  The quantum theory of free Dirac's massive fermions is reconstructed around
the new conserved spin operator and its corresponding position one proposed
initially by Pryce long time ago and re-defined recently with the help of a new
spin symmetry and suitable spectral representations. [I. I. Cot\u{a}escu, Eur.
Phys. J. C (2022) 82:1073]. This approach is generalized here defining the
operator action in passive mode, associating to any integral operator in
configuration representation a pair of integral operators acting directly on
particle and antiparticle wave spinors in momentum representation instead on
the mode spinors. This framework allows an effective quantization procedure
giving a large set of one-particle operators with physical meaning as the spin
and orbital parts of the isometry generators, the Pauli-Lubanski and position
operators or other spin-type operators proposed so far. A special attention is
paid to the operators which mix the particle and antiparticle sectors whose
off-diagonal associated operators have oscillating terms producing
zitterbevegung. The principal operators of this type including the usual
coordinate operator are derived here for the first time. As an application, it
is shown that an apparatus measuring these new observables may prepare and
detect one-particle wave-packets moving uniformly without zitterbewegung or
spin dynamics, spreading in time normally as any other relativistic even
non-relativistic wave-packet.
