Basic scientific information and facts about radiation
Tomaz Amon
Center for scientific visualization
Email: tomaz.amon@bioanim.com
Heinz Oberhummer
Behacker & Partner, AT
Email: ohu@behacker.at
1. Types of radiation
What is radiation?
Radiation are waves or particles travelling through space which can transmit all or part of their energy on contact to matter.
What types of radiation do exist?
The most important type of radiation are electromagnetic waves. Equivalently the can also be described as particles which are called photons. All electromagnetic waves or photons can be characterised in groups according to their wave lengths or equivalently energy and can be depicted what we call the electromagnetic spectrum (see Fig. 1). According to their energy electromagnetic waves can be classified from short to long wave lengths high low energies: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves.
Fig.1: The electromagnetic spectrum [Source: NASA]
2. Radioactivity
Ionising and non-ionising radiation: Ionising radiation like gamma rays or X-rays has such a high energy that it alters an atom or a molecule permanently. For instance, electrons can be kicked out from the atom molecule through ionising radiation. Ionising radiation is much more effective and dangerous for living beings than non-ionising radiation like ultraviolet, visible light, infrared, microwaves and radio waves, because non-ionising radiation can alter atoms or molecules only for a very short time. An analogue that radiation with high energy is much more dangerous than radiation with low energy is that either a stone or sand having both 1 kg fall on your head from a building. Of course, the stone is much more dangerous than the sand.
Radioactive rays is radiation of very high energy and is therefore an ionising radiation. There exist three kinds of radioactive rays:
- Alpha rays are emitted from naturally occurring heavy elements such as uranium and radium, as well as from some man-made elements. They have little penetrating power and can be stopped by the first layer of skin or a sheet of paper (see Fig. 2). However, if alpha sources are taken into the body, for example by breathing or swallowing radioactive dust, alpha particles can affect the body's cells. Inside the body, because they give up their energy over a relatively short distance, alpha particles can inflict more severe biological damage than other radiations.
- Beta rays are much smaller than alpha particles and can penetrate up to
several millimetres of aluminium or one to two centimetres of water or human
flesh (see Fig. 2). Beta particles are emitted from many radioactive elements.
They can be stopped by a sheet of aluminium a few millimetres thick.
- Gamma rays is electromagnetic radiation like light. Unlike light, gamma
rays have great penetrating power and can pass through the human body. Thick
barriers of concrete, lead or water are used as protection from them (see
Fig. 2).
Fig. 2: Penetrating powers of radioactive rays [Source: Comega]
3. Radiation sources
Natural radiation: Radiation has always existed in nature and comes from
the sky (sun, cosmic radiation), from the ground (terrestrial radiation), from
the air (mainly radon), and also from our own bodies (internal radiation).
Man-made radiation: Following main types of man-made radiation sources exist:
Light sources, radio, TV, power supply lines, cellular phone network, nuclear
medicine, nuclear power plants, commercial products like tobacco, fertilizer,
luminous watch dials, and industrial activities.
Radioactive sources: Radioactive sources emit high-energy ionising radiation.
Human beings are exposed to natural sources as well as man-made sources (see
Fig. 3). The soil we walk on, the food we eat, the water we drink, and the
air we breathe are naturally radioactive and about 80% of the radiation comes
from such natural sources. The main component is radon, a gas contained in
the air, which comes from substances like rocks containing uranium. Man-made
radioactive sources contribute only 18% to the total amount of radiation, most
of the man-made sources belonging to the medical sector.
Fig. 3: Sources of radioactive exposure [Source: Comega]
Units of radioactivity: The amount of radioactivity can be measured. There
are three international units for such a measure. Each of them measures something
a different quantity:
- Radioactivity itself is measured in becquerel (Bq), a unit that measures the
number of decays per second of a radioactive source.
- The amount of radiation absorbed by an exposed organism or object is measured
in gray (Gy), a unit that measures the energy deposited by the radiation in a
kilogram of matter.
- The biological effects of radiation on an exposed living organism are calculated
in sievert (Sv).
4. Radiation exposure from radioactive sources
The average annual radiation exposure from natural sources to an individual
is on the world average about 2,4 millisieverts (mSv) (1 mSv = 1 milliSievert
= 1/1000 Sv). No adverse health effects have been discerned from doses arising
from these levels of natural radiation exposure.
? In addition, man-made sources of radiation contribute to another 0.6 mSv
to our annual radiation exposure, one of the largest sources of exposure being
medical X-rays.
? Radioactive radiation exposure, from natural cosmic sources, increases with
altitude. The amount of natural radiation in 2500 m is about twice as high
as at sea level. Also it depends very much on the place you live: it can range
from 0,2 mSv up to 10 mSV.
| Source | Average amount Per Year |
| Inside the body (air-radon) | 1.2 mSv |
| Earth's crust | 0.9 mSv |
| Outer space (2500 meters) | 0.53 mSv |
| Inside the body (food and water) | 0.3 mSv |
| Outer space (sea level) | 0.26 mSv |
| Medical X-Ray | 0.4 mSv |
| Living in stone. brick or concrete building | 0.07 mSv |
| Watching television | 0.01 - 0.02 mSv |
| Airline flights (per 1.000 km flown) | 0.01 mSv |
| Computer terminal | 0.001 mSv |
| Luminous Wrist Watch | 0.0006 mSv |
5. Radiation exposure from the Sun
-The Sun is responsible for the development and continued existence of life
on Earth. We are warmed by the Sun's infrared rays and we can see with eyes
which respond to the visible part of the Sun's terrestrial spectrum. More importantly,
visible light is an essential component of photosynthesis, the process whereby
plants, which are necessary for man's nutrition, derive their energy. However,
the deleterious effects of sunlight on biological systems are due almost entirely
to radiation within the ultraviolet (UV) spectrum of the Sun's emission.
-The observable biological effects in man due to exposure from solar UV-radiation
are limited to the skin and to the eyes because of its low penetrating properties
in human tissues. The penetration into skin is less than 1 mm and it is absorbed
by ocular tissues (mainly the cornea and the lens) before it reaches the retina.
6. Radiation from mobile telephone systems
-The electromagnetic radiation used in the mobile telephone system has frequencies
in the range of radio waves (see Fig. 1). The radiation coming from radio and
television transmitters are about a factor 2 - 100 larger than from mobile
phone transmitters. The distance to the respective transmitters play a primary
role in the biological effectiveness of the radiation.
-The biological effectiveness of electromagnetic radiation
in the radio and microwave range is are twofold: thermal and athermal
effects.
Thermal effects
lead to an increasing temperature in human bodies. Athermal effects would be
all other biological effects, like for instance the increase of cancerogenesis
(creation of cancer).
-The maximum permissible value for electromagnetic radiation in the radio
and microwave range is defined that for the general population the temperature
rise should be not more than 0.02O C. This corresponds to an absorption of
radiation of 0.08 Watt/kg or 1 SAR (SAR = Specific absorption rate).
Conversion: Temperature rise in degrees Celsius = SAR-value/4.
-No harmful athermal effects like the creation of brain cancer have been found
yet in many long-term scientific investigations like from the World Health
Organisation (WHO).