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Radioactivity is a natural process in which unstable atomic nuclei break down into more stable ones, releasing subatomic particles and energy in the process. Since the discovery of radiation in the late 19th century, it has fascinated scientists and the public alike. From radioactive thorium once being used in facial creams to fictional stories like Spider-Man gaining powers from a radioactive spider bite, radiation has long been seen as mysterious and intriguing. Today, we understand far more about what radiation is, how it can be identified and used, and, most importantly, how its dangers can be managed.
To understand radiation, we first need to learn about the composition of an atom. An atom is made up of three subatomic particles:
The properties and roles of these subatomic particles define every element in the periodic table.
Elements in the periodic table are written using nuclide notation, which gives important information about the atom. There are three parts to this notation:
The identity of an element is determined by the number of protons it has. However, atoms of the same element can have different numbers of neutrons, resulting in different mass numbers and relative atomic masses. Atoms of the same element with different numbers of neutrons are called isotopes.
Because protons determine the identity of an element, isotopes have the same chemical properties. However, their different numbers of neutrons give them different atomic masses and may affect some physical properties.
We have learned that the nucleus of an atom is made up of protons and neutrons. For a nucleus to be stable, these particles must be in the right balance.
You can think of it like trying to hold a fixed number of balls in your arms. If there are too many, it becomes harder to keep everything balanced. In a similar way, when a nucleus has an unstable arrangement of protons and neutrons, it may undergo nuclear decay. This is the process in which an unstable nucleus emits subatomic particles or energy as radiation in order to become more stable. This is why heavier atoms are generally more likely to decay, since their nuclei are often less stable. Some isotopes of common elements undergo nuclear decay due to unstable nucleus confirmation, such as helium-3 (tritium), carbon-14 and oxygen-18.
There are three forms of nuclear decay, each differing in the type of particle emitted, its penetrating power, and its ionising strength. All forms of nuclear decay produce ionising radiation, which can remove electrons from atoms or molecules, a process known as ionisation. This is especially dangerous to living organisms because ionising radiation can damage molecular bonds and break strands of cellular DNA.
During alpha decay, helium nuclei (⁴₂He) containing 2 protons and 2 neutrons are emitted. This reduces the parent atom’s mass by 4 and its atomic number by 2, producing a different element.
The general equation for alpha decay is: 
An example of alpha decay is the decay of uranium-238 into thorium-234: 
The helium nucleus emitted during alpha decay is known as an alpha particle. Because alpha particles are relatively large and heavy, they have low penetrating power and cannot pass through materials such as paper or the outer layer of skin. However, due to their high ionising ability, if alpha particle-emitting substances enter the body through inhalation or ingestion, they can cause severe damage to living tissue.
During beta decay, a neutron decays into a proton (+1 charge) and an electron (-1 charge). This results in an increase in proton number by 1, while the mass number remains constant. The emitted electron is known as a beta particle.
The general equation for beta decay is: 
An example of alpha decay is the decay of carbon-14 into nitrogen-14. 
Beta particles are moderately penetrating and moderately ionising. They are much lighter than alpha particles and can be stopped by a thin sheet of aluminium or plastic.
During gamma decay, the nucleus emits gamma rays, which are a highly energetic form of electromagnetic radiation. Gamma rays have no mass and no charge, so the atomic number and mass number of the nucleus remain unchanged.
The general equation for gamma decay is: 
An example of gamma decay is Technetium-99m (the name of the metastable isomer) decaying to technetium-99: 
Gamma rays are weakly ionising but highly penetrating. Because of this, they are more difficult to block and usually require thick lead or concrete shielding for protection. Workers handling strong gamma sources use shielding and safety procedures to reduce exposure.
Alpha and beta particles, as well as gamma rays, can be detected using a Geiger counter, which is used to detect and measure radiation. Each time radiation is detected, the Geiger counter records a count. The level of radiation can then be estimated from the number of counts recorded per minute.
Nuclear decay and radioactivity occur randomly, so we cannot predict when a particular unstable nucleus will decay. However, when dealing with a large number of atoms, we can estimate the rate of decay using half-life. Half-life is the time taken for half of the radioactive nuclei in a sample to undergo decay.
