Radiation protection, sometimes known as radiological protection, is the science of protecting people and the environment from the harmful effects of ionizing radiation, which includes both particle radiation and high energy electromagnetic radiation.
Ionizing radiation is widely used in industry and medicine, but presents a significant health hazard. It causes microscopic damage to living tissue, resulting in skin burns and radiation sickness at high exposures and statistically elevated risks of cancer, tumors and genetic damage at low exposures.
Contents |
Radiation protection can be divided into occupational radiation protection, which is the protection of workers, medical radiation protection, which is the protection of patients and the radiographer, and public radiation protection, which is protection of individual members of the public, and of the population as a whole. The types of exposure, as well as government regulations and legal exposure limits are different for each of these groups, so they must be considered separately.
There are three factors that control the amount, or dose, of radiation received from a source. Radiation exposure can be managed by a combination of these factors:
Practical radiation protection tends to be a job of juggling the three factors to identify the most cost effective solution.
In most countries a national regulatory authority works towards ensuring a secure radiation environment in society by setting requirements that are also based on the international recommendations for ionizing radiation (ICRP - International Commission on Radiological Protection):
Different types of ionizing radiation behave in different ways, so different shielding techniques are used.
In some cases, improper shielding can actually make the situation worse, when the radiation interacts with the shielding material and creates secondary radiation that absorbs in the organisms more readily.
Shielding reduces the intensity of radiation exponentially depending on the thickness.
This means when added thicknesses are used, the shielding multiplies. For example, a practical shield in a fallout shelter is ten halving-thicknesses of packed dirt, which is 90 cm (3 ft) of dirt. This reduces gamma rays to 1/1,024 of their original intensity (1/2 multiplied by itself ten times). Halving thicknesses of some materials, that reduce gamma ray intensity by 50% (1/2) include[2]:
| Material | Halving Thickness, inches | Halving Thickness, cm | Density, g/cm³ | Halving Mass, g/cm² |
|---|---|---|---|---|
| lead | 0.4 | 1.0 | 11.3 | 12 |
| concrete | 2.4 | 6.1 | 3.33 | 20 |
| steel | 0.99 | 2.5 | 7.86 | 20 |
| packed soil | 3.6 | 9.1 | 1.99 | 18 |
| water | 7.2 | 18 | 1.00 | 18 |
| lumber or other wood | 11 | 29 | 0.56 | 16 |
| air | 6000 | 15000 | 0.0012 | 18 |
Column Halving Mass in the chart above indicates mass of material, required to cut radiation by 50%, in grams per square centimetre of protected area.
The effectiveness of a shielding material in general increases with its density.
Graded-Z shielding is a laminate of several materials with different Z values (atomic numbers) designed to protect against ionizing radiation. Compared to single-material shielding, the same mass of graded-Z shielding has been shown to reduce electron penetration over 60%.[3] It is commonly used to in satellite-based particle detectors, offering several benefits:
Designs vary, but typically involve a gradient from high-Z (usually tantalum) through successively lower-Z elements such as tin, steel, and copper, usually ending with aluminium. Sometimes even lighter materials such as polypropylene or boron carbide are used. [4][5]
In a typical graded-Z shield, the high-Z layer effectively scatters protons and electrons. It also absorbs gamma rays, which produces X-ray fluorescence. Each subsequent layers absorbs the X-ray fluorescence of the previous material, eventually reducing the energy to a suitable level. Each decrease in energy produces bremsstrahlung and Auger electrons, which are below the detector's energy threshold. Some designs also include an outer layer of aluminium, which may simply be the skin of the satellite.
ALARP, is an acronym for an important principle in exposure to radiation and other occupational health risks and stands for "As Low As Reasonably Practicable".[6] The aim is to minimize the risk of radioactive exposure or other hazard while keeping in mind that some exposure may be acceptable in order to further the task at hand. The equivalent term ALARA, "As Low As Reasonably Achievable", is more commonly used in the United States and Canada.
This compromise is well illustrated in radiology. The application of radiation can aid the patient by providing doctors and other health care professionals with a medical diagnosis, but the exposure should be reasonably low enough to keep the statistical probability of cancers or sarcomas (stochastic effects) below an acceptable level, and to eliminate deterministic effects (e.g. skin reddening or cataracts). An acceptable level of incidence of stochastic effects is considered to be equal for a worker to the risk in another work generally considered to be safe.
This policy is based on the principle that any amount of radiation exposure, no matter how small, can increase the chance of negative biological effects such as cancer. It is also based on the principle that the probability of the occurrence of negative effects of radiation exposure increases with cumulative lifetime dose. These ideas are combined to form the linear no-threshold model. At the same time, radiology and other practices that involve use of radiations bring benefits to population, so reducing radiation exposure can reduce the efficacy of a medical practice. The economic cost, for example of adding a barrier against radiation, must also be considered when applying the ALARP principle.
There are four major ways to reduce radiation exposure to workers or to population:
|
|||||||||||