Q: Calculate the binding energy of an α- particle. Given that mass of proton = 1.0073 u , mass of neutron =

1.0087 u. and mass of α – particle = 4.0015 u.

Sol: m_{p} = 1.0073 u , m_{n} = 1.0087 u , M = 4.0015 u

N = A – Z = 4 – 2 = 2 (∵ _{2}He^{4} = _{Z}X^{A} )

B.E = Δ m x 931.5 MeV

= {[ Z m_{p} + (A-Z)m_{n} ]- M } × 931.5

[(2 ×1.0073)+ (2 × 1.00987)– 4.0015] × 931.5 MeV

= 0.0305 × 931.5 MeV ; B.E = 28.4 MeV.