A decay curve is an exponential graph that shows how radioactivity decreases over time. It falls quickly at first, then gradually levels off, approaching zero but never quite reaching it. This is because each half-life reduces the amount of radioactive substance by half, so the quantity becomes smaller and smaller over time. As a result, a radioactive substance emits less and less radiation as time passes, but it never stops emitting completely.
Now that we understand radiation and half-lives, we know that radioactive materials never stop emitting radiation completely. As a result, there is always a small amount of low-level radiation in our environment, even when no obvious source is nearby. This is known as background radiation, and it can be detected using a Geiger counter.
Background radiation comes from both natural and man-made sources. Natural sources include rocks and soil that contain traces of radioactive materials, as well as cosmic rays from space. Man-made sources include the use of radiation in medical imaging and treatment, as well as radiation produced by nuclear power plants.
Since a Geiger counter detects both background radiation and radiation from a radioactive source, the background count should be measured first and then subtracted from the total reading when determining the radiation level of the source.
Unlike chemical reactions, which do not alter the identity of atoms, nuclear reactions involve changes in the nucleus and may lead to changes in both atomic number and mass number. In a nuclear reaction, an atomic nucleus collides with another particle or nucleus, producing one or more new nuclides and releasing a substantial amount of energy. Nuclear fusion and fission are the main types of nuclear reactions.
Nuclear fusion occurs when two or more nuclei combine to form a heavier nucleus, releasing energy in the process. One example is the fusion of deuterium and tritium to form helium. 
During fusion, energy is released because the products are more stable than the original nuclei. The energy may appear as kinetic energy of the particles formed or as radiation released into the surroundings.
Because atomic nuclei are positively charged, they repel each other. A very large amount of energy is therefore needed to bring them close enough for fusion to occur, but once fusion happens, even more energy is released.
Nuclear fission occurs when a neutron collides with the nucleus of an atom, causing the larger nucleus to split into two smaller nuclei and release a large amount of energy.
For example, when uranium-235 undergoes fission, it can produce barium and krypton. 
Nuclear fission is a chain reaction. When one nucleus splits, the neutrons released can trigger further fission in other nuclei, producing more reactions and releasing immense amounts of energy.
The energy released during nuclear decay makes radiation useful in many applications, including diagnostic imaging, radiotherapy, sterilizing medical equipment, preserving food, generating nuclear power, and powering household safety devices such as smoke detectors.
Nuclear medicine is an important branch of healthcare. Using radioactive isotopes in safe, controlled doses, doctors can perform advanced imaging to diagnose disease more accurately. Radiation can also be used to target and destroy diseased cells, making it especially valuable in treating conditions such as cancer. In the same way, radiation is used to sterilize medical equipment by killing harmful microorganisms, helping ensure that it is safe for patient use.
When carefully controlled, nuclear fission reactions can be used to generate energy for household electricity. The heat produced by fission is used to boil water into steam, which then drives a turbine connected to a generator. Compared with many other fuel sources, nuclear power produces far fewer air pollutants during electricity generation. For this reason, it has often been seen as a promising, clean, and efficient source of energy.
Nuclear decay releases energy in the form of ionising radiation. If this radiation were to interact with our cells and DNA, it could cause serious damage. Although background radiation and the low levels used in routine medical imaging are generally safe, exposure to a high dose of radiation can lead to severe effects such as cell damage, genetic mutations, cancer, burns, radiation sickness, and harm to future offspring.
Because of these risks, there are strict regulations to limit exposure to radiation and prevent the accumulation of damage in the body. For example, personnel who carry an R1 license to work with radioactive materials in Singapore are required to carry a badge which records radiation exposure. These badges are monitored by NEA to ensure that no one has had too much exposure within a short frame of time.
What happens when someone is exposed to a high dose of radiation over a very short period of time? This can occur in an accident involving radioactive material. One well-known example is the Chernobyl disaster, in which an accident at the Chernobyl nuclear power plant released large amounts of radiation into the surrounding area. The release of radioactive iodine has been linked to an increase in thyroid cancer among former residents near the site.
The phenomenon of nuclear decay and radiation is fascinating, and the energy released by these reactions may hold the key to a cleaner, more sustainable future. However, with great power comes great risk, and mistakes in nuclear technology can have catastrophic consequences. With a better understanding of radioactivity, we can all play a part in building a safer, more efficient, and more sustainable future grounded in science.
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Prepared by: Michelle
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