﻿ Ionizing Radiation - College Physics

Ionizing Radiation


Ionizing Radiation is defined as particles or electromagnetic radiation, that is so energetic that it can remove electrons from atoms or molecules. During this process, the atoms become reactive ions which can cause great damage in living tissue. It is said that the atoms are ionized.

The following radiation is classified as ionizing:

Particle radiation: alpha particles (helium ions), beta particles (electrons, positrons)

Electromagnetic radiation: X-ray (~100 \( eV \) up to ~250 \( keV \)), gamma ray (higher energies)

Hazard symbols

International hazard symbols are usually located close to radioactive substances.

Since 2007 there is an additonal radioactivity danger symbol, that is attached directly to dangerous radioactives, to point out the danger of these substances and the right behavior also to non-professionals.

Shielding and protection

The types of radiation differ in their ability to penetrate matter. While alpha particles can already be shielded by a piece of paper or some centimeters air, you need at least a thin aluminum sheet for shielding beta particles. Gamma rays penetrate matter very well and can even pass through lead walls.


Units and formulas

In nuclear physics in general and in radiation protection several units are used to indicate the magnitude and danger of radiation.

Absorbed dose

The absorbed dose of an irradiated object (e.g. body tissue) represents the mean energy imparted to matter per unit mass.

Physical quantity:

\( \mathrm{D} \)


\( 1 \, \mathrm{Gy} \)  (Gray) = \( 1 \, \dfrac{\mathrm{J}}{\mathrm{kg}} \)  (Joule pro Kilogramm)


\( \mathrm{D} = \mathrm{J} \cdot f \)

Radiation weighting factor \( \omega_\mathrm{R} \)

The types of radiation differ in their biological activity. Thus, alpha radiation, for example, is a lot more dangerous to living organisms as gamma radiation with the same absorbed dose.

Therefore, the so-called radiation weighting factor has been introduced which assesses the radiations according to their biological effect.

Radiation \( \omega_\mathrm{R} \)
Alpha particle 20
Beta particle 1
Gamma ray 1

Equivalent dose

The equivalent dose is now obtained from the product of the absorbed dose and the radiation weighting factor. Equivalent doses of equal strength are therefore comparable in their biological effects on living organisms regardless of the type of radiation and energy.

Physical quantity:

\( \mathrm{H} \)


\( 1 \, \mathrm{Sv} \)  (Sievert) = \( 1 \, \dfrac{\mathrm{J}}{\mathrm{kg}} \)  (Joule pro Kilogramm)


\( \mathrm{H} = \mathrm{D} \cdot \omega_\mathrm{R} \)

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