Permissible exposure doses for humans

Radiation is a factor of impact on living organisms, which is not recognized by them. Even in humans, there are no unique receptors that would sense the presence of radiation background. Specialists carefully studied the effect of radiation on human health and life. There were also created devices with which you can record the indicators. Doses of radiation characterize the level of radiation, under the influence of which a person was within a year.

What is the measurement of radiation?

In the World Wide Web, you can find a lot of literature on radioactive radiation. Practically in each source there are numerical indicators of norms of irradiation and consequences of their excess. To understand the incomprehensible units of measurement can not immediately. The abundance of information characterizing the maximum permissible exposure doses to the population can easily confuse a knowledgeable person. Consider concepts in a minimal and more understandable scope.

What is the measurement of radiation? The list of values is quite impressive: curie, rad, gray, becquerel, rem - these are just the main characteristics of the dose of irradiation. Why so many? They are used for certain areas of medicine and environmental protection. For the unit of radiation exposure to a substance, take an absorbed dose of 1 gram (Gy), equal to 1 J / kg.

When exposed to radiation on living organisms, talk about an equivalent dose. It is equal to the dose absorbed by the body tissues in recalculation per unit of mass multiplied by the damage coefficient. The constant is allocated for each organ. As a result of the calculations, a number with a new unit of measurement - sievert (Sv) is obtained.

Based on the data already received on the effect of the radiation received on the tissues of a particular organ, an effective equivalent dose of irradiation is determined. This index is calculated by multiplying the previous number in sievert by a factor that takes into account the different sensitivity of tissues to radioactive radiation. Its value allows one to estimate the amount of absorbed energy, taking into account the biological reaction of the organism.

What are the allowable doses of radiation and when did they appear?

Radiation safety specialists based on data on the effects of radiation on human health have developed the maximum permissible energy values that can be absorbed by the body without harm. The maximum permissible dose (SDA) is indicated for single or long-term exposure. At the same time, radiation safety standards take into account the characteristics of persons exposed to the radiation background.

There are the following categories:

• A - persons working with sources of ionizing radiation. During the performance of their work duties are exposed to irradiation.
• B - population of a certain zone, workers whose duties are not related to obtaining radiation.
• B is the population of the country.

There are two groups of personnel among the personnel: workers in the controlled area (radiation doses exceed 0.3 from annual traffic rules) and employees outside such a zone (0.3 from SDA is not exceeded). Within the limits of doses, 4 types of critical organs are distinguished, that is, those in whose tissues the greatest amount of damage is observed in connection with ionized radiation. Taking into account the above categories of persons among the population and workers, as well as critical bodies, radiation safety establishes SDA.

For the first time the limits of irradiation appeared in 1928. The amount of annual radiation background absorption was 600 millisievert (mSv). It was established for medical workers - radiologists. With the study of the effect of ionized radiation on the duration and quality of life SDA became tougher. Already in 1956, the bar dropped to 50 millisievert, and in 1996 the International Commission on Protection from Radiation reduced it to 20 mSv. It is worth noting that when establishing the traffic rules in the calculation do not take the natural absorption of ionized energy.

Natural radiation

If you avoid meeting with radioactive elements and their radiation is still somehow possible, then from the natural background can not hide anywhere. Natural exposure in each of the regions has individual indicators. It has always been and will not disappear over the years, but only accumulates.

The level of natural radiation depends on several factors:

• The altitude indicator above sea level (the lower, the less the background, and vice versa);
• Structure of soil, water, rocks;
• Artificial causes (production, nuclear power plants).

A person receives radiation through food, radiation of soil, sun, during medical examination. Additional sources of radiation are manufacturing plants, nuclear power plants, test ranges and launching airfields.

Specialists consider irradiation to be the most acceptable, which does not exceed 0.2 μSv in one hour. And the upper limit of the radiation norm is determined at 0.5 μSv per hour. After some time of continuous exposure to ionized substances, the permissible radiation doses for humans increase to 10 μSv / h.

According to doctors, for a lifetime a person can receive radiation in the amount of not more than 100-700 millisievert. In fact, people living in mountainous areas are exposed to radiation in several large sizes. The average absorption of ionized energy per year is about 2-3 millisievert.

How exactly does radiation affect cells?

A number of chemical compounds have the property of radiation. There is an active fission of atomic nuclei, which leads to the release of a large amount of energy. This force is able to literally pull electrons from the atoms of the cells of matter. The process itself was called ionization. The atom that underwent such a procedure changes its properties, which leads to a change in the entire structure of the substance. Behind the atoms, molecules change, behind molecules the general properties of living tissue. With the increase in the level of irradiation, the number of changed cells also increases, which leads to more global changes. In this connection, the permissible radiation doses for humans were calculated. The fact is that changes in living cells affect the DNA molecule. The immune system actively restores tissues and even is able to "repair" damaged DNA. But in cases of significant irradiation or damage to the body's defenses, diseases develop.

