Question

a) An atomic nucleus A is composed of 84 protons and 128 neutrons. The nucleus A emits an α-particle, and is transformed into a nucleus B. What is the composition of B?
b) The nucleus B emits a β-particle and is transformed into a nucleus C. What is the composition of C?
c) What is the mass number of the nucleus A?
d) Does the composition of nucleus C change if it emits γ-radiation.

Answer 1

(a) Composition of nucleus A :
Protons number = 84,
Neutrons number = 128,
Mass number (A) = sum of protons and
neutrons
= 84 + 128 = 212
Atomic number (Z) = number of protons
= 84

${}_{84}^{212}\text{A}{\to }_{82}^{208}\text{B}{+}_2^4\text{He}$
(b) On emission of a $\beta$-particle, the number of nucleons remains the same, as one neutron changes into a proton. Thus the mass number of parent nucleus remains same but atomic number increases by one unit.
${}_{82}^{208}\text{B}{\to }_{83}^{208}\text{C}{+}_{-1}^0\beta$
(c)Given, for nucleus,
Protons number = 84,
Neutrons number = 128,
Mass number = sum of protons and neutrons
= 84 + 128
= 212 unit
(d) No, composition of C does not change because when a gamma particle emitted, atomic number Z and mass number A both remain same. It does not change anything in the nucleus, Only the energy of the nucleus decreases.
${}_{83}^{208}\text{C}{\to }_{83}^{208}\text{C}{+}_{-1}^0\gamma$