Nuclear Physics And Radioactivity Question 382
Question: A count rate meter shows a count of 240 per minute from a given radioactive source. One hour later the meter shows a count rate of 30 per minute. The half-life of the source is [KCET 2004]
Options:
A) 120 min
B) 80 min
C) 30 min
D) 20 min
Show Answer
Answer:
Correct Answer: D
Solution:
$ A=A_{0}{{( \frac{1}{2} )}^{n}} $
$ \Rightarrow 30=240{{( \frac{1}{2} )}^{n}} $
$ \Rightarrow {{( \frac{1}{2} )}^{3}}={{( \frac{1}{2} )}^{n}} $
Þ n=3 \ $ \frac{t}{{T_{1/2}}}=3 $ $ \frac{v^{2}}{r}=\frac{n^{2}r^{2}}{4{{\pi }^{2}}m^{2}r^{2}} $ = 20 min.
BETA
