Types of ionizing radiation

The emitted radiation spectrum of a radioactive disintegration process or from a radiation-emitting device can be continuous or discrete.

Discrete spectrum – certain energies can be emitted. 

Continuous spectrum – all energies in a specific range can be emitted.

Particle radiation – the energy is the kinetic energy of the particle that depends on the particle mass and velocity.

Photons – the energy depends on the photon's frequency.

Alpha radiation

The alpha particle has a relatively large charge and mass, being the nucleus of a positively charged helium (two protons and two neutrons).

Alpha radiation is emitted in the range of 4-8 MEV.

The depth of penetration in solid or liquid material is up to dozens of microns.

In air, alpha particles penetration depth is about 5 cm.

Beta radiation

The beta particle has an electric charge (negative to electron and positive to positron) and a very small mass. Radiation is emitted in a continuous spectrum, from zero to the highest energy value that is typical of a specific radionuclide. The depth of penetration in solid or liquid is up to tens of millimeters. In air, beta particles are stopped after tens of centimeters, up to two meters, depending on the radiation energy.

Gamma radiation

Gamma radiation consists of photons emitted from an unstable nucleus. Photons are not electrically charged and don’t have rest mass, so part of them are able to pass through material without interaction.

Gamma radiation has a discrete spectrum, which is typical of each radionuclide and is an "identification code" to the radioactive material.

Intensity reduction- Photons have no final range in the material. The radiation intensity decreases in dependence on the photon's penetration depth in the material.


X-radiation (also called roentgen radiation) consists of photons emitted by the jumps of electrons from energy levels in atoms of the anode caused by other electrons accelerated from the cathode.  

The energy spectrum of X radiation consists of the following:

Braking radiation - continuous spectrum. The energy range is from zero to the energy of the voltage applied on the handset.

Discrete X-radiation spectrum, characteristic of the element the target hit by the accelerating electrons, is made of.