you the non-radioactive isotopes), so the goal is to add neutrons. I fail to see any emission which adds neutrons only. A results in higher atomic mass, B results in lower atomic mass, C does nothing, and D results in lower atomic mass.
  2. jcsd
  3. Jan 6, 2015 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Red herring. They're just telling you what isotopes of Mg are stable. You've also been told in class that mass number of a stable nucleus is usually at least twice the atomic number, in the case of Mg, 2 x 12 is 24, so the light isotopes are going to fall apart.
    So, you've got to get rid of excess protons (positive charge) in the nucleus to get to a lower atomic number. Help?
  4. Jan 18, 2015 #3
    Sorry for the extremely late reply. But thanks, that makes so much more sense!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted