Radiation Basics

Key Facts About Radiation:

• There are two types of radiation: non-ionising and ionising radiation and they can be naturally occurring or man-made.
• We are exposed to natural background radiation on a daily basis.
• Man-made sources of radiation have many beneficial applications, including uses in medicine, industry, agriculture and research.
• Some examples of non-ionising radiation include visible light, radio waves and microwaves.
• Some examples of ionising radiation include x-rays, cosmic rays and naturally occurring radioactive materials in soil and food.
• Exposure to high levels of radiation in a short period can cause acute health effects.
  

What is Radiation?

Radiation is a natural part of our living environment, and is commonly described as energy travelling as waves or particles . Radiation sources can be natural or artificial (man-made).  Some common forms of radiation include wireless communication, x-rays and sunlight.

Natural Background Radiation

We are exposed to natural background radiation on a daily basis and it accounts for about 80 per cent of the radiation doses which we are exposed to. This radiation mainly comes from space (i.e. cosmic rays) and from naturally-occurring radioactive materials found in the soil. Radon, a naturally-occurring gas present in rocks, soil, bricks, mortar, tiles and concrete, is also a contributor. Some foods such as bananas and potatoes are naturally radioactive. By far the largest source of natural radiation exposure comes from varying amounts of uranium and thorium in the soil around the world. The level of natural background radiation can vary by several hundred per cent from one place to another on the globe. In Singapore, the natural background radiation is about 0.1 micro-Sieverts per hour. 

Man-Made Sources of Radiation

Radiation can also come from a variety of man-made sources. Medical use of radiation is the most significant source of man-made radiation. This includes x-ray radiology, nuclear medicine imaging and radiation therapy. Radiation arising from human activities typically accounts for about 20 percent of public exposure. Exposure due to fallout from past testing of nuclear weapons and generation of electricity in nuclear power plants constitutes less than 0.3 percent.

Types of Radiation

All electromagnetic radiation can be broadly grouped into two categories:

• Non-ionising radiation (e.g. visible light, radio waves and microwaves) – Non-ionising radiation moves atoms in a molecule around or causes them to vibrate but does not have enough energy to remove electrons from atoms.
• Ionising radiation (e.g. x-rays, cosmic rays and naturally occurring radioactive materials in soil and food) - Ionising radiation possesses enough energy to knock electrons out of atoms and poses a health risk by damaging tissue and DNA in genes. Long-term exposure to ionising radiation at high levels can harm people’s health.

In general, ionising electromagnetic radiation travel at high frequency/short wavelength and has high energy. On the other hand, non-ionising radiation travels at a low frequency/long wavelength and thus possesses lower amounts of energy. The different kinds of non-ionising and ionising radiation as they fall on the electromagnetic spectrum is depicted below.

Source: Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) - www.arpansa.gov.au/understanding-radiation/what-is-radiation

Common Types of Ionising Radiation

• Alpha (α) particles have little penetration power and are easily stopped by a sheet of paper or outer layer of skin. However, alpha emitting materials are harmful to health if they enter the body by inhalation or ingestion of food and water.
• Beta (β) particles are high speed electrons and are more penetrating than alpha particles. A sheet of aluminium of a few millimetres thick can stop beta particles.
• X-rays and gamma (γ) rays are both very penetrating and can pass right through the human body. Dense materials such as lead or concrete are more effective in absorbing these rays.
• Neutrons do not carry any electric charge and are constituents of atomic nuclei. Hydrogen-rich materials such as water or paraffin can shield against these highly penetrating particles.