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SCIPP Summer Outreach Project

SCIPP Summer Outreach Project. July 2005. Topics. Cosmic Ray Detectors Detector Testing Muon Lifetime Experiment Count Rate Analysis Exponential Decay. Cosmic Ray Detectors. CCRT from SLAC BERKELEY from LBNL WALTA from FNAL New Power Supply and Housing Detector Testing

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SCIPP Summer Outreach Project

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  1. SCIPP Summer Outreach Project July 2005

  2. Topics • Cosmic Ray Detectors • Detector Testing • Muon Lifetime Experiment • Count Rate Analysis • Exponential Decay

  3. Cosmic Ray Detectors • CCRT from SLAC • BERKELEY from LBNL • WALTA from FNAL • New Power Supply and Housing • Detector Testing • Tektronix scope interface and decay times

  4. CCRT from SLAC

  5. BERKELEY from LBNL

  6. WALTA from FNAL

  7. New Power Supply and Housing

  8. Detector Testing Pulse shapes, widths, thresholds, and decay times Singles & Coincidence Rates

  9. Detector Testing • Three Scintillator detectors: A, B, & CUsing 8” x 6” x ½” plastic scintillator, Hammamatsu 931A tubes & HC122-01 bases • Typical Pulses for CCRT from SLAC • Output of base: width = 10 ns, amplitude = -300 mV • Logic pulse in CCRT: width = 100 ns, amplitude = +4 V • Time to stabilize PM Tube: at least 45 minutes • Singles rates: • Base input voltage: 6 to 8 V • Threshold voltage: 0.1 to 0.7 V • Optimum Settings: • Detector A: Base = 7.00 V, Threshold = 0.30 V • Detector B: Base = 7.30 V, Threshold = 0.40 V • Detector C: Base = 6.50 V, Threshold = 0.35 V • Singles Count Rates = 30 to 60 counts / minute

  10. Time to Stabilize

  11. Optimizing Threshold and Base Voltages

  12. Statistics Statistics based on sets of 5 counts after 50 minutes each set to stabilize the base and tube.

  13. Tektronix Scope Interface and Decay Times

  14. Muon Lifetime Experiment Muon Lifetime Experiment

  15. Count Rate Analysis Muon Lifetime Experiment: Design #1 Area of detectors A-D = 15 x 75 cm2 = 1125 cm2 Area of detector B or C = 30 x 75 cm2 = 2250 cm2 Angle subtended by B or C ≈ /2 = 90 Muon Decay times are measured: Start condition = A and not (B or C) Stop condition = B or C or time-out (20 µs) Once started, the clock continues to run until a stop is triggered or a time-out. Second start signals, while the clock is running, are ignored. A time output is generated only if a stop is triggered before time-out. The Veto output for B or C takes about 30 ns. The input to the logic gate for A should, therefore, be delayed by 30 ns and the data adjusted accordingly.

  16. Count Rate Analysis µ A e B D µ e C µ e-+e+µ

  17. Muon Energy Distribution Muons of all energies: N = Expected flux of muons of any energy ≈ 0.02 Hz/cm2 N(A) = Expected muon count rate through detector A ≈ 18 Hz N (B) = Expected muon count rate through detector B or C ≈ 0.5 N (A) Muons with E < 1 GeV dN/dE = Expected muon count rate per energy ≈ 0.004 Hz/GeV cm2 dE/dx (paper) = energy loss rate for paper and E  50MeV ≈ 1.7 MeV/cm Emax = max. muon energy that can be trapped in the cavity ≈ 40 MeV Emin = min. Electron energy that can escape the cavity ≈ 20 MeV f1 = Fraction of all muons with E < Emax ≈ 0.010 f2 = Fraction of decay electrons with E > Emin ≈ 0.7 Nd = Expected count rate of decays ≈ 0.13 Hz

  18. Detector/Discriminator Settings VA = PM Tube Voltage input for A = V VB = PM Tube Voltage input for B = V VC = PM Tube Voltage input for C = V A = Discriminator pulse width for A = 50 ns B = Discriminator pulse width for B = 50 ns C = Discriminator pulse width for C = 50 ns

  19. Detector/Discriminator Efficiencies Detector A: TA = Threshold voltage = mV SA = Singles rate = Hz CA = Coincidence efficiency [(A and B and C)/(B and C)] = Detector B: TB = Threshold voltage = mV SB = Singles rate = Hz CB = Coincidence efficiency [(A and B and C)/(A and C)] = Detector C: TC = Threshold voltage = mV SC = Singles rate = Hz CC = Coincidence efficiency [(A and B and C)/(A and B)] =

  20. Possible Timing Events • While clock is stopped, A is triggered by: [As ] • Random event in A only False Start • Charged particle [N(A) ] • a) Accidental coincidence in AB, AC, or AD Missed Start • b) Misses B, C, or D False Start • c). Continues through B, C, or D • d). And is detected - • e). Is not detected False Start • Captured in chamber Start

  21. Possible Timing Events • While clock is running • 1. Second Start signal is received • A. Accidental coincidence with False Start [ • B. Captured muon [ • 2. No stop before time-out - • 3. Stop signal • A. Random event in B or C [ • B. Coincidence with second muon [ • C. Coincidence with decay of another muon [ • D. Muon decay detected STOP

  22. Exponential decay A sample of radioactive atoms all have the same probability of decaying. We can say that the rate (atoms / sec) of decay is proportional to the number of atoms. Once this decay event happens the atom is no longer a part of the original population so there are now fewer atoms and therefore a lower rate of decay. If half of the atoms decay in 1 day then half of the remaining atoms will decay in the next day and so on.

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