  In this paper, which is the first in a series of papers devoted to a detailed
analysis of the death line of radio pulsars, we consider a possibility of
producing secondary particles at a sufficiently long pulsar period P. To this
end, we reconsidered the potential drop necessary for secondary plasma
generation in the inner gap over magnetic polar caps. Our research made it
possible to refine the conditions for generating secondary plasma, such as the
multiplicity of the production of secondary particles and their spatial
distribution. Our research also made it possible to further quantitatively
analyse the dependence of the possibility of secondary plasma generation on all
parameters, including the inclination angle of the magnetic axis to the
rotation axis, the polar cap size and the magnetic field geometry.
