Proton/Neutron/Electron ratio calculation incorrectly accounts for material composition

[austinschneider]

In the SetMaterialModel function, the PNE ratios are computed by examining the PDG particle codes for each isotope in the material which lists the number of baryons and the number of protons. This calculation should account for the relative abundance of each isotope to compute the PNE ratios. However, the current calculation effectively assumes equal abundance between the components in the material.

In practice this does not change the nucleon density used for injection because these numbers are not referenced for nucleon density. However, this bug does result in approximately a 5% overestimation in the electron density, which will in turn affect the injection of Glashow resonance events.

The loop over as material's isotopes is here:

LeptonInjector/private/earthmodel-service/EarthModelService.cxx

Line 1983 in 3d722fb

for (it2 = mats.begin(); it2 != mats.end(); ++it2) {