3he ionization chambers as neutron beam flux monitors for...
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Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
3He Ionization Chambers as Neutron Beam
Flux Monitors for the NPDGamma
Experiment
Chad Gillis
Indiana University NSERC Canada
APS DNP MeetingNashville, Tennessee
October 2006
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma ExperimentA precision measurement of the coupling constant for weak pion exchangebetween nucleons
ReactionThe NPDGamma
+
p
d
+n
(2.2 MeV)
γ800 MeV Linactarget
strikes production Pulsed (20 Hz) proton beam
Cold (meV) neutrons from LH moderator2
The Los Alamos Neutron Science Center
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma Apparatus
beampolarizer
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
M3
spinflipper
pulsed coldneutrons
20 Hz
gamma detectors
2
targetLH
M1 M2
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma Apparatus
beampolarizer
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
M3
spinflipper
pulsed coldneutrons
20 Hz
gamma detectors
2
targetLH
M1 M2
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma Apparatus
beampolarizer
gamma detectors
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
spinflipper
pulsed coldneutrons
20 Hz
M3
2
targetLH
M1 M2
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma Apparatus
gamma detectors
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
M3
spinflipper
pulsed coldneutrons
20 Hz
beampolarizer
2
targetLH
M1 M2
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma Apparatus
beampolarizer
gamma detectors
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
M3
spinflipper
pulsed coldneutrons
20 Hz
2
targetLH
M1 M2
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma Apparatus
beampolarizer
gamma detectors
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
M3
spinflipper
pulsed coldneutrons
20 Hz
2
targetLH
M1 M2
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma Apparatus
beampolarizer
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
M3
spinflipper
pulsed coldneutrons
20 Hz
gamma detectors
2
targetLH
M1 M2
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The NPDGamma Apparatus
beampolarizer
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
M3
spinflipper
pulsed coldneutrons
20 Hz
gamma detectors
2
targetLH
M1 M2
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
A Gamma Asymmetry Measurement
A Pn =1
cos()
[N() N( + )]
[N() + N( + )]
A = gamma asymmetryPn= beam polarization
Pn> 0
nn
n nnn nn
nn
n nn
CsI
nn
n
2LH
pp
pp
ppp
p
p
p
p
pppp
pp
p
π + θ
θ
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
A Gamma Asymmetry Measurement
A Pn =1
cos()
[N( + ) N()]
[N( + ) + N()]
A = gamma asymmetryPn= beam polarization
Pn< 0
n nn
CsI
nnnn
n
2LH
pp
p
ppp
p
p
p
p
pp
p
p
π + θ
θ
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
A Gamma Asymmetry Measurement
A Pn =1
cos()
[N( + ) N()]
[N( + ) + N()]
A = gamma asymmetryPn= beam polarization
Pn< 0
n nn
CsI
nnnn
n
2LH
pp
p
ppp
p
p
p
p
pp
p
p
π + θ
θ
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The Beam Monitors
I Ionization chambers containing 3He, 4He, N2.
I Function by application of a high voltage.
I Placed directly in the beam.
I Run in current mode.
I Output current signal depends only on neutron energy and
incident neutron rate
I Very low noise
hellooo
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The Beam Monitors
I Ionization chambers containing 3He, 4He, N2.
I Function by application of a high voltage.
I Placed directly in the beam.
I Run in current mode.
I Output current signal depends only on neutron energy and
incident neutron rate
I Very low noise
hellooo
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The Beam Monitors
I Ionization chambers containing 3He, 4He, N2.
I Function by application of a high voltage.
I Placed directly in the beam.
I Run in current mode.
I Output current signal depends only on neutron energy and
incident neutron rate
I Very low noise
hellooo
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The Beam Monitors
I Ionization chambers containing 3He, 4He, N2.
I Function by application of a high voltage.
I Placed directly in the beam.
I Run in current mode.
I Output current signal depends only on neutron energy and
incident neutron rate
I Very low noise
hellooo
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The Beam Monitors
I Ionization chambers containing 3He, 4He, N2.
I Function by application of a high voltage.
I Placed directly in the beam.
I Run in current mode.
I Output current signal depends only on neutron energy and
incident neutron rate
I Very low noise
hellooo
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The Beam Monitors
I Ionization chambers containing 3He, 4He, N2.
I Function by application of a high voltage.
I Placed directly in the beam.
I Run in current mode.
I Output current signal depends only on neutron energy and
incident neutron rate
I Very low noise
hellooo
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The Beam Monitors
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The n + 3He reaction
I To detect low energy neutrons, use an exothermicreaction that produces charged particles.
n + 3He p + t + 764 keV
He4
Jπ 0+=
Jπ 0+=
0.5 MeV wide
20.6 MeV
energy
0 MeV
ground state
20.2 MeV
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The n + 3He reaction
I Dominated by: n + 3He ! p + t+ 764 keV KE
I Cross section is huge and has a very clean energy dependence.
