The ionization Beam Cross section Monitor (BCSM) provides
non-destructive measurements of transverse beam parameters in INR
RAS proton linac. Operation of the monitor is based on utilization
of residual gas ionization. The monitor enables to observe position,
two-dimensional beam cross section, beam profiles obtained from it
and emittance ellipses reconstructed from profiles data as well as
their evolution in real-time within a wide range of energies and
beam intensities. The BCSM design and image processing system are
described. The monitor accuracy and precision analysis and
estimations of influence of the linac radiation background are
discussed. The available experimental results of proton beam
transverse parameters measurements at the linac exit are presented.