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Radiation is everywhere. Although we do not see or feel it, we are exposed to ionizing radiation anytime and anywhere – while walking, eating or sleeping. What exactly is ionizing radiation? What are its types and how does it affect the human body?
Ionizing radiation – what is it?
According to the World Health Organization (WHO), ionizing radiation is a type of energy released by atoms that travels as electromagnetic waves (gamma or X-rays) or particles (neutrons, beta or alpha). The spontaneous decay of atoms is called radioactivity, and the excess energy emitted is a form of ionizing radiation. Unstable elements that decay and emit ionizing radiation are called radionuclides.
All radionuclides are uniquely identified by the type of radiation emitted, radiation energy and half-life. Activity – used as a measure of the amount of radionuclide present – is expressed in a unit called becquerel (Bq): one becquerel equals one decay per second.
The half-life is the time required for the activity of the radionuclide to decline to half its original value upon degradation. The half-life of a radioactive element is the time it takes for half of its atoms to decay. This can range from as little as a fraction of a second to millions of years (e.g., iodine-131 has a half-life of 8 days, while carbon-14 has a half-life of 5730 years).
Ionizing radiation has four basic types:
- gamma radiation,
- beta particles,
- alpha particles,
- X-rays,
- neutrons.
They have different physical properties and biological effectiveness in causing tissue damage.
See: You get used to radiation
Ionizing radiation – sources and exposure
People are exposed to natural sources of radiation as well as man-made sources on a daily basis. Natural radiation comes from many sources, including more than 60 naturally occurring radioactive materials found in soil, water and air. Radon, a naturally occurring gas, comes from rock and soil and is the main source of natural radiation. Every day, people inhale and ingest radionuclides from air, food and water.
Humans are also exposed to natural cosmic rays, especially at high altitudes. On average, 80% of the annual background radiation dose a person receives is due to naturally occurring terrestrial and cosmic radiation sources. Background radiation levels vary geographically due to geological differences. Exposure in some areas may be over 200 times higher than the global average.
Human exposure to radiation also comes from man-made sources, from the generation of nuclear energy to the medical uses of radiation for diagnosis or treatment. Currently, the most common sources of man-made ionizing radiation are medical devices, including X-ray machines.
Radiation exposure can be internal or external and can be obtained through different routes of exposure. Internal exposure to ionizing radiation occurs when a radionuclide is inhaled, swallowed, or otherwise enters the bloodstream (for example, by injection or through wounds). Internal exposure ceases when the radionuclide is cleared from the body, either spontaneously (e.g. by excreta) or by treatment.
External exposure can occur when airborne radioactive material (such as dust, liquids, or aerosols) is deposited on the skin or clothing. This type of radioactive material can often be removed from the body simply by washing.
Exposure to ionizing radiation can also result from irradiation from an external source, such as medical x-ray exposure. External irradiation ceases when the radiation source is shielded or when the person moves outside the radiation field.
People can be exposed to ionizing radiation in a variety of circumstances, at home or in public places (public exposure), in the workplace (occupational exposure), or in a medical setting (as well as patients, carers and volunteers).
Read also: Obligation to inform about telephone radiation
Ionizing radiation – types
Ionizing radiation – alpha particles
Alpha (α) particles are positively charged and consist of two protons and two neutrons from the nucleus of the atom. Alpha particles come from the decay of the heaviest radioactive elements such as uranium, radium and polonium. Although alpha particles are very energetic, they are so heavy that they consume their energy short distances and cannot travel very far from the atom.
The health effects of exposure to alpha particles depend a lot on how a person is exposed. Alpha molecules lack the energy to penetrate even the outer layer of the skin, so exposure to the outside of the body is not much of a problem. However, alpha particles inside the body can be very harmful.
If alpha-emitters are inhaled, swallowed, or enter the body through an incision, 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 to each other – they can release all of their energy in several cells. This causes more serious damage to cells and DNA.
Ionizing radiation – beta particles
Beta (β) particles are small, fast-moving, negatively charged particleswhich are emitted from the nucleus of an atom during radioactive decay. These particles are emitted by certain unstable atoms, such as hydrogen-3 (tritium), carbon-14, and strontium-90.
Beta particles are more penetrating than alpha particles, but are less harmful to living tissue and DNA because the ionizations they produce are more widely distributed. They travel farther through the air than alpha particles, but can be trapped by a layer of clothing or a thin layer of a substance such as aluminum. Some beta particles are capable of penetrating the skin and causing damage such as skin burns. However, as with alpha emitters, beta emitters are most dangerous when inhaled or swallowed.
Ionizing radiation – gamma radiation
Gamma (γ) rays are weightless packets of energy called photons. Unlike alpha and beta particles which have both energy and mass, gamma rays are pure energy. Gamma radiation is similar to visible lightbut has much higher energy. Gamma rays are often emitted along with alpha or beta particles during radioactive decay.
