What’s Radioactivity?

Radioactivity is the process by which unstable atomic nuclei release energetic subatomic particles or electromagnetic radiation (EMR). This phenomenon can transform one element into another and is partly responsible for the heat of the earth’s core. Radioactivity has a wide variety of uses, including in nuclear energy, in medicine, and in dating organic and geological specimens. It’s also potentially dangerous, as high-energy radiation and particles can damage and kill cells and alter DNA, causing cancer.

Radioactive decay

Unstable atomic nuclei are said to decay, meaning they lose some of their mass or energy to reach a more stable, low-energy state. This process is most often seen in heavier elements, such as uranium. None of the elements heavier than lead have stable isotopes, but lighter elements can also exist in unstable, radioactive forms, such as carbon-14. It is thought that the heat from the decay of radioactive elements maintains the very high temperature of the earth’s core, keeping it in a liquid state, which is essential for maintaining the magnetic field that shields the planet from harmful radiation.

Radioactive decay is a random process, which means that it is physically impossible to predict whether or not a given atomic nucleus will decay and emit radiation at any given time. Instead, it’s quantified by half-life, which is the length of time it takes for half of a given sample of nuclei to decay. The half-life applies to a sample of any size, from a microscopic amount to all atoms of that type in the universe. The different radioactive isotopes vary widely in their half-lives, ranging from a few seconds in the case of astatine-218 to billions of years for uranium-238.

Types of decay

To be stable, a nucleus cannot be too heavy and must have the right balance of protons and neutrons. A heavy nucleus – one that has large numbers of protons and neutrons – will sooner or later lose weight, or mass, by emitting an alpha particle, which consists of two protons and two neutrons bonded together. These particles have a positive electrical charge and, compared to other particles that may be emitted, are heavy and slow moving. Alpha decay in an element causes it to change to a lighter element.

Beta decay occurs when a nucleus has too many neutrons for its number of protons. In this process, a neutron, which is electrically neutral, spontaneously transforms into a positively charged proton by emitting a negatively charged electron. These high energy electrons are known as beta rays or beta particles. As this increases the number of protons in the nucleus, it means that the atom changes into a different element with more protons.

The reverse process can occur where there are too many protons, compared to neutrons. In other words, a proton turns into a neutron by emitting a positron, which is the positively charged antiparticle of the electron. This is sometimes called positive beta decay and causes the atom to change into an element with fewer protons. Both types of beta decay produce electrically charged particles that are very light and fast.
While these transformations release energy in the form of mass, they can also leave the remaining nucleus in an “excited” state, where it has more than its minimum amount of energy. It will then lose this extra energy by emitting a gamma ray, a form of very high frequency electromagnetic radiation. Gamma rays have no weight and travel at the speed of light.

Some heavy nuclei can, instead of emitting alpha particles, actually split, releasing a lot of energy, a process known as nuclear fission. It can occur spontaneously in some isotopes of heavy elements, such as uranium-235. The process also releases neutrons. As well as spontaneously, fission can be caused by a heavy nucleus absorbing a neutron. If enough fissile material is thrown together, a chain reaction can take place in which the neutrons produced by the fission cause other nuclei to split, releasing more neutrons, and so on.
it is used
The best known uses of radioactivity are perhaps in nuclear power plants and nuclear weapons. The first atomic weapons used a runaway chain reaction to release enormous amounts of energy in the form of intense heat, light, and ionizing radiation. Although modern nuclear weapons primarily use fusion to release energy, it is still initiated by a fission reaction. Nuclear power plants use carefully controlled fission to produce the heat needed to drive steam turbines that generate electricity.

In medicine, radioactivity can be used in a targeted way to destroy cancerous growths. Being easily detectable, it is also used to trace the progress and uptake of drugs by the organs, or to verify their correct functioning. Radioactive isotopes are often used to date material samples. Organic substances can be dated by measuring the amount of carbon-14 they contain, while the age of a rock sample can be determined by comparing the amounts of the various radioactive isotopes present. This technique has allowed scientists to measure the age of the Earth.
Health effects
In a healthcare context, all emissions from decaying atomic nuclei, whether particles or EMR, tend to be described as radiation and are all potentially dangerous. These emissions are either ionizing in their own right or interact with body matter in a way that produces ionizing radiation. This means that they can remove electrons from atoms, turning them into positively charged ions. These can then react with other atoms in a molecule or nearby molecules, causing chemical changes that can kill cells or cause cancer, especially if the radiation has interacted with the DNA.
The type of radiation most dangerous to humans depends on the circumstances in which it is encountered. Alpha particles can only travel a short distance in the air and cannot penetrate through the outer layer of skin. If they come into contact with living tissue, however, they are the most dangerous form of radiation. This can happen if something that emits alpha radiation is ingested or inhaled.
Beta radiation can penetrate the skin, but is stopped by a thin layer of metal, such as aluminum foil. Neutrons and gamma radiation are much more penetrating and thick shielding is required to protect health. Because most gamma radiation passes through the body, it is typically less likely to cause disease at low levels, but is still a very serious hazard. If materials, including living tissue, absorb neutrons, they can themselves become radioactive.
Exposure to harmful radiation is typically measured in terms of the amount of energy absorbed by the exposed material, a measure that can be applied to all forms of radiation and materials, although it is most commonly used in the context of human health. The SI unit for exposure is gray, where one gray equals one joule of energy absorbed per kilogram of matter. In the United States, however, another unit is often used, the rad, which equals 0.01 gray.
Because different types of radioactivity behave in different ways, another measurement, the sievert, is used to give a better idea of ​​the likely health effects of a given dose. It is calculated by multiplying the gray dose by a quality factor specific to the particular type of radiation. For example, the quality factor for gamma radiation is 1, but the value for alpha particles is 20. Therefore, exposing living tissue to 0.1 grays of alpha particles would result in a dose of 2.0 sievert, and one would expect which has twenty times the biological effect as a gray of gamma radiation. A dose of four to five sieverts, received over a short period of time, carries a 50% risk of death within 30 days.

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