A quick primer on ionizing radiation
With an eye towards discussing the effects of ionizing radiation on humans, particularly with respect to cancer, I thought it would be best to write up a quick and dirty reference post on what exactly ionizing radiation is. This is a good example of my continuing struggle to find an appropriate voice for this blog. I never really know what I can safely assume my readers know. So, let’s (hopefully) review:
Ionizing radiation consists of particles or photons capable of inducing detachment of electrons from their atoms resulting in free electrons and a corresponding positive ion. There are five broad types of ionizing radiation: alpha-particles, beta-particles, neutron radiation, gamma rays, and X-rays.
- alpha-particles: result from radioactive decay, and consist of two protons and two neutrons. They are directly ionizing.
- beta-particles: result from radioactive decay, and consist of either an electron or positron. They are directly ionizing.
- neutron radiation: results from nuclear fission, and is simply a free neutron. They are indirectly ionizing as they have no charge themselves, but can collide with and excite charged particles that then directly ionize.
- gamma rays: are high frequency photons emitted to right the energy of a decayed atomic nucleus. They are also indirectly ionizing as they are chargeless wave-packets that when absorbed can cause electron expulsion which then ionizes directly.
- X-rays: kind of overlap with gamma rays. They are high frequency photons. The only major difference is their origin.
The ionizing capability is dependent on the energy of the individual unit (particle or photon) interacting with the atom (this is why high frequency electromagnetic waves are ionizing and low frequency are not). Thus, high energy, low concentration radiation can still have an ionizing effect.
As we will discuss next time, it is generally the chemical characteristics of the resulting ions that cause damage in cell physiology and DNA.