Gamma rays pose a radiation hazard to the entire body. It can easily penetrate barriers that can trap alpha and beta particles, such as skin and clothing. Gamma radiation has such a great penetrating power that it takes several centimeters of dense material, such as lead, or even concrete, to stop it. Gamma rays can pass completely through the human body – when they penetrate, they can cause ionizations that damage tissue and DNA.
Ionizing radiation – X radiation
X-rays, or X-rays, are widely used in medicine. X-rays are similar to gamma rays in that they are photons of pure energy. X rays and gamma rays share the same basic properties but come from different parts of the atom.
X-rays are emitted from processes outside the nucleus, but gamma rays come from the nucleus. They are also generally less energetic and therefore less penetrating than gamma rays. X-rays can be produced naturally or by machines that use electricity.
Literally thousands of x-ray machines are used in medicine every day. Computed tomography uses special x-ray equipment to take detailed images of the bones and soft tissues in the body. Medical x-rays are the largest single source of human-induced radiation exposure.
Ionizing radiation – terminology
The quantity for radioactive material is ‘activity’ (having an average number of radioactive decays per unit time) becquerel = 1 decay per second. However, the basis for describing the biological effects of ionizing radiation and the basic dosimetric quantity in radiological protection is the “absorbed dose”. The absorbed dose is measured in Gray (Gy = J / Kg).
The dose is defined for any substance and any type of radiation. On the other hand, even when the dose is equal, the response after irradiation with different types of IR may be different, depending in particular on the ionization density. These differences are referred to as relative biological radiation efficacy and are taken into account in the definition of the “equivalent dose” (H) quantity.
See: Natural protection against radiation
How does ionizing radiation affect living organisms?
The human body is made up of various cells. We distinguish between brain cells, muscle cells, blood cells, etc. The genetic material of a cell is found in the nucleus in the form of genes, which are in turn linked into thread-like structures called chromosomes. It is the genes in the cell that determine how it works. If the genes are damaged, it is possible to develop cancer. This means that the cell has lost its ability to control the rate of reproduction. If genes are damaged in the reproductive organs, a mutation can occur. Such a mutation can be passed on to children.
Tumors and hereditary mutations are called stochastic (probabilistic) effects. A tumor or mutation behaves the same whether an organ has received a large absorbed dose or a low dose, all this turns into the likelihood of a tumor or a mutation occurring. There are no common types of cancer that arise solely from irradiation.
However, some types of cancer show a greater increase in the rate for a given radiation dose than others. It is also known that the risk of developing cancer varies with the age of exposure – with the risk being higher in those exposed as children.
Read: Scientists: The risk of breast cancer can be reduced by up to 70%
Health effects of ionizing radiation
When ionizing radiation interacts with cells, it can damage cells and genetic material (i.e., deoxyribonucleic acid or DNA). If not properly repaired, the damage can result in cell death or potentially harmful changes in DNA (ie, mutations). The health effects of ionizing radiation doses can be divided into two categories: deterministic and stochastic.
Deterministic effects appear when a threshold dose is reached, which means that a dose below the threshold is not expected to cause a specific effect. The severity of the effect increases with the dose. Reddening of the skin (erythema) is an example of a deterministic effect with a threshold dose of about 300 rad (3 Gy). Deterministic health effects, sometimes described as “short-term” health effects.
Stochastic effects occur randomly. The probability of an effect occurring in the population increases with the dose received, and the severity of the effect is independent of dose. Tumors are the major stochastic effect that can result from a radiation dose, often many years after exposure.
It is assumed that stochastic health effects do not have a dose threshold below which they do not occur. This is the reason no radiation dose level is considered completely “safe” and therefore doses should always be kept as low as possible (ALARA). Stochastic health effects, sometimes described as “long-term” health effects.
Stochastic health effects
Some workers, such as radiology workers, may repeatedly be exposed to low levels of ionizing radiation in the course of their work. The resulting dose levels are almost always below the threshold doses needed for deterministic health effects. Stochastic health effects such as cancer can occur years after the administration of a radiation dose. The probability of adverse health effects is proportional to the radiation dose received.
Research studies have shown a significant association between cancer and radiation dose levels of about 10 rem (0,1 Sv) or more, with the risk of developing the disease increasing with increasing radiation dose. For low-level radiation exposure (ie whole body doses below about 10 rem (0,1 Sv)), statistical limitations in studies made it difficult to assess cancer risk.
The most dangerous effect of radiation
The world learned about the effects of ionizing radiation by studying the consequences of tragic events (the bombing of Hiroshima and Nagasaki, nuclear tests in the northern Altai, the failure of the Windscale or Chernobyl reactors) and people learned to associate the concept of ionizing radiation with such circumstances. However, as it turned out from the perspective of many years of research on the effects of these disasters, one of the greatest threats posed by radiation is fear and the lack of reliable information.
An example is the fact that, shortly after the Chernobyl disaster, thousands of Ukrainian and Belarusian women who were expecting children decided (for no real reason) to terminate the pregnancy. The number of unnecessary abortions between 1986 and 1987 in these two countries was 1/3 of all babies born in Eastern Europe at that time.