Half life question?
2016-09-20 11:00 pm
The half life of radium 226 is 1620 years. If the current mass of a sample is 100g, what was the mass 200 years ago. How long will it take for the sample to be reduced by 75 percent.
回答 (1)
2016-09-20 11:41 pm
100 g / (1/2)^(200 yr / 1620 yr) = 109 g
If the sample is reduced by 75%, 25% remains.
Let z be the number of years to be found:
0.25 = (1/2)^(z / 1620 yr)
log 0.25 = (z / 1620 yr) log (1/2)
log 0.25 / log (1/2) = z / 1620 yr
1620 yr log 0.25 / log (1/2) = z = 3240 years
If the sample is reduced by 75%, 25% remains.
Let z be the number of years to be found:
0.25 = (1/2)^(z / 1620 yr)
log 0.25 = (z / 1620 yr) log (1/2)
log 0.25 / log (1/2) = z / 1620 yr
1620 yr log 0.25 / log (1/2) = z = 3240 years
收錄日期: 2021-04-21 21:56:47
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20160920150046AAKFQ7g