Question

In a certain hypothetical radioactive decay process, species $$A$$ decays into species $$B$$ and species $$B$$ decays into species $$C$$ according to the reactions :
$$\eqalign{ & A \to 2B + {\text{particles}} + {\text{energy}} \cr & B \to 3C + {\text{particles}} + {\text{energy}} \cr} $$
The decay constant for species is $${\lambda _1} = 1\,{\sec ^{ - 1}}$$   and that for the species $$B$$ is $${\lambda _2} = 100\,{\sec ^{ - 1}}.$$    Initially $${10^4}$$ moles of species of $$A$$ were present while there was none of $$B$$ and $$C.$$ It was found that species $$B$$ reaches its maximum number at a time $${t_0} = 2\,\ln \left( {10} \right)\sec .$$    Calculate the value of maximum number of moles of $$B.$$

A. 1
B. 2  
C. 5
D. 4
Answer :   2
Solution :
$$\eqalign{ & \frac{{d{N_A}}}{{dt}} = - {\lambda _1}{N_A},\frac{{d{N_B}}}{{dt}} = 2{\lambda _1}{N_A} - {\lambda _2}{N_B}, \cr & {N_B} = {\text{maximum}} \Rightarrow \frac{{d{N_B}}}{{dt}} = 0 \cr & \Rightarrow 2{\lambda _1}{N_A} = {\lambda _2}{N_B}_{_{\max }} \cr & \Rightarrow {N_B}_{_{\max }} = \frac{{2{\lambda _1}}}{{{\lambda _2}}}{N_A} \cr & \Rightarrow {N_B}_{_{\max }} = \frac{{2{\lambda _1}}}{{{\lambda _2}}}{N_0}{e^{ - {\lambda _1}t}} = 2 \cr} $$

Releted MCQ Question on
Modern Physics >> Radioactivity

Releted Question 1

An alpha particle of energy $$5\,MeV$$  is scattered through $${180^ \circ }$$ by a fixed uranium nucleus. The distance of closest approach is of the order of

A. $$1\, \mathop {\text{A}}\limits^ \circ $$
B. $${10^{ - 10}}cm$$
C. $${10^{ - 12}}cm$$
D. $${10^{ - 15}}cm$$
Releted Question 2

Beta rays emitted by a radioactive material are

A. electromagnetic radiations
B. the electrons orbiting around the nucleus
C. charged particles emitted by the nucleus
D. neutral particles
Releted Question 3

Consider $$\alpha $$ particles, $$\beta $$ particles and $$\gamma $$ - rays, each having an energy of $$0.5\,MeV.$$  In increasing order of penetrating powers, the radiations are:

A. $$\alpha ,\beta ,\gamma $$
B. $$\alpha ,\gamma ,\beta $$
C. $$\beta ,\gamma ,\alpha $$
D. $$\gamma ,\beta ,\alpha $$
Releted Question 4

A radioactive material decays by simultaneous emission of two particles with respective half-lives 1620 and 810 years. The time, in years, after which one-fourth of the material remains is

A. 1080
B. 2430
C. 3240
D. 4860

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Radioactivity


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