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Probably everyone has experienced an x-ray check of baggage at the airport. Passenger baggage is put on a conveyer and sent through an x-ray device. The security officer can see on the monitor if some suspicious objects are in the baggage. The method is very similar to that used in medicine. In the nuclear industry, ionising radiation is not used but is a product of the nuclear reaction.

For electricity production, we use heat generated during the reaction. The radioactive atoms that also originate from a nuclear reaction emit ionising radiation. Since these radioactive atoms and ionising radiation is the by product and cannot be used in the process, it becomes radioactive waste. Workplaces with ionising radiation are designated as controlled and supervised areas.

Designated Areas are a legal requirement and the responsibility to designate those areas is that of the employer. Their purpose is to help manage the radiation risk by identifying and segregating higher risk activities from lower and thus control the extent of radiation exposure. The higher category is Controlled Area, and thus tighter controls are required in Controlled Areas than in Supervised Areas.

A controlled area is one that has been designated by an employer to assist in controlling and restricting radiation exposures. Controlled areas will be designated because the employer has recognised the need for people entering an area to follow special procedures. In controlled areas, persons may receive an effective dose of more than 6 millisievert or organ doses higher than 45 millisievert for the eye lens or millisievert for the skin, hands, forearms, feet and ankles in a calendar year.

Entrance into controlled areas is strictly controlled by the employer. Other employees should only be allowed conditional access and only in accordance with prior written arrangements. Supervised areas are areas that do not belong to the controlled areas and in which persons may receive an effective dose of more than 1 millisievert or organ doses higher than 15 millisievert for the eye lens or 50 millisievert for the skin, hands, forearms, feet and ankles in a calendar year.

Ionising radiation ionises atoms in all matter including the human body. Ionisation can cause cell damage. In the worst case, the radiation damages cell DNA, which contains genetic information. If the damaged cell survives, it can mutate and reproduce and cancer can occur. Such a harmful effect and its probability increases with the dose of ionising radiation absorbed in the tissue. Deterministic effects only occur once a threshold of exposure has been exceeded.

The severity of deterministic effects increases as the dose of exposure increases. Because of an identifiable threshold level, appropriate radiation protection mechanisms and occupational exposure dose limits can be put in place to reduce the likelihood of these effects occurring.

Deterministic effects are caused by significant cell damage or death. The physical effects will occur when the cell death burden is large enough to cause obvious functional impairment of a tissue or organ. Such effects are skin erythema, necrosis or epilation. The deterministic effect includes eye cataracts or sterility. At doses above mSv, radiation sickness can occur. Signs of radiation sickness are nausea and vomiting, headaches, fatigue, fever and short periods of skin reddening.

These symptoms are common to many illnesses and are often not recognised as the consequence of high radiation exposure. At doses above mSv, death occurs. Teratogenic mutations result from the exposure of foetuses unborn children to radiation. They can include smaller head or brain size, poorly formed eyes, abnormally slow growth and mental retardation. Studies indicate that foetuses are most sensitive between about eight to fifteen weeks after conception.

They remain somewhat less sensitive between six and twenty-five weeks old. Radiation effects can be categorised by when they appear as either prompt effects or delayed effects. Prompt effects are those seen immediately after large doses of radiation delivered over a short period of time.

Such effects are radiation sickness or skin erythema. Delayed effects appear months or years after the exposure. Such effects are eye cataracts or cancer. Every use of ionising radiation can cause harmful effects. Of course, we are using ionising radiation because it is useful, for example in medicine for diagnostics or treatment. Every use of ionising radiation must be justified [1] [2]. The principle of justification is that no practice involving exposure to radiation should be adopted unless it produces sufficient benefit to the exposed individuals or to society to offset the radiation detriment it causes.

It means that the benefits of the use of ionising radiation must be greater than the harm caused by it. In order to prevent unjustified uses of radiation, the radiation practice must by authorised by a competent authority. In the process of authorisation, the licensee should prove that the use of ionising radiation has benefits that outcome the risk due to exposure. In that process, all the aspects should be taken into account: doses to the workers, patients, impact to the environment, benefits and any other social or economic factors.

The responsible party must reassess the justification for practices that have already begun whenever new information becomes available that could affect the justification. The justification must also be reassessed whenever suitable new alternative methods for achieving the same objective become available that does not involve exposure to ionising radiation.

If a practice ceases to yield adequate benefits in relation to its drawbacks, its continuation is no longer justified. In all exposure situations, radiation protection shall be optimised with the aim of keeping the magnitude and likelihood of exposure and the number of individuals exposed as low as reasonably achievable, taking into account economic and societal factors. Whenever ionising radiation is used, there are workers that work with the ionising radiation source. They are exposed to ionising radiation, and since it is dangerous, the doses to the workers must be kept low.

