Investigation into the aging effect of experiment use on x-ray diode photocathodes, and the calibration of p-i-n silicon diodes

Vacuum x-ray diode photocathodes are commonly employed in temperature diagnostic instruments on the Helen laser at AWE Aldermaston, UK. The photocathodes are used in a Dante filtered x-ray diode spectrometer and in conjunction with a compound x-ray filter to yield a quasi-flat response detector the flat response diode. Investigations carried out in 1999 indicated that the response of these photocathodes diminished over time. Following these investigations [C. D. Bentley and A. C. Simmons, Rev. Sci. Instrum. 72, 1202 (2001)] a number of refurbished photocathodes were produced and the effect of their use in the above instruments investigated. Initial characterization was carried out using the hot cathode Excalibur soft x-ray calibration facility at AWE and at the National Synchrotron Light Source (NSLS) at Brookhaven. Diode sensitivity was remeasured 14 months later again at Brookhaven and at AWE. These results are compared with the earlier study and some degradation in sensitivity is noted. Possible reasons for this change are discussed. Additionally in the latest study the sensitivity of a number of silicon p-i-n diodes was measured at the NSLS and at AWE. The different detector characteristics demand different approaches and these are discussed. Sensitivity results are presented and compared.