PSR B1133+16: radio emission height and plasma composition

Recent operation of LOFAR by Hassall et al. has produced severe constraints on the size and altitude of the 40 MHz emission region in this pulsar. It is shown that these limits, given a limited number of unexceptionable assumptions, demonstrate that an electron-positron plasma cannot be the source of the emission. A physically acceptable plasma source composed of protons and ions arises naturally in pulsars having positive corotational polar-cap charge density. Acceptance of this would greatly clarify the classification of pulsar types within the whole.