A radioactive nucleus undergoes a series of ...

ICSE Class 10 Physics 2013 Paper

Question : 31 of 70

Marks: +1, -0

A radioactive nucleus undergoes a series of decays according to the sequence

X \xrightarrow[\beta]{} X_1 \xrightarrow[\alpha]{} X_2 \xrightarrow[\alpha]{} X_3 \; \text{". "}\;

If the mass number and atomic number of

X_3

are 172 and 69 respectively, what is the mass number and atomic number of

X

Solution:

{}^{A}_{Z}X \overset{\beta}{\rightarrow} {}^{A}_{Z+1}X_1 \overset{\alpha}{\rightarrow} {}^{A-4}_{Z+1-2}X_2

\overset{\alpha}{\rightarrow} {}^{A-8}_{Z-3}X_3

Given : Atomic number of

X_3=69

and mass number of

X_3=172

i.e.

{}^{172}_{69}X_3

{}_{72}X^{180} \overset{\beta}{\rightarrow} {}_{73}X_1^{180} \overset{\alpha}{\rightarrow} {}_{71}X_2^{176} \xrightarrow[\alpha]{} {}_{69}X_3^{172}

Mass number of

X=180

Atomic number of

X=72

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