Emission secondary

The spectrum of the secondary emission, that is, the intensity of X-ray radiation as a function of wavelength is established using a crystal analyzer based on Bragg s law. 

Confusingly, FAB is sometimes called secondary ion mass spectrometry (SIMS), the secondary referring to the nature of the process (primary bombardment, secondary emission), but see next item. 

Secondary Emissions from Basic Oxygen Process Steelmaking Facilities for Which Construction Commenced after January 20, 1983 Sewage Treatment Plants Primary Copper Smelters Primary Zinc Smelters... 

Because the various types of particle can appear in both primary excitation and secondary emission, most authors and reviewers have found it convenient to group the techniques in a matrix, in which the columns refer to the nature of the exciting particle and the rows to the nature of the emitted particle [1.1-1.9]. Such a matrix of techniques is given in Tab. 1.1., which uses the acronyms now accepted. The meanings of the acronyms, together with some of the alternatives that have appeared in the literature, are given in Listing 1. 

Secondary Emission - Electrons striking the surface of a cathode could cause the release of some electrons and, hence, a net amplification in the number of electrons. This principle is used in the construction of photomultipliers where light photons strike a photoemitting cathode releasing photoelectrons. These electrons are subsequently amplified striking a number of electrodes (called dynodes) before they are finally collected by the anode. 

Booths are often used for work prtKedures with momentum-driven emissions. In such cases the capture devices must be placed to rake advantage of this momentum. For example, a spray paint booth would have the exhaust location downstream of the painting location, most likely at the back of the booth. The capture devices in the back wall should be suitable to reduce the momenriim of the emitted particles in such a way that they are not reflected back into the work area. Floor exhaust should be able to keep the heavier particles dowm so that they cannot be a source for secondary emissions. 

Step 1 Determine primary emission heat content. This step should be taken early in the design stage to determine if the enclosure will capture both primary and secondary emissions. The heat content of furnace emissions and the temperature limitation on the fume collector are considered for this task. The off-gas heat content is calculated for furnace reactions during melting and refining periods. The maximum heat content should be used for design. Assuming a fabric... 

For the remaining steps, a small, low-production furnace is under consideration with both primary and secondary emissions being captured by the enclosure. 

Step 2 Determine secondary emission plume flow rate. The plume flow rate for charging and tapping is predicted by design equations for plume flow rates (compare Section 7.5). The enclosure height is taken as the limit of plume rise. The plume rise from the open furnace before charging should also be calculated. This event is also considered as a prolonged emission. 

Haas GA. 1972. Work Function and Secondary Emission. American Institute of Physics Handbook. New York McGraw-Hill. pp. 172-181. 

High sensitivity is featured by the electrical methods used to detect EEPs. These are based on measuring small currents that occur in the course of selective ionization of EEPs, or currents of secondary emission of electrons or ions knocked by EEPs out of the surface of solid targets (if such emission is taking place). 

The dependence of the initial velocity of changes in the electrical conductivity of Au/ZnO being acted upon by He on the surface concentration of Au (curve 2) also has its clear maximum at some point of 2 10 atoms/cm. The fact that peaks of curves / and 2 are abscissaspaced apart almost an order of magnitude engages our attention, i.e. we see that there is no direct correlation between the secondary emission currents and the sensitivity of Au/ZnO film to metastable atoms. 

SCR systems at stationary diesel engines profit from the high exhaust gas temperatures of about 350-400 C, caused by the usually constant high load operation conditions of the diesel engine. In this temperature window nearly all known SCR catalysts are very active. Moreover, weight and size of the exhaust gas catalyst are usually not strictly limited, which results in a good NO, reduction efficiency (DeNOJ. However, DeNO, is not the only criterion for an SCR catalyst. Further requirements are excellent selectivities regarding NO and urea/ammonia as well as low ammonia slip, which is an undesired secondary emission of the SCR process. Therefore, all SCR catalysts exhibit surface acidity, which is necessary to store ammonia on the catalyst surface and, thus, to prevent ammonia slip. 

Schwartz, M., and P.L. Copeland Secondary emission by positive ion bomb. 

