To measure the IPC position resolution, data acquired with the hole pattern obscuring the IPC face is used. For each hole image, the sum of a Gaussian and a quadratic is fit to the binned x and y coordinates. We correct for the finite size of the holes in the hole pattern to find the x or the y position resolution:

where sigmaobs is the standard deviation of the distribution as given by the Gaussian part of the fit and sigmah is equal to one-half of the hole radius (0.125 mm) and is the correction factor for the finite size of the holes.

Figures 5.5-6a to 5.5-6d show the x and y position resolutions averaged over the IPC face vs. x-ray energy. The trend of improving position resolution with increasing energy is apparent for both x and y position resolutions. Figures 5.5-7a to 5.5-7d show the x and y position resolutions averaged over the IPC face vs. Gas Gain. The trend of improving position resolution with increasing Gas Gain is apparent for both x and y position resolutions. Tables 27 to 30 display the data used in producing Figures 5.5-6a to 5.5-6d and 5.5-7a to 5.5-7d.

Figure 5.5-8 shows the corrected images in the low energy window when LE1 and LE2 are illuminated with the palladium anode in the x-ray source. Using the palladium anode provides an x-ray emission excess at 2.84 keV. For each IPC, the images are shown at Gas Gains of 10,000 and 20,000. The image in the low energy window using 2.84 keV x-rays is displayed because IPC position resolution has the largest impact on the polarization sensitivity of the graphite polarimeter.

Table 27: LE1 Position Resolution

Table 28: LE2 Position Resolution

Table 29: HE1 Position Resolution

Table 30: HE2 Position Resolution

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