Lead is the end-point of several different radioactive decay series.  Only
hydrogen and helium were produced in the original big bang, all of our other
elements were produced in stars/suns.  Hydrogen and/or Helium nuclei happened
to pass closely enough together, because of the extreme pressure and density
inside a star, to come within range of the short-range "strong" interaction and
stick together.  Usually the result was unstable, "radioactive", and decayed
into a slightly less heavy atom.
The nucleus of Iodine contains 53 protons- that is the definition of "Iodine".
The form/isotope found in nature contains 74 nuetrons and does not decay.
Other than that one, the isotopes of Iodine containing from 65 to 86 nuetrons
are radioactive.  Those with 75 to 86 nuetrons decay by beta emission, turning
into Xenon, a noble gas.  Those with 65 to 73 nuetrons decay by positron
emission, turning into Tellurium, a rare earth metal.  We obtain radioisotopes
by exposing selected elements to nuetron irradiation in nuclear reactors.  The
only radioisotopes found in nature are those that are constantly being formed
in the upper atmosphere by cosmic rays, like carbon 14, or those with extremely
long half-lives, in the billions of years.

A couple of sites you may find interesting:

http://ovcr.ucdavis.edu/mnrc/i125.html for info on I-125

http://search.netscape.com/ns/boomframe.jsp?query=u-232&page=1&offset=0&result_u
rl=redir%3Fsrc%3Dwebsearch%26requestId%3D19ed60d6357edaec%26clickedItemRank%3D6%
26userQuery%3Du-232%26clickedItemURN%3Dhttp%253A%252F%252Fwww.nuclides.net%252FN
UCLIDES_2000%252FU-232.htm%26invocationType%3D-%26fromPage%3DnsBrowserRoll%26amp
%3BampTest%3D1&remove_url=http%3A%2F%2Fwww.nuclides.net%2FNUCLIDES_2000%2FU-232.
htm
U-232

Probably more than you're looking for, but interesting.

Rich