Question 564: Atoms & Nuclei

Question

The half-life of a radioactive substance is 30 minutes. The time (in minutes) taken between 40% decay and 85% decay of the same radioactive substance is

Accepted Answer

N
0
= Nuclei at time t = 0
N
1
= Remaining nuclei after 40% decay
= (1 Ã¢ÂÂ 0.4) N
0
= 0.6 N
0
N
2
= Remaining nuclei after 85% decay
= (1 Ã¢ÂÂ 0.85) N
0
= 0.15 N
0
$$ 	herefore $$ $${{{N_2}} \over {{N_1}}}$$ = $${{0.15{N_0}} \over {0.6{N_0}}}$$ = $${\left( {{1 \over 2}} ight)^2}$$
Hence number of half-lives is 2, so the time needed
is :
t = 2 ÃÂ 30 = 60 mints

Answer

15

Answer

30

Answer

45

Answer

60

Atoms & Nuclei

The half-life of a radioactive substance is 30 minutes. The time (in minutes) taken between 40% decay and 85% decay of the same radioactive substance is

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