In a second estimate, we recorded the flu screen current readout obtained when exposed to the parallel beam at each setting. These current readings (in amperes) were divided by the charge of an electron (1.602 x 10 -19 C) and the size of the illuminated area (in Å 2 ) from each trial to achieve measures of flux density in e-/Å 2 /s. These were determined as 0.0252 e-/Å 2 /s for spot size 9 and 0.0147 e-/Å 2 /s for spot size 10. The screen current readout at spot size 11 was below the threshold of detection and read out as 0 nA. For this report, we use flux and fluence values as measured by the Apollo detector.