# Learner lab record: Isotope decay and detection record

Course: Atoms, nuclei, and radiation

Name: ____________________  Date: ____________________  Group: ____________________

## Investigation question

How do elapsed half-lives change remaining nuclei, present activity, total transformations, and expected detector counts?

## Setup

Use only the simulated isotope ledger. Do not handle radiation sources. Change elapsed half-lives first, then test mass defect and detector efficiency separately.

## Variables

| Variable | Role | Unit |
| --- | --- | --- |
| Starting nuclei and half-life | model inputs | count and s |
| Elapsed half-lives | independent | half-lives |
| Remaining nuclei and activity | dependent | count and Bq |
| Detector efficiency | measurement input | % |

## Predict before changing controls

1. Predict the remaining fraction after three half-lives.

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2. Predict whether 50% efficiency changes the physical decay count.

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## Observation table

| half-lives | remaining | transformations | activity | efficiency | detected counts |
| --- | --- | --- | --- | --- | --- |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |

## Analyze

1. Does each half-life remove half of the original or half of what remains?

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2. Why does present activity fall while total transformations rise?

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3. Which quantity changes when efficiency changes?

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4. Why is emitted energy not absorbed dose?

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## Evidence-bounded conclusion

After ___ half-lives, ___ of the original nuclei remained; detector efficiency changed ___ but did not change ___.

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