• 900 V
  • LaBr3_900V_UG_Am_20240801_094057.root → 1 min, threshold too high, visible some gamma and alpha peak?
  • LaBr3_900V_UG_Th_20240801_094933.root → 1 min, 10 RMS threshold, visible several peaks. I suspect the upper region are mostly alphas (different Chi2)
  • LaBr3_900V_UG_Am_20240801_101756.root → 1 min, 5 RMS threshold, the 59 keV peak from Am should be the one on the very left, before the continuum.
  • LaBr3_900V_UG_bkg_20240801_102059.root → 1 min, 5 RMS threshold. The peak on the very left is not visible anymore. Very large peak in the middle of the spectrum, with a resolution of 1.16% (sigma). Maybe 40K?
• 950 V
  • LaBr3_950V_UG_bkg_20240801_102506.root → 1 min, 5 RMS threshold. Resolution of the unknown peak: 1.04% (sigma).
  • LaBr3_950V_UG_Am_20240801_103450.root → 1 min, 5 RMS threshold. 59 keV peak from 241Am visible on the left of the spectrum. At this point the unknown peak could be the 662keV peak from 137Cs, even though I have the suspicion the response is non-linear.
  • LaBr3_950V_UG_Th_20240801_104540.root and LaBr3_950V_UG_Th_20240801_105223.root –> 1 min, first run with “unshielded” source, second run with source embedded in few mm thick lead layer. Unclear how to interpret the spectrum.
• 1000 V
  • LaBr3_1000V_UG_bkg_20240801_105721.root → 1 min, 5 RMS threshold. Resolution of unknown peak: 0.99% (sigma).
  • LaBr3_1000V_UG_Am_20240801_110337.root → 1 min, 5 RMS threshold. 59 keV gamma from 241Am clearly visible.
  • LaBr3_1000V_UG_Th_20240801_111101.root → 10 min, 5 RMS threshold.
• 1050 V
  • LaBr3_1050V_UG_bkg_20240801_112617.root → 1 min, 5 RMS threshold. Resolution on unknown peak: 0.84% (sigma)
• 1100 V
  • LaBr3_1100V_UG_bkg_20240801_113554.root → 1 min, 5 RMS threshold. Resolution on unknown peak: 0.81% (sigma)
• 1150 V
  • LaBr3_1150V_UG_bkg_20240801_113948.root → 1 min, 5 RMS threshold. Resolution on unknown peak: 0.81% (sigma)
• 1200 V
  • LaBr3_1200V_UG_bkg_20240801_114335.root → 1 min, 5 RMS threshold. Resolution on unknown peak: 0.77% (sigma)

Since the PMT seems to saturate even at 900 V, let's do another HV scan down to lower voltage.

• 900 V
  • LaBr3_900V_UG_Th_20240820_153224.root –> 2 min, 10 RMS threshold.
• 850 V
  • LaBr3_850V_UG_Th_20240820_155012.root –> 2 min, 10 RMS threshold.

Detector re-assembled to try making a precision measurement of the 215Po half-life using the delayed coincidence technique.

Detector parameters:

• PMT H2431 attached with optical grease and tape to the crystal. Black box made with (used) trash bag.
• HV: 1250 V, so that we have a good signal-to-noise ratio without saturating the alpha events.
• Threshold: 50 rms for the calibration, 650 rms for the background data, corresponding to roughly 1200 keV.
• Detector placed in a lead castle of >=5 cm thickness in all directions.
• Acquisition windows of 400 ns length with ~100 ns pretrigger to minimize disk-space usage.

Acquired data:

• 232Th calibration run, 10 min long, threshold ~80 keV, file LaBr3_H2431_1250V_UG_232Th_20241126_170543.root
• Background data, 12 hr long, threshold ~1200 keV, files from LaBr3_H2431_1250V_UG_bkg_20241126_180924.root to …

Processed data:

• Available in /data/Reconstructed_LaBr3/
• To plot PSD vs integral: global→Draw(“chi2_poweraverage.amplitude/integral:integral»(1000,,,1000)”,“fabs(slope)<1.e8 && delay>8.5e-8 && delay<1.15e-7”,“colz”)