Radioactivity. Detection, shielding, dating and half-life

Types of ionizing radiation

Radiation emitted by unstable nuclei has ionizing effects. This means it has enough energy to knock electrons out of the atoms it collides with, altering the structure of matter. Depending on the nature of the emission, physicists classify this radiation into three broad categories.

Alpha (α) radiation: heavy particles

Alpha radiation occurs when an atom’s nucleus is too large and needs to lose mass quickly. The nucleus emits an alpha particle, which consists of two protons and two neutrons (equivalent to a helium nucleus). Because these particles are so large and heavy, they have a high positive electric charge and move at relatively slow speeds. Due to their large size, they have very little penetrating power: a single sheet of paper or the outer layer of our skin is enough to stop them completely.

Beta radiation (β): escaping electrons

Beta radiation occurs when the nucleus has an imbalance between its protons and neutrons. To correct this, a neutron transforms into a proton, and in the process, the nucleus ejects an electron at extremely high speed, known as a beta particle. Since they are thousands of times smaller than alpha particles, they have moderate penetrating power. They can pass through paper and travel a few meters through the air, but they can be easily stopped by a thin sheet of aluminum or a piece of wood.

Gamma rays (γ): pure energy

Unlike the previous types, gamma radiation does not involve the emission of material particles, but rather the emission of high-energy electromagnetic waves (photons). It occurs when the nucleus, following an alpha or beta decay, still has excess accumulated energy and needs to fully stabilize. Since they have no mass or electric charge, gamma rays travel at the speed of light and have extremely high penetrating power. They can pass through the human body and require very dense materials, such as thick concrete walls or lead plates, to be stopped.

Half-life. How long does radioactivity last?

The decay of an atom is a purely random event; it is impossible to predict exactly which millisecond a specific nucleus will decay. However, when we analyze a sample containing millions of unstable atoms, the behavior becomes predictable and follows a strict mathematical law.

To measure the rate at which an element’s radioactivity decays, we use the concept of half-life, a term you’ll also find in physics and chemistry textbooks referred to as the half-life period. Both concepts mean exactly the same thing: it is the time required for half of the radioactive nuclei in an initial sample to decay and transform into stable elements.

For example, if you have a sample of 100 grams of a radioisotope with a half-life of one year, after twelve months you will have 50 grams of radioactive material left. After another year, the amount will be reduced to half of what remained, that is, 25 grams, and so on.

This rate of decay varies drastically depending on the chemical element being measured:

–    Uranium-238 has a half-life of about 4.5 billion years, nearly the age of the Earth.

–    Carbon-14 has a half-life of 5,730 years, which allows archaeologists to date ancient organic remains.

–    Iodine-131, used in medical treatments, has a half-life of just 8 days, ensuring that it does not remain in the body for very long.

Practical applications of radioisotopes

Despite the negative reputation that often surrounds nuclear energy, controlled radiation is an indispensable tool in modern society. By knowing the exact half-life of each radioisotope and the type of particle it emits, science has learned to use them for the benefit of health and technical progress.

Nuclear medicine and diagnostics

In hospitals, very short-lived radioisotopes are used for two main purposes: diagnosis and treatment. For diagnosis, small doses of radioactive substances are introduced into the patient’s body to act as tracers, allowing advanced scanners such as PET to obtain detailed images of the interior of organs. In the field of treatment, techniques such as radiation therapy use intense sources of gamma radiation directed with pinpoint accuracy to destroy cancer cells and slow tumor growth.

Nuclear energy and industry

In the industrial sector, radioisotopes are used as high-precision inspection tools. Gamma emissions enable industrial radiography to check the quality of welds in pipes or detect invisible cracks in aircraft structures without having to disassemble them. On the other hand, the best-known application is electricity generation in nuclear power plants, where the immense amount of thermal energy released during the fission of heavy nuclei such as uranium is harnessed.

Risks Associated with Radioactivity

Radioactivity can be dangerous to living organisms if there is excessive exposure or if radioactive materials are released into the environment in an uncontrolled manner. Prolonged exposure to ionizing radiation can have harmful health effects, such as cellular damage, genetic mutations, and an increased risk of developing cancer. Therefore, precautions must be taken and safety limits established to minimize exposure to radioactivity and protect people and the environment.

To work safely with radioactive materials, medical physics and engineering rely on three fundamental pillars of radiation protection:

Time

The accumulated radiation dose is directly proportional to the time spent near the source. Reducing handling time to the absolute minimum is the first line of defense.

Distance

The intensity of radiation decreases dramatically as we move away from the source. Doubling the distance reduces exposure to one-fourth.

Shielding

Placing adequate physical barriers between the source and people blocks the particles. As we saw when analyzing the types of radiation, aluminum sheets are used for beta particles, and thick walls of lead or concrete are used to contain gamma rays.

In the event of a nuclear or radiological incident, it is important to follow the instructions of the authorities and evacuate or take protective measures as necessary. Regulatory agencies and nuclear safety programs are responsible for overseeing and regulating the use of radioactive materials to ensure the protection of public health and the environment.