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Radioactivity

Radioactivity

What is radioactivity?

We define radioactivity as the spontaneous emission of particles (alpha particles, beta particles, neutrons) or radiation (gamma, capture K), or both at the same time, from the disintegration of certain nucleides that form them, because of an arrangement in its internal structure

Radioactive decay occurs in unstable atomic nuclei, that is, those that do not have enough binding energy to hold the nucleus together due to an excess of protons or neutrons.

Radioactivity can be natural or artificial. In natural radioactivity, the substance already possesses it in the natural state. In artificial radioactivity, radioactivity has been induced by irradiation.

Natural radioactivity

What is natural radioactivity?

Natural radioactivity is the radioactivity that occurs in nature due to the chains of natural radioactive elements and non-anthropogenic origin. Natural radioactivity is constantly present in the environment and in the air its concentration varies according to the movements of the air masses, atmospheric pressure, pollution and other factors.

Natural radioactivity can also increase by one focus for natural causes (for example, the eruption of a volcano), or for indirect human causes (for example an excavation in the ground to make the foundations of a building).

Artificial radioactivity

What is artificial radioactivity?

Artificial radioactivity is all radioactivity or ionizing radiation of human origin. The only difference between natural radiation and artificial radiation is its origin. The effects of both radiations are identical. In both cases the directly ionizing radiations are alpha radiation and beta decay formed by electrons. On the other hand, indirectly ionizing radiation is electromagnetic radiation, such as gamma rays, which are photons.

Sources of artificial radiation can include any type of device or system that generates radiation from the same natural elements and also those formed by artificial radionuclides. In this second group there are, for example, diagnostic procedures and medical treatments, such as radiographs, radiotherapy, nuclear medicine, some industrial procedures, for obtaining electrical energy in nuclear power plants, particle accelerators and nuclear weapons.

When using or manipulating artificial radiation sources, as with natural sources, it is generally common for radioactive waste to occur.

Types of radioactive emissions

Among the light elements, the most frequent radiations are:

  • The beta b - radiation , which are electrons from the nucleus
  • Beta b + radiation , which are positrons from the nucleus
  • Gamma rays (g), which are high energy electromagnetic waves
  • Electronic capture (disintegrations K)
  • Alpha radiation is characteristic of heavy elements.

Each type of radioactive emission has different power of penetration into matter and different power of ionization (ability to tear electrons from atoms or molecules with which it collides). They can cause serious damage to living things.

Alpha particles

Alpha (α) particles or alpha rays are a form of high-energy ionizing corpuscular radiation and with a low penetration capacity due to the high cross section. They consist of two protons and two neutrons joined by a strong force. Alpha particles belong to the elion family. Beta decay is mediated by a weak force, while alpha decay is mediated by a strong force.

Alpha particles are typically emitted by heavy element radioactive nuclides, for example, uranium isotopes, thorium plutonium, radio, etc., in a process called alpha decay. Sometimes, this decomposition leaves the nuclei in an excited state and, consequently, the excess energy can be eliminated with the emission of gamma rays.

Alpha rays, due to their electric charge, interact strongly with matter and, therefore, are easily absorbed by materials and can travel only a few centimeters in the air. They can be absorbed by the outermost layers of human skin and, therefore, are not life threatening unless the source is inhaled or ingested. In this case, the damage would instead be greater than those caused by any other ionizing radiation. If the dose were high enough, all the typical symptoms of radiation poisoning would appear.

Beta particles

Beta radiation is a form of ionizing radiation emitted by certain types of radioactive nuclei.

Beta radiation takes the form of beta (β) particles, which are high-energy particles, expelled from an atomic nucleus in a process known as beta decay. There are two forms of beta decay, β - and β +, which respectively emit an electron or a positron.

In β- decay, a neutron becomes a proton, an electron and an electron antineutrino.

In β + decay (observable in proton-rich nuclei), a proton interacts with an electronic antineutrino to obtain a neutron and a positron (direct proton decay in the positron has not yet been observed).

The interaction of beta particles with matter generally has a range of action ten times greater and an ionizing power equal to one tenth compared to the interaction of alpha particles. They are completely locked with a few millimeters of aluminum.

Gamma rays

Gamma rays are electromagnetic radiation produced by radioactivity. They stabilize the nucleus without changing its proton content. Normally radiation usually accompanies another type of emission. They penetrate more deeply than aob beta radiation, but are less ionizing.

Gamma rays can cause serious damage to the nucleus of cells, so they are used to sterilize medical equipment and food.

Radioactive cores: Radionuclides

A radionuclide is the set of radioactive nuclei of the same species. All radioactive nuclei that form a radionuclide have a well-defined radioactivity, common to all of them, that identifies them; in the same way that a type of chemical reaction identifies the elements that participate.

