X-ray Line Flux Density at HRMA Entrance

As described in section 6.2.1 an absolute effective area measurement requires a normalization to the x-ray flux density at the HRMA entrance. For DCM measurements in the 2 to 10 keV range the x-ray beam incident on the HRMA was measured to be non-uniform to approximately the 10% level. We have estimated the incident flux by taking the average of the four BND's at the HRMA location. Higher spectral orders from the DCM are not expected to be present in the 3 to 10 keV range.

For the present reduction of the BND spectra we have chosen a region of interest approach. The extracted x-ray line count rate is divided by the quantum efficiency of the BND at the x-ray line energy. We have assumed the same theoretical quantum efficiency (QE) function for the four BND-H detectors. The quantum efficiency of the BND flow proportional counter for this analysis was based on theoretical calculations assuming a 1 $\mu$m polyimide (C₂₂H₁₀O₄N₂) thick counter window with a density of 1.3 gr cm^-3, a 200 $\AA$ layer of Al, a counter gas of P10 at 400 torr and at 50 F with a gas depth of 2.16 inches. The area of a BND counter at the HRMA location was taken to be 32.3 cm². We have incorporated a correction for mesh obscuration in the BND area.