Mass Defect Calculator
Calculate the mass defect of a nucleus from its number of protons, neutrons, and measured atomic mass.
Mass Defect
0.514226 u
Mass Defect vs Number of Protons (Z)
Formule
## Nuclear Mass Defect The mass defect is the difference between the total mass of individual nucleons and the actual mass of the assembled nucleus. ### Formula **delta_m = (Z × m_p + N × m_n) - M_atom** where m_p = 1.007276 u (proton), m_n = 1.008665 u (neutron), and M_atom is the measured atomic mass. The mass defect is converted to binding energy via E = delta_m × 931.494 MeV/u.
Exemple Résolu
Fe-56: Z=26, N=30, measured mass = 55.9349 u.
- 01Expected mass = 26 × 1.007276 + 30 × 1.008665
- 02Expected = 26.1891 + 30.2600 = 56.4491 u
- 03Mass defect = 56.4491 - 55.9349 = 0.5142 u
- 04BE = 0.5142 × 931.494 = 479.1 MeV
Questions Fréquentes
Why is the mass defect positive?
The nucleus weighs less than its parts. The missing mass has been converted to binding energy that holds the nucleus together. More stable nuclei have larger mass defects per nucleon.
Should I use proton mass or hydrogen atom mass?
If using nuclear masses, use proton mass (1.007276 u). If using atomic masses (which include electrons), use hydrogen mass (1.007825 u) and the electron masses cancel approximately.
What is packing fraction?
Packing fraction = (M - A) / A × 10⁴, where A is the mass number. It measures deviation from whole-number atomic mass. Negative values indicate tighter binding. Fe-56 has the most negative packing fraction.
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