Error radiation measurements

The first report of radiation trapping in a solid was given by Varsanyi and co-workers (42) for 0.05 per cent ruby. Chromium is admittedly not a rare earth, but the results they obtained are so interesting that they deserve further mention. They clearly indicate a potential error in measurement to fee expected for rare-earth systems. 

There are certain practical aspects that need to be taken into account in assessing the significance of temperature factors. Errors in measurement of intensities, arising for example from incomplete correction of radiation damage or absorption, will have more serious effects on temperature factors than on atomic positions. The data must extend to a resolution of better than 2 A, otherwise temperature factors tend to be underestimated. Restraints in the refinement which assume that positional disorders of bonded atoms are highly correlated may bias the results. However, it is encouraging that in several structures (e.g., rubredoxin [193] and avian pancreatic polypeptide [194]) where the restraints were relaxed these assumptions were found to be valid. 

To reduce the error in the temperature evaluation caused by the uncertainty of the emissivity, radiation measurements for two or multiple distinct wavelengths may resolve the problem. For each wavelength, both spectral radiance temperature equations can be respectively written as... 

Radiation data gathered from full-scale testing is critical information used to design a flare therefore, accurate measurements are important. Several tips to help eliminate potential error and improve the accuracy of radiation measurements include the following (1) select the right radiometer, (2) avoid convective cooling effects,... 

Consider a radioactive source emitting electrons and assume that one attempts to measure the number of electrons per unit time emitted by the source. For every atom of the source there is a probability, not a certainty, that an electron will be emitted during the next unit of time. One can never measure the exact number. The number of particles emitted per unit time is different for successive units of time. Therefore, one can only determine the average number of particles emitted. That average, like any average, carries with it an uncertainty, an error. The determination of this error is an integral part of any radiation measurement. 

This chapter discusses statistics at the level needed for radiation measurements and analysis of their results. People who perform experiments need statistics for analysis of experiments that are statistical in nature, treatment of errors, and fitting a function to the experimental data. The first two uses are presented in this chapter. Data fitting is discussed in Chap. 11. 

The first chapter defines the energy range of the different types of radiation for which instruments and methods of measurement are considered it gives a brief discussion of errors that emphasizes their importance and, finally, it presents a very general description of the components of a counting system. This last part of the chapter is necessary because a course on radiation measurements involves laboratory work, and for this reason the students should be familiar from the very beginning with the general features and functions of radiation instruments. 

All spectrometric measurements are subject to indeterminate (random) error, which will affect the accuracy and precision of the concentrations determined using spectrometric methods. A very common source of random error in spectrometric analysis is instrumental noise . Noise can be due to instability in the light source of the instmment, instabihty in the detector, variation in placement of the sample in the hght path, and is often a combination of all these sources of noise and more. Because these errors are random, they cannot be eliminated. Errors in measurement of radiation intensity lead directly to errors in measurement of concentration when using cahbration curves and Beer s Law. 

The results that guide emergency response decisions must be susceptible to subsequent evaluation. Chain-of-custody information, procedural instructions and instruction changes, analyst comments, radiation measurement records, and QC data must be in writing and preserved despite the confusion that tends to accompany emergency response. Occurrence of contamination, instrument failure, analytical problems, and calculating error must be annotated. Samples and measured sources must be retrievable for subsequent confirmatory or expanded measurements. 

A significant fraction of laboratory effort mnst be devoted to weeding out false results by consistent application of the QA techniques discussed in the earlier sections of this chapter, preferably before such results are reported. The QC program and interlaboratory comparisons are designed to identify systematic errors in chemical analysis and radiation measurement due to problematic methods or analysts. By chance, QC results instead may identify an occasional error due to lack of attention in analysis, measurement, recording, or calculation. More commonly, occasional errors are found during data review (see Section 10.6). 

Errors in measuring the reflectivities AR/R for calculation of the optical constants of layers can be divided into two groups [467] (1) errors connected with the photometric accuracy with which R is determined and (2) errors inherent in the method of obtaining the spectra, including inaccuracy in the angle of incidence of radiation, convergence of the radiation beam and its influence on the accuracy, and the ideality of the polarizer. 

An important characteristic of the Poisson distribution is that the mean and variance are equal. Thus, if N counts are measured in an arbitrary time T, then the mean deviation for the number of counts can be estimated as sJN. If a background measurement shows Nb counts in time T, then N-N, counts are due to the sample. The mean deviation for this is / N + Nf,). The relative error of radiation measurement can be decreased by increasing the number of counts. Two alternatives are obvious increasing the amount of radioactivity and increasing the counting time. 

The heat transport phenomena conduction, radiation, convection, and heat transfer are of central importance in all calorimeters. On the one hand, the occurrence of a temperature difference causes a heat flow and thus creates the possibility of heat losses toward the surroundings (heat leaks) - namely, heat flows not detected by the measuring sensor and therefore not measured by the calorimeter. On the other hand, no heat exchange can take place in the absence of a temperature difference. The experimenters find themselves in a dilemma to be measured, heat must be made to flow, but every heat exchange is associated with temperature differences that create errors in measurement (e.g., heat leaks). 

This method has a distinct advantage because no moving parts are inside the fluid container. It provides high repeatability and little hysteresis error. Primary disadvantages, besides those inherent to any radiation measurement, include the need for windows transparent to the radiation (or long counting times) and the need for a fairly long adsorption path. 

The temperature of the gas leaving the sulfur burner is a good indication of SO2 concentration, even though the thermocouples employed for temperature measurement (qv) frequently read somewhat lower than the tme temperatures, because of radiation and convection errors. A temperature of 970°C corresponds to about 10.0 vol % SO2, 1050°C to 11.0 vol % SO2, and 1130°C to 12.0 vol % SO2. Other temperatures and concentrations are in similar proportion. 

Contact temperature measurement is based on a sensor or a probe, which is in direct contact with the fluid or material. A basic factor to understand is that in using the contact measurement principle, the result of measurement is the temperature of the measurement sensor itself. In unfavorable situations, the sensor temperature is not necessarily close to the fluid or material temperature, which is the point of interest. The reason for this is that the sensor usually has a heat transfer connection with other surrounding temperatures by radiation, conduction, or convection, or a combination of these. As a consequence, heat flow to or from the sensor will influence the sensor temperature. The sensor temperature will stabilize to a level different from the measured medium temperature. The expressions radiation error and conduction error relate to the mode of heat transfer involved. Careful planning of the measurements will assist in avoiding these errors. 

The value of k is determined experimentally by gas temperature measurement. The measurement error of a simple pyrometer can be 250 to 300 K, due to re-radiation to water-cooled surroundings, and the values given below are based on measurement by a Land multi-shielded high-velocity suction pyrometer. Typical values for normal excess air at or near full boiler load are ... 

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