  Since the time of Rutherford it was commonly believed that with no electric
field, the nucleus of an atom is at the centre of the electron cloud, so that
all kinds of atoms do not have permanent electric dipole moment (EDM). In the
fact, the idea is untested hypothesis. Using two special capacitors containing
Sodium vapor we find the electric susceptibility Xe of Na atoms is directly
proportional to its density N, and inversely to the absolute temperature T, as
polar molecules. Xe=A+B/T, where A is approximately to zero, B=126.6 (K) and
N=1.49*1020 m-3. A ground state neutral Na atom has a large permanent EDM: d(
Na)=1.28*10-8e.cm. The non-zero observation of EDM in any non-degenerate system
will be a direct proof of time-reversal violation in nature, and new example of
CP violation occurred in Na atoms. We work out the most linear Stark shift of
Na atoms is only 0.0033nm, and so its linear Stark effect has not been observed
till now! The experimental Na material with purity 0.9995 is supplied by Strem
Chemicals Co. USA. The previous measurements have given d(K), d(Rb) and d(Cs).
These results can be repeated in other laboratories, we welcome anyone who is
interested in the experiments to visit and examine them.
