Radiation and its Sources


What is Radiation?

Certain types of atoms are unstable and may split or transform into other kinds of atoms. As they do so, they will release energy and in some cases electrically-charged particles. The energy and particles travel naturally through spaces such as the air around us and they are known as radiation.


Types of Radiation

There are many kinds of radiation, with each having its own unique characteristics. The most common types of radiation are:

Alpha radiation: Cannot penetrate the skin and can be blocked out easily by a sheet of paper
Beta radiation: Can penetrate shallowly into the body but can be blocked out by a sheet of aluminum foil
Gamma radiation: Can go right through the body and requires several centimetres of lead or concrete or a metre or so of water to block

Sources of Radiation

Radiation can come from both natural and artificial sources. Radioactive substances are artificially produced during the nuclear fission process. Radiation also comes from substances that are all around us every day. Examples of these natural sources of radiation include soil, seawater and cosmic rays from space. But radiation effect is measured by its intensity and not whether it is artificial or natural in origin.


About 85% of Our Radiation is Completely Natural


All of us are exposed to a certain amount of radiation in our everyday lives. The exposure of radiation level varies according to the geological constituents and environment of our surroundings, our lifestyles and our distance from outer space. As a result, the radiation dose for those living on higher ground will be higher than that of people living at sea level. As a Hong Kong resident, you are likely exposed to an annual dose of around 2.4mSv from your environment (or background radiation) and over 3 mSv from all sources. This is a very low dose level and will not affect human health. According to medical studies, health effects may be demonstrated only if the annual radiation dose exposure reaches 100mSv or above.


Background Radiation around the World
(Cosmic ray, ground and radon in the air)
Hong Kong 2.4 mSv per year
Ukraine (Chernobyl) 5 mSv per year
The United Kingdom (Cornwall) 7 mSv per year
India (Kerala and Madras States) 15 mSv per year
Iran (Ramsar) 260 mSv per year
Natural radiation: global averages 2.4 mSv per year
- Cosmic ray 0.4 mSv
- Ground 0.5 mSv
- Food 0.3 mSv
- Radon in the air 1.2 mSv