# Model Half-Life

Part of the Nuclear Science Merit Badge Digital Resource Guide: [Introduction & Overview](https://merit-badge.university/merit-badges/nuclear-science/guide/index.md)

*4. Classic Experiments*

> **4c.** Perform an experiment demonstrating half-life. Discuss decay chains.

Half-life is one of the most important ideas in nuclear science because it shows how something can be random for each atom but still predictable for a large group. You cannot point to one unstable atom and know exactly when it will decay, but you can predict how a big sample will change over time.

## What half-life means

A **half-life** is the time it takes for half of the radioactive atoms in a sample to decay. After one half-life, about half remain. After two half-lives, about one-fourth remain. After three, about one-eighth remain.

That pattern is why Scouts often model half-life with candies, coins, dice, or other objects. Each round stands in for a time interval. The exact items that "decay" each round change, but the general trend is clear.

Video: [How Radioactive Decay Works | Decay Chains (video)](https://youtu.be/fo1tgibNLss?si=K2DrEfEaGW5MSdOR)

Video: [Skittles Half Life Lab | Radioactive Isotope Decay | Half Life Graph (video)](https://youtu.be/mCSXJNVdK0Y?si=A3UPqOjowKtkSmxk)

## How to discuss your experiment

Your counselor will likely want more than a graph. Be ready to explain the pattern.

**What your discussion should include** — Explain the idea, not just the procedure

- [ ] **What represented the atoms** in your model
- [ ] **What counted as decay** during each round
- [ ] **How the number changed over time**
- [ ] **Why the graph is not perfectly smooth** but still shows the half-life pattern

## What a decay chain is

A **decay chain** happens when one unstable isotope decays into another isotope that is also unstable. That new isotope may decay again, and the process can continue through several steps until a stable isotope is reached.

This matters because radiation hazards and measurements do not always come from just one isotope. Sometimes scientists must think about a whole family of related decay products.

> **Did You Know?**
>
> Some radioactive materials do not decay straight to a stable ending in one step. They move through a chain of different daughter products, each with its own properties and half-life.

If classic experiments showed how radiation can be detected and modeled, the next requirement shows how to protect people from it.

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