Scintillation Device

An ion beam causes secondary electrons to be ejected from a metal surface. These secondaries can be measured as an electric current directly through a Faraday cup or indirectly after amplification, as with an electron multiplier or a scintillation device. These ion collectors are located at a fixed point in a mass spectrometer, and all ions are focused on that point — hence the name, point ion collector. In all cases, the resultant flow of an electric current is used to drive some form of recorder or is passed to an information storage device (data system). 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

A scintillation device is a material that, upon interaction with any radiation, produces light that is proportional to the energy of the radiation. Sodium iodide crystals or germanium serve as scintillation materials. 

Spectrophotometric devices, called microplate readers, collect raw data resulting from colorimetric or fluorescent screens. Similarly, scintillation devices measure the amount of radioactivity in samples from drug screens. The computer format of the data will then allow it to be exported into a spreadsheet or statistical analysis computer program for analysis. 

Figure 9 Scheme of the scintillation device for determining the amount of radiotracer deposited in head, neck, and thorax. The configuration of scintillation detectors and shielding allows detection of particle removal from the thorax regardless of the spatial distribution of particles within thorax and stomach. 

This paper describes a solid state scintillator device into which gamma isotope labeled radioassay samples can be placed for subsequent counting in a liquid scintillation counter. 

By placing a suitable detector at the focus (a point detector), the arrival of ions can be recorded. Point detectors are usually a Faraday cup (a relatively insensitive device) or, more likely, an electron multiplier (a very sensitive device) or, less likely, a scintillator (another sensitive device). 

Electronic Applications. Electronic appHcations make up a significant sector of the cesium market. The main appHcations are in vacuum tubes, photoemissive devices, and scintillation counters (see Electronic materials). 

The equipment used in gamma spectroscopy includes a detector, a pulse sorter (multichannel analyzer), and associated amplifiers and data readout devices. The detector is normally a sodium iodide (Nal) scintillation counter. Figure 27 shows a block diagram of a gamma spectrometer. 

The concentration of 222Rn in air was determined with a radon measurement detector. The detector allows realizing continuous radon monitoring. It consists of an electronic unit and a scintillation cell. The electronic unit contains power supply, amplifier, discriminator, timer, counter, and indicator. The scintillation cell contains the zinc sulfide scintillator, photomultiplier, preamplifier, high voltage power supply and chamber with a volume of 200 mL over the scintillator. This chamber is filled with the gas to be analyzed. The air is either pumped or diffuses into the scintillation cell. The scintillation count is processed by electronics, and radon concentrations for predetermined intervals are stored in the memory of the device. 

Radiations outside the ultraviolet, visible and infrared regions cannot be detected by conventional photoelectric devices. X-rays and y-rays are detected by gas ionization, solid-state ionization, or scintillation effects in crystals. Non-dispersive scintillation or solid-state detectors combine the functions of monochromator and detector by generating signals which are proportional in size to the energy of the incident radiation. These signals are converted into electrical pulses of directly proportional sizes and thence processed to produce a spectrum. For radiowaves and microwaves, the radiation is essentially monochromatic, and detection is by a radio receiver tuned to the source frequency or by a crystal detector. 

A single channel pulse height analyser utilizes an electronic gate typically 0.1 V wide, which only accepts pulses between the preset upper and lower limits. Scintillation counters frequently employ such devices to remove small noise pulses and large pulses initiated by cosmic rays, as well... 

Light is strong enough to knock off electrons from cesium, which makes this phenomenon useful as a coating for photoelectric cells and electric eye devices. Cesium iodide (Csl) is used in scintillation counters (Geiger counters) to measure levels of external radiation. It is also useful as a getter to remove air molecules remaining in vacuum tubes. 

Geiger counter. Also known as a scintillation counter. A device used to detect, measure, and record radiation. The instrument gets its name from one of its parts, the Geiger tube, which is a gas-fiUed tube containing coaxial cylindrical electrodes. 

Neon is also used in scintillation counters, neutron fission counters, proportional counters, and ionization chambers for detection of charged particles. Its mixtures with bromine vapors or chlorine are used in Geiger tubes for counting nuclear particles. Helium-neon mixture is used in gas lasers. Some other applications of neon are in antifog devices, electrical current detectors, and lightning arrestors. The gas is also used in welding and preparative reactions. In preparative reactions it provides an inert atmosphere to shield the reaction from air contact. 

So far, we have seen that if we measure the Bragg angle of the reflections and successfully index them, then we get information on the size of the unit cell and, if it possesses any translational symmetry elements, also on the symmetry. In addition, we have seen that the intensity of each reflection is different and this too can be measured. In early photographic work, the relative intensities of the spots on the film were assessed by eye with reference to a standard, and later a scanning microdensitometer was used. In modern diffractometers, the beam is intercepted by a detector, either a charge coupled device (CCD) plate or a scintillation counter, and the intensity of each reflection is recorded electronically. 

A further alternative to the Faraday cup - the Daly detector13 - is illustrated in Figure 4.6 a. In the Daly detector a conversion dynode, which is at a high negative potential ( — 40 kV), is applied to convert ions into electrons. The Daly detector was developed from an earlier device using a scintillator (e.g., of phosphorus) for the direct detection of positive ions. 

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