The question is how low the doses must be. No dose to workers at all? Every unnecessary dose must be prevented. In the majority of cases, gamma and X-ray sources are used. The nature of gamma and X-ray radiation means that we can never totally stop all the gamma or X-rays.

Whatever we do to absorb them, some of them will penetrate and cause doses to workers or to the public. So, it is impossible to have radiation workers that will receive no dose. This does not mean that no effort is necessary to minimise doses. Optimisation means that doses of exposed workers must be kept as low as reasonably achievable using all the measures to control exposures, shielding, etc.

If the use of ionising radiation sources is justified and optimised, the final step to protect workers is the limitation of the doses. Every country should have legislation where these limits are defined.

The limits are established in numerous epidemiological studies of survivors of Hiroshima and Nagasaki atomic bomb explosions, from many accidents with ionising radiation sources and from studies of the large cohorts of workers in the nuclear industry.

The dose limits are defined in publications of the International Commission on Radiological Protection ICRP where the most eminent scientists from the radiation protection field are members. The most important dose limit is the annual dose limit of 20 mSv. It means that a worker can receive a dose of 20 mSv per year from ionising sources they are working with. To have a picture of what that dose is, we will use a comparison with natural background radiation.

All over the world, there is natural background radiation due to radioactivity in soil, water, air, food, etc. Since we live in such a radioactive environment, every person on our planet receives annual doses of natural background.

Of course, the natural background is not the same all over the world. There are some places where there is a really high natural background but on average the annual dose is around 2 mSv. So a worker using ionising radiation sources can receive ten times the dose of the natural background at the workplace. For women, there are special limitations during pregnancy or breast feeding.

Pregnant woman can work in a radiation area but the dose to the foetus must be below 1 mSv during pregnancy. Breast feeding woman can work in a radiation area when only exposure to external radiation is possible X-ray devices or encapsulated radioactivity sources. In that case, the limit of 20 mSv per year applies.

A breastfeeding mother is not allowed to work in an area where contamination and intake of radioactivity is possible. As soon as a breastfeeding woman informs the undertaking of her condition, she shall not be employed in work involving a significant risk of bodily radioactive contamination. The dose limits for apprentices aged 18 years or over and students aged 18 years or over who, in the course of their studies, are obliged to use sources shall be the same as the dose limits for exposed workers.

The limit for the effective dose for apprentices aged between 16 and 18 years and for students aged between 16 and 18 years who, in the course of their studies, are obliged to use sources shall be 6 mSv per year. All organs and tissues are not equally sensitive to ionising radiation. Some tissues are more sensitive than others. Also, during the working process, only specific organs or tissues can be exposed to radiation and not the whole body.

Due to these facts, the doses to the skin and eye lens are different. The annual skin dose is limited to mSv and to the eye lens to 20 mSv. Besides dose limits, in order to optimise radiation protection, dose constraints are also used. Dose constraints are doses that shall not be exceeded during the particular practice with the source.

But dose constraints are not the dose limits. They are selected at some fraction of the dose limit and are based on good practice and on what can reasonably be achieved. In order to establish what was the dose was that the worker received, the dose must be measured.

Unfortunately, humans do not feel the radiation, i. Therefore, we need instruments to measure the dose. Personal dose is measured using by the personal dosimeters Figure 2.

The worker wears it somewhere between their waist and neck during the whole working time. After a defined period of time, usually one month, the personal dosimeter is sent for reading to an authorised service. The report on received doses is send to the employee and to the competent regulatory authority. The most frequent dosimetry systems use thermoluminescent dosimeters. If these dosimeters are exposed to radiation, the material comes into a higher energy state.

When such dosimeter is later heated, it emits light and returns to its previous state. The quantity of emitted light is connected with the dose the dosimeter worker received. Older dosimetry systems used films where the blackness is connected with the radiation dose. Some new systems use optically stimulated luminescence, where light is used instead of heat to return to the original state.

The mentioned dosimetry systems are passive. It means that a worker does not know what their dose is until the report comes. In some situations where workers work in high radiation areas, it is of utmost importance that workers knows their dose at every moment and can leave the area in case the dose approaches the predefined limit.

Such workplaces can be found in the nuclear industry and in some therapy procedures in medicine. In that case, the worker, besides a passive dosimeter, wears an active dosimeter. Active dosimeters are so called electronic dosimeters that use semiconductors as detector material.

Figure 2: Panasonic personal dosimetry system Source: Provided by the author. To keep radiation doses low, three methods are used: time, distance and shielding. The dose is proportional to the time of exposure. This means that if someone is exposed for two hours, the dose would be two times the dose compared to if the exposure was one hour.

The radiation reduces with the distance from the source. If the distance is increased from 1 m to 2 m, the dose will be reduced by a factor of 4. If the distance is increased from 1 m to 3 m, the dose will be reduced by a factor of 9. We say that radiation is reduced by the square law by distance. Whenever necessary, we can reduce doses through the use of shields. Different shielding material is used depending on the nature of the ionising radiation.

