Dose-rate field of the HERMES III flash X-ray source

Measurements show that the HERMES III flash X-ray source produces a peak dose-rate radiation field of (5±0.5)×10¹² rad(Si)/s over a useful area of 1000 cm², with a pulse width of ~20 ns. The primary goals of HERMES III were to produce a radiation pulse with an FWHM (full width, half maximum) of ~20 ns, a peak dose rate of 5×10¹² rad(Si)/s, and a dose-rate variation of less than a factor of two over a 500-cm² area. The secondary goals were to keep the dose-rate variation less than a factor of four over the volume defined by extending the 500-cm² area downstream by 15 cm and to maintain a minimum dose rate over this volume in excess of 2.5×10¹² rad(Si)/s. The dose and dose-rate pulse were measured in the hostile near-field region, where dose rates exceed 10¹² rad(Si)/s, and in the far-field region, when the diode is operated with a 53-cm anode-cathode gap. Specifically, it is shown that operation with a 53-cm gap permits both the primary and secondary goals to be achieved. The model predictions of radiation-pulse shape and width in the intense near-field and far-field regions are in excellent agreement with the measurements