Effects of irradiation on Hall probe sensitivity

Four Hall probes from two different manufacturers were exposed to increasing amounts of radiation at the Advanced Test Accelerator and were compared periodically to a nuclear magnetic resonance (NMR) gaussmeter at magnetic field values of 2 to 8 kG. The radiation was primarily bremsstrahlung from a 45-MeV electron beam. The probes were mounted near a beam dump, along with LiF thermoluminescent detectors to keep track of the cumulative dose. The data show a threshold near 100 kRd, beyond which the probes tend to lose sensitivity and perform outside their nominal error limits. It is conjectured that the loss in sensitivity may be caused by crystal dislocations in the InAs Hall chip arising from neutrons generated in gamma-n reactions. It is observed that the radiation effects are not monotonic with cumulative dose, and in some cases appear to go away at the higher doses; this is attributed to annealing of the probe material during or in between the successive irradiations