Radioactivity

When we hear the word radioactivity, our mind tends to drift to catastrophic incidents, such as the nuclear fallout at Chernobyl. However, the same radioactivity that so many fear is used in medicine, academics, industry, and in generating electricity.

But what is radioactivity? Radioactivity occurs when an unstable atom emits radiation to achieve stability.

Why does radioactivity even occur?

Everything you see around you is made up of stable atoms. Otherwise, your carbon table would degenerate into something else.

Inside the atom's nucleus, some protons are positively charged, while neutrons are neutrally charged. The two are supposed to repel each other, except that there is a strong nuclear force that keeps the nucleons intact. This glue-like force has a very short range and depends on the ratio of protons and neutrons inside the nucleus.

Carbon 12 is a stable element with six protons and six neutrons. Carbon 14, however, with eight neutrons and six protons, is an unstable isotope. Isotopes are formed when an atom's proton numbers are the same as the stable atom but the number of neutrons varies.

The scenarios above lay the foundations for unstable isotopes. Just as your body gets rid of waste material, the isotopes emit particles with energy to restore balance. However, during this emission of energy, isotopes form a new nucleus.

This property of turning from one thing into something else to attain stability is what we call radioactivity. And the process in which an unstable atomic nucleus releases energy to become stable is known as radioactive decay. Materials that have unstable nuclei are, therefore, radioactive.

Radioactivity: Radioactive decay

Unstable isotopes with three kinds of energy particles, which means that there are three types of radiation that are released by an unstable nucleus.

Radioactivity: Alpha (α)

An alpha particle has a helium nucleus that consists of two protons and two neutrons.

An alpha particle consists of two protons and two neutrons

Alpha particles are somewhat heavy and only travel a few centimetres. Alphas are not that harmful either, as they can be easily halted by a sheet of paper or plastic.

Radioactivity: Beta (β)

An electron or a positron (a particle having the same mass as an electron and a numerically equal but positive charge) is emitted by a nucleus of a heavy element as the result of a conversion in which neutrons are converted into protons.

Beta particles have more energy than is found in alpha radiation, and they travel for longer distances than alpha particles. Beta particles can be held by a thin sheet of metal or by protective clothing.

The emission of an electron or a positron constitutes a beta-minus or a beta-plus decay

Radioactivity: Gamma (γ)

Gamma radiation is by far the most dangerous. After the emission of alpha and beta particles, if the nucleus is still at a high energy state and must return to a lower, stable energy state, then gamma rays, a form of high-energy light radiation, are released.

A nucleus can undergo these processes spontaneously. But how long does it take for the unstable element to attain stability? The answer to this can vary for different elements, as it may take seconds, weeks, months, years, or even centuries.

Gamma rays have the smallest wavelength and the highest energy amongst all waves in the electromagnetic spectrum

The rate of decay is determined by the half-life of the radioactive substance. The half-life of an isotope is the average time it takes for unstable nuclei to halve. Note that the half-life is not measured by counting nuclei but by measuring the time it takes for their activity to halve.

A long half-life can be dangerous because of the danger caused by radioactive elements. We need to be careful when it comes to storing or disposing of nuclear waste products because they can have a very long half-life and can damage the environment if radiation is released into the air, land, or water.

Do all radioactive isotopes decay at the same rate?

Isotopes do not all decay at the same rate. Most isotopes are stable. Hydrogen, for instance, has three isotopes, only one of which is radioactive while the other two are stable.

For elements that do decay, radioactive decay is a very random process. To predict which nuclei will decay and when is, therefore, difficult. However, if you take a very large number of nuclei, their behaviour can reveal a certain pattern because the rate of decay for a given isotope over a specific period is constant. This means that during that period, a predictable number of nuclei will decay.

The rate of decay is measured by the decay constant (\(\lambda\)), which estimates how much a nucleus will decay per second. A larger value of \(\lambda\) indicates a faster rate of decay. For instance, when \(\lambda\) is twice as large, the decay rate per second is twice as high. See the formula below:

\[\text{Activity} = \text{decay constant} \cdot \text{number of nuclei}\]

\[\text{Activity} = \lambda \cdot \text{number of nuclei}\]

Radioactivity: Is radiation harmful?

Ionizing and nuclear radiation have been categorized as harmful to all biological beings. Some radiation can even be deadly.

However, low levels of radiation are not dangerous. Examples of this include the radiation emitted by your phone when you receive a call, the light bouncing off of your skin, and the food being heated in a microwave.

Even radioactive material can be put to good use. While exposure to limitless amounts of radioactive material can cause lethal amounts of genetic mutation and cancer, controlled amounts of the same material can be used to cure cancer. Radioactive iodine, for instance, is used in radiation therapy to treat cancer and for imaging in the thyroid gland.