PDK-769
6/26/2001
Impact of Tracking Cutoffs on Electromagnetic Shower
Simulations in Soudan 2
Ben Speakman, Hugh Gallagher
University of Minnesota
The Soudan 2 Monte Carlo simulation tracked electron showers to 1 MeV, due to a limitation in the simulation code EGS(Electron Gamma Shower). This limitation, imposed by the version called EGS3, was lowered to 10 keV with EGS4 in 1985. When a shower is tracked from 1 MeV to 10 keV, the electrons will lose all energy to ionization in steel, with a moderate probability of escaping the steel and ionizing gas to create a hit in a cell where a hit hasn't already occurred. Photons will drop in energy from 1 MeV to 100 keV via Compton scattering, and below 100 keV will be absorbed by the photo-electric effect. These photonic processes will produce numerous electrons with an additional probability of generating a hit.
We sought to quantify this effect computationally, and used EGS4 in a
stand-alone simulation with a simple rectangular geometry. The new
geometry was designed to be as simple as possible, while still matching
the gross charateristics of Soudan 2. Under these new simulations,
we compared the number of hits a given shower energy would produce
when tracked to 1 MeV, to the increase in hits when tracked to 10 keV.
The ratio of the increase in hits to hits at 1 MeV tracking is measured
by the simulation to be 
(statistical error only), and
is found to be independent of shower energy.