1. In Current Science, The SI atomic mass unit (amu) is based on 1/12th of the mass of a C-12 atom, approximately equal to 1.660 538 921 x 10-27 kg. With this standard the relative mass of a neutron is equal to 1.008 666 amu.
2. In Neu Theory, by definition sets the neutron equal to 1.000 000 amu. The Neu Theory amu is called the neu (neutron equivalent unit) and its measured value is approximately equal to 1.674 929 351 x 10-27 kg of atomic mass. See neu mole.
- In principle, the neu is an absolute unit – a precise invariant quantity – numerically equal to exactly one unit of mass. In practice, the value of the neu in kilograms can only be approximated, because the mass of the neutron is so small, and the kilogram is based on a much larger physical artifact.
- The neu is slightly larger than the C-12 amu representing an increase in relative mass value of approximately 0.8666 %. The atomic masses of the natural isotopes are now compared to the neu quantity with a corresponding decrease in relative mass value of approximately 0.8592 % as compared to the C-12 value. The absolute neu value of C-12 is 11.896 901 instead of 12.000000. The Neu Mass & Charge Radii Table gives the starting C-12 and the reworked neu mass value of selected isotopes.
- It should be emphasized that actual measured mass of atoms in kilograms and the equivalent energy value in joules, electron volts, or any other unit, is not changed in the slightest by using a neutron amu. The numerically smaller neu mass value of an isotope is exactly balanced by the numerically larger neu mass unit giving us precisely the same quantity of mass expressed in kilograms, that we had before.
- The reason the neu is so useful is that it allows mass and energy to be counted with the same numeric scale, and allows us in principle to estimate the ratio of matter to energy in the cosmos.