8. Absolute Flux Measurements

Abstract

Publisher Summary This chapter focuses on absolute flux measurements. It presents a review that discusses detectors as devices for absolute flux measurements in the vacuum ultraviolet (VUV) and the soft x-ray (SXR) spectral range. Radiation generated by different sources in the VUV and the SXR has a very wide set of characteristics. The quantitative measurement of photon fluxes from an electron storage ring, a tokamak, a dense plasma discharge, a SXR laser, or astrophysical objects demand essentially different approaches and instrumentation. Accordingly, many different kinds of radiation detectors have been developed and modified including thermocouples, bolometers, semiconductor and emissive photodiodes, photomultipliers, charge-coupled devices (CCDs), photographic film, scintillators, photoelectron spectrometers, and many others. In metrology, the radiation detector standards are divided into primary standards and secondary, or transfer, standards. Currently, an electron storage ring is considered to be an almost ideal source for quantitative radiometry of electromagnetic radiation in a wide spectral range from the infrared up to far VUV and the hard x-ray spectral range. It is evident that accurately calculable spectral irradiation (or photon flux) from a storage ring is widely used not only for the calibration of transfer radiator sources, but also for the calibration of transfer detector standard. The photoionization chamber and its modifications are almost ideal primary photodetectors in the VUV. They have been used and are used in many measurements of the absolute photon flux intensity.