Open questions in x-ray measurement results Marco Rossini Institute - PowerPoint PPT Presentation

Open questions in x-ray measurement results Marco Rossini Institute for Particle Physics, ETH Zürich 26. March 2012 Marco Rossini (ETH) X-ray measurement issues 26. March 2012 1 / 8

Overview ◮ Shift of threshold when doing s-curves under x-ray radiation ◮ Shift in pulse height when under x-ray radiation ◮ Strange behaviour with WBC → 0 Marco Rossini (ETH) X-ray measurement issues 26. March 2012 2 / 8

Threshold shift Measurement and observations: ◮ S-curve test run without x-rays (just a scan varying VCal) [blue] compared to an s-curve test with x-rays on [red] ◮ Noise increases as one would expect ◮ Threshold seems to go up (or VCal weaker) ∼ 100 MHz/cm 2 ∼ 100 MHz/cm 2 Threshold (xray) Noise (xray) Entries Entries 4089 4089 Mean Mean 4.648 4.648 # Pixels # Pixels 1800 RMS RMS 0.6896 0.6896 1200 Entries Entries 4089 4089 Underflow Underflow 0 0 Mean Mean 61.22 61.22 1600 Overflow Overflow 2 2 RMS RMS 1.238 1.238 1000 Integral Integral 4087 4087 1400 Underflow Underflow 0 0 Overflow Overflow 0 0 1200 800 Integral Integral 4089 4089 Xray on 1000 Xray on 600 800 Xray off Xray off 400 600 400 200 200 0 0 52 54 56 58 60 62 64 66 68 70 0 1 2 3 4 5 6 7 8 9 10 Threshold (VCal units) Noise (VCal units) Marco Rossini (ETH) X-ray measurement issues 26. March 2012 3 / 8

Threshold shift Difference in threshold and noise for each pixel: Threshold offset Sigma offset # Pixels # Pixels Entries Entries 4089 4089 Entries Entries 4089 4089 1200 1200 Mean Mean 3.226 3.226 Mean Mean 1.624 1.624 RMS RMS 0.8115 0.8115 RMS RMS 0.7627 0.7627 1000 1000 Underflow Underflow 0 0 Underflow Underflow 0 0 Overflow Overflow 0 0 Overflow Overflow 33 33 Integral Integral 800 4089 4089 800 Integral Integral 4056 4056 600 600 400 400 200 200 0 0 -10 -8 -6 -4 -2 0 2 4 6 8 10 -5 -4 -3 -2 -1 0 1 2 3 4 5 Threshold difference (VCal units) Noise difference (VCal units) Marco Rossini (ETH) X-ray measurement issues 26. March 2012 4 / 8

Pulse height shift Measurement: ◮ High rate pixel map with additional calibrate signal into one pixel ◮ With [red] and without x-rays [blue] ◮ Pulse height for all pixels is stored in a histogram ◮ Pulse height (gain) calibration used to convert to VCal units VCal = 60 VCal = 200 Xray on Xray on Xray off Xray off Marco Rossini (ETH) X-ray measurement issues 26. March 2012 5 / 8

Pulse height shift Rate dependence (Xray: green = off, red = 2 mA, blue = 80 mA): 100 MHz/cm 2 Marco Rossini (ETH) X-ray measurement issues 26. March 2012 6 / 8

Strange WBC behaviour Setting WBC to insensible values produces results nonetheless. ◮ Even WBC = 0 works ◮ Rate does not depend on WBC (at low rate) ◮ Pixel decoding errors occur below WBC = 20 and their rate increases toward WBC = 0 Pixel hit map module (double edge) Pixel hit map module (double edge) 35 80 80 35 70 70 30 30 60 60 25 25 50 50 40 40 20 20 30 30 15 15 20 20 10 10 10 10 0 5 0 0 10 20 30 40 50 0 10 20 30 40 50 WBC = 1 WBC = 100 Marco Rossini (ETH) X-ray measurement issues 26. March 2012 7 / 8

Strange WBC behaviour Marco Rossini (ETH) X-ray measurement issues 26. March 2012 8 / 8