P4.4 - Detection head for radiation measurement in the „water window” region

Abstract

For the detection of the energy radiation a detection system is necessary. The sysytem usually consists of optical filters detectors and electronics units It should provide to measure energy radiation with defined uncertainty in the specific wavelength range. The wavelength range is determined by features of optical filters. As the filters, the multilayer mirrors, Fresnel lens or absorption layers could be used. It is worth to notice, that it is very difficult to separate water widow spectrum using single optical element. The efficient filtration can be achieved by using a system of filters. For example the determination of the band-pass filter could be accomplished by two filters operated in the shorter wavelength range and in the longer one. Analysis of the literature and databases from some research centers show that for the detection system some multilayer mirrors or absorption filters can be appropriate. The simulation procedure was proposed for designing of the mirrors with high reflectivity in the water window spectrum. The three models of mirrors (Cr/Sc, Cr/V, Cr/Ti ) were taken into consideration in mentioned above analysis. The results of the simulations are presented in Fig. 1. Fig. 1. Reflectance of the simulated multilayer mirrors. The curves were determined theoretically. Basis on the results the two types of multilayer mirrors were selected for further considerations. The calculations were made together with scientists from Fraunhoffer Institute (Jena, Germany). The conclusions from the results were implemented practically during technological process. The results showed that better parameters of fabricated mirrors achieved for Cr/Ti structures. For optimal features of the structure (layer period of 4.235 nm, layers number of 150, incidence angle of 70 °), the reflectivity characteristics were determined. The analyzed mirrors show both high reflectivity and spectral selectivity. It is worth to note, that the energy measurements for the whole water window region are not provided because of shortcomings of mirror selectivity. During the next