# Why actually are some elements radioactive?

1. Jan 13, 2010

Can anyone explain to me why actually are some elements radioactive? I have the explanation in my textbook but i want to know the main reason why these elements are not stable..........

2. Jan 13, 2010

### bcrowell

Staff Emeritus

Hi, Desconcertado -- welcome to Physics Forums!

Here's an online treatment that you could try as an alternative to your text, to see if you just need to see it from a different perspective to make it "click:" http://www.lightandmatter.com/html_books/4em/ch02/ch02.html [Broken]

It will be hard for anyone here to answer your question in any detail unless you tell us what it is specifically about your textbook that you don't understand, or that isn't satisfying you.

Last edited by a moderator: May 4, 2017
3. Jan 14, 2010

My textbook tells me that, as given by the stabliity curve, certain neutron proton ratios are stable and with the increase in atomic number the neutron proton ration diverges from being the stable one.

I do not understand why certain neutron proton ratios are stable and others are not...
The hypertext that brocwell sent was nice.. but i did not get my answer exactly.. It would be great if somebody could explain or give the site where it is explained!

4. Jan 14, 2010

### hamster143

Every nucleus has a certain value of binding energy. For example, the mass of a helium-4 nucleus is smaller than the mass of 2 free protons and 2 free neutrons. The difference is called binding energy.

The exact value of binding energy can be measured experimentally, by weighing the nucleus. The theory behind this is quite complicated and the truth is that we can't compute the binding energy exactly. There are, however, approximation formulas that work quite well.

Any nucleus is radioactive if and only if it has something to decay into. Helium-4 is stable, because it has a high value of binding energy and all its possible decays are prohibited by the law of conservation of energy. Helium-6 is unstable, because it's energetically allowed for it to decay into Lithium-6 and an electron.

5. Jan 14, 2010

### bcrowell

Staff Emeritus