Experiment 3 In general, sonoluminescence emission is not discemable with the naked eye. The luminosity of the secondary emission from luminol (oxidised by sonochemically produced OH radicals) however, is several orders of magnitude brighter and is easily seen in a dark room. Prepare a 0.1 mM aqueous luminol solution in 0.1 M NaOH. Sonicate this solution and observe the emission pattern. This will appear as bands of light and dark if a standing wave reactor is used or in more elaborate forms in different reactors. If a 20 kHz horn is used, a cone shaped zone of luminescence will be observed. Explain the emission pattern. 

Wire radius Collector rod i US Wire roughness Secondary emission Avoidnche coefficient Ionizing radiation... 

In testing the possibility of proton transfer as a quenching mechanism of tyrosine in oligopeptide/polynucleotide complexes, Brun et a/.(102) compared the fluorescence emission spectra of the tyrosine and O-methyltyrosine tripeptides. They noted that, in the complex, the O-methyltyrosine tripeptide had a unique secondary emission near 410 nm. Whether this emission is related to that observed by Libertini and Small(94) is an important question. While one must consider the possibility that two tyrosine side chains could be converted to dityrosine, (96) which has a fluorescence at 400 nm, another intriguing possibility is ambient temperature tyrosine phosphorescence. This could happen if the tyrosine side chain is in a rigid, protective environment, very effectively shielded from collisions with quenchers, particularly oxygen. 

Once electrons have been emitted by the photocathode, they are accelerated by an applied voltage induced between the photocathode and the first dynode (Uq in Figure 3.17). The dynodes are made of CsSb, which has a high coefficient for secondary electron emission. Thus, when an electron emitted by the photocathode reaches the first dynode, several electrons are emitted from it. The amplification factor is given by the coefficient of secondary emission, S. This coefficient is defined as the number of electrons emitted by the dynode per incident electron. Consequently, after passing the first dynode, the number of electrons is multiplied by a factor of 5 with respect to the number of electrons emitted by the photocathode. The electrons emitted by this first dynode are then accelerated to a second dynode, where a new multiplication process takes place, and so on. The gain of the photomultiplier, G, will depend on the number of dynodes, n, and on the secondary emission coefficient, 5, so that... 

Now calculate the minimum light power that can be measured with a photomultiplier using the photocathode of Exercise 3.5 and with 10 dynodes, each of which has a secondary emission coefficient of 5 = 6. Estimate these minimum powers if the photocathode is cooled down to 5 °C. Assume a bandpass width of 1 Hz. 

Fig. 9. Relative secondary-electron yield as a function of ion energy for Ne "—Na ", Ar —K ", and Kr —Rb. A constant quantity equal to the estimated potential-secondary-emission coefficient has been substracted from the raw noble gas data. (From Ref. )...

Emissions of organic fragmentation products, so-called secondary emission products and reactive species from wood-based furniture coatings have been studied (Saltham-mer et al., 1999). Aliphatic aldehydes and some photoinitiator fragments have a strong... 

PHOTOEMISSION AND PHOTOMULTIPLIERS. Photoemission is the ejection of electrons from a substance as a result of radiation filling on it Photomultipliers make use of the phenomena of photoemission and secondary-electron emission in order to detect very low light levels The electrons released from the photocathode by incident light are accelerated and focused onto a secondary-emission surface (called a dynode). Several electrons are emitted from the dynode for each incident primary electron. These secondary electrons are then directed onto a second dynode where more electrons are released. The whole process is repealed a number of times depending upon the number of dynodes used, In this manner, it is possible to amplify the initial photocurrent by a factor of 10s or more in practical photomultipliers. Thus, the photomultiplier is a very sensitive detector of light. 

Dark noise in photomultipliers is caused by (1) leakage current across insulating supports (2) field emission from electrodes (3) thermal emission from the photocathode and dynodes (4) positive ion feedback to the photocathode and (5) fluorescence from dynodes and insulator supports. Careful design can eliminate all but item (3). Associated with the photocurrent from the photocathode is shot noise. There is also shot noise from secondary emission in the multiplier structure. 

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