Re: Can we force a nucleus to be unstable?

Kenneth:

The quick answer to your question is yes! The how to do it is a bit more 
complicated. The only way to have a radioactive atom decay in a shorter 
period of time is to change its half life. That is the length of time it 
takes for 1/2 of a group of atoms of one radioactive isotope to decay. 
A radioisotope is a radioactive isotope of a given element--all 
radioisotopes of a given element have the same number of protons, so 
that they are all the same element, but different numbers of neutrons. 
The word isotope means "same place"; the same atomic number (number of 
protons).

That reduces the amount left by 1/2. The hitch is that the half life is a 
characteristic property of every different radionuclide (a radionuclide is 
any radioactive nucleus). Since it is a nuclear property, it basically 
cannot be changed by chemical reactions. An example is Sodium-24 which has 
a half life of about 15 hours. It has the same half life as sodium metal, 
sodium chloride, or any other chemical form it is in. The same is true for 
Uranium, Plutonium, and all other radioactive materials commonly 
encountered as wastes or fission products. In order to change the half life 
and make the material decay faster, we have to change the structure of the 
nucleus.

This can be done by placing the material in a nuclear reactor and exposing 
it to neutrons. Or, it could be done by placing the material in the beam of 
a particle accelerator and using protons, deuterons, or helium nuclei as 
the bombarding particles. In almost all cases, the addition of a neutron or 
charged particle to the original nucleus changes it to one with a shorter 
half life. These are not inexpensive alternatives, although for small 
quantities of extremely long lived transuranic materials, the process may 
prove to be feasible. At least several groups are looking at the process. 

One physical fact to be aware of is that at the numbers of neutrons 
available in a reactor, it takes a long time to react with all the atoms to 
be changed. The probability that an atom undergoes transformation is on the 
order of 1E-10 per second in a research reactor with a very high number of 
neutrons available per second (around 1E14 which is attained at only a few 
research reactors in the world).

The equations for conversion in a reactor or accelerator are given in 
Nuclear and Radiochemistry, 3rd Edition
Friedlander, Kennedy, Macias, and Miller
Wiley-Interscience, 1981 (but the equations are still valid today)

or

Radiochemistry and Nuclear Methods of Analysis
Ehmann and Vance
Wiley-Interscience, 1991