With an accuracy of the probability of the development of diseases that arise at the cellular level, with the usual absorption of radiation is difficult. If, however, the effective radiation dose (this is about 20 mSv per year for industrial workers) exceeds the recommended values by hundreds of times, the overall health state is significantly reduced. The immune system malfunctions, which entails the development of various diseases.

The huge doses of radiation that can be obtained from a nuclear power plant accident or an atomic bomb explosion are not always compatible with life. The tissues under the influence of altered cells die in large numbers and simply do not have time to recover, which entails a violation of vital functions. If part of the tissues are preserved, then the person will have a chance to recover.

Indicators of permissible radiation doses

According to the norms of radiation safety, the maximum permissible values of ionizing radiation per year are established. Let's consider the resulted indicators in the table.

As can be seen from the table, the permissible radiation dose per year for workers in hazardous industries and nuclear power plants is very different from the indices deduced for the population of sanitary protected areas. The thing is that with prolonged absorption of permissible ionizing radiation, the body copes with the timely restoration of cells without disrupting health.

Single doses of human irradiation

A significant increase in the radiation background leads to more serious damage to the tissues, which is why the organs start to function improperly or completely. A critical state occurs only when a huge amount of ionizing energy is received. A slight excess of recommended doses can lead to diseases that can be cured.

Single receipt of a large amount of radiation radiation adversely affects the state of the body: the cells are rapidly destroyed, not having time to recover. The stronger the impact, the more lesions occur.

Development of radiation sickness: causes

Radiation sickness is the general condition of the body caused by the influence of radioactive radiation exceeding the SDA. Defeat is observed on the part of all systems. According to the International Commission on Radiological Protection, radiation doses that cause radiation sickness start at 500 mSv at a time or more than 150 mSv per year.

The high-intensity lesion (more than 500 mSv one-time) is due to the use of atomic weapons, their testing, the occurrence of man-made disasters, and the implementation of intensive irradiation procedures in the treatment of oncological, rheumatological diseases and blood diseases.

The development of chronic radiation sickness is subject to medical workers who are in the department of radiotherapy and diagnostics, as well as patients who are often exposed to radionuclide and X-ray studies.

Classification of radiation sickness, depending on the radiation dose

The disease is characterized on the basis of the dose of ionizing radiation received by the patient and how long it took place. A single exposure leads to an acute condition, but a recurring, but less massive, chronic process.

Consider the main forms of radiation sickness, depending on the received single exposure:

• Radiation injury (less than 1 Sv) - reversible changes occur;
• Bone marrow form (from 1 to 6 Sv) - has four degrees, depending on the dose received. Mortality with this diagnosis is more than 50%. The cells of the red bone marrow are affected. The condition can improve transplantation. The recovery period is long;
• Gastrointestinal (10-20 Sv) is characterized by a severe condition, sepsis, gastrointestinal bleeding;
• Cardiovascular (20-80 Sv) - there are hemodynamic disorders and severe intoxication of the organism;
• Cerebral (80 Sv) - a lethal outcome within 1-3 days due to cerebral edema.

The chance for recovery and rehabilitation is for patients with bone marrow form (in half of the cases). Heavier conditions can not be treated. Death occurs within a few days or weeks.

The course of acute radiation sickness

After a high dose of radiation was received and the radiation dose reached 1-6 Sv, acute radiation sickness develops. Doctors share the states that succeed one another in four stages:

1. Primary reactivity. Comes in the first hours after irradiation. It is characterized by weakness, lowering of arterial pressure, nausea and vomiting. When irradiated above 10 Sv passes directly into the third phase.
2. Latent period. After 3-4 days from the moment of irradiation and up to a month's time, the condition improves.
3. Intense symptomatology. It is accompanied by infectious, anemic, intestinal, hemorrhagic syndromes. The condition is heavy.
4. Recovery.

An acute condition is treated depending on the nature of the clinical picture. In general, disintoxication therapy is administered by administering means that neutralize radioactive substances. If necessary, blood transfusion is performed, bone marrow transplantation.

Patients who manage to survive the first 12 weeks of acute radiation sickness mainly have a favorable prognosis. But even with complete recovery, such people are at increased risk of developing cancer, as well as the birth of offspring with genetic abnormalities.

Chronic radiation sickness

With the constant exposure to radioactive radiation in smaller doses, but in total exceeding 150 mSv per year (not counting the natural background), the chronic form of radiation sickness begins. Its development goes through three stages: formation, recovery, outcome.

The first stage takes place for several years (up to 3). The severity of the condition can be determined from mild to severe. If the patient is isolated from the place where radioactive radiation is received, the recovery phase will occur within three years. After that, complete recovery or, on the contrary, progression of the disease with a rapid fatal outcome is possible.

Ionized radiation can destroy cells in an instant and disable it. That is why compliance with radiation doses is an important criterion for working in hazardous production and life near nuclear power plants and test sites.