I Products do not leave the chamber.
I Gas can be mixed to produce required attenuation and response.
I Response to gamma background is negligible.
10-2
10-1
100
101
102
103
104
105
106
10-6 10-4 10-2 100 102 104 106 108
Cross Sectionbarns
neutron energy E (eV)
/ 1pE/ tof
! energy range
of interest
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The n + 3He reaction
I Dominated by: n + 3He ! p + t+ 764 keV KE
I Cross section is huge and has a very clean energy dependence.
I Products do not leave the chamber.
I Gas can be mixed to produce required attenuation and response.
I Response to gamma background is negligible.
10-2
10-1
100
101
102
103
104
105
106
10-6 10-4 10-2 100 102 104 106 108
Cross Sectionbarns
neutron energy E (eV)
/ 1pE/ tof
! energy range
of interest
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The n + 3He reaction
I Dominated by: n + 3He ! p + t+ 764 keV KE
I Cross section is huge and has a very clean energy dependence.
I Products do not leave the chamber.
I Gas can be mixed to produce required attenuation and response.
I Response to gamma background is negligible.
10-2
10-1
100
101
102
103
104
105
106
10-6 10-4 10-2 100 102 104 106 108
Cross Sectionbarns
neutron energy E (eV)
/ 1pE/ tof
! energy range
of interest
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The n + 3He reaction
I Dominated by: n + 3He ! p + t+ 764 keV KE
I Cross section is huge and has a very clean energy dependence.
I Products do not leave the chamber.
I Gas can be mixed to produce required attenuation and response.
I Response to gamma background is negligible.
10-2
10-1
100
101
102
103
104
105
106
10-6 10-4 10-2 100 102 104 106 108
Cross Sectionbarns
neutron energy E (eV)
/ 1pE/ tof
! energy range
of interest
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
The n + 3He reaction
I Dominated by: n + 3He ! p + t+ 764 keV KE
I Cross section is huge and has a very clean energy dependence.
I Products do not leave the chamber.
I Gas can be mixed to produce required attenuation and response.
I Response to gamma background is negligible.
10-2
10-1
100
101
102
103
104
105
106
10-6 10-4 10-2 100 102 104 106 108
Cross Sectionbarns
neutron energy E (eV)
/ 1pE/ tof
! energy range
of interest
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Workings of the Beam Monitors
p
t
voltage signal
I
0.5 cmtriton recoil
neutron beam
proton recoil1.6 cm
HVHV
V
R = 5−350 MΩ
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
Source is pulsed at 20 Hz.
Frame overlap chopper prevents overlap of neighbouring pulses.
Time-dependent signal allows time of ight analysis.
E = 12m
` Lt
´2
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
Source is pulsed at 20 Hz.
Frame overlap chopper prevents overlap of neighbouring pulses.
Time-dependent signal allows time of ight analysis.
E = 12m
` Lt
´2
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
Source is pulsed at 20 Hz.
Frame overlap chopper prevents overlap of neighbouring pulses.
Time-dependent signal allows time of ight analysis.
E = 12m
` Lt
´2
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
V = NPQR
output voltage
neutron rate
capture probability
charge per neutron
amplier gainConstant time of ight:V / N
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
V = NPQR
output voltage
neutron rate
capture probability
charge per neutron
amplier gainConstant time of ight:V / N
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
V = NPQR
output voltage
neutron rate
capture probability
charge per neutron
amplier gainConstant time of ight:V / N
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
V = NPQR
output voltage
neutron rate
capture probability
charge per neutron
amplier gainConstant time of ight:V / N
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
V = NPQR
output voltage
neutron rate
capture probability
charge per neutron
amplier gainConstant time of ight:V / N
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Monitor Signal
V = NPQR
output voltage
neutron rate
capture probability
charge per neutron
amplier gainConstant time of ight:V / N
0
0.5
1
1.5
2
2.5
3
3.5
4
130 120 110 100 90 80 70 60 50 40 30 20 10
beam
mon
itor
prea
mpl
ifier
out
put (
volts
)
time (ms)
Beam Monitor Signal
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
0
1
2
3
4
0 5 10 15 20 25 30 35 40 45 50
prea
mp
outp
ut (
Vol
ts/p
ulse
)
tof (ms) at 21 meters
frame overlap chopper cuts beam
Bragg scattering from aluminum in flight path
-5
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40 45 50
109 n
eutr
ons/
sec/
puls
e
tof (ms) at 21 meters
Monte Carlo calculationNormalized Flux From Monitor Signal
