SCIPP SCIPP Summer Outreach ProjectSummer Outreach Project

July 2005July 2005

Cosmic Ray DetectorsCosmic Ray Detectors

Detector TestingDetector Testing

Muon Lifetime Muon Lifetime ExperimentExperiment

Count Rate AnalysisCount Rate Analysis

Exponential DecayExponential Decay

TopicsTopics

Cosmic Ray DetectorsCosmic Ray Detectors

CCRT from SLACCCRT from SLAC BERKELEY from LBNLBERKELEY from LBNL WALTA from FNALWALTA from FNAL

New Power Supply and HousingNew Power Supply and Housing Detector TestingDetector Testing Tektronix scope interface and decay timesTektronix scope interface and decay times

CCRT from SLACCCRT from SLAC

BERKELEY from LBNLBERKELEY from LBNL

WALTA from FNALWALTA from FNAL

New Power Supply and HousingNew Power Supply and Housing

Detector TestingDetector Testing

Singles & Coincidence RatesPulse shapes, widths, thresholds, and decay times

Detector TestingDetector Testing Three Scintillator detectors: A, B, & CThree Scintillator detectors: A, B, & C

Using 8” x 6” x ½” plastic scintillator, Hammamatsu 931A tubes & HC122-01 basesUsing 8” x 6” x ½” plastic scintillator, Hammamatsu 931A tubes & HC122-01 bases Typical Pulses for CCRT from SLACTypical Pulses for CCRT from SLAC

Output of base: width = 10 ns, amplitude = -300 mVOutput of base: width = 10 ns, amplitude = -300 mV Logic pulse in CCRT: width = 100 ns, amplitude = +4 VLogic pulse in CCRT: width = 100 ns, amplitude = +4 V

Time to stabilize PM Tube: at least 45 minutesTime to stabilize PM Tube: at least 45 minutes Singles rates:Singles rates:

Base input voltage: 6 to 8 VBase input voltage: 6 to 8 V Threshold voltage: 0.1 to 0.7 VThreshold voltage: 0.1 to 0.7 V Optimum Settings: Optimum Settings:

Detector A: Base = 7.00 V, Threshold = 0.30 VDetector A: Base = 7.00 V, Threshold = 0.30 V Detector B: Base = 7.30 V, Threshold = 0.40 VDetector B: Base = 7.30 V, Threshold = 0.40 V Detector C: Base = 6.50 V, Threshold = 0.35 VDetector C: Base = 6.50 V, Threshold = 0.35 V

Singles Count Rates = 30 to 60 counts / minuteSingles Count Rates = 30 to 60 counts / minute

Time to StabilizeTime to StabilizeDetector B, channel 2

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Time since start

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un

ts/2

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Count

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Optimizing Threshold Optimizing Threshold and Base Voltagesand Base Voltages

Detector B, channel 2

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Threshold VoltageC

ount

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CCRT SinglesRates

Detector B, channel 2

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6.4 6.6 6.8 7 7.2 7.4 7.6 7.8 8

Base Voltage

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CCRT Singles Rates

StatisticsStatistics

Detector B, channel 2

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7 7.1 7.2 7.3 7.4 7.5 7.6 7.7

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n

sSampling

n

xxs

n

xx

nn

in

i

:Error

1

)( :Deviation Std

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2

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

Tektronix Scope Interface and Tektronix Scope Interface and Decay TimesDecay Times

Muon Lifetime ExperimentMuon Lifetime Experiment

Muon Lifetime

Experiment

Count Rate AnalysisCount Rate AnalysisMuon 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.

Count Rate AnalysisCount Rate Analysis

A

B

C

D

µ

e

e

µ

µ e- + e + µ

Muon Energy DistributionMuon Energy DistributionMuons 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

Detector/Discriminator SettingsDetector/Discriminator SettingsVA = 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

Detector/Discriminator EfficienciesDetector/Discriminator EfficienciesDetector 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)] =

Possible Timing EventsPossible Timing EventsWhile clock is stopped, A is triggered by: [As ]

1. Random event in A onlyFalse Start

2. Charged particle [N(A) ]

a) Accidental coincidence in AB, AC, or ADMissed Start

b) Misses B, C, or DFalse Start

c). Continues through B, C, or D

d). And is detected -

e). Is not detected False Start

3. Captured in chamberStart

Possible Timing EventsPossible Timing EventsWhile 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 detectedSTOP

Exponential decayExponential decayA 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.

t

tt

tt

eNN

NN

NNN

0

0

021

0

3/1

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2)(