Calibration and characterization of a pulsed soft x-ray source

Abstract

Typical x-ray flux measurement methods (diodes, thermopiles, sensitized photographic film, photoresist, etc.) yield questionable accuracy and poor precision. A commercially available nylon-based radiochromic film, developed for monitoring dose during radiation processing of food products, was used to calibrate and characterize a high brightness (106–107 W/srad), pulsed, laser plasma, soft x-ray source. The response of this film can be calibrated using NIST radiation standards, has negligible x-ray wavelength and environmental dependence, and is dose-rate insensitive over a large range. The change in optical density (ΔOD) of exposed film is directly proportional to the incident dose. Excellent agreement was observed for film response to both broadband soft x rays (0.6≤λ≤2.2 nm) and 20 keV electrons. An incident dose of 100 mJ/cm2 resulted in a ΔOD of 1.00 with a measurement precision of ±2%, with no evidence of saturation found up to 120 mJ/cm2. The laser plasma source demonstrated flux stability of better than 5% over a five-month period. Dosimetry film was also used to measure illumination uniformity, measure soft x-ray transmission through various materials, and calibrate an on-board miniature x-ray diode for dose integration.