Radiation is energy emitted in the form of electromagnetic waves or particles. There are two types: non-ionizing radiation like radio waves which has enough energy to excite atoms but not remove electrons, and ionizing radiation like x-rays and gamma rays which can remove electrons. Ionizing radiation includes alpha particles, beta particles, neutrons, protons, x-rays and gamma rays. The amount of time for a radioactive substance to decay to half its original amount is called its half-life, which is useful in applications like radioactive dating and nuclear medicine.

1. What is Radiation?
by Robert Miltenberger, CHP
Website: www.RadiationEffects.org
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2. Group of radiation specialists from around the world whose
goal is to answer the public's questions about the effects low
levels of radiation in order to promote clean energy, nuclear
medicine and other beneficial technologies that employ the
use radiation.

3. The Atom
• Atoms are the smallest unit of matter that forms the unique chemical and nuclear
properties of elements.
• The atoms are made of three smaller particles, the proton, neutron and electron.
• The proton has a positive electrical charge while the neutron has no charge.
• The electrons that orbit the nucleus, have a negative charge and a mass that is ~ 1836
times smaller than the protons.

4. Radiation
Radiation is simply energy emitted by a source in the form of electromagnetic (EM) waves or
particles. There are two classification of radiation:
• Non-ionizing Radiation
• Ionizing Radiation

5. Non-Ionizing Radiation
Non-Ionizing radiation has sufficient energy to excite atoms but not enough to remove the
atom’s electrons from their orbits. Examples of non-ionizing radiation include radio waves,
microwaves and visible light. Microwave ovens impart enough energy to our food to cause
the molecules to move rapidly and produce heat.
Diagram of the electromagnetic spectrum (OSHA 2016).

6. Ionizing Radiation
As electromagnetic (EM) radiation energy increases, its frequency (waves per unit time) also
increases and is able to remove electrons from the atom’s orbit. Examples of these are x-ray
and gamma rays. Examples of ionizing particle radiation include alpha particles (helium
nuclei), beta particles (free electrons), neutrons and protons. Examples of ionizing
electromagnetic radiation include x-rays and gamma rays.

7. Types of Ionizing Radiation
The table above summaries the basic properties of the ionizing radiation.
Radiation Form
Mass
(amu)
Charge LET
Primary
Hazard
What Stops the
Radiation
Alpha Particle 4 +2 High Internal
Paper, outer layer of
dead skin
Beta Particle 0.0005 -1 Low Skin, Eyes, Internal
Plastic, Aluminum,
Safety Glasses
Neutron Particle 1 0 High External Water, Concrete, Plastic
Proton Particle 1 +1 High External Lead, Iron, Steel
Gamma EM 0 0 Low External Lead, Steel, Concrete
X-ray EM 0 0 Low External Lead, Steel, Concrete

8. Half-life (T½)
Half-life (T½) is the amount of time it takes for a radioactive isotope to decay to one-
half of its original activity. Some radioactive isotopes have half-lives of billions of years
while other just a few yoctoseconds (10-24 seconds). The properties of radioactive
decay and half-life are very useful for determining the age of rocks and fossils. In
radiometric and carbon dating, the activity of a known isotope is measured to
determine how many half-lives have passed since the rock has formed or a living
organism has died (USGS 2016). The property of radioactive decay is also very useful in
nuclear medicine. Doctors can use isotopes with half-lives just long to perform the
diagnosis or treat the disease but that then decay away soon afterwards to greatly
reduce the radiation dose received by the patient.

9. Thank you for watching!
Our next presentation
will be on:
“The Sources of Radiation”
Website: www.RadiationEffects.org
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