We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is a Half-Life?

Niki Acker
Updated May 21, 2024
Our promise to you
All The Science is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At All The Science, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

A half-life is the amount of time required for half of a given substance to decay. This measurement is applied to materials that experience exponential decay, meaning that the rate of decay is directly proportional to the amount of the substance, slowing down as the substance depletes. Half-life varies widely — it can be a few seconds or millions of years, depending upon the stability of the substance. The concept has applications throughout the world of science.

A given substance always has the same half-life until it reaches very small amounts, even though the rate of decay slows over time. Imagine an element has a half-life of five minutes, for example. If we start out with 20 ounces of it, five minutes later we will have 10 ounces remaining, and in another five minutes only 5 ounces remaining. The rate of decay has slowed from 2 ounces per minute to 1 ounce per minute, but the half-life is constant at five minutes.

Half-life is perhaps best known in the context of radioactivity. Radioactive "parent" elements transform into stable, or non-radioactive, "daughter" elements and emit radiation as they decay. Knowing the daughter element and half-life of a radioactive element, therefore, allows one to date a partially decayed sample by comparing the ratio of parent to daughter element. This method of dating is commonly used to determine the age of various entities in our universe, from fossils to meteorites. Carbon-14, a radioactive element present in living materials on Earth, begins decaying at the moment of death and can be used to date once-living materials such as bone and wood.

This measurement is also important in biology, where it indicates the amount of time in which half of a given substance is metabolized and/or eliminated by the body. In this sense, half-life is used in pharmacology to determine appropriate dosage amounts and intervals. It can also be applied in toxicology to determine the effects of toxins in the body over time.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Niki Acker
By Niki Acker
"In addition to her role as a All The Science editor, Niki Foster is passionate about educating herself on a wide range of interesting and unusual topics to gather ideas for her own articles. A graduate of UCLA with a double major in Linguistics and Anthropology, Niki's diverse academic background and curiosity make her well-suited to create engaging content for WiseGeekreaders. "
Discussion Comments
By anon140222 — On Jan 06, 2011

there is no "other half." Once the "first half" as you say, has decayed, the "other half" will divide in half, and then that quarter will divide in half, etc. so the "other half" is not really a half at all.

By anon79779 — On Apr 24, 2010

why did we choose half life? why not full life. or t75? please explain.

By anon66584 — On Feb 20, 2010

I've been on dynacirc cr for about six months and haven't had any problems until now with irregular heartbeats. I went off the drug this morning and wondering how long before the drug clears my system.

By anon38206 — On Jul 24, 2009

It doesn't mean that only half of the substance decays. It means that a substance with a particular atomic weight, in course of time, gets reduced to half of the original atomic weight by emitting the radiations. that period is'half life'. --Manjunatha K.S

By Bangaram — On Jun 02, 2009

I found this site very useful. It has everything in detail. It's very good for every student like me.

By anon17824 — On Sep 08, 2008

Half-life is simply the rate of decay. Whether any given molecule decays or not is completely random.

By bozobucks — On Sep 06, 2008

if a half life of a substance is the time it takes half of it to decay...what determines which half decays and which half doesn't? Why would one half decay and not the other?

Niki Acker
Niki Acker
"In addition to her role as a All The Science editor, Niki Foster is passionate about educating herself on a wide range...
Learn more
All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.

All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.