Focal spot size

The sensitivity curves are plots of maximum achieved sensitivity as a function of thickness of the object for a given focal spot size and source to detector distance. The best attainable sensitivity in image intensifier systems is a function of tube voltage, current, scattered radiation and the screen gamma. As a first step, stainless steel plates with thicknesses ranging from 5 mm-30 mm in steps of 5 mm were chosen. These plates had a length of 950 mm and width of 280 mm. The plate is positioned very close and at the center to the LI. tube. The extraneous... 

The maximum power of a conventional X-ray tube is 2.4 kW for broad focus (approx.. 2x 12 mm focal spot size). Modern rotating anodes consume 18 kW and deliver fine focus (approx.. 0.1 x 1 mm focal spot size). Most important for high intensity is not the power consumption, but the product of focal spot power density and focal spot size or, more accurately, the flux on the sample measured in photons/s (cf. Sect. 7.6). 

Shaping of the cathode and hooded anode to minimize focal spot size is a speciahzed art. Apparent focal spots of 1 mm (as viewed from the detectors) are typical for baggage systems. Tube currents are commonly in the range of... 

The femtosecond laser pulses shaped by the AOPDF are amplified by the CPA up to 0.5mJ/pulse. Ethanol vapor is continuously flow into the vacuum chamber through a micro-syringe (70 pm) with stagnation pressure of 7 Torr at room temperature. The laser pulses are focused on a skimmed molecular beam of the ethanol vapor with an achromatic lens (/ = 145 mm). The focal spot size of the laser beam is 20 pm(j>. The peak intensity of the transform-limited laser pulse is calculated to 4 x 1015 W/cm2. The fragment ions are mass-separated with Wiley-McLaren type time-of-flight (TOF) mass spectrometer, and are detected with a microchannel plate (MCP) detector. 

We have used several different frequencies between 0.25 and 2 MHz. The use of lower frequencies not only increases the focal spot size but also reduces the number of erythrocyte extravasations per unit area (9). The reduction in the diameter of the transducer, or increase in the radius of curvature, also increases the focal spot size. Examples of the 50% focal spot dimensions for different transducers are given in Table 2. The electrical impedance of the transducer is, typically, matched to the output impedance of the amplifier by an external LC-matching network to allow optimum power transfer. Although, we manufactured our own transducers in-house, custom MRI compatible transducers can be purchased from several manufacturers such as Imasonic, Inc. (Besancon, France). 

The most important characteristic of an X-ray source is the radiation flux density that it can generate. This is a function of the power at which it is operated and the size of the focal spot produced on the anode. The ratio of these factors is the specific loading of the source. A standard sealed, broad focus tube is normally operated with a cathode-to-anode voltage difference of 40 kV, an emission current of 20 mA, and a focal spot size of 1 x 10 mm, or a specific load of 80 w/mm2. Rotating anode machines can be run at 50kV and 50 mA, with a focal spot size of 0.2 x 1.0 mm. The specific loading under these conditions is 1.25 x 104 w/mm2. 

In SR-scattering, a focus of 10 40 pm2 has been realized for a microprobe instrument, using two cylindrical mirrors (Kirkpatrick-Baez geometry [38]) as substrates. Such an optic appears to be suitable to reach focal spot sizes of 1 1 pm2 [39]. 

The finite size of the source (3-mm diameter) produces a larger focal spot than would be expected for a point source (2.0-cm diameter instead of 1.7 cm for an ideal point source). For several of the experiments performed, we required a focal spot size smaller than the pixel surface, so a collimator consisting of a lead brick (10 cm thick) with a cylindrical hole (8-mm diameter) was used. 

The used FIB instmment has a focal spot size of 0.4 pm and a 0.2 pm ion beam deflection... 

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