Hollow cathode electron source

Anodic arcs can he categorized as the source of electrons. The electrons can arise from a heated thermoelectron-emitting surface, a hot or cold hollow cathode, or an arc cathode. By bending the e-beam in a magnetic held, the vaporized material may be kept from impinging on the electron source. Commercial sources for anodic arc deposition are available with most using a hollow cathode electron source. 

It is necessary that the hollow-cathode lamp source be pulsed or modulated at a certain frequency and for the amplifier to be locked in to this frequency to permit discrimination against the continuous emission signal coming from the atomiser. Only the resonance radiation from the lamp must be seen. In modem digital electronic instruments the lamp cycle is controlled by a sophisticated electronic clock which is sampled to provide the short pulses of... 

When water vapor is passed through the discharge of a hollow-cathode ion source it is ionized by primary electrons, basically by EL Due to ion-molecule reaction sequences the product ion mixture forms HsO" ions with high selectivity of up to 99.5% (Chap. 7.2.5) [51,52]. Even or ions from nitrogen rapidly react with water molecules in the source region to result in more HsO" ions. Thus, a high (typical count rates of 10 counts s ) and almost pure flux of hydronium primary ions is provided that may then serve as reactant ions in a PICI process ... 

In a hot hollow cathode source, the gas pressure in a tube is raised by having an orifice restricting the exit of gas from the tube and the thermoelectrons are trapped in the anode cavity, A high density plasma beam exits the orifice and the electrons may be used to evaporate material or ionize gases. The hot hollow cathode is capable of much higher electron and ion densities than the cold hollow cathode system. The hollow cathode electron soirrce can be used to augment plasma generation. 

The temperature in a Scandinavian source is, for example, around 1000°C. If this is not enough for certain elements, one may use a hollow cathode source which operates at 1500 - 2000°C or even a special high-temperature source using electron bombardment for the vaporization of the material. In that way one may achieve temperatures as high as 3000°... 

The hollow cathode is the most frequently used atomic absorption line source. A cupped cathode made of the element to be quantitated and a tungsten anode are positioned in a glass tube which is filled with an inert gas at reduced pressure. The end of the tube is sealed with an optically transparent quartz window. When an electrical potential is struck between the electrodes, the inert gas at the anode is ionized and moves toward the cathode. The element in the cup is sputtered into the gas and excited by the discharge to higher electronic states. The lamp emits intense lines due to resonance radiation. The emission will also show lines characteristic of the electrode itself as an impurity. When feasible, the electrode may be made of the element to be analyzed, thereby avoiding this possible interference. Lamps are available for over 60 different elements and are readily obtainable,... 

A typical setup is shown in Figure 10.12. The two light beams from the lamps are combined by a half-coated mirror (e.g., coated with small reflecting circles so that it will reflect the continuum radiation but will allow space in the mirror for the radiation from the hollow-cathode lamp to pass). Each lamp is pulsed electronically to provide an AC signal, but the two lamps are 180° out of phase. A phase-sensitive detection system then measures the difference of the two signal intensities (which are initially balanced). The sharp-line source measures both atomic absorption and... 

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