Figure 5.

Using a source with $\text{HVL}=3.02\text{\hspace{0.5em}mm\hspace{0.5em}Al}$, $\text{kV}=72.59$, the spectra for alternative additive filtrations are shown. The spectrum with added filtration 21 mm of aluminum (Type 1090, 99.9%) is shown as a solid line. The spectrum with added filtration of 0.5 mm of copper plus 2.8 mm of aluminum (Type 1100) is shown as points. The points have been reduced by a factor of 0.514 to produce the same exposure (mR) as the line. Both spectra have HVL=6.80.