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→SiPM Performance Requirements
consisting of a several cm long scintillating fiber connected to a clear acrylic fiber
consisting of a several cm long scintillating fiber connected to a clear acrylic fiber
light guide.
light guide.
A tagging electron travels axially down the length of a scintillating fiber depositing 4 MeV of energy in the fiber,
A tagging electron travels axially down the length of a scintillating fiber depositing an average of 4 MeV of energy in the fiber,
resulting in 1600 scintillation photons within the forward capture cone of
resulting in ~1600 scintillation photons within the forward capture cone of
the fiber. Assuming that 80% of these are delivered to the SiPM active
the fiber. Assuming that 80% of these are delivered to the SiPM active
surface and a conservative estimate of 15% for the efficiency of the SiPM
surface and a conservative estimate of 15% for the efficiency of the SiPM
with the above number of photons still yields a signal of 130 photons. However,
with the above number of photons still yields a signal of 130 photons. However,
given that the scintillator ([http://www.detectors.saint-gobain.com/Media/Documents/S0000000000000001004/SGC%20Scintillating%20Optical%20Fibers%20Brochure%20605.pdf BCF-20])
given that the scintillator ([http://www.detectors.saint-gobain.com/Media/Documents/S0000000000000001004/SGC%20Scintillating%20Optical%20Fibers%20Brochure%20605.pdf BCF-20])
has a finite decay time (2.7ns) the more photons are produced the more clearly resolved is the time of the pulse.
has a finite decay time (2.7ns) the more photons are produced the more clearly resolved is the leading-edge time of the pulse.
The device is expected to have a high enough gain (measured in electrons per photon detected) - around 10<sup>6</sup>. in order for such a small light signal to be recorded by conventional electronics. Such devices are also susceptible to spurious, thermally excited pixel breakdowns, each showing up as a single photon hit ("dark count"). High rate of these single-pixel events may create a pileup above the signal threshold. All of the above parameters (detection efficiency, gain and "dark rate") depend on applied bias voltage and temperature. Stability of performance despite expected fluctuations of these variables is an important requirement.
The device is expected to have a high enough gain (measured in electrons per photon detected) - around 10<sup>6</sup> in order for such a small light signal to be recorded by conventional electronics. SiPM devices are also susceptible to spurious, thermally excited pixel breakdowns, each showing up as a single photon hit ("dark count"). Very high rates of these single-pixel events may create pileup above the signal threshold. All of the above parameters (detection efficiency, gain and dark rate) depend on applied bias voltage and temperature. Stability of performance within the expected fluctuations of these environmental variables is an important requirement.
Another criterion in SiPM selection is its dynamic range. Although this readout device essentially provides digital output - scintillation detected or not - enough of a range is necessary to set a threshold above the noise floor and to account for some pixels being not having required from a previous hit .
Another criterion in SiPM selection is its dynamic range. Although the tagger essentially provides digital information - scintillation detected or not in each energy channel within each beam bucket - sufficient range is necessary to set a threshold above the noise floor and to allow for some degree of gain variation at high rates arising from the finite pixel recovery time.
= Bench Test Setup =
= Bench Test Setup =