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 - + ν e 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

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?