Nuclear Chemistry - Result Question 3
####4. The radioactive isotope, tritium, $( _1^{3} H)$ has a halflife of 12.3 years. If the initial amount of tritium is $32 mg$, how many milligrams of it would remain after 49.2 years?
[2003]
(a) $8 mg$
(b) $1 mg$
(c) $2 mg$
(d) $4 mg$
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Solution:
- (c) Given $t _{1 / 2}=12.3$ years
Initial amount $(N_0)=32 mg$
Total time $=49.2$ years
No. of half lives $(n)=\frac{T}{t _{1 / 2}}=\frac{49.2}{12.3}=4$
Now $N_t=N_0(\frac{1}{2})^{n}=32(\frac{1}{2})^{4}=\frac{32}{16}=2 mg$
Hence $32 mg$ becomes $2 mg$ in 49.2 years
(a) $ _{92} U^{235}+ _0 n^{1} \to _{54} Xe^{139}+ _{38} Sr^{94}+X$
$92+0=54+38+a \Rightarrow a=0$
$235+1=139+94+b \Rightarrow b=3$ So, $X=3 _0 n^{1}$
i.e 3 neutrons.
