Silver active

The photometer is adequately described in Figure 3-2. In the phosphor-photoelectric detector (2.10), the x-ray beam strikes a silver-activated zinc sulfide phosphor to produce blue-violet light that is changed by the multiplier phototube (Type 931-A) into an electric current that is amplified and read on a suitable micro- or milliammeter. A stable power supply for both x-ray tube and detector circuit are essential, as is clear from the circuit diagrams.10... 

Some oxide-type minerals have been found to luminesce when irradiated. A simple example is ruby (aluminium oxide with chromium activator), which emits bright-red light. The phosphors are incorporated into colour television screens to emit the colours blue (silver-activated zinc sulphide), green (manganese-activated zinc orthosilicate), and red (europium-activated yttrium vanadate). 

The standard potential of these ISEs, analogous to halide ISEs, depends on the activities of silver and sulphur in the membrane. When metallic silver is used as a contact soldered directly onto the membrane, the silver activity in the membrane equals one and the Ag2 S ISE has properties identical with a silver electrode of the first kind or with a silver sulphide electrode of the second kind, depending on the solution with which it is in contact [203], The membrane that is in contact with electrolyte on both sides behaves similarly [106],... 

If the graphite contact in cell (6.2.1) is replaced by a silver contact, quantity 6 corresponds to saturation of silver sulphide with silver and the silver activity in Ag2 S equals unity. Then juQ = ju and E=0. The standard potential of the Ag2 S ISE is identical with the standard potential of the silver electrode, O.ISE AgVAg = + 0.799 V versus SCE. On the other hand, when Ag2 S is in equilibrium with elementary sulphur (for example, when Ag2 S is prepared in an oxidizing medium [417]) then... 

Neutron Howitzer Irradiation. Whole-coin irradiation, however, has the advantage that the internal portions of the coin are irradiated and activated, thus permitting nondestructive analysis of the entire coin. One method we have devised is based on such irradiation but in a neutron beam that is about 100,000,000th as intense as that in a reactor. Only the silver in the coin is activated sufficiently for detection. None of the 255-day half-life isotope is detected, and the analysis is based on silver isotopes with half-lives of 24 sec (110Ag) and 2.4 min (108Ag). This silver activity dissipates in 10-15 min, and the coin is unharmed. We have analyzed over 4000 coins by this method which is described in Refs. 2, 3, 4. 

Silver Activation. Doping zinc sulfide with silver leads to the appearance of an intense emission band in the blue region of the spectrum at 440 nm, which has a short decay time. Weak luminescence in the green (520 nm) and red regions can also occur. The blue band is assigned to recombination at substitutionally incorporated silver ions [5.314], [5.315]. The red band is caused by luminescence processes in associates of silver ions occupying zinc positions with neighboring sulfur vacancies... 

Industrial silver-activated zinc sulfide phosphors use the intense blue emission exclusively. The ZnS Ag phosphor for cathode ray tubes is obtained by firing zinc sulfide and silver nitrate at ca. 1000 °C in the presence of sodium chloride (coactivator Cl-) [5.318]. The afterglow can be further reduced by addition of 10-3-10-4% of nickel ions. 

As a second kinetic example we investigate the spread of a perturbation in the Ag activity from the surface of the Ag2S crystal into the bulk. The experimental situation is shown in Figure 15-10a. An electrochemical cell is set up which allows one to change the silver activity (or the composition from <5 to <5 +A J) at one end of the sulfide sample by a perturbing voltage pulse which injects Ag+ ions and... 

As on the chlorine side the contact AgCl/Cl2 establishes a well-defined silver activity, it can also be regarded as a chlorine or silver activity cell analogously the contact Ag/AgCl provides a well-defined partial pressure of chlorine. 

Figure 24. Silver activates diazo compounds The WoUf reaction.

Clusters of three phosphors are used for each dot in a color television or computer display screen. Commonly used phosphors for this purpose are europium-activated yttrium orthovanadate, YVO4, for the red color, silver-activated zinc sulfide for blue, and copper-activated zinc sulfide for green. 

Silver use is prevalent for anti-bacterial applications, particularly in Japan where some 70% of the silver actives are currently sold. 

Catalysts with a manganese oxide active phase are more efficient than the ones with the silver active phase. In Figitre 2, the maximum temperature of 180°C is slightly below the maximum adiabatic maximum temperature of around 220°C, indicating a good catalytic behaviour. The ignition delay depends on the starting temperature of the system. 

Main mercury species in ambient air are elemental mercury (Hg°), reactive gaseous mercury (Hg(II)), mercury bound to aerosols, and methylmercury. Though dimethyl-mercury is together with Hg° the most volatile form of Hg, it has not been detected unequivocally in the atmosphere. Elemental mercury represents >95% of Hg in the atmosphere with ambient concentrations at the order of 1-5 ng m whereas MeHg in air was found to be in the range of 1 to 20 pg m (Pirrone et al. 2001). For this reason, in most cases mercury is pre-con-centrated on solid absorbers (gold, silver, activated carbon traps, etc.) prior to analysis (Drabaeck and Iverfeldt 1992, Horvat 1996). 

A much more plausible explemation considers the silver activator to have the Ag- electronic configuration. The ground state would then be ... 

Silver-activated zinc sulfide [ZnS(Ag)] has been used since radioactivity was first measured to detect alpha particles. It is relatively insensitive to electrons and gamma rays because it is not transparent to its own radiation. Radiation interactions within the detector are not recorded only its surface, where alpha particles interact, emits scintillations. The ZnS is doped with silver to shift its scintillations to a longer wavelength for better PMT response. 

Several techniques to measure air concentrations are outlined by Breslin (1980). Most of the techniques for measuring radon use the fact that both radon-222 and the short-lived daughters are alpha- emitting nuclides. The sample is collected and taken back to the laboratory for "alpha-counting" or an alpha-detector is taken to the field for on-site measurement. There are several ways to measure alpha decay. A scintillation flask is one of the oldest and most commonly used methods. The flask is equipped with valves which are lined with a phosphor (silver-activated zinc sulfide) and emit light flashes when bombarded with alpha particles. Other methods draw the air through a filter (or filters) for a variety of time intervals and then count the number of alpha-decays occurring on the filter. EPA (1986) and NCRP (1988) reports provide more in-depth discussions of these methods. 

Nickel-coated poly-p-phenylene terephthalamide film was prepared as follows. A section of poly-p-phenylene terephthalamide film was immersed momentarily in a 0.1 M solution of K+ 0-t-Bu in DHSO and then in a 0.1 M solution of silver trifluoroacetate in DHSO. The film was washed liberally with water and dried. Nickel was plated onto this silver-activated film using a known method of electroless plating as follows a section of film weighing 0.038 g was immersed in a solution of 5.0 g of nickel chloride hydrate and 0.2 g of dimethyl amine borane in a mixture of 50 mL of water and 50 mL of dimethyl formamide for 1.5 hrs. The film was then rinsed liberally with water and dried in a vacuum oven at 110 C for 2 hrs. The resulting nickel coated film weighed 0.095 g and was electrically conductive. 

This method involves filling a container with an air sample of radon and transferring it to a laboratory for analysis. One of the most useful devices is the scintillation flask, known as the Lucas cell. This consists of a chamber whose walls are coated with a scintillating material such as silver-activated zinc sulfide. The cell is optically coupled to a photomultiplier tube to count the light pulses (scintillation) induced by the a-particles interacting with the zinc sulfide coating. The scintillation flask can be filled either by evacuation or by airflow using a... 

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