Scintillation Cube Tests

HBD Meeting 3/18/08A.Caccavano & B.Azmoun, C.Woody

•Number of photoelectrons calculated by finding the probability of zeros in pulse height spectrum: #pe’s=-ln(P(0))

•Done using two methods:

•Calculating ratio of areas using fits

•Directly counting number of events in zero bins and dividing by total number of counts.

Calculating Photoelectron Yield

Black: PMT R6835-90 Sig. through PA6 2-25-08

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Black: SBD Sig. 2-25-08

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ts•SBD signal shows true alpha hits and false zeros from noise.

•By taking the ratio of these false hits to actual counts, one can correct for false zeros in PMT signal.

•All data corrected for “noisy” zeros.

Corrections

Lucite2: PMT R6835-90 Sig. through PA6 3-13-08

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False zeros

Noise-free spectrum

•Calculated #pe’s using arithmetic mean of pulse height spectrum in mV, the Pre-amp calib. and the measured PMT gain.

•PMT gain follows power law: G = AVkn (assuming 100% coll. eff.)

•A=characteristic constant, V=supply voltage, k=dynode dep. constant,

n=# stages.

•At 1600V,

Gain=146400

Alternate Calculation of pe Yield

Cube#pe’s (zero-

method, using areas under fits)

#pe’s (zero-method, counting

bins directly)

#pe’s (using arith. mean, PA calib & PMT

gain)

Spectralon2: 2.283 2.042 1.464

Black: 2.185 2.116 1.865

Lucite1: 3.020 2.967 2.247

Lucite2: 3.018 2.888 2.097

Results:

•First lucite cube showed no significant increase in photoelectron yield over black cube thought to be due to thin aluminum deposition.

•Second lucite cube with thicker deposition showed no improvement.

•Geometry not optimal?

•Next iteration will have a plane mirror closer to the extended light source.

•Reflectance of aluminum at 160nm is 70-85%

Summary

Light Intensity vs Number of Reflections

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85%

70%

•Geometry of cube cavity is critical if a substantial number of photons undergo 10 or more reflections they are lost.