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Frequently Asked Questions
Radiation is the general term used to describe electromagnetic waves such as radio waves, visible light, and gamma rays and particles which are emitted from radioactive materials. Some forms of radiation have sufficient energy to ionise atoms (remove an electron from the atom) as they strike them. These types of radiation are called ionising radiation. Ionising radiation is the type of radiation that can deliver a radiation dose to people. There are five major kinds of ionising radiation; alpha particles, beta particles, gamma rays, x-rays and neutrons. Each of these may be emitted spontaneously by atoms which are unstable. These atoms are defined to be radioactive. Effectively all of the radiation which may come from a uranium mine is in the form of gamma rays, alpha particles and beta particles.
With most environmental pollutants, there is a concentration level (called the 'threshold level') below which it is believed that people are not adversely affected by the pollutant. Whether or not there is a threshold (i.e. "safe") level of radiation is a controversial subject. Because this topic has yet to be settled scientifically, regulators have decided to take a conservative approach and assume that there is no such thing as a 100% safe level of radiation. Rather, in the case of low-level radiation it is assumed that the risk of developing an adverse effect (such as a cancer) scales proportionately with the amount of radiation. In other words, doubling the amount of radiation is assumed to lead to a doubling in the chance of developing an effect.
Some human activities lead to an increase in radiation dose to people. Examples include some medical procedures (such as X-rays), flying in airplanes, operation of nuclear power plants, and some mining operations (including uranium mining). Usually, the resultant doses will be very small, and therefore so will be the assumed risk to people.
Regulators have to balance the benefits of allowing the activity to take place with the risk to people. As part of this balancing, dose limits are set for many of these activities. These dose limits are the maximum amount by which the people carrying out the activity (for example those doing the mining) are allowed to increase the radiation levels which people receive.
At present, the Australian dose limit for an activity such as uranium mining is 1 mSv per year to a member of the public, and 20 mSv per year (averaged over 5 years) for a worker at the mine.
No. Changing the background radiation people receive would be very disruptive and costly (for example, requiring people to move their place of living if it happens to be in an area of elevated natural radiation). Situations of very high background radiation are uncommon and it is best to allow people to decide each case on its merits, rather than setting inflexible dose limits.
Sometimes regulators recommend certain radiation levels which can be used as an indicator of whether or not the situation needs further investigation. An example of this is the Australian recommendations on levels of radioactivity in drinking water supplies. These are not inflexible limits, but rather indicative levels. Where such levels are exceeded, the situation will need to be assessed.
For assessment of radiation risk, the main item of interest is known as the effective dose. The effective dose gives us a way to translate the radiation a person receives into an overall risk to the person, without having to worry about details such as the type of radiation or what parts of the body receive the radiation. The standard unit of radiation dose is the Sievert. Its symbol is Sv. A mSv (millisievert) is one thousandth of a sievert.
As discussed above, there is still controversy over whether low radiation doses (doses in the range of tens of mSv or less) cause radiation effects. Furthermore, the size of any radiation effect will depend on the age of the recipient individual at the time the dose is received. However, as an example, the current assumptions (based on recommendations of the International Commission for Radiological Protection) are that a dose of 1 mSv per year, received every year for 50 years over the working lifetime of a person, will increase the risk to that person of contracting a fatal cancer by about 0.2%. In addition, there will be an increased risk of another radiation effect occurring (a non-fatal cancer or a hereditary effect) of about 0.1%.
On average, no. The level of radiation varies quite a lot from place to place on the Earth's surface. This is because it depends on factors such as height above sea level (because this affects the amount of cosmic radiation that reaches the surface) and the geology of the area. Also, radiation levels vary between the indoors and outdoors environment (usually being higher indoors). Although Kakadu is in a region with significant uranium mineralization, this is mainly confined to small orebodies buried below the ground surface. There are small areas near uranium orebodies which have somewhat elevated radiation levels (including places where uranium mining has occurred). There is also some measurable uranium-series radioactivity in streams due to erosion of orebodies and of uranium mine workings (particularly in the upper South Alligator River area). However, on average radiation levels in the park are close to the Australian average of approximately 2 mSv per year.
