Anybody know about "iron radiation"?

I see the term here:
http://science.nasa.gov/headlines/y2..._telomeres.htm
but i don't know which type of radiation is "iron radiation"?

Galactic Cosmic Radiation consists of about 85% protons, the nuclei of hydrogen atoms. About 13% nuclei of helium, known as alpha particles. And about 2% nuclei of common heavier atoms including oxygen, nitrogen and iron, all traveling at tremendous speeds and known as the "heavies". Those of galactic origin have been brought to near light speed by powerful events such as supernovae and have energy levels some 10,000 times those of solar origin.