The 55 Fe X-Ray Energy Response of Mercury Cadmium Telluride Near-Infrared Detector Arrays

A technique involving 55 Fe X-rays provides a straightforward method to measure the response of a detector. The detector's response can lead directly to a calculation of the conversion gain (eADU � 1 ), as well as aid detector design and performance studies. We calibrate the 55 Fe X-ray energy response and pair production energy of HgCdTe using 8 HST WFC3 1.7 μm flight grade detectors. The results show that each Kα X-ray generates 2273 � 137 electrons, which corresponds to a pair-production energy of 2:61 � 0:16 eV. The uncertainties are dominated by our knowledge of the conversion gain. In future studies, we plan to eliminate this uncertainty by directly mea- suring conversion gain at very low light levels.