(i) A radioactive nucleus 'A' undergoes a series of decays as given below: $A \xrightarrow{\;\alpha\;} A_1 \xrightarrow{\;\beta\;} A_2 \xrightarrow{\;\alpha\;} A_3 \xrightarrow{\;\gamma\;} A_4$. The mass number and atomic number of $A_2$ are 176 and 71 respectively. Determine the mass and atomic numbers of $A_4$ and $A$. (ii) Write the basic nuclear processes underlying $\beta^{+}$ and $\beta^{-}$ decays.

$A=(180,72)$, $A_4=(172,69)$; $\beta^-: n\to p+e^-+\bar\nu$, $\beta^+: p\to n+e^++\nu$.

CBSE Class 12 · 2017 · Delhi · Modern PhysicsShort Answer

(i) A radioactive nucleus 'A' undergoes a series of decays as given below:

A α A_{1} β A_{2} α A_{3} γ A_{4}

. The mass number and atomic number of

A_{2}

are 176 and 71 respectively. Determine the mass and atomic numbers of

A_{4}

and

A

.
(ii) Write the basic nuclear processes underlying

β^{+}

and

β^{-}

decays.

Answer: $A = (180, 72)$ , $A_{4} = (172, 69)$ ; $β^{-} : n \to p + e^{-} + \overset{ν}{ˉ}$ , $β^{+} : p \to n + e^{+} + ν$ .

(i) Given

A_{2} (176, 71)

. Going backward (

A_{1} β^{-} A_{2}

raises

Z

by 1, so

A_{1}

has

Z = 70

;

A α A_{1}

means

A

has

A + 4, Z + 2

A_{1} (176, 70), A (180, 72) .

Going forward from

A_{2}

A_{2} α A_{3} (172, 69) γ A_{4} (172, 69)

A : (180, 72); A_{4} : (172, 69)

(ii) Basic processes:

β^{-} : n \to p + e^{-} + \overset{ν}{ˉ}; β^{+} : p \to n + e^{+} + ν .

CBSE Class 12 Board · 2017 · Delhi · Subjective