Sample detectors

Experiments were carried out during several runs of DORIS III (E = 4.5 GeV). The beam size was 1 x 1 mm2, the sample-detector distance was 1200 mm and the detector aperture 9x9 mm2, co stepscans were applied with 1 s per step for the stronger and 3 s per step for the weak reflections. The sample was a sphere of 190 pm diameter. 

Table 2.1. Subareas of scattering as a function of the sample-detector distance R assuming an X-ray wavelength of A 0.15nm...

Now a sample in the carrier gas goes by one detector. This sample has a thermal conductivity different from that of pure carrier gas. So the sample detector loses heat at a different rate from the reference detector. (Remember, the reference is the detector that NEVER sees samples — only carrier gas.) The detectors are in different surroundings. They are not really equal any more. So the bridge circuit becomes unbalanced and a signal goes to the chart recorder, giving a GC peak. 

Sampling Detector Changes rate Changes noise level in... 

Air-sampling detector Actively and continuously samples the air from a protected space and is able to sense the pre-combustion stages of incipient fire. 

Figure 6. Chromatograms of polydisparse dextran calihra-tion standard and dextran T-1 0 sample. Detector refractive index.

The concept of the coherence area may also be described as follows. Suppose one of the sample dimensions in the plane perpendicular to the sample-detector line is a. Then, the angular range of light accepted in that direction Aa must be on the order of... 

Figure 2A.1 Cross-sectional view of a low-level anti-coincidence beta-particle counter A. Sample on a planchet. B. Thin window detector. C. Guard detector. Lead shielding surrounds the entire detector system. Typical background count rates are about 1 count per minute for beta particles and 0.1 count per minute for alpha particles. A sample mounted on a planchet (A) is placed below the thin window. When the guard detector (C) is triggered by an extraneous radiation that penetrates the lead shield, the sample detector (B) is inactivated. Immediately following, the detector (B) responds to beta particles from the sample. For low-activity samples, the probability is low that a particle from the sample registers a pulse at the same time that the counter is inactivated.

Figure 8. Close-up view of contrast-matched signals. The error hars are much larger for the large sample-detector distances d, because the signal intensity decreases as I let. The signal from the phenol is zero within the level of the noise. The phenol is therefore mainly distributed uniformly in the liquid. Symbols are the same as in Figure 7.

The thermal conductivity detector (TCD) is based on changes in the thermal conductivity of the gas stream brought about by the presence of separated sample molecules. The detector elements are two electrically heated platinum wires, one in a chamber through which only the carrier gas flows (the reference detector cell), and the other in a chamber that takes the gas flow from the column (the sample detector cell). In the presence of a constant gas flow, the temperature of the wires (and therefore their electrical resistance) is dependent on the thermal conductivity of the gas. Analytes in the gas stream are detected by temperature-dependent changes in resistance based on the thermal conductivity of each separated molecule the size of the signal is directly related to concentration of the analyte. 

Fig. 4-6. Detector circuits for vapor-phase chromatography, (a) Thermistor detector Di, D=, Victory Eng. Corp. 32A12 thermistors Ri, Ri, 1,0000 wire wound resistors Rz, 1,0000 Helipot Rt, 10,0000 1% carbon film resistor Rs, 5,0000 1 % carbon film resistor Rt, Rj, 2,5000 1 % carbon film resistor Sw, single-pole four-position switch, (b) Hot-wire detector Rz, filament current control, to adjust filament current between 150—300 ma ( 20 ohm 5w) Ri, R4, reference detectors Rs, R, sample detectors Re, zero control 20 Re, 600 1 % carbon film resistor R, 300 1 /, carbon film resistor R, 150 1% carbon film resistor Rse, 7.5Q 1 % carbon film resistor Rs, 7.SCI 1 % carbon film resistor M, 300 ma meter,- S, single-pole six-position sv/itch.

SANS measurements were made using the PAXE instrument installed at the Orphe reactor, Laboratoire Leon Brillouin, Gif-sur-Yvette, France. Measurements were made on intact membranes (47 mm diameter) which were oriented either perpendicular or parallel to the incident neutron beam. SANS was measured at sample/detector distances of 1.5 m with a neutron wavelength, X, of 6 A and at 3.5 m with A. of 15 A, respectively. Analysis of the scattering, measured on a 2D detector, was carried out using procedures described previously... 

If the slide is ready to receive the sample, a green lamp lights up at the DTSC module (Fig. 18) and a beep is emitted. 10 pi of the sample is now applied by means of the electric air displacement pipette. Application of the sample is monitored by an automatic sample detector system. After successful application of the sample the slide travels fully automatically to the pre-incu-... 

The rays reach the sample detector via an interference filter. A reference detector receives the rays reflected by the wall of the Ulbricht s sphere. The concentration of the analyte can be inferred from the difference between the two reflectance values. In addition, by this formation of difference values the optical system equalizes fluctuations of the xenon flashlight. A sapphire window placed before the sample and reference detector minimises excessive evaporation of surface moisture from the test area of the test strip. The interference filter, which is also situated before the detectors, is method-dependent and is inserted into the instrument with the plug-in module (Fig. 47). 

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