Spark Gaps

["Laurence E. Auman" <73002.1706@CompuServe.COM>]

I'm looking for information on spark gaps containing radioactive material that
were used in old transformers.

1.  What was their intended purpose?
2.  How long were they used?
3.  What isotopes were used and why?  I understand Ra and Cs were used, any
others?
4.  Was there a relationship between the size of the gap, amount of radioactive
material used             and intended function? 
5.  Any regulatory concerns or vendor requirements for using/labeling these
devices?

Any information or references relating to the above questions would be greatly
appreciated.

Larry Auman
NUS Corporation
Aiken, SC
803-649-7963
800-368-5497