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Re: radioactivity

Cliff is correct (see below) in saying that classical physics can
not explain radioactivity or to predict half-lives. But there is a
way to answer some of his questions. It is the semi-empirical
mass formula. For any given (Z+N) one can calculate masses
of nuclei with different Z. When this is done one finds out
which nucleus (or nuclei) are stable and which is not.

This is not a very profound explanation but it is better than
nothing. For more information see, for example, "Nuclear
and Radiochemistry", by Friedlander et al.
Ludwik Kowalski

cliff parker wrote:

I will expose my ignorance with this question but here goes. I
have been thinking about radioactivity. Some of my high school
chemistry students asked me why elements with nuclei larger than
uranium were radioactive. I said that the electromagnetic force
causes positive protons to repel each other while the strong
nuclear force holds protons and neutrons together. The strong
force is stronger than electromagnetic force and wins the battle
when nuclei are formed. The strong force however has limited
range and when nuclei reach about the size of U the strong force
can no longer attract the particles with enough force to overcome
electromagnetic repulsion therefor such large nuclei do not last
long. I believe in as far as my explanation goes it is correct.
However I am sure there is more because this explanation says
nothing about why lighter nuclei are radioactive. It also says
nothing about why heavy nuclei have varying half-lifes. My guess
is that most of the rest of the story lies with the weak force
which I know little about. Will some of my cyber mentors shed
some light and or point me in the right direction for I fear that
in the process of explaining this to my students, I may have
"expressed myself more clearly than I can think" and I hate it
when that happens!

--
Cliff Parker

Never express yourself more clearly than you can think. --
Niels Bohr