(New tips are continually added to these pages. Check back in a few months' time for more)
TOPIC 17: Atomic Physics
In radioactivity, the Half-Life T½ is the expected time taken for half the radioactive nuclei to decay.
For example, if T½ is 3 hours and we started off with only 32 radioactive nuclei. After 3 hours, we will be left with 16; after another 3 hours (ie. total 6 hours), we will be left with 8; after yet another 3 hours (ie. total 9 hours), we will be left with 4 radioactive nuclei, and so on.
The general formula to compute the number of radioactive nuclei remaining is:
N = No (½)n
where N is the number of radioactive nuclei remaining; No the number initially; "n" the number of Half-Lives, ie. n = t/T½ where t is the time that has elapsed.
Using the same example as above, when the time elapsed was 6 hours, then n = 6/3 = 2.
N = No (½)n = 32 (½)2 = 32 (¼) = 8
This formula is especially useful if the time "t" is less than one Half-Life, eg. 2 hours. Then, n = 2/3 = 0.667
N = No (½)n = 32 (½)0.667 = 32 (0.63) = 20
© Copyright Physics.com.sg (Registration No. 52890077C). All rights reserved.
® First Class in Physics Tuition is the Registered Trademark (TM No. T02/02149B) of Physics.com.sg