The e Backscatter Background in the aCORN experiment G' Noid, R' Ashkar, E' Stephenson Indiana Unive

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The e- Backscatter Backgroundin the aCORN
experimentG. Noid, R. Ashkar, E. Stephenson
Indiana University Cyclotron Facility
The Problem
Two Sources of the Background
A Beta Bounce Electron
An aCORN event
Electrostatic Reflection

• Reflection off the -25 kV potential on the proton
  detector
• Confined to lower energy electrons
• Solutions affect proton focusing

Electrons which reflect or scatter from the
proton detector region and then are detected in
the ß spectrometer are a significant background
in our experiment.
Proton detector with -25 kV for detecting p.
Matter Interaction
Proton

• Occurs at all electron energies
• Tested with Monte Carlo simulation Pensim

The low energy protons are all pushed towards
their detector by the electrostatic mirror but
the higher energy electrons are free to travel in
either direction.
Beta bounce and electron coll. interactions
Neutron decay
3 kV mirror potential difference
The simulated background
Electron
Goal
Electron coll. interactions
ß spectrometer located here
The Solution
Off Axis Proton Detector with Veto Cone
Pensim Results
Off Axis Detector

• Decay ps easier to steer than es
• Moves the reflecting potential away from the
  central axis
• Maintains 100 proton focusing efficiency as
  shown below.

Plastic Cone
Vacuum Can
Si Detector
Focus Ring
Magnet Coils
Grid
Scintillator Veto Cone
Proton Collimator

• Cone deflects electrons away from the central
  axis
• Low z material absorbs electrons
• Mounted on PMT to veto electrons which arent
  absorbed

Electrode
Simulating the Solution
Proton Focusing in Amaze
yellow double bounce
hit cone and didnt veto
black good events

• Pensim monte carlo
• Penelope for electron matter interactions
• Simion for calculating electric fields
• Neutron generator creates realistic decay events

Proton detector
Veto cone
Proton collimator
coils
electrodes

• Amaze calculates fields in the presence of
  dielectrics and runs proton trajectories.
• 100 proton focusing must be preserved to avoid
  creating a systematic effect.

Electron energy (keV)
The line is the background upper limit for a 0.5
measurement of little a in each 20 keV bin.
Positive electrode 800 V Negative electrodes
-27 kV Proton Detector -29 kV
all of 9996 protons detected in 1.6 cm spot