aCORN Proton Det' Update

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aCORN Proton Det. Update
aCORN Collaboration March 26th 2008 George Noid,
Ed Stephenson
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aCORN apparatus
proton detector
360 G axial B field and internal
collimation restrict observed coincidences to
those with momenta close to the axis.
The difference in up and down rates measures a.
With this restriction, neutrinos emerge either up
or down.
aCORN measures an asymmetry between the
two branches.
up
neutron beam
down
beta spectrometer
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The Beta Bounce Problem
Electrostatic Reflection
-25kV for detecting p.
ß spectrometer
Confined to low electron energies because the
longitudinal kinetic energy must be less than
-25keV
Matter Interaction
goal

• Occurs at all electron energies
• Moves an event from one energy to another

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Plastic Scint. Veto Cone
Negative electrodes assumed transparent
Plan IIIg
Si. Detector (-28kV)
Field Map limits (ground)
Positive Electrode (800V)
Not all coll. visible
Top Proton Collim.
Teflon Mirror
Geometry used in Pensim monte carlo. Combines
electron matter interactions of penelope,
electric fields of simion, and realistic decay
events from F. Wietfeldt code. Electrons examined
are all associated with a detected proton
(calculated analytically).
Aluminum Rings
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Plan 3g Results

• 7543457 Electrons
• 136337 Right Way Electrons
• Inelastic
• Double Bounce
• 47 Vetoed
• 86 Below Threshold (lt25keV)
• Wrong Way Electrons
• 407 Vetoed
• 697 Below Threshold (lt25keV)
• Hit Teflon
• 4 Hit Ring

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Detector Concept
PMT
Scintillator Cone
LN Tanks
Alpha Source
Thermometer
Be-Oxide Support
-25kV Si Detector
-20kV Ring
-20kV Grid
1kV Electrode
Proton Coll.
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Utilities for proton detector region
plate HV 1 kV
thermo.
grid HV -20 kV
also include LN2 for cryopanels alpha source
handle
PMT HV
signal
HV cage
thermo.
PMT
det. HV
pre-amp
amp
pulser
optical link
power
BeO
LN2
AC power isolation transformer
HV -25 kV
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Walt Fox Concept
Note VacCan, Coils, Beta Spec., etc. not visible
Protons Detected here
neutrons
Decay Here
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Proton Focusing
Adapted from Walts design into Fieldp software
package. Changes include going from 45 degrees
to 40 degrees, shrinking the ring, and adding
wires. Many elements that are far from the
protons were not included.
Fieldp software calculates the Electric fields in
the presence of dielectrics and runs particle
trajectories.
-29kV on the detector -27kV on the grid and the
ring .8kV on the electrode
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Proton Focusing
9996 decay protons distributed in energy and
momentum according to F. Wietfeldts neutron
decay simulation. Then accelerated by the
electrostatic mirror and collimated while in our
B field
The spot is about 1.7 cm across. The detectors we
have are about 1.9 cm in diameter. Off the shelf
detectors from Ortec go up to 2.3 cm.
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Detectors

• We have 300 mm2 Si detectors
• Consider purchasing a 450 mm2 Si detector
• Ortec doesnt make guard ring segmented
  detectors
• Partially depleted detectors?

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Optimization Schemes

• The Plateau method
• Requires many passes with small adjustments
• Normalized count rate method
• Requires fewer passes
• Requires accurate relative neutron rate
• Requires second detector mounting
• Singles rate?

Work in Progress
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Beta bounce

• Matter interaction
• The detector face and focusing elements are
  outside the inner radius of the beta collimators
• It is assumed the get-lost will remove these
  events
• Electrostatic interaction
• Simulations have been done for 45 degree bend
• Assuming an 80 keV lower cut off this problem is
  eliminated

1000 50 keV electrons
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