Dead-time correction and I0 normalization in germanium solid-state detector systems using an incoming count rate monitor (abstract)

Abstract

The rate limitation of a photon counting germanium solid-state detector system is largely determined by the shaping time of the amplifier, which is in turn set by the required system resolution. This rate limitation arises because when an event passes into the shaping amplifier, it is paralyzed for a time referred to as the dead time, which is a function of the shaping time. If any further events pass into the shaping amplifier during this time, one or both events may be corrupted or lost. This phenomenon is known as pulse pileup. However, if one uses an incident count rate monitor (ICR) which gives an accurate indication of the incident photon rate but no energy information, one can correct for any pulses lost in the shaping amplifier due to pileup. This allows one to run the detector system at higher rates and still retain throughput linearity. This has been shown by the work of Zhang et al. The authors also showed that with respect to EXAFS, the loss of linearity due to pulse pileup at high rates has two main effects: (1) The EXAFS oscillations and edge step height are reduced and (2) noise and glitches present in I0 do not normalize out. This work has been extended to higher input count rates and in addition to using the paralyzable model to correct for the loss of throughput linearity as the input rate increases, was also used the ICR monitor to give an I0 value which when itself corrected can give improvements over an ion chamber I0 in normalizing noise and glitches out. Data has been taken with station 9.3 on the SRS at Daresbury Laboratory using 18 mM CuNO3 solution at ICR values of 20, 47, 84, 120, and 180 kHz. In addition, data has also been taken for 0.02 at. % As implanted to 1 μm depth in a-Si using reflexafs. This data was collected at 120 kHz as opposed to the usual 40 kHz and normalized using these techniques. It will be shown using this data that using pileup correction and an ICR I0, the linearity of the system can be retained at higher count rates and thus significant improvements in the signal-to-noise ratio can be gained.