What type of ionizing radiation consists of helium nuclei

Beta radiation consists of high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus. Instead, they form when a neutron splits into a proton and an electron. The electron then shoots out of the nucleus at high speed, leaving the new proton behind in the nucleus.

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. Beta radiation is less easily absorbed by matter than alpha radiation and thus has a longer range: the penetrating power of beta particles ranges from a few centimetres to metres in air and a few millimetres to centimetres in soft tissue and plastic.

Beta radiation can be shielded quite easily, for example, by an aluminium sheet a few millimetres thick. Radioactive particles which emit beta radiation can also lead to a considerable radiation exposure when they are taken up by the body incorporated via inhaled air or food. In the case of external exposure, beta radiation can also damage tissue as it can penetrate the body, even if not very deeply. However, it loses significantly less energy over a certain distance than alpha radiation.

Beta radiation is thus said to have a lower biological effectiveness than alpha radiation. In the case of gamma radiation, energy is transferred as an electromagnetic wave. Electromagnetic radiation can be described in terms of its frequency or wavelength: the higher the frequency and the shorter the wavelength, the more energetic the radiation. Gamma radiation is at the high energy end of the electromagnetic spectrum, for example at the high frequency or short wavelength end.

Gamma radiation arises from the radioactive decay of atomic nuclei, often in addition to alpha or beta radiation. It penetrates matter very easily. Heavy materials such as lead and concrete are used for shielding.