Issue # 47 Origin of Nuclear Energy?
A short reminding on ordinary chemical reactions. In a chemical reaction, atoms involved in the reaction do not change, only the way they are combined changes; in other words, only the chemical bonds change during a chemical reaction. The difference between the bond energies in the compounds and the bond energies in the reactant explains why some reactions are exothermic, other endothermic. Since only chemical bonds are concerned, this justifies the Lavoisier’s mass conservation law.
In 1930s, Scientists discovered that the masses of nuclei combined are always less than these nucleons individually.
Example: Helium nucleus (2 p + 2 n)
Mass of 2 protons = 2 x 1.00728 amu = 2.01456 amu
Mass of 2 neutrons = 2 x 1.00867 amu = 2.01734 amu
Expected total mass of nucleons: 4.03190 amu
The observed mass of He-4: 4.0150 amu, causing a mass defect of 0.0304 amu
The origin of that mass defect is due to some of the mass converted into binding energy which binds the nucleons together in the nucleus (Einstein’s Principle of mass-energy equivalence: E = mc2, where m= mass, c = velocity of light).
This explains the origin of high energy generated during Nuclear Fusion and Nuclear Fission reactions, where a part of mass (mass defect) is converted into energy.
Nuclear Fission: n + 235U → 236U → 92Kr + 141Ba + 3n
Nuclear Fusion: 2D + 3T → 4He + n
Although the above nuclear equations seem to show the conservation of mass, in real terms, there is a mass defect in the products, mass defect that has been converted into energy.
The term c2 shows that a small mass loss can cause a large energy loss (or energy release). For example, combustion of one mole of methane (16 g), loses 9.9 x 10-9 g, which is negligible.
In nuclear reaction, this mass change are much greater, 50,000 times greater (4.95 x 10-4g) than methane combustion.
Example: 23892U → 23490Th + 42He
23892U = 238.0003 amu; 23490Th = 233.9942 amu, and 42He = 4.0015 amu
The mass defect : 233.9942 g + 4.0015 g – 238.0003 g = -0.0046 g
E = mc2 = (-0.0046 x 10-3kg)(3.00 x 108 m/s)2 = -0.0414 x 1013 kg.m2/s2= -4.14 x 1011 kg m2/s2 = -4.14 x 1011J