Download SCIPP Internships 2005

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
Tektronix scope interface and decay times
CCRT from SLAC
BERKELEY from LBNL
WALTA from FNAL
New Power Supply and Housing
Detector Testing
Pulse shapes, widths,
thresholds, and decay times
Singles & Coincidence Rates
Detector Testing

Three Scintillator detectors: A, B, & C

Typical Pulses for CCRT from SLAC
Using 8” x 6” x ½” plastic scintillator, Hammamatsu 931A tubes & HC122-01 bases




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
Time to Stabilize
Detector B, channel 2
180
160
Counts/2min
140
120
100
Count
Avg
80
60
40
20
0
0
20
40
60
80
Tim e since start
100
120
Optimizing Threshold
and Base Voltages
Detector B, channel 2
Detector B, channel 2
1600
500
1200
1000
800
CCRT Singles Rates
600
400
Counts/2min
Counts/2min
1400
400
300
CCRT Singles
Rates
200
100
200
0
0
6.4 6.6 6.8 7 7.2 7.4 7.6 7.8 8
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Base Voltage
Threshold Voltage
Statistics
Detector B, channel 2
350
Mean :
300
x

x
i
n
Counts/2min
250
200
Count
Avg
150
Std Deviation :
sn 
2
(
x

x
)
 i
100
50
0
7
7.1
7.2
7.3
7.4
7.5
7.6
7.7
sn
Sampling Error :  n 
n
Base Voltage
Statistics based on sets of 5 counts after 50 minutes each set to
stabilize the base and tube.
n 1
Tektronix Scope Interface and
Decay Times
Muon Lifetime Experiment
Muon Lifetime
Experiment
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 timeout. 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 Analysis
µ
A
e
B
D
µ
e
C
µ  e- + e + µ
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
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
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)]
=
Possible Timing Events
While clock is stopped, A is triggered by:
1.
[As ]
Random event in A only
False
Charged particle
[N(A) ]
Start
2.
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
3.
d). And is detected
-
e). Is not detected
False Start
Captured in chamber
Start
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
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.
NN ( )
1
0 2
N  N0 3
t
t1 / 3
t
N  N 0e 
t
t1 / 2
 N0 2
