Exposure to Ionising Radiation
How can radiation harm people?
Living tissue in the human body can be damaged by ionising radiation. This damage can be caused either directly by the radiation damaging the genetic code (DNA) or indirectly by producing highly reactive chemicals (free radicals) which then go on to damage the DNA. The body attempts to repair the damage, but sometimes the damage is too severe or widespread. Cells may die if the damage is too great.
How can radiation cause Cancer?
As early as 1910, radiation was known to cause skin cancer. Among the best known long-term studies are those of Japanese atomic bomb blast survivors, other populations exposed to fallout from nuclear testing (for example, natives of the Marshall Islands), and uranium miners. All cancers, whether solid tumors or leukemia (blood cancer) are preceded by a period of time before the cancer develops (i.e. a latency period). It is not precisely understood how radiation damage may lead to a cancer years later. It is likely that the radiation damage acts in combination with other factors (e.g. chemicals, genetic make-up, health, etc.) which eventually lead to the cells multiplying uncontrollably.
What amount of ionising radiation is safe?
The effects of very low levels of ionising radiation have proved very difficult to study, since they are well below the levels of natural background radiation. In fact, the conclusions we make about the effects of low levels of radiation come from the known effects of higher levels of radiation exposure. As a result, there is no conclusive evidence for setting a ‘safe’ level of exposure above background. It is internationally recognised that any exposure carries some risk and that the risk increases as the exposure increases.
What can shield people from ionising radiation?
How far the ionising radiation can penetrate a material depends upon its type, and how much energy it has. In nuclear terms, alpha particles are large and slow and can be simply blocked by a sheet of paper, or the layer of dead skin cells which cover our bodies. Beta particles are much smaller travel at higher speeds but can be blocked by a thin sheet of aluminium or Perspex. Gamma radiation and X-rays are electromagnetic radiation, consisting of waves of energy (photons) which travel at high speed and require dense shielding materials (e.g. lead and concrete) to reduce their number to an acceptable level.
Can we prevent exposure to ionising radiation?
We cannot prevent our exposure to background radiation (but can minimise radon exposure if living in ‘radon affected areas’ ), and the benefits of medical exposure far outweigh any risks. Therefore, there is little we can do to minimise our exposure which will have any significant effect on our long term health. The human body is very good at repairing radiation damage. Therefore, the best protection is perhaps to live healthily to encourage a robust immune system!
How much ionising radiation is needed to cause skin burns, hair loss or death?
These effects of radiation exposure are known as ‘early effects’. They only occur if an individual has received a relatively large dose, in a short period of time, which exceeds a certain threshold level. If a dose is received below this threshold then no early effects are observed. The thresholds for these early effects start at around 1 Sv. A dose of 5 Sv is generally considered lethal.
How have the current dose limits been decided upon?
The annual worker dose limit of 20 mSv has been set at a level which represents a 1 in 1000 risk of contracting cancer. That is to say, if 1000 people were exposed to 20 mSv in one year (on top of our annual background dose) then we would expect one person to develop a cancer later in life as a result of this exposure. This limit of 20 mSv has been arrived at by reference to evidence from the Japanese bomb blast survivors and other groups exposed to radiation. However, for exposures in the workplace this dose limit is seen as a backstop and is the very maximum that is permissible. The over-riding principle which is applied in the SA is that all radiation doses should be kept ‘as low as reasonably achievable’ (ALARA). In SA the occupational exposure of any worker is controlled to ensure that the limits of an average effective dose of 20mSv per rear averaged over five consecutive years is not exceeded.
Ionising radiations occurs as either electromagnetic rays (such as X-rays and gamma rays) or particles (such as alpha and beta particles). It occurs naturally (e.g. from the radioactive decay of natural radioactive substances such as radon gas and its decay products) but can also be produced artificially. People can be exposed externally, to radiation from a radioactive material or a generator such as an X-ray set, or internally, by inhaling or ingesting radioactive substances. Wounds that become contaminated by radioactive material can also cause radioactive exposure.
Radiation Protection
It has long been recognized that large doses of ionizing radiation can damage human tissues. Over the years, as more was learned, scientists became increasingly concerned about the potentially damaging effects of exposure to large doses of radiation. The need to regulate exposure to radiation prompted the formation of a number of expert bodies to consider what is needed to be done. In 1928, an independent non-governmental body of experts in the field, the International X-ray and Radium Protection Committee was established. It later was renamed the International Commission on Radiological Protection (ICRP). Its purpose is to establish basic principles for, and issue recommendations on, radiation protection.
These principles and recommendations form the basis for national regulations governing the exposure of radiation workers and members of the public. They also have been incorporated by the International Atomic Energy Agency (IAEA) into its Basic Safety Standards for Radiation Protection published jointly with the World Health Organization (WHO), International Labour Organization (ILO), and the OECD Nuclear Energy Agency (NEA). These standards are used worldwide to ensure safety and radiation protection of radiation workers and the general public.
An intergovernmental body was formed in 1955 by the General Assembly of the United Nations as the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). UNSCEAR is directed to assemble, study and disseminate information on observed levels of ionizing radiation and radioactivity (natural and man-made) in the environment, and on the effects of such radiation on man and the environment.
