  Evidence derived with minimal assumptions from existing published
observations is presented to show that an ion-proton plasma is the source of
radio-frequency emission in millisecond and in normal isolated pulsars. There
is no primary involvement of electron-positron pairs. This conclusion has also
been reached by studies of the plasma composition based on well-established
particle-physics processes in neutron stars with positive polar-cap
corotational charge density. This work has been published in a series of papers
which are also summarized here. It is now confirmed by simple analyses of the
observed radio-frequency characteristics, and its implications for the further
study of neutron stars are outlined.
