Ionizing Radiation Hazard for Laser Material Processing Applications Using an Ultrashort Pulse Laser.

Abstract

Ionizing radiation hazards from material processing using an ultrashort pulsed laser at high rep rates, which emits bremsstrahlung x rays below 10 keV, were measured with survey meters and passive dosimeters. A laser-optic system was set up to scan thin tungsten foils at six laser intensities between 1013 and 1015 W cm-2, which were characterized in this study. Ssurvey meters with open beta slide and closed beta slide configurations, as well as dosimeters, were used (at different distances and directions) to measure shallow and deep dose rates, respectively. The default dose algorithm and the dose algorithm developed from this study were both used to convert the element signals to H'(0.07) and H*(10). Irradiations with standard x-ray beams were used to derive the calibration factors of survey meter and dosimeter for the low-energy laser-induced x-ray beams. Additional corrections, such as air attenuation and volume effect needed for meter response, were also made. Survey meters show shallow dose rates ranging from 10 mSv h-1 W-1 at 2.8 × 1015 W cm-2 down to 1 mSv h-1 W-1 at 6.6 × 1013 W cm-2 at 28 cm. The deep dose rates are at least a factor of 10 lower than the shallow dose rates. With corrections, dosimeters measured shallow doses of 42 mSv h-1 W-1 at 2.8 × 1015 W cm-2 at a distance of 12 cm, which were comparable to 77 mSv h-1 W-1 measured by survey meters. Uncertainties associated with deep dose measurements were much higher than those for shallow doses, and shallow dose uncertainties are higher for the dosimeter than for the survey meter. Dosimeters have difficulty in measuring shallow doses at lower intensities and deep doses at all intensities.