Online course introduction to radiation
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Click here to start!. Online Course : Introduction to Radiation. This online course, designed and developed by the Radiation Safety Institute of Canada, is meant to give you a brief introduction to radiation. The following topics will be covered : What is radiation?

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Online Course : Introduction to Radiation

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Online course introduction to radiation

Click here to start!

Online Course :Introduction to Radiation


  • This online course, designed and developed by the Radiation Safety Institute of Canada, is meant to give you a brief introduction to radiation.

  • The following topics will be covered :

  • What is radiation?

  • The different types of ionizing radiation

  • Introduction to units and regulatory limits on exposure

  • Background radiation

  • Uses of ionizing radiation

  • Effects of radiation on your body

  • Simple safety measures to reduce your exposure

  • If you are interested in learning more about radiation, please contact the Radiation Safety Institute of Canada ( We offer an array of courses for professionals, and information for the public.

  • Enjoy!









All matter is made up of atoms. The different elements are simply made up of atoms with different numbers of protons, neutrons, and electrons.

Click on the different particles to learn more about them!





Nuclear Forceskeep the nucleus together. When they are not strong enough, the nucleus is unstable and must release energy to become stable.

Anything emitted from an unstable nucleus as it become stable is radiation, and the atom is called a radioactive atom, a radioisotope, or a radionuclide

Unstable Atom





Types of radioactive decay

Types of Radioactive Decay

A radioactive decay is a process in which the unstable nucleus releases energy. There are several types of radioactive decays. Click on each to lean more about them!

Alpha Decay

Beta Decay

Radioactive Decay

Gamma Decay

Neutron Radiation





When radiation is energetic enough, it interacts with matter by knocking electrons out of their orbits. Alpha and beta particles interact with atoms electrically, and strip electrons from their orbit in that manner, where as photons can give all or a fraction of their energy to electrons, liberating them from their orbit.

Either way, you are left with two pieces of an atom, a positive and a negative one. These are called ions, and the process of forming these is called ionization.


Negative Ion

Positive Ion



Neutral Atom

Ionizing and non ionizing radiation

Ionizing and Non-Ionizing Radiation


Ionizing Radiation is radiation which can create ions. Alpha particles, beta particles, gamma rays and X-rays are always ionizing. This is dangerous radiation, since ions travelling through your body can break your DNA and the cells in your body, potentially leading to mutated cells, which can form cancer.

Non-ionizing radiation, on the other hand, is photons which are not energetic enough to create ions. It therefore will not produce breaks in your cells and DNA, and should not lead to cancers related to radiation exposure.

Radio waves



Click on the types of non-ionizing radiation to learn more!

Non-Ionizing Rad.

Visible Light




Units and limits of radiation

Units and Limits of Radiation


There are two types of SI units used to describe a dose of radiation : a Gray (Gy), and a Sievert (Sv). Grays measure absorbed dose, whereas Sieverts account for the type of radiation which delivered the dose. For beta particles and photons, a Gray is equivalent to a Sievert. However alpha particles are much more damaging than photons, so a Gray of absorbed dose is translated to 20 Sieverts of equivalent dose.

Other common units are the rad, where 1 rad = 0.01Gy, and the rem = 0.01Sv.

Effective Dose Limits in Canada:




Typical doses

Typical Doses

Here are average doses received from typical diagnostic procedures. Note that these numbers are highly dependant on the anatomy to be imaged and on the size of the patient.

Background radiation will be discussed on the next page.

* MRIs do not use ionizing radiation, therefore do not deliver a dose. Instead, they exploit the magnetic properties of hydrogen atoms to produce an image.



Background radiation

Background Radiation

There are several types of radiation which give you a continuous dose, and which you can do very little about. This background radiation is estimated to give Canadians a dose of about 2-4 mSv/year, and is not counted in the dose limits listed previously.

Click on the different types of background radiation to learn more about them!

Contributions to the Background Radiation:

Consumer products, 3%

Nuclear medicine, 3%



Note : Doses received from industries such as uranium mining and nuclear power plants are too small to be accounted for, assuming no major incident.





Cosmic, 8%





Industrial and medical uses of radioactivity

Industrial and Medical Uses of Radioactivity

Radiation and radioactivity are commonly used in medicine, academia, and industry. If good work habits and appropriate safety measures are followed, the advantages of using radiation far outweigh the possible negative effects.

Nuclear Power Plants

Medical Applications

Here are a few examples of areas in which a radioactive isotope or radiation is used.

Click on the different branches of industry to learn more!

