  High energy particle showers produce coherent Cherenkov radio emission in
dense, radio-transparent media such as cold ice. Using PYTHIA and GEANT
simulation tools, we make a comparative study among electromagnetic (EM) and
hadronic showers initiated by single particles and neutrino showers initiated
by multiple particles produced at the neutrino-nucleon event vertex. We include
all the physics processes and do a complete 3-D simulation up to 100 TeV for
all showers and to 1 PeV for electron and neutrino induced showers. We
calculate the radio pulses for energies between 100 GeV and 1 PeV and find
hadron showers, and consequently neutrino showers, are not as efficient below 1
PeV at producing radio pulses as the electromagnetic showers. The agreement
improves as energy increases, however, and by a PeV and above the difference
disappears. By looking at the 3-D structure of the showers in time, we show
that the hadronic showers are not as compact as the EM showers and hence the
radiation is not as coherent as EM shower emission at the same frequency. We
show that the ratio of emitted pulse strength to shower tracklength is a
function only of a single, coherence parameter, independent of species and
energy of initiating particle.
