When an alpha particle is emitted, the atomic number of the daughter nucleus decreases by two units and the mass number of the daughter also decreases by four units compared to those of the parent nucleus.
Since we expect that the isotopes formed by alpha emission will have a mass number less than that of the parent isotope by four units and an atomic number less than that of the parent isotope by two units; we will have the following nuclear reactions;
1) [tex]\frac{175}{78} Pt ----> \frac{171}{76} Os + \alpha[/tex]
2) [tex]\frac{149}{64} Gd -----> \frac{145}{62} Sm + \alpha[/tex]
3) [tex]\frac{241}{95} Am -----> \frac{237}{93} Np + \alpha[/tex]
4) [tex]\frac{232}{90} Th -------> \frac{228}{88} Ra + \alpha[/tex]
We can observe the same pattern in all the equations, the mass number of the daughter nucleus decreases by 4 while the atomic number of the daughter nucleus decreases by 2.
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