QQuestion
What do you mean by mass defect? Actual mass of proton, neutron and helium nucleus are 1.00728 amu, 1.00867 amu and 4.0015 amu, respectively. What is the mass defect of ⁴₂He (helium) nucleus? [1+2]
✓Answer
Mass Defect : Mass defect is the difference between the sum of the masses of the individual nucleons (protons and neutrons) and the actual mass of the nucleus.
Given,
Mass of one proton = 1.00728 amu
Mass of one neutron = 1.00867 amu
Mass of helium nucleus = 4.0015 amu
A helium nucleus contains: 2 protons and 2 neutrons
Mass of 2 protons = 2 × 1.00728 = 2.01456 amu
Mass of 2 neutrons = 2 × 1.00867 = 2.01734 amu
Total mass of nucleons
= 2.01456 + 2.01734
= 4.03190 amu
Mass defect = Total mass of nucleons − Actual mass of nucleus
= 4.03190 − 4.00150
= 0.03040 amu
Hence, the mass defect of the helium nucleus is 0.0304 amu.
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