Modern Physics Ques 121
- A freshly prepared radioactive source of half-life $2$ $ h$ emits radiation of intensity which is $64$ times the permissible safe level. The minimum time after which it would be possible to work safely with this source is
(1988, 2M)
(a) $6 $ $h$
(b) $12 $ $h$
(c) $24 $ $h$
(d) $128 $ $h$
Show Answer
Answer:
Correct Answer: 121.(b)
Solution:
Formula:
- From $R=R _0 (\frac{1}{2})^{n}$
we have, $1=64 (\frac{1}{2})^{n}$
or $\quad n=6=$ number of half lives
$\therefore \quad t=n \times t _{t _{1 / 2}}=6 \times 2=12 h$
BETA