Radioactivity - emitted particles

Quantitatively, radioactivity is a statistical phenomenon. For this reason, to assess it, we must observe the behavior of a set of nuclei of the same species. By the law of large numbers, a radioactive constant λ is defined as the probability of disintegration of a nucleus per unit of time.

With this definition, the number N of radioactive nuclei of the same species found in a substance at an instant t is given by N = No · e-λt, where it is not the number of radioactive nuclei that existed before the end of the time t. In reality, hardly a radioactive substance is formed by a single radionuclide, although each of its components in disintegration is transformed into a different nucleus that, in turn, can also be radioactive.

The initial radionuclide is called father, and the derivative, son. This situation can continue throughout multiple affiliations and the set of all is called family or radioactive series. In this case, the relationship given by the number of radioactive nuclei present is more complex because, in addition to taking into account the number of each of them at the initial moment, it is necessary to consider that, due to the disintegration of some, others are formed.

The problem is simplified when you want to achieve radioactive equilibrium (also called secular equilibrium in natural radioactive series), which is when a sufficiently long time has passed since the process of filiation has begun, because then the rate of decay is imposed by the radionuclide that has the smallest radioactive constant.

Natural radioactive nuclei

In nature there are about 300 different nuclides, of which 25 are radioactive with a sufficiently long period so that there are still today; another 35 have a much shorter period and are created and disintegrated continuously in the radioactive series.

Artificial Radioactive Nucleides

More than 1000 artificial radionuclides have been created and identified. Radioactive series are called the longer period parent nucleid. There are four. Three of these radioactive series are natural: that of thorium, that of uranium and that of actinium, which end up in their own stable lead isotopes.

These isotopes respectively have mass numbers 208, 206 and 207. Regarding the series of the neptunium, as the radionuclides that compose it have a short period compared to the duration of the geological ages, it is not found in nature and has been obtained artificially The last nuclide of this series is isotope 209 of bismuth.

Origin of the radioactivity

Radioactivity was discovered in 1896 by Antoine-Henri Becquerel, who, when doing studies on the phosphorescence of the substances, observed that a uranium mineral was capable of veiling photographic plates that were stored next to it.

The effects of radioactivity on human health

There are two main health effects caused by radiation, which act in the short and long term and also at shorter and larger distances.

Radiation causes health problems by killing cells in the body, and the amount and type of damage caused depends on the dose of radiation received and the time during which the dose is extended.

In the event of a nuclear accident, emergency workers can receive a maximum of 100 millisieverts (mSv) for an action to save assets. If the emergency action is to save lives, a radiation exposure of a maximum of 250 mSv is admitted.

If a person receives between 250 millisieverts (mSv) and 1 sievert ( Sv) in a single day, radioactive exposure is likely to cause symptoms of radiation poisoning. These symptoms of radiation poisoning can be nausea, damage to the lymph nodes and damage to the bone marrow.

If the radioactive dose is increased up to 3 sieverts, these same effects are more severe with a chance of getting infections due to a reduced number of white blood cells in the body; With treatment, survival is likely but not guaranteed.

The larger doses, in addition to the symptoms mentioned above, will cause bleeding, sterility and shedding of the skin; an untreated dose of more than 3.5 Sv will be fatal, and death is expected even with treatment for doses of more than 6 Sv.

The radiation level decreases with the square of the distance from its source, so that someone who is twice as far from an external source will receive a quarter of the radiation.

Usually, receiving a high dose in less time causes more acute damage, since higher doses kill more cells, while the body may have had time to repair some damage over the course of more time between doses.

However, radioactive material that spreads to a wider area can cause long-term health effects through prolonged exposure, especially if they enter the food chain or if inhaled or ingested directly.

Bringing radioactive materials to the body also presents the greatest danger of atoms that suffer from alpha decay, since alpha particles are not very penetrating and are easily absorbed by a few centimeters of air. It was polonium-210 alpha emitter that was used to assassinate Alexander Litvinenko in 2006.

Radioactive isotopes of iodine, which suffer from beta decay, can accumulate in the thyroid gland and cause thyroid cancer. Attempts to prevent this involve the distribution of pills that include non-radioactive iodine 127 and that flood the thyroid, preventing the absorption of radioactive iodine.

For single doses, such as those from medical examinations, the risk of developing cancer later is estimated at around 1 in 20,000 per mSv received.

It is estimated that the absorption of a cumulative dose of 1 Sv over a longer period of time can cause cancer in 5% of people.

However, there is disagreement about whether very small doses, comparable to the level of background radiation, really contribute to health effects.

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References

Last review: January 31, 2020