21Ne has 10 protons and 11 neutrons.
21Ne is a stable isotope.
The mass excess of 21Ne is -5731.776 with an uncertainty of ±0.038.
The mass was measured using Nuclear Physics and the related equations include:
Influence Equations
100% 20Ne(n,γ)21Ne 1
Reference
1. E Selin (1970), A Nuclear Structure Study of 23Ne and 21Ne by Means of Thermal Neutron Capture in Natural Neon
Physica Scripta 2(4-5)
https://iopscience.iop.org/article/10.1088/0031-8949/2/4-5/008