Radioactivity is spontaenous, the change of one nuclei into another is instantaneous
Radioactivity is random, the change of one nuclei into another can not be predicted.
However, different radioisotope sample decay at different rates - this is termed as the half life.
The half life is a probability measurement of time that states the time for half the amount of a sample to decay/transmute.
Radioactivity is random, the change of one nuclei into another can not be predicted.
However, different radioisotope sample decay at different rates - this is termed as the half life.
The half life is a probability measurement of time that states the time for half the amount of a sample to decay/transmute.
Interactive
Lets' explore this concept further with this interactive from pHET
Lets' explore this concept further with this interactive from pHET
- Start first with the Single atom
- You will get a model of the decay of Polonium-211 into Lead-207, with the release of an alpha particle
- You will need to reset the nuclei each time the decay occurs
- Now got to Multiple Atoms
- Add a large portion of atoms and start the animation
So
- after 1 half life - 50% has decayed
- after 2 half lives - 75% has decayed (50% of 50% more)
- after 3 half life - 87.5% has decayed
- after 1 half life - 90.75% has decayed
- etc
Experiment and discussion
What is the decay rate of a head of beer? This video looks at that and uses the results to help you understand the concept of half-life in radioactivity.
What is the decay rate of a head of beer? This video looks at that and uses the results to help you understand the concept of half-life in radioactivity.
Sample Problem
We are now ready to try a sample problem
Below is a sample problem with a video that explain how to solve it. It is suggested you try the problem beforehand, as this actually aids understanding, even if you are unsure if you are correct.
We are now ready to try a sample problem
Below is a sample problem with a video that explain how to solve it. It is suggested you try the problem beforehand, as this actually aids understanding, even if you are unsure if you are correct.
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More Problems
Given that the half lives as shown (As-81 = 33s; Au-198 - 2.69 days; C-14 = 5730 years)
a. How long does it take a 100.00g sample of As-81 to decay to 6.25g? (4 x 33 = 132s)
b. What percent of a sample of As-81 remains un-decayed after 43.2 seconds? (40.3%)
c. How old is a bone if it presently contains 0.3125g of C-14, but it was estimated to have originally contained 80.000g of C-14? (45,840 y)
a. How long does it take a 100.00g sample of As-81 to decay to 6.25g? (4 x 33 = 132s)
b. What percent of a sample of As-81 remains un-decayed after 43.2 seconds? (40.3%)
c. How old is a bone if it presently contains 0.3125g of C-14, but it was estimated to have originally contained 80.000g of C-14? (45,840 y)
If you wish to the experiment yourself , here is the experiment on half life
| l_halflife_beer-2.pdf |
