Abstract-Electron Multiplying Charge-Coupled Devices (EMCCDs) are used in low-light-level (L3) applications for detecting optical, Ultra-Violet (UV) and Near Infra-Red (NIR) photons (10 nm to 1100 nm). The on-chip gain process is able to increase the detectability of any signal collected by the device through the multiplication of the signal before the output node, thus the effective read-out noise can be reduced to sub-electron levels, allowing the detection of single photons; however, this gain process introduces an additional noise component due to the stochastic nature of the multiplication. In optical applications this additional noise has been characterised. The broadening of the detected peak is described by the Excess Noise Factor. This factor tends to a value of √ 2 at high gain (>100x). In X-ray applications the situation is improved by the effect the Fano factor, f , has on the shot noise associated with X-ray photon detection (f ≈ 0.12 at X-ray energies). In this paper the effect of the detection of X-ray photons in silicon is assessed both analytically and through a Monte Carlo model of the gain amplification process. The Excess Noise on the signal is predicted (termed the Modified Fano Factor) for photon detection in an EM-CCD at X-ray energies. A hypothesis is made that the Modified Fano Factor should tend to 1.115 at high levels of gain (>10x). In order to validate the predictions made, measurements were taken using an 55 Fe source with Mn k-alpha X-ray energy of 5898 eV. These measurements allowed the hypothesis to be verified.
Abstract-The use of EM-CCDs for high resolution soft Xray spectroscopy has been proposed in previous studies and the analysis that followed identified and verified experimentally a Modified Fano Factor for X-ray detection using an 55 Fe X-ray source. However, further experiments with soft X-rays at 1000 eV were less successful, attributed to excessive split events. More recently, through the use of a deep depletion e2v CCD220 and on-chip binning, it was possible to greatly reduce the number of split events allowing the result for the Modified Fano Factor at soft X-ray energies to be verified. This paper looks at the earlier attempt to verify the Modified Fano Factor at 1000 eV with a e2v CCD97 and shows the issues created by the splitting of the charge cloud between pixels. It then compares these earlier results with new data collected using the e2v CCD220, investigating how split event reduction allows the Modified Fano Factor to be verified for low energy X-rays.
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