Radiation comes naturally from a wide range of sourcesincluding our food, the ground, buildings and even outer space.Over 80% of the radiation that most of us are exposed to comes fromthese natural sources, while the rest comes from medicine. Lessthan 1% is a result of the nuclear industry.
"We all experience radiation fromnatural sources everyday"
What is radiation?
Radiation is a form of energy that travels outwards from anatom. We are all familiar with sunlight, which is a form orelectromagnetic radiation, however what we usually think of asradiation is ionising radiation. There are three basic kinds:
The nucleus (centre) of an atom contains a fixed number ofnumbers of protons and neutrons. There are many possiblecombinations, known as an isotopes, but some are stable whileothers are less so. The more unstable an isotope is, thequicker it will decay by emitting radiation and in so doing end upwith a different number of protons and neutrons (and be labelled asa different isotope accordingly). If this new nucleus is stillunstable then this process will continue.
Scientists can measure radioactivity in several different ways,often with extreme precision. The total radioactivity of materials,for example two rocks containing uranium, can be measured inradioactive decays per second (Becquerels). This always depends onthe amount and type of isotopes present. Two different isotopesmight be compared by their half-lives, which describe the amount oftime it takes for half of their atoms to undergo one decay (atwhich time they become another isotope with another half-life).This can sometimes be confusing because a longer half-life means amaterial decays more slowly and is therefore less radioactive. Ingeneral, the shorter an isotope's half-life, the moredangerous is can be.
[pullquote: All radioactive materials become less radioactiveover time]
[pullquote if there is space: At low-levels there are noobservable health effects from radiation at all]
[Picture: Radiation doses chart to be created]
Is radiation dangerous?
Like many other things - including oxygen, food, water andsunlight - radiation can be dangerous in large amounts. It cancause sickness and increase people's chances of developing cancer.Scientists have studied the health effects of radiation exposurefor over 50 years and know very well the levels at which radiationstarts to becomes dangerous. A person's radiation dose (typicallymeasured in milliSieverts), is determined by the amount and type ofradiation a person receives.
Professionals who work closely with radiation take simplemeasures to keep their doses low. For example, they block radiationwith dense materials like water, steel or concrete; they useequipment like gloves or even full body suits; and they might usemasks to make sure they don't accidentally breathe in radioactivematerial. Time is also useful and workers might delay a job to giveradioactive materials with short half-lives time to decay. Allnuclear workers wear monitors to warn them if the dose rate is toohigh.
Nuclear power is just one amazing technology that relies onradiation. Others include X-rays and nuclear medicine,archaeological carbon dating, and novel forms of space exploration.Many other essential industries, such as mining use radioactivetechnology for, and can also produce radioactive materials as aby-product. NASA's Curiosity Rover uses a plutonium radioactivesource that produces a steady level of heat as it decays. The heatis used to generate a small flow of electricity that will power therover and all its instruments for at least 14 years.
Radiation is energy travelling through space.
Sunshine is one of the most familiar forms of radiation. It delivers light, heat and suntans. While enjoying and depending on it, we control our exposure to it.
Beyond ultraviolet radiation from the sun are higher-energy kinds of radiation which are used in medicine and which we all get in low doses from space, from the air, and from the earth and rocks.
Collectively we can refer to these kinds of radiation as ionising radiation. It can cause damage to matter, particularly living tissue. At high levels it is therefore dangerous, so it is necessary to control our exposure.
Living things have evolved in an environment which has significant levels of ionising radiation.
Furthermore, many people owe their lives and health to such radiation produced artificially. Medical and dental X-rays discern hidden problems. Other kinds of ionising radiation are used to diagnose ailments, and some people are treated with radiation to cure disease.
Ionising radiation, such as occurs from uranium ores and nuclear wastes, is part of our human environment, and always has been so. At high levels it is hazardous, but at low levels such as we all experience naturally, it is harmless. Considerable effort is devoted to ensuring that those working with nuclear power are not exposed to harmful levels of radiation from it. Standards for the general public are set about 20 times lower still, well below the levels normally experienced by any of us from natural sources.
Background radiation is that ionizing radiation which is naturally and inevitably present in our environment. Levels of this can vary greatly. People living in granite areas or on mineralised sands receive more terrestrial radiation than others, while people living or working at high altitudes receive more cosmic radiation. A lot of our natural exposure is due to radon, a gas which seeps from the Earth's crust and is present in the air we breathe.
Radioactivity in material
Apart from the normal measures of mass and volume, the amount of radioactive material is measured in becquerel (Bq), which enables us to compare the typical radioactivity of some natural and other materials. A becquerel is one atomic decay per second, so a household smoke detector with 30,000 Bq contains enough americium to produce that many disintegrations per second. A kilogram of coffee or granite might have 1000 Bq of activity and an adult human 7000 Bq. Each atomic disintegration produces some ionizing radiation.
Ionising radiation – alpha, beta and gamma
Ionising radiation comes from the nuclei of atoms, the basic building blocks of matter. Most atoms are stable, but certain atoms change or disintegrate into totally new atoms. These kinds of atoms are said to be 'unstable' or 'radioactive'. An unstable atom has excess internal energy, with the result that the nucleus can undergo a spontaneous change. This is called 'radioactive decay'.
An unstable nucleus emits excess energy as radiation in the form of gamma rays or fast-moving sub-atomic particles. If it decays with emission of an alpha or beta particle, it becomes a new element. One can describe the emissions as gamma, beta and alpha radiation. All the time, the atom is progressing in one or more steps towards a stable state where it is no longer radioactive.
Alpha particles consist of two protons and two neutrons, in the form of atomic nuclei. Because of their relatively large size, alpha particles collide readily with matter and lose their energy quickly. They therefore have little penetrating power and can be stopped by the first layer of skin or a sheet of paper. But inside the body they can inflict more severe biological damage than other types of radiation.
Beta particles are fast-moving electrons ejected from the nuclei of many kinds of radioactive atoms. These particles are much smaller than alpha particles and can penetrate up to 1 to 2 centimetres of water or human flesh. They can be stopped by a sheet of aluminium a few millimetres thick.
Gamma rays, like light, represent energy transmitted in a wave without the movement of material, just like heat and light. Gamma rays and X-rays are virtually identical except that X-rays are generally produced artificially rather than coming from the atomic nucleus. But unlike light, these rays have great penetrating power and can pass through the human body. Mass in the form of concrete, lead or water are used to shield us from them.
The effective dose of all these kinds of radiation is measured in a unit called the Sievert, most commonly as the millisievert (MSv).