"Microchannel plates typically show considerable count rate
non-linearities at high fluxes because of local charge extraction.
The MCP has a finite recharge time after an event occurs, and if the
rate is large enough, the local gain can drop so that events are lost
below the lower level discriminator. The HRC-S count rate linearity
(CRL) was determined simply by measuring the detector rate versus the
BND-H rate as the source flux was stepped up. The BND-H rate is
proportional to the incident flux, and should be linear to at least a
few thousand counts per second. The telescope was in focus, and
illuminated a region near the edge of the detector to avoid extracting
a large amount of charge from a central region. A plot of the HRC-S
rate versus one of the BND-H rates is shown in the Figure(Postscript,GIF) (both rates have been
background subtracted). As can be seen from the figure, there is some
marginal evidence for non-linearity at about 15 cts/s. We have made
linear fits to this data, and the statistical significance of this is
low. We conclude that HRC-S is approximately linear at rates of 30
cts/s or less."
(from "Performance and Calibration of the AXAF High Resolution
Camera II: the Spectroscopic Detector"; Kraft, Chappel, Kenter,
Kobayashi, Meehan, Murray, Zombeck, Fraser, Pearson, Lees, Brunton,
Barbera, Collura, & Serio; SPIE 3114, 1997)
Last modified:
09/25/12