The most common material is lead due to its high density and convenient price. Only in some very rare cases, we can achieve that workers are not exposed.

Basic radiation protection principles are justification, optimisation and dose limitation. The principle of dose limits is not applied in medical exposures. When we use radiation in medicine, we primarily search for a disease or treat diseases that can be in some cases be fatal.

Still, we are not allowed to expose patients to high doses, but they must be kept below so called reference levels. Radiation protection has improved over the last 20 years, and today doses to workers are normally low. Time: The more time one is exposed to ionising radiation, the larger the dose that will be received and the more harmful the radiation will be.

The relationship is linear: doubling the exposure time doubles the dose that is received.. It is very important that we minimise the exposure time in order to minimise the dose. Distance: The second very efficient way of minimising the doses is increasing distance.

The nature of ionising radiation is such that there is an inverse square law relationship between dose and distance. If we increase the distance from the source from one metre to two metres, the dose will decrease by a factor of four. If the distance is increased from one metre to three metres, the dose will decrease by a factor of nine. So whenever possible, we must be as far as possible from the source. Unfortunately, this is not always possible. Shielding: There are activities that require workers to be close to the source and in a high radiation field.

In that case, we minimise the doses by using shielding and protective clothing. When working with X-ray devices in medicine, the most common personal protective clothing is lead aprons. Led aprons made of 0. In some cases when eyes are exposed, spectacles made of lead glass are used as protection.

Also, lead gloves can be used, however such gloves are quite thick and not appropriate for detailed work. Personal protection such as gloves is intended for protection against external radiation. That means that the ionising radiation source is outside the human body and radiation is coming from that source to the body.

In case of internal irradiation, the person has an ionising radiation source in the body. When such a source is in the body, no protective clothing will help. So it is very important that we prevent ingestion or inhalation of radioactive material. Ionizing radiation has so much energy it can knock electrons out of atoms, a process known as ionization.

Ionizing radiation can affect the atoms in living things, so it poses a health risk by damaging tissue and DNA in genes.

Ionizing radiation comes from x-ray machines, cosmic particles from outer space and radioactive elements. Radioactive elements emit ionizing radiation as their atoms undergo radioactive decay.

Radioactive decay is the emission of energy in the form of ionizing radiation ionizing radiation Radiation with so much energy it can knock electrons out of atoms.

The ionizing radiation that is emitted can include alpha particles alpha particles A form of particulate ionizing radiation made up of two neutrons and two protons. Alpha particles pose no direct or external radiation threat; however, they can pose a serious health threat if ingested or inhaled. Some beta particles are capable of penetrating the skin and causing damage such as skin burns. Beta-emitters are most hazardous when they are inhaled or swallowed. Gamma rays can pass completely through the human body; as they pass through, they can cause damage to tissue and DNA.

Radioactive decay occurs in unstable atoms called radionuclides. The energy of the radiation shown on the spectrum below increases from left to right as the frequency rises. Other agencies regulate the non-ionizing radiation that is emitted by electrical devices such as radio transmitters or cell phones See: Radiation Resources Outside of EPA.

Alpha particles come from the decay of the heaviest radioactive elements, such as uranium , radium and polonium. Even though alpha particles are very energetic, they are so heavy that they use up their energy over short distances and are unable to travel very far from the atom. The health effect from exposure to alpha particles depends greatly on how a person is exposed.

Alpha particles lack the energy to penetrate even the outer layer of skin, so exposure to the outside of the body is not a major concern.

Inside the body, however, they can be very harmful. If alpha-emitters are inhaled, swallowed, or get into the body through a cut, the alpha particles can damage sensitive living tissue. The way these large, heavy particles cause damage makes them more dangerous than other types of radiation. The ionizations they cause are very close together - they can release all their energy in a few cells. This results in more severe damage to cells and DNA. These particles are emitted by certain unstable atoms such as hydrogen-3 tritium , carbon and strontium Beta particles are more penetrating than alpha particles, but are less damaging to living tissue and DNA because the ionizations they produce are more widely spaced.

They travel farther in air than alpha particles, but can be stopped by a layer of clothing or by a thin layer of a substance such as aluminum.

However, as with alpha-emitters, beta-emitters are most hazardous when they are inhaled or swallowed. Unlike alpha and beta particles, which have both energy and mass, gamma rays are pure energy.

Gamma rays are similar to visible light, but have much higher energy. Gamma rays are often emitted along with alpha or beta particles during radioactive decay. Gamma rays are a radiation hazard for the entire body. They can easily penetrate barriers that can stop alpha and beta particles, such as skin and clothing. Gamma rays have so much penetrating power that several inches of a dense material like lead, or even a few feet of concrete may be required to stop them.

Gamma rays can pass completely through the human body; as they pass through, they can cause ionizations that damage tissue and DNA. Because of their use in medicine, almost everyone has heard of x-rays.