construction of a 1 mev electron accelerator for high precision beta-decay studies
DESCRIPTION
Construction of a 1 MeV Electron Accelerator for High Precision Beta-Decay Studies. REU Student: Brenden Longfellow, University of North Carolina at Chapel Hill Advisor: Albert Young, North Carolina State University. Neutron Beta-Decay. sprawls.org. pfnicholls.com. n → p + e - + ν e. - PowerPoint PPT PresentationTRANSCRIPT
Construction of a 1 MeV Electron Accelerator for High Precision Beta-Decay Studies
REU Student: Brenden Longfellow, University of North Carolina at Chapel Hill
Advisor: Albert Young, North Carolina State University
Neutron Beta-Decay
n → p + e- + νe
pfnicholls.com sprawls.org
Beta-decay energy calibration for detectors typically established with conversion sources (Cd-109, Ce-139, In-114m, Sn-113, Sr-85, Bi-207)
Internal Conversion: excited nucleus interacts electromagnetically with electron in lower atomic orbital, ejecting it
Achieved by placing mylar foils of conversion sources into spectrometer (next slide)
Detector Calibration
Young
Calibration points are not evenly distributed over beta energy spectrum and foil backing produces perturbations in calibration spectrum
For improvement, use external, tunable electron beam, coupled by magnetic field to calibrate detector
Problem and Solution
Pelletron Charging System: particle accelerator in which charge is induced on chain of metal pellets connected by insulating nylon links
Electron Gun: electrons/s with energy range of 50 keV to 1 MeV; pulsed at 10 kHz rate with few ns width
Magnetic field in spectrometer of 1 T and guiding fields of 0.01 to 0.05 T for electron gun to create range of pitch angles (can be determined by spread in arrival time)
Electron Accelerator
Electron Accelerator
Chain rotates on two wheels, driven by motor
Charge induced on chain as it leaves grounded end by inductor (negatively charged electrode biased by high-voltage supply)
As wheel rotates, contact between pellets and wheel is broken and positive charge is trapped on the pellets by the insulating nylon connecting links
Pelletron
Westerfeldt
Charged pellets pass another electrode as they arrive in terminal causing electrode to develop mirror (negative) charge
Conductive pickoff wheel underneath electrode picks up charge as chain passes and applies it to inductor on opposite side of terminal wheel
This inductor (positive) induces negative charge on pellets leaving terminal
Pelletron
Westerfeldt
Charged pellets arriving in terminal contact conductive rim of terminal pulley, transferring charge to terminal
Pellets leaving terminal that have been inductively charged by positive inductor double charging efficiency
High voltage built up at terminal is used to accelerate charged particles
Pelletron
Westerfeldt
Attached electrodes to accelerator column, and installed motor control system
Progress
Developed tensioning system for motor to provide sufficient tension to chain (first iteration failed to provide enough tension, second iteration currently in machine shop)
Progress
Used COMSOL model of accelerator column geometry to simulate electron response
For testing, tensioned motor sufficiently by brute force
Progress
Generated current of 7 μA through terminal Resistor string of 30 GΩ gives voltage across
column of 210 kV
Results of Testing
Replace current motor with smaller one and install tensioning system
Enclose accelerator in pressure vessel
Create map of magnetic fields for electron accelerator and spectrometer
Next Steps
Special thanks to Dr. Chris Westerfeldt for all of his help with this project
Any questions?