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Silicon Photonic Nanostructures for Radiation Calorimetry

R Tosh1*, F Bateman2 , (1) NIST, Gaithersburg, MD, (2) NIST, Gaithersburg, MD


(Wednesday, 7/17/2019) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 4

Purpose: To demonstrate the feasibility of using silicon photonic devices for calorimetry of ~1 MeV electron beams.

Methods: Micro-loop resonators and Bragg waveguides with spatial dimensions of order 10 microns were fabricated on silicon chips of ~1 mm thickness. Silicon chips were irradiated with 1.8 MeV electron beams provided by a Van de Graaff, at nominal dose rates of ~10 Gy/s to ~100 Gy/s. Silicon photonic devices were interrogated with a C-band laser swept over the resonance peaks, and resonance wavelength was logged as a function of time throughout radiation runs involving multiple 30-s exposures with beam currents varying from 0.2 μA to 5.0 μA (hence a factor of 25x variation in dose per exposure). Calibration of devices before and after irradiation runs in a temperature bath enabled conversion of wavelength data to temperature, from which temperature rise per irradiation, hence dose per exposure, was determined for each beam current.

Results: Step-like response of the devices to radiation exposures was observed at all beam currents. Also evident were characteristic distortions due to heat conduction effects, in spite of which it was possible to obtain a linear plot of step height vs. beam current that corresponded to approximately 0.06 nm/μA per exposure, which converts to about 1.0 K/μA per exposure.

Conclusion: As our previous work has shown such devices to be radiation hard to MGy exposures in Co-60, the linear response with dose we observed here is a promising indicator that, with refinements in instrumentation and technique, silicon photonics may offer a way to perform calorimetry at mm-scale or smaller. Additional analysis is underway to convert these preliminary results to absorbed dose for comparison with Monte Carlo simulations.


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