A signal-to-background ratio

However, a nonzero background in the experiment always produces a small contribution from the detection events that fall in the central Nq peak. For example, a signal-to-background ratio of 7 leads to an Nc/Nl ratio of about 0.2. In the present case, an Nc/Nl ratio of 0.06 was determined. Hence, the Nc/Nl value also indicates that the present nanocrystal behaves as a single-photon source. 

One-dimensional and multiple-layer models have been developed to simulate the transportation of gaseous away from a uranium ore source (Jeter et al., 1977 Jeter, 1980), Calculations suggest that a 1 m thick planar ore deposit (0.6% U O ) located 100 m below surface and with 20% emanation efficiency should be detectable within 15 m with a signal to background ratio of 5 1. Experimental results, using confirm... 

A plot of the square root of the scan rate (10 to 60 mV s Ws. peak current density for the electrochemical oxidation was linear, and this shows that the oxidation current is diffusion-controlled, with negligible adsorption of the electroactive species on the electrode surface. The peak potential value of the irreversible wave was also observed to shift positively with increasing sweep rate. A linear increase of peak current density was found for the concentration range from 0.01 mM to 0.5 mM of analyte in 0.1 M phosphate buffer (pH 6.7) at a constant sweep rate of 60 mV s l A signal to background ratio of 3 was obtained in this case at a concentration as low as 5 pM. 

Figure Bl.10.9. Plot of the reduced relative uncertainty of a double coincidence experiment as a fimction of the signal-to-background ratio. Note that the relative uncertainty decreases as the signal-to-background rate decreases.

The concentration of is determined by measurement of the specific P-activity. Usually, the carbon from the sample is converted into a gas, eg, carbon dioxide, methane, or acetylene, and introduced into a gas-proportional counter. Alternatively, Hquid-scintiHation counting is used after a benzene synthesis. The limit of the technique, ca 50,000 yr, is determined largely by the signal to background ratio and counting statistics. 

ENHANCED SIGNAL-TO-BACKGROUND RATIO WITH A HIGHLY ORDERED PYROLYTIC CARBON FILM AS AN ELECTROCHEMICAL INTERFACE... 

An interesting variant of a CEMS counter is the parallel-plate avalanche counter (PPAC) [18, 19], which carries the sample between parallel electrodes made of Perspex coated with graphite (Fig. 3.8, left). A counter gas is used to amplify the low conversion-electron current emitted by the sample, with an avalanche effect taking place between the plates. Compared with the CEMS proportional counters, PPAC gives a larger signal-to-background ratio, faster time response, simpler construction, and better performance at low temperatures. 

Column and detector properties determine the minimum amount of a component that can be reliably distinguished from the background noise. If we arbitrarily select a signal to noise ratio of 4 as the minimum value for the confident determination of a peak in a chromatogram then for a mass sensitive detector the minimum detectable amount is given by... 

The low y-ray intensity relative to the K x-ray background therefore presents a problem of obtaining a reasonably good signal-to-background ratio. 

PET offers the possibility to quantitatively measure the myocardial blood flow (MBF). MBF tracers can be divided into two groups. The first group is freely diffusible and represented by [ 0]H20. These tracers do not show any specific absorption and their distribution is completely determined by diffusion. Consequently, the measurement of the MBF is based on the first-pass extraction and clearance data. Because of the low heart-to-blood radioactivity ratio, the freely diffusible tracers provide myocardial images with low signal-to-background ratios. The second class is composed of highly extractable heart tracers. The tracer p NjNHs belongs to this family. These radiolabeled compounds are characterized by a selective extraction and retention in the myocardium. The... 

Limit of Quantification For the limit of quantification, or limit of determination, definitions and formulas are very similar to those of LOD, except that for LOQ, is taken to be 5, 6, or even 10 [2, 4,15, 56,72, 96]. A value of 10 for means that the %RSD at the limit of quantification is 10%. The LOQ thus corresponds to that concentration or amount of analyte quantifiable with a variation coefficient not higher than 10% [98]. The LOQ is always higher than the LOD and is often taken as a fixed multiple (typically 2) of the detection limit [4]. Also, the determination limit is referred to as the signal 10 times above the noise or background signal, corresponding to a signal-to-noise ratio of 10 1 [72, 85]. 

A depleted uranium instead of lead collimator was used to increase signal-to-background ratio due to its higher density (19.0 vs 11.3)... 

Fast Response CO Sensor. The sensor requirements for eddy covariance measurements are extreme. To be used within a few meters of a plant canopy, the sensor must have a frequency response in excess of 20 Hz. Additionally, because the large mean density of CO2 in the atmosphere (about 560 mg m-3) and the deviations around the mean associated with turbulent transfer are small (>10 mg m-3), the sensor must have a signal to noise ratio in excess of 3500 1. The sensor must maintain these specifications for long durations, while mounted on a tower above the canopy, where it is exposed to constant changes in temperature, solar irradiation, and background gas concentrations. The instrument must unobtrusively sense the natural turbulant fluctuations of the atmosphere. To effectively accomplish this it must be small and streamlined. 

Fig. 29 Lifetime measurements with the Zeiss Plate Vision of DBO (= 2,3-diazabicyclo [2.2.2]oct-2-ene) for three different oligopeptide protease substrate. For the uncleaved substrates the signal decays fast (r = 59 ns, 95 ns and 35 ns) due to the collisional, dynamic quenching of the DBO by tryptophan or trypsin. Upon cleavage the quencher and DBO are separated, which results in a lifetime increase (r = 234 ns, 287 ns and 315 ns). This lifetime change allows a time-gated FTRF detection (delay = 100 ns and gate = 700 ns) of the enzymatic reaction with a high signal-to-background ratio. Data by courtesy of T. Enderle, Hoffmann-La Roche, Pharmaceuticals Division, Assay Development and HTS, Basel/Switzerland [192]...

---