# Geant4 Simulations of a Scintillator Cosmic-Ray Detector
## 4 Results
### Photons  
The behaviour of photons is more complicated. First of all, the detector is much less sensitive to gamma particles than to muons or electrons. The sensitivity is on a level between 5% to 30% depending on the inclination angles \(\theta\) and \(\phi\). Following the geometrical acceptance of the scintillator, the sensitivity increases with the zenith angle (Figure 13).  
Simulations with different types of shields proved that the sensitivity can be increased by using a thicker and denser shield. A larger distance from the shield to the scintillator or variation in the material between the scintillator and the SiPM has a smaller impact than that in the case of electrons. This is confirmed by the visualisation of the performed simulations in Figure 14 where the spread of the positions of photons is smaller than that for electrons in Figure 10.  
Figure 12: Sensitivity to electrons as a function of their momentum for different values of internal parameters of the device at \(\theta~{}=~{}30^{\circ}\) and \(\phi~{}=~{}45^{\circ}\). 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 \(\eta_{eff}=100\%\cdot A_{eff}(30^{\circ},45^{\circ})/A_{0}\).  
Figure 13: Sensitivity to photons as a function of their momentum for different inclination angles and 1.5 mm steel shielding 3 cm above the detector. The gray histogram shows the distribution of photons in a vertical EAS initiated by 1000 TeV CR protons simulated with CORSIKA.  
As in the case of electrons, the conclusion is that the best option is to use sufficiently thick shielding right above the detector (Figure 15).  
Figure 14: Maps of sensitivity to photons for the shield placed at distances, \(d\), above the scintillator: 0.5 cm (**left**), 3 cm (**middle**), and 6 cm (**right**), respectively. Sensitivity was estimated for photons with \(p\leavevmode\
obreak\ =\leavevmode\
obreak\ 0.012656\leavevmode\
obreak\ \mathrm{GeV}/c^{2}\) for \(\theta\leavevmode\
obreak\ =\leavevmode\
obreak\ 30^{\circ}\) and \(\phi\leavevmode\
obreak\ =\leavevmode\
obreak\ 45^{\circ}\). The 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 15: Sensitivity to photons as a function of their momentum for different shielding configurations at \(\theta\leavevmode\
obreak\ =\leavevmode\
obreak\ 30^{\circ}\) and \(\phi\leavevmode\
obreak\ =\leavevmode\
obreak\ 45^{\circ}\): (**a**) different shields’ materials and thickness, \(z\); (**b**) different distance, \(d\), between the device and 1.5 mm steel shielding. The gray histogram shows distribution of photons in a vertical EAS initiated by 1000 TeV CR protons simulated with CORSIKA.  
Again, 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 16).