Half Life
AQA Seperate Science Physics : 2B Electricity and the Atom.
Mindpap Covering
- Half Life Definition
- Decrease in Radioactivity
- Examples of Half Life
- Created by: Ellie
- Created on: 05-02-14 17:49
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- Half Life
- Radioactivity decreases over time
- Each time decay happens an alpha, beta or gamma is given out.
- This means one more radioactive nucleus has disspaeared.
- As the unstable Nuclei sll disappear the activity will decrease. So the older the sample the less radiation will be emitted
- Activity : the number of nuclei that decay per second
- We cant measure activity because the activity never reaches zero
- Each time decay happens an alpha, beta or gamma is given out.
- THE AVERAGE TIME IT TAKES FOR THE NUMBER OF NUCLEI IN A RADIOACTIVE ISOTOPE SAMPLE TO HALVE.
- A SHORT HALF LIFE: means the activity falls quickly because lots of the nuclei decay quickly
- A LONG HALF LIFE: means the activity falls slowly because most of the nuclei wont decay for a long time
- EXAMPLE:
- The activity of a radioisotope is 640cpm. Two hours later it has dropped to 80cpm. Find the half life of the sample
- Initial Count: 640
- After one half Life: 320
- After two half lives: 160
- After three half lives: 80
- 2 hours represents 3 half lives. 2 hours = 120 minutes.
- 120 / 3 = 40 minutes
- The activity of a radioisotope is 640cpm. Two hours later it has dropped to 80cpm. Find the half life of the sample
- Initial Count: 640
- After one half Life: 320
- After two half lives: 160
- After three half lives: 80
- 2 hours represents 3 half lives. 2 hours = 120 minutes.
- 120 / 3 = 40 minutes
- 120 / 3 = 40 minutes
- 2 hours represents 3 half lives. 2 hours = 120 minutes.
- After three half lives: 80
- After two half lives: 160
- After one half Life: 320
- Initial Count: 640
- The activity of a radioisotope is 640cpm. Two hours later it has dropped to 80cpm. Find the half life of the sample
- 120 / 3 = 40 minutes
- 2 hours represents 3 half lives. 2 hours = 120 minutes.
- After three half lives: 80
- After two half lives: 160
- After one half Life: 320
- Initial Count: 640
- The activity of a radioisotope is 640cpm. Two hours later it has dropped to 80cpm. Find the half life of the sample
- Reading The Half Life of Graphs
- The half life is found from the graph by finding the interval time on the bottom axis corresponding to a halving of the activity on the vertical axis
- Radioactivity decreases over time
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