Figure 5 Maximum fluorescence flux dependence on the capillary radius during capillary scan. Experimental and simulated data. Figure 6 X-ray collection using cylindrical monocapillary. Dependence of the collected flux on capillary radius and length. In both configurations, the signal magnitude click here is the same. Is it possible to increase this signal by decreasing WD? It is well known that cylindrical capillaries allow to significantly increase the collected signal by comparison with a pinhole with the same radius placed
at the detector entry and positioned at the same WD + L distance (Figure 7a,b) [10]. At high WD, the capillary nozzle is seen under a solid angle θ 1 < θ c from a point source (Figure 7b). Thus, all X-rays emitted by the point source within this solid angle will be transmitted through the capillary, assuming a total reflection of X-rays below the critical angle. The capillary gain G regarding a pinhole of the same radius is given by the equation [10]: (5) Figure 7 X-ray collection using cylindrical monocapillary. Dependence of the collected flux on capillary working distance WD at constant sample detector distance. The detection through a capillary increases the collection solid angle. (a) Detection through a pinhole. For short capillary length (b), the signal magnitude S 1 is higher than S 0 detected in case (a); (c) if WD is shortened Dasatinib concentration until WDc, the signal magnitude S 2 increases until
θ 2 = θ c; (d) for WD lower than WDc, the signal remains constant. If WD decreases, keeping WD + L constant, the collected signal magnitude first increases since the collection solid angle increases until it reaches θ 2 = θ c Casein kinase 1 value. At this point (Figure 7c), WD reaches WDc value given by: (6) In this case, the capillary gain is given by: (7) If WD is further decreased, the solid angle θ 3 under which the capillary nozzle is seen from the point source is higher than θ c (Figure 7d). The collected signal
is no more limited by the capillary acceptance: the capillary gain as well as the collected signal remain constant. Because the WDc value depends on the capillary radius and the smallest value of WDc is 1 mm for the capillaries tested in this work, this optimum value was chosen and taken constant in all these experiments. Because the fluorescent emitting source in the experiments is not punctual, we have started simulations to estimate the flux collected with a 0.5-μm radius capillary positioned at a WD of 1 mm. These simulations are based on a finite element method calculation from fundamental parameter equations and will be presented elsewhere. Figure 5 shows the dependence of the collected signal with the capillary radius in the range of 0.5 to 50 μm. The calculated values are in good agreement with the experimental ones. The estimated flux with a 0.5-radius capillary is 0.07 photons/s. This value is obtained at 1 mm WD. However, the maximum signal should be reached at 100 μm WDc value.