What is Ionizing Radiation?

Since ionising radiation is the harmful kind, what does it actually mean if cells are Ionised? Also, are different ions of an atom unstable,or are only different isotopes?
- Luca (age 15)
Melbourne, Victoria, Australia

It's a strange fact of quantum  mechanics that the main way the light energy gets absorbed is one quantum at a time. A quantum of energy is hf, where f is the frequency and h is Planck's universal constant. Ionizing radiation has a high enough f so that a single quantum of its energy can knock an electron off of a typical biological molecule.  In practice, this means that ultraviolet light and higher frequencies (x-rays, gamma rays) are ionizing. One particularly nasty effect of ultraviolet light is that it can be absorbed by DNA and trigger a chemical reaction leading to a mutation.

Some isotopes are radioactive and some aren't. Those atomic nuclei  don't much notice what's going on around them in the cell. Unlike the nuclei, ions and other ordinary chemicals may be stable or not depending on the chemical environment. For example, the ions Na⁺ and Cl^- are stable in a dilute salt solution. In a very concentrated one they aren't stable and will combine to make NaCl crystals.

Mike W.

(published on 04/14/2015)