1. Scintillation Cube Tests HBD Meeting 3/18/08 A.Caccavano & B.Azmoun, C.Woody

2. 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

3. 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 False zeros Noise-free spectrum

4. 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 = AV kn (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

5. 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) Spectralon2:2.2832.0421.464 Black:2.1852.1161.865 Lucite1:3.0202.9672.247 Lucite2:3.0182.8882.097 Results:

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