Quality Control (Industrial Radiography)


Academic Research

Density and moisture content evaluation



Effects of radiation on your body

Effects of Radiation on your body

As we saw previously, ionizing radiation breaks atoms apart into positive and negative components. When this occurs in a cell, it can damage the cell beyond repair, killing it, or it can damage chromosomes, leading to defects in cell reproduction. The radiation can thereby lead to two types of effects :



(Click on the above to learn more)

A damaged chromosome can typically repair itself. However, an incorrect repair can lead to cell death or to a mutation. A typical mutation may involve a cell which has lost the ability to control its reproduction. In this case it can divide at a fast rate, creating a tumour.



The basics of radioprotection

The Basics of Radioprotection

Measures to insure radiation safety are very dependant on the type of radiation used, its

energy, its form (gas, liquid, powder, ...), its activity, etc. Before using any radiation source or device, make sure you are qualified to do so and understand the safety procedures associated with the source or device.

This course is not meant as a radioprotection guide. However the absolute basics of radiation protection are listed below (Click to learn more) :


Note : These safety principles do not apply to internal radiation (radiation which has been ingested, inhaled, or absorbed by the skin). In these cases, methods for limiting exposure are entirely dependant on the type of radiation.







In summary, there are several types of ionizing radiation : alpha, beta, gamma and X-ray. These are all produced by unstable particles, except for X-rays, which are produced when electrons lose energy.

Background radiation, which arises from multiple sources, delivers about 2-4 mSv of dose to average Canadians. Excluding this radiation, the maximum permissible dose a member of the public can receive, for example from living or working near a nuclear substance, is 1 mSv.

Ionizing radiation can break the atoms in your body and deposit energy in your cells. If a large dose is received (> 250mGy), radiation sickness can ensue within hours. Smaller doses received chronically (say 25 mSv/year for 40 years) lead to an increased risk in developing cancer (4% increase after 40 years, for 25 mSv/yr). On average, cancer develops 8 years (thyroid cancer) to 30 years (most other cancers) after exposure.

The most basic and most important radioprotection principles are time, distance, and shielding.

Take the quiz!

Online course introduction to radiation


1. All types of radiation are dangerous and exposure to them can lead to cancer.



2. Beta particles are :

Bundles of energy, also known as photons

Made up of two protons and two neutrons, in other words the nucleus of Helium

Small, charged particles. Examples are electrons and positrons.

Neutral hadrons, the most common being neutrons


Online course introduction to radiation


3. Which of the following is acurate?

Except if you work in a nuclear power plant or in a hospital, in principle you should never receive any type of dose from ionizing radiation

A CT scan gives you about 1-10 mSv of dose, a chest X-ray about 0.1 mSv, and background radiation gives you an annual dose of about 3.6 mSv (Canada).

The main source of background radiation, radiation which everyone is constantly exposed to, is from nuclear power plants

Of the medical imaging procedures, MRIs give you the most radiation dose.


Online course introduction to radiation


4. Which of the following is accurate :

Radiation sickness, which occurs after an acute dose of at least 250 mSv, includes symptoms such as vomiting, nausea, diarrhoea, and fatigue.

A subject is likely to develop cancer within 1-3 years of receiving a dose of 250 mSv.

A stochastic effect, such as cancer, is one which will surely occur once a certain level of radiation has been reached.

Following an acute dose of 3.5 mSv, half of the people exposed are expected to die within days, if untreated.


Online course introduction to radiation


5. Which of the following is accurate :

Alpha particles are extremely problematic as a source of external radiation, because being doubly charged and massive, their radiation is very difficult to shield from.

Most X-rays and gamma rays can be stopped with a thin layer of plastic.

The amount of dose you receive from a gamma source is inversely proportional to the square of the time which you spend around it : if you spend half the time you typically do around a source, your dose decreases by a factor of four.

Alpha particles are the easiest to stop, followed by beta and then X-rays and gamma rays.


The end

The End

That’s it!

We hope you enjoyed this introduction to radiation. Of course there is much more to learn in this field, especially if your work involves working with nuclear substances or radiation devices.

For more information on these subjects, and to learn about the other courses offered by the Radiation Safety Institute of Canada, we encourage you to return to our website.

If you have comments or questions regarding this course, please send them to

ccohalan <AT> radiationsafety <DOT> ca

Also, loads of information can be found from the following people :

International Atomic Energy Agency (

Health Canada (

Canadian Nuclear Safety Commission (

International Commission on Radiological Protection (




  • The Radiation Safety Institute of Canada wishes to express its appreciation to the following contributors to this online course :

  • Claire Cohalan

  • Tara Hargreaves

  • Justin McKinnon

  • Don Bell

  • Reza Moridi

  • Brian Bjorndal

  • Ian Watson


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