Construction of a 1 MeV Electron Accelerator for High Precision Beta-Decay Studies REU Student:...

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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

Transcript of Construction of a 1 MeV Electron Accelerator for High Precision Beta-Decay Studies REU Student:...

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?