Sensitivity curve, positive

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... 

Powder diffraction studies with neutrons are perfonned both at nuclear reactors and at spallation sources. In both cases a cylindrical sample is observed by multiple detectors or, in some cases, by a curved, position-sensitive detector. In a powder diffractometer at a reactor, collimators and detectors at many different 20 angles are scaimed over small angular ranges to fill in the pattern. At a spallation source, pulses of neutrons of different wavelengdis strike the sample at different times and detectors at different angles see the entire powder pattern, also at different times. These slightly displaced patterns are then time focused , either by electronic hardware or by software in the subsequent data analysis. 

D Position Sensitive Detectors. Position sensitivity is accomplished by a so-called delay line. For every pulse11 arriving at the wire the time is measured that it needs to travel to each of the two ends of the wire. Thus the position of the incident photon along the wire can be computed from the time difference, i.e., the delay. Bent high-resolution ID position sensitive detectors (cf. Fig. 4.14) are advantageously used in laboratory equipment for the recording of WAXS curves. 

Figure 7. Deep UV sensitivity curves of SPP positive node (A) compared with that of SPP negative mode (B). In positive mode, a 0.4 izm thick SPP layer was exposed to deep UV and then dip-developed in a 1.6 wt% TMAH solution for 60 s at 25 °C. In negative mode, SPP was exposed to deep UV followed by a flood exposure using near UV radiation and then dip-developed in a 0.7 wt% TMAH solution for 60 s at 25 C.

A variety of techniques have been used in the present work to establish the relative sensitivity of positive electron-beam resists made from copolymers of maleic anhydride (Table I). The term sensitivity is used rather loosely at times. In the most practical sense, sensitivity is a comparative measure of the speed with which an exposure can be made. Thus, the exposure conditions, film thickness, developing solvent and temperature may be involved. Most often, the contrast curve is invoked as a more-or-less objective measure of sensitivity. The dose needed to allow removal of exposed film without removing more than about 70% of the unexposed film can be a measure of sensitivity. The initial film thickness and the developing conditions still must be specified so that this measure is not, strictly speaking, an intrinsic property of the polymeric material. 

Figure 3.14. The schematic of a powder diffractometer with the vertical goniometer axis, cylindrical sample in the transmission mode and a curved position sensitive detector (PSD). Solid arrows indicate the incident beam and broken arrows indicate the diffracted beams pathways. F - focal point of the x-ray source, M - monochromator, DS - divergence slit, T -incident beam trap.

In principle, curved position sensitive detector can be replaced by a linear position sensitive detector covering segments 5 to 10° (20) wide. This approach considerably increases resolution and decreases Bragg peak widths, but the problem of the enhanced background remains. 

A) Sealed x-ray tube source, curved position sensitive detector, the radius of its goniometer is 150 mm and difflaction data are collected in the transmission mode using cylindrical specimens. You employed this equipment to characterize the phase purity of your materials. 

Figure 15-2 Receiver operating characteristic curve of prostate-specific antigen (PSA). Each point on the curves represents a different decision level.The sensitivity (true-positive rate) and I— the specificity (false-positive rate) can be read for Tests A and B. The true-positive and false-positive rates are demonstrated using 4 and IO Xg/L as decision thresholds.

Figure 2.28 shows a schematic drawing of a Debye-Scherrer device equipped with a curved position sensitive detector. 

The sample is a fine cylinder usually comprised of a capillary filled with the powder we wish to study. It can also be made of a thin wire, particularly when the material we wish to study is a metal. In any case, this sample is placed in the center of a curved, position sensitive gas detector used to simultaneously detect all of the diffracted beams. We saw before that when these gas detectors are irradiated with X photons, the gas is ionized and a local avalanche effect takes place which leads to the ionization of the neighboring atoms. The size of this ionized zone depends on... 

These laboratory parallel geometry configurations lead to average angitlar resolutions, but have the advantage of requiring limited acquisition times. Therefore, they are used for apphcations where the acquisition speed is a key factor. From this point of view, they constitute an alternative to the Debye-Scherrer and Hull systems with a curved position sensitive detector, for example, when conducting thermodiffraction measurements. 

A four-reflection monochromator comprised of plane single crystals is placed between the source and the sample (see Figure 2.36). The beam irradiates the sample, which is placed on a three axes sample holder. The sample holder makes it possible to orient the normal to any family of ctystal planes in the diffraction plane defined by the axis of the incident beam and the directions of the diffracted beams. Since the beam is strictly parallel, it is not necessary to inclnde a slit between the sample and the monochromator. The intensity of the diffracted beams is meastrred by using a detector which moves along a circle, centered on the sample or with a curved position sensitive detector. This last featrrre makes this system a distant relative of the Debye-Scherrer diffractometers, for which the sample is, by definition, the center of the detection circle. 

Figure 3.7. Calculation of the instrumental resolution function of a diffractometer equipped with a four-reflection monochromator and a curved position sensitive deteetor...

We then produced another diffraction pattern for the same sample with a system equipped with a front monochromator and a curved position sensitive detector [MAS 96a]. The pattern, produced in reflection on a flat plate sample (see Chapter... 

Whichever of these two modes is chosen, this type of incremental measurement necessarily implies long measurement times. An alternative to these methods consists of using a curved position sensitive detector. For each value of the incidence angle to, a direct measurement of the intensity distribution according to 20 is made [BOU 02a, BOU 02c, BOU 04]. This makes the mapping much quicker, between 10 and 100 times shorter more than with a punctual detector. We should point out, however, that this method prohibits the use of analyzer crystals. 

LOU 92] LOUER D., LOUER M., TOUBOUL M., Crystal structure determination of lithium diborate hydrate, LiB203(0h).H20, from x-ray powder diffraction data collected with a curved position sensitive detector , J. Appl. Cryst, vol. 25, p. 617-623,1992. 

MAS 98a] MASSON O., GUINEBRETIERE R., DAUGER A., Profile analysis in asymmetric powder diffraction with parallel beam geometry and curved position sensitive detector . Mater. Sci. Forum, Trans. Tech. Pub., Switzerland, vol. 278-281, p. 115-120,1998. 

STA 92] STAHL K., THOMASSON R., Using CPS120 curved position sensitive detector covering 120°. Powder diffraction data in Rietveld analysis. The dehydration process in the zeolite Thomsonite , J. Appl. Cryst., vol. 25, p. 251-258, 1992. 

WOL 83] WOLFEL E.R., A novel curved position sensitive proportional counter for x-ray diffractometry ,/. Appl. Cryst, vol. 16, p. 341-348, 1983. 

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