Nu-Trek developed four types of GaAs PCDs: bremsstrahlung (two types), soft x-ray, and gamma for pulsed reactors. GaAs PCDs are advantageous in applications that require fast response, high dose rate, and/or neutron insensitivity. Desired detector sensitivity and response was obtained through modification of carrier lifetime by neutron irradiation, size of the sensing element, and orientation of the sensing element. The GaAs PCDs were used to characterize pulsed radiation sources in over 10 different tests.

Bremsstrahlung : GaAs PCDs (E7 – E11 rad/s) for use with pulsed bremsstrahlung sources were tested at MBS (AEDC), LINAC (Idaho Accelerator Center), LINAC (White Sands), PITHON (Titan Pulse Sciences), Hybrid Radiation Source (NRL), GAMBLE II (NRL), and HERMES III (Sandia).

Gamma : GaAs PCDs for gamma characterization in pulsed reactors (E6 – E7 rad/s) were calibrated with a LINAC (White Sands), checked for high dose rate (E12 rad/s) response at HERMES III, checked for low dose rate response (5 – 500 rad/s) and stability at a Co-60 source (Sandia), and checked for stability, sensitivity, and residual radioactivity at the ACCR reactor (Sandia).

Inside view of the “Reactor” PCD. It has a large detector, does not use a bypass capacitor to apply the bias, and is potted in order to reduce air ionization.

Soft x-ray : Soft x-ray (1 to 15 keV) GaAs PCDs (E2-E6 Watts/cm 2) were used to measure the argon plasma free-bound continuum temperature from Double-EAGLE (Titan Pulse Sciences) and compared with the plasma temperature obtained from line ratio measurements. Figure shows 4 soft x-ray GaAs PCDs mounted on a plate prior to the Double eagle tests.