Nuclei · Question 16

A radioactive material P first decays into Q and then Q decays to non-radioactive material R. Which of the following figure represents time dependent mass of P, Q and R ?

1. [figure]
2. [figure]
3. [figure]
4. [figure]

Answer

(2) [figure]

Solution

P (parent) decays exponentially: mP=m0e- 1 t, so its mass falls continuously from its maximum value

Q is formed from P and also decays: its mass starts from zero, rises while the rate of formation exceeds the rate of decay, reaches a maximum and then decreases towards zero

R is stable: its mass starts from zero and increases continuously, finally approaching the initial mass m0 (saturation)

Only figure (2) shows P decreasing, Q rising to a maximum and then falling, and R rising to saturation

Answer: (2)