An atomic nucleus A is composed of 84 protons and 128 neutrons.
The atomic nucleus A emits an alpha particle and is transformed into nucleus B. The atomic nucleus B emits a β - particle and is transformed into a nucleus C. What is the composition of atomic nucleus C?
In nucleus B atomic number is decreased by 2 and the mass number is decreased by 4. Thus, the resulting nucleus has 2 protons and 2 neutrons less than parent (A) nucleus.
21284A→ 42He+ 20882B
While emitting a β - particle, the number of nucleons in nucleus C remains the same but the number of neutrons is decreased by one and the number of protons is increased by one.
20882B→ 0−1e+ 20883C