V = NPQR
Q;R constant
P increases with tof( / tof)
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
A Transmission Measurement
T
α N
1)(E 2(E2)
1(E1) 2(E2)R1 R2
N~~
attenuator
α N
~~ ~2 V =T1= V N f
~αN f
N
1= V N f1 αN2 V = f
monitor
preamplifier
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
A Transmission Measurement
T
α N
1)(E 2(E2)
1(E1)
N
1= V N f1 αN2 V = f
monitor
preamplifier
N~~
attenuator
α N
~~ ~2 V =T1= V N f
~αN f2(E2)
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
A Transmission Measurement
T
α N
1)(E 2(E2)
1(E1)
N
1= V N f1 αN2 V = f
monitor
N~~ α N
~~ ~2 V =T1= V N f
~αN f2(E2)
preamplifier
attenuator
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
A Transmission Measurement
ff
T
α N
1)(E 2(E2)
1(E1)
N
1= V N f1 αN2 V = f
monitor
N~~ α N
~~ ~2 V =T1= V N f
~αN f2(E2)
preamplifier
attenuator
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
3He As a Spin Filter
I Resonance requires J = 0+
I Polarized 3He preferentially attenuates neutrons of one spin
direction
I The attenuation is observed using the beam monitors
p + t + 764 keV
He4
Jπ 0+=
20.2 MeV
20.6 MeV
energy
0 MeV
ground state
0.5 MeV wide
n + 3He
π = +J 12
π = +J 12
=Jπ 0+
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
3He As a Spin Filter
I Resonance requires J = 0+
I Polarized 3He preferentially attenuates neutrons of one spin
direction
I The attenuation is observed using the beam monitors
p + t + 764 keV
He4
Jπ 0+=
20.2 MeV
20.6 MeV
energy
0 MeV
ground state
0.5 MeV wide
n + 3He
π = +J 12
π = +J 12
=Jπ 0+
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
3He As a Spin Filter
I Resonance requires J = 0+
I Polarized 3He preferentially attenuates neutrons of one spin
direction
I The attenuation is observed using the beam monitors
beampolarizer
Helmholtz coils provide uniform vertical magnetic field.
neutron guide
monitorbeam
monitorbeam
monitorbeam
spinflipper
pulsed coldneutrons
20 Hz
gamma detectors
2
targetLH
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
Beam Polarization measurement
I The polarization-dependent transmission of the 3He cell
can be seen by observing the ux-normalized signal ofthe second monitor.
0
2
4
6
8
10
0 5 10 15 20 25 30 35
prea
mp
outp
ut (
arbi
trar
y un
its)
time of flight in ms
Signal of downstream monitor
polarizedunpolarized
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
-2
-1.5
-1
-0.5
0
0 5 10 15 20 25 30
natu
ral l
og o
f tra
nsm
issi
on
time of flight at 21.4 meters
Unpolarized Cell Transmission
entire cellcorrected for glass walls
best fit: nσ = 0.0714 ms-1 tof
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
J.D. Bowman (Spokesperson), G.S. Mitchell, S.I. Penttila, A. Salas-Bacci,W.S. Wilburn and V.W. Yuan Los Alamos National LaboratoryS.J. Freedman and B. Lauss University of California, Berkeley
G.L. Jones Hamilton College P.-N. Seo North Carolina State UniversityT. Ino, Y. Masuda and S. Muto High Energy Accelerator Research
Organization, JapanR.C. Gillis, M. Leuschner, B. Lozowski, J. Mei, H. Nann, D.R. Rich, S. Santra
and W.M. Snow Indiana UniversityM. Gericke, S.A. Page and W.D. Ramsay University of Manitoba and TRIUMF
E.I. Sharapov Joint Institute for Nuclear Research, DubnaT.E. Chupp, K. Coulter, M. Kandes and M. Sharma University of Michigan
S. Covrig, M. Dabaghyan, F.W. Hersman, T.-U. Lee and H. Zhu University ofNew Hampshire
W. Chen and T.R. Gentile National Institute of Standards and TechnologyC. Crawford, D. Desai, G.L. Greene, T. Ito, R. Mahurin and A. Yue University
of Tennessee and ORNLR. Alarcon, L. Barron Palos Arizona State University
R.D. Carlini Thomas Jeerson National Accelerator FacilityT.B. Smith University of Dayton
Beam Monitors ofthe NPDGamma
ExperimentChad Gillis
BackgroundThe NPDGammaExperimentExperimental SetupA Gamma AsymmetryMeasurementThe BeamMonitorsWhat they areHow they workA transmissionmeasurementBeam MonitorAnalysisPolarimetryPolarizer TransmissionMeasurementThe NPDGammaCollaborationSummary andConclusion
I NPDGamma: to provide a precise measurement of h1,the coupling constant for weak meson exchange.
I To perform this measurement, the neutron beampolarization must be known.
I The beam monitors: ionization chambers that provide asignal proportional to incident beam ux.
I Beam monitors are reliable, low noise and lowbackground.
I Beam monitors have been used to measure the beamtransmission through components of the apparatus.
I Beam monitors allow for a continuous measurement ofbeam polarization.
I Beam monitors will be useful for similar measurementsin the future.
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