# Geant4 Simulations of a Scintillator Cosmic-Ray Detector
## 4 Results
### Electrons  
Sensitivity to electrons, as expected, is also very high at large momenta, but for the standard setup it drops to 0 for \(p\) less than the limit of terrestrial background equal to 0.03 GeV as the low-momentum electrons are stopped in the shield (Figure 9).  
The value of momentum at which this decrease in the sensitivity starts depends on the zenith angle of electrons. At greater angles the effective thickness of the shield is larger; thus, electrons with higher momenta are also stopped in it. The presence of the shield leads also to another effect. The electrons passing through it undergo multiple scattering which is most significant at low momenta and, in addition, may interact by knocking other electrons or emit photons.  
The scattering means that some electrons may miss the scintillator, but on the other hand some of those that are not expected to be detected are registered. The net effect is a decrease in sensitivity. On the other hand, the additional particles created in the shield may reach the scintillator and produce a signal even if an electron passes so far that it has no chance to be directly registered, as can be seen in Figure 10.  
Figure 10: A presentation of sensitivity to electrons for the shield placed at different distances, \(d\), above the scintillator: 0.5 cm (**left**), 3 cm (**middle**), and 6 cm (**right**). Sensitivity was estimated for electrons with \(p~{}=~{}0.012656\) GeV/c\({}^{2}\) for \(\theta~{}=~{}30^{\circ}\) and \(\phi~{}=~{}45^{\circ}\). Value of each point was calculated from a beam of 100 particles aiming at the \(x\) and \(y\) coordinates of a plane placed on the top of the scintillator. Dotted lines represent the border of the scintillator while the solid square indicates position of the SiPM. The black arrow shows the direction of the primary cosmic-ray particle.  
Figure 9: Sensitivity to electrons as function of their momentum for different inclination angles and 1.5 mm steel shielding 3 cm above detector. Gray histogram shows distribution of electrons in vertical EAS initiated by 1000 TeV CR protons simulated with CORSIKA. Different horizontal lines represent \(\eta_{eff}=100\%\cdot A_{eff}(\theta,\phi)/A_{0}\).  
The larger is the distance of the shield from the scintillator is, the more distant electrons have a chance to be indirectly detected. This, in the case of detector array with sensors placed very close, may cause false double-signal events from a single electron. To reduce this effect the shielding should be placed as close as possible to the scintillators. The results presented in Figure 11 suggest that shielding to provide the best signal-to-noise ratio for electrons should be a dense metal plate thicker than 1 mm.  
As for muons, the only internal parameters of the device that have a significant impact on effective sensitivity are the reflectivity of the aluminium coating and the type of medium between the scintillator and the SiPM (Figure 12).  
Figure 11: Sensitivity to electrons as a function of their momentum for different shielding configurations at \(\theta\ =\ 30^{\circ}\) and \(\phi\ =\ 45^{\circ}\): (**a**) different shields’ materials and thickness, \(z\); (**b**) different distances, \(d\), between the device and 1.5 mm steel shielding. The gray histogram shows the distribution of electrons in a vertical EAS initiated by 1000 TeV CR protons simulated with CORSIKA. The red dashed horizontal line represents \(\eta_{eff}=100\%\cdot A_{eff}(30^{\circ},45^{\circ})/A_{0}\).