Changes

== SiPM Measurements ==

== SiPM Measurements ==

[[Image:PhotonPeaks_SSPM05.png|frame|Illustration of discrete peaks seen in the collected SiPM charge frequency histogram. The first peak shows the number of events in which no photons were detected, the next shows one and so forth. Note the even spacing of the peaks, showing the linearity of the device.]]

[[Image:PhotonPeaks_SSPM05.png|frame|Illustration of discrete peaks seen in the collected SiPM charge frequency histogram. The first peak shows the number of events in which no photons were detected, the next shows one and so forth. Note the even spacing of the peaks, showing the linearity of the device.]]

This procedure is repeated with the LED and/or SiPM covered to measure the dark rate. Depending on which distribution showed the photon peaks more distinctly, either the illuminated or dark datasets were used for the gain calculation and pedestal calculation. Either way, a mean was extracted from the dark distribution to calculate the dark rate and to subtract the average dark pixel count measured from the average pixel count measured while illuminated.

This procedure is repeated with the LED and/or SiPM covered to measure the dark rate. Depending on which distribution showed the photon peaks more distinctly, either the illuminated or dark datasets were used for the gain calculation and pedestal calculation. Either way, a mean was extracted from the dark distribution to calculate the dark rate and to subtract the average dark pixel count measured from the average pixel count measured while illuminated.

Below is the summary of results obtained from these measurements performed on the two SiPMs acquired from Photonique.

Below is the summary of results obtained from these measurements performed on the two SiPMs acquired from Photonique.

| 1.5×10⁵ || 2.5×10⁵ || 27% || 20-23% || 15 MHz || 8.9 MHz

| 1.5×10⁵ || 2.5×10⁵ || 27% || 20-23% || 15 MHz || 8.9 MHz

|}

|}

Since the SiPM performance is sensitive to the bias voltage applied and the ambient temperature, a measurement SiPM properties as functions of bias voltage (V_b) and temperature (T) was performed on the SSPM-06~. (By this point, the SSPM-06~ was judged to a better sensor for the tagger microscope, owing to higher sensitivity in the blue-green range and better active area match to the fiber cross-section.  Aside from gains in efficiency and dynamic range of the resulting readout, higher photon detection implies higher time resolution because of the scintillation decay time of 2.7ns in the fiber.)

Since the SiPM performance is sensitive to the bias voltage applied and the ambient temperature, a measurement SiPM properties as functions of bias voltage (V_b) and temperature (T) was performed on the SSPM-06~. (By this point, the SSPM-06~ was judged to a better sensor for the tagger microscope, owing to higher sensitivity in the blue-green range and better active area match to the fiber cross-section.  Aside from gains in efficiency and dynamic range of the resulting readout, higher photon detection implies higher time resolution because of the scintillation decay time of 2.7ns in the fiber.)

* T: 0-above room temp., in practice 3°C (to avoid growing snow) to 25°C

* T: 0-above room temp., in practice 3°C (to avoid growing snow) to 25°C

However, it was found that the peaks were very indistinct by at bias voltages below 20V and temperatures above 20°C. This was probably due to the narrowing of the peaks due to smaller gain or convolution of the additional dark counts detected. The solution to this was to abandon the manual location of pedestals, peak spacing etc. Instead, a model was created by Prof. Richard Jones based on which fitting of the histograms was performed. It has the form:

However, it was found that the peaks were very indistinct by at bias voltages below 20V and temperatures above 20°C. This was probably due to the narrowing of the peaks due to smaller gain or convolution of the additional dark counts detected.  

 

 

The solution to this was to abandon the manual location of pedestals, peak spacing etc. Instead, a model was created by Prof. Richard Jones based on which fitting of the histograms was performed. It has the form:

<math>

<math>

Now, with this powerful instrument at hand used with a fitter in Paw, the histograms collected as function of T and V_b were analyzed. It turned out that even histograms with nearly indistinguishable peaks  yielded a best fit to this model and suggested the appropriate gain and other parameters.

Now, with this powerful instrument at hand used with a fitter in Paw, the histograms collected as function of T and V_b were analyzed. It turned out that even histograms with nearly indistinguishable peaks  yielded a best fit to this model and suggested the appropriate gain and other parameters.

Below is the analyzed data on dark rate, gain and photon detection efficiency (PDE) as function of T and V_b. An attempt was also made at mapping the rate of secondaries (multi-Poisson parameter) as a function of these variables but small trends perceived in the data were within the parameter's error bars.

Below is the analyzed data on dark rate, gain and photon detection efficiency (PDE) as function of T and V_b. An attempt was also made at mapping the rate of secondaries (multi-Poisson parameter) as a function of these variables but small trends perceived in the data were within the parameter's error bars.