Increasing the gain resulted in a linear increase of peak position. The resolution is observed to increase quadratically with gain. These relationships are outlined in Figure 2.
Voltage caused a exponential shift in peak position, whilst the resolution was recorded to increase in a linear manner with respect to PMT voltage. Figure 3 shows this trend.
The complete spectrum for each isotope can be found in Apenndix A of this report. The interpretation of each spectrum is as follows.
The attenuation coefficients of each material with respect to the gamma-ray energy is shown in Figures 4-7 for lead, steel, aluminium and polyethylene. Reference data for each material was also plotted \cite{Kumar_1997}. Some measurements did not provide reliable values as the source was either completely attenuated or not affected by the thickness of material. These cases were disregarded to maintain a result which coincided with recordings of attenuated gamma-rays from the source.
Results of the attenuation coefficients were processed by dividing the attenuation by the density of the material. This is shown in Figures 4-7.
An assumption was applied: each attenuating material was treated as if it were comprised of its majority elemental composition. This results in Lead, aluminium, steel and polyethylene being treated as pure lead, pure aluminium, iron and carbon respectively. Plots of the attenuation coefficients are shown in Figures 8 and 9.