What Is a Half-Life and How Is It Used to Measure Radioactivity?

Key Points

• Half-life is the amount of time it takes for an object to reduce its quantity by fifty percent.
• Radioactivity is the release of energy from the decay of radioactive nuclei.
• There are four primary types of radiation: alpha, beta, gamma, and X-ray.
• Exposure to radiation can be harmful to our health, and different devices have varying half-life values.

Half-Life and Radioactivity: An Exact Definition

Half-life is a value that represents the amount of time it will take for an object to reduce its quantity by fifty percent. The nuclei of specific types of isotopes and atoms release their energy through radiation.

The radiation emission may last for a few seconds, a few million years, or somewhere in between. Half-life defines the duration of time it takes (the rate of decay) for fifty percent (half) of the radioactive atoms to decay.

What Is Radioactivity: A Complete Explanation

To understand radioactivity and half-life, we need to have a rudimentary understanding of the structure of atoms. Rest assured, in our prior life, we worked with protons and electrons daily. We’ve gotcha covered! Ready? Let’s go!

Atom

An atom contains three microscopic subatomic particles: electrons, neutrons, and protons. The nucleus is the center of the atom. It contains protons and neutrons.

Electrons fly in a circle around the nucleus and have a negative electrical charge. The protons carry a positive electrical charge. The neutrons have no electrical charge. In a neutral atom, the number of protons and the number of electrons are equal.

Negative electrons attract positive protons (just like a magnet). The opposite forces between the electron and the proton hold the atom together. If the number of electrons is the same as the number of protons, we have a stable nucleus.

Unstable Nucleus

If the protons and neutrons in the nucleus aren’t in balance, the atom is considered an “unstable nucleus.” And an unstable nucleus occurs when the neutron count exceeds the proton count. The instability in the nucleus causes a neutron to convert into a proton.

This conversion releases a beta particle. The unstable nucleus will continue to shed or decay as it releases photons, electrons, neutrons, or alphas. An alpha is two neutrons bound to two protons.

Radioactivity

The unstable nucleus releases energy as the nuclei decay. Radioactivity is the released energy from the nucleus.

In short, radioactivity is the release of energy from the decay of radioactive nuclei. The decay only relates to certain kinds of atoms and isotopes, though.

The nucleus seeks a state of balance, so it sheds whatever it needs to in order to bring about balance. Let’s take a look at a few different types of energy releases:

1. If the nucleus has too many neutrons, it will emit a negative beta particle, which changes one neutron into a proton.
2. If there are too many protons in the nucleus, it will create a positively charged electron (positron), which changes one proton into a neutron.
3. Too much energy causes the nucleus to generate a gamma ray, which discharges a lot of energy without modifying any particles in the atom’s nucleus.
4. If there’s too much mass in the atom, the nuclei emit an alpha particle, which ejects four particles in total: two neutrons and two protons.

Different Types of Radiation

There are four primary types of radiation that we’ll touch on. Some types of radiation aren’t dangerous, while others are deadly.

Alpha

An alpha particle (α) has a positive charge. It’s created from two neutrons and two protons from the nucleus of an atom. Heavy elements, like radium and uranium, create alpha particles that have radiation.

Alpha particles are heavy and don’t travel very far. They also lack the energy to pierce through the outer layer of our skin.

If an alpha particle is inhaled, swallowed, or passed into our bodies through a cut, it will cause significant damage. You’ll find alpha particles in smoke detectors, industrial mechanical static electricity removal, and probes used in telescopes in space.

Beta

A beta (β) particle has a negative charge and is generated from the nucleus during radioactive decay. Beta particles are generated when a neutron in the nucleus converts into a proton and electron. The electon is ejected as a beta emission.

Hydrogen-3, strontium-90, and carbon-14 generate beta particles. A beta particle penetrates further than an alpha particle.

A T-shirt, jacket, or pants will stop a beta particle (or aluminum, if you want to wear a tin foil hat). Similarly to alpha particles, beta particles are most dangerous if inhaled or ingested.

Medical applications such as PET scans, eye cancer, and bone cancer treatment use beta particles. Beta particles are used to calculate material thickness.

A stream of beta particles is shot toward a thin film (like a piece of paper). A measurement of the amount of particles that reach a collection unit on the far side of the paper is used to calculate the thickness of the paper.

Gamma

We’re getting serious now! Gamma radiation is pure photon energy. And you’ll find gamma rays together with beta or alpha particles during the radioactive decay process.

Gamma rays are dangerous to humans. They will pass through clothing, skin, and your tinfoil hat. A gammy ray is capable of passing through walls, dirt, underground bunkers, and lead. It will also cause severe tissue and DNA damage.

If you take a quick look at the electromagnetic spectrum (EMS), you’ll see that gamma rays are all the way on the far right side of the EMS. Gamma rays have the smallest wavelength and pack the most significant penetrating power.

Supernova explosions, black holes, neutron stars, pulsars, lightning, nuclear explosions, and radioactive decay emit gamma rays.

X-Ray

We’ve all heard of X-rays! Like a gamma ray, an X-ray is a photon of pure energy. An X-ray, generated outside the nucleus, has lower energy than gamma rays. CAT scans, images of bones, soft tissues, and dental work all use X-rays.

Why Do We Care About Radiation?

Exposure to radiation can be harmful to our health. Have you noticed how careful the dental hygienists are when shooting X-rays at the doctor’s office? They’ll leave the room when it’s time to “snap the picture” of your X-ray. It’s all about radiation!

Below is a chart of typical and less commonly used devices that emit radiation. As we progress further down the chart, we’ll note that the half-life increases quite a bit.

How Does Half-Life Measure Radioactivity?

As mentioned above, half-life is the amount of time it will take for fifty percent (half) of the radioactive elements of an atom to decay. As an example, take seven half-lives of radioactive material and you’ll end up with less than one percent of the original radioactive material. (It works, we checked the math!)

Radioactive isotopes break down through gamma, beta, and gamma decay. Decay occurs in the parent source over time. Once the parent has released the child, the child is no longer radioactive, nor will the child produce further radioactive material.

Scientists can’t predict the quantum behavior of a single atom, but they can predict the statistical behavior of millions and billions of atoms. The half-life values of radioactive materials used in medicine allow physicians to determine the proper safe dosage levels in the treatment or exploration of the heart, liver, thyroid, etc. organs.

Commercial applications use half-life calculations every day. Radioactivity and half-life values are of paramount concern in industrial applications such as in thickness, moisture, density, specific gravity, and density measurements.

The image featured at the top of this post is ©Yurchanka Siarhei/Shutterstock.com.