Half-Life

Lab Brief #3

🎯 Your mission

Learn the rule. Then catch nature using it.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

Half-life is the time for half the unstable nuclei in a sample to decay, or for the count rate to halve. It is constant for a given nuclide, ranging from fractions of a second to billions of years, and it is what makes radiometric dating possible.

Key words

half-life
The time taken for half the unstable nuclei in a sample to decay.
count rate
The number of decays detected per second, measured with a Geiger-Müller tube.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

Say your guess out loud — then find out if you were right.

Step 1 of 4 · Read

Think about what you just learned: say what "half-life" and "count rate" mean in your own words before you start.

Step 2 of 4 · Do

From a decay curve, read off the half-life at three different starting points and confirm it is constant. Then calculate what fraction of a sample remains after four half-lives.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

After three half-lives, the fraction of original nuclei remaining is:

How sure are you?😐 maybe

Question 2 of 2

The half-life of a particular nuclide is:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 2 right.

Next: Uses and Dangers of Radiation All lessons

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✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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