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Construction of a 1 MeV Electron Accelerator for High Precision Beta-Decay Studies

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.

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Construction of a 1 MeV Electron Accelerator for High Precision Beta-Decay Studies

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  1. 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

  2. Neutron Beta-Decay sprawls.org pfnicholls.com n → p + e- + νe

  3. Detector Calibration 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)

  4. Young

  5. Problem and Solution 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

  6. Electron Accelerator • 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)

  7. Electron Accelerator

  8. Pelletron Westerfeldt 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

  9. 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

  10. 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

  11. Progress Attached electrodes to accelerator column, and installed motor control system

  12. 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)

  13. Progress Used COMSOL model of accelerator column geometry to simulate electron response For testing, tensioned motor sufficiently by brute force

  14. Results of Testing Generated current of 7 μA through terminal Resistor string of 30 GΩ gives voltage across column of 210 kV

  15. Next Steps 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

  16. Special thanks to Dr. Chris Westerfeldt for all of his help with this project Any questions?

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