Radiation detector

Photographic emulsions and photoelectric detection devices can be used as detectors for electromagnetic radiation between 150 and 800 nm. Among the photoelectric devices, photomultipliers are the most important but new solid state devices have become a useful alternative. 

These were frequently used for analytical spectrography. They allow the whole spectrum to be recorded simultaneously and, accordingly, for multielement survey analysis they have a high information capacity. However, their processing is long, the precision obtainable is low and they do not allow on-line data processing. Ac- 

When a photographic emulsion is exposed to radiation a blackening is produced, which is a function of the radiant energy accumulated during the exposure time. It is given by  

Originally, only the linear part of the characteristic was used for quantitative work. However, soon transformations were described, which also allowed this characteristic to be linearized at low blackenings. The P-transformation has been 

Yo is the inertia of the emulsion and the constants k and y describe the properties of the emulsion but they also depend on the densitometer. Yo in most cases is not known as AP or AY values are usually used, y = tan a and is the contrast of the emulsion. The emulsion can be calibrated with the aid of a step filter which is placed in front of the spectrometer. When the ratio of the intensities passing through two sectors of the filter is given by  

X is the transmission, (Sq is the flux through a non-irradiated part of the emulsion and is the flux obtained for an exposed part of the emulsion, when a white light beam is sent through the emulsion in a so-called densitometer. The emulsion characteristic for a selected illumination time gives the relationship between the logarithm of the intensity (Y = log 1) and the blackening and has an S-shape (Fig. 22). 

Organic phosphors (commonly loaded plastics) exhibit luminescence, of which the fastest process is fluorescence a gamma ray releases an energetic electron which then excites molecules in the phosphor these lose energy in decaying to an intermediate state and then de-excite with photoemission. 

Inorganic phosphors can have their luminescent efficiency improved by the addition of an activator, e.g., 0.1% T1 in Nal (then referred to as Nal(Tl) excitation energy of Nal molecules is transferred to impurity centres in the crystal lattice, which de-excite with photoemission characteristic of the impurity. The higher atomic number of these phosphors improves the probability of photoelectric effect events. Nal is deliquescent and has to be sealed in an A1 pot with glass window. The useable light output is improved by painting white to improve reflection from the surface. 

The light output of NaI(Tl) is about 104 photons, of wavelength 410 nm, per MeV of incident gamma energy. Loaded plastic scintillators yield about 4000 photons per MeV in a wavelength range 350—480 nm. 

The rate of emission of photons from a scintillator is XNoeh, where N0 is the total number of photons emitted and X is the decay constant of the phosphor. For Nal(Tl) the decay time x (=A I) 220ns, whereas for fast plastic x 2ns (i.e., in the first ns 40% of the light from a plastic scintillator is typically emitted, whereas only 0.5% is emitted from Nal(Tl)). 

Scintillators like NaI(Tl) can be made position-sensitive for applications like 2D-ACAR (section 7) and medical imaging [19]. Light from a large-diameter crystal is detected by a close-packed array of PM tubes. 

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The method is based on the international standard ISO 4053/IV. A small amount of the radioactive tracer is injected instantaneously into the flare gas flow through e.g. a valve, representing the only physical interference with the process. Radiation detectors are mounted outside the pipe and the variation of tracer concentration with time is recorded as the tracer moves with the gas stream and passes by the detectors. A control, supply and data registration unit including PC is used for on site data treatment... 

For this kind of case, a modification of the dilution method is being developed. Instead of using an external fixed-geometry measurement chamber, a suitable part of the process, e.g. a stretch of pipe, is used. A radiation detector is mounted on the outside of the pipe, and a tracer emitting sufficiently hard gamma radiation is used. As sufficient mixing can be achieved by injecting upstream the separator the radiation level found will be strictly proportional to the concentration and thus inversely proportional to the true flow rate. 

In situ measurement of the concentration of radioactive tracers in the different phases requires that the phases are separated and arranged according to density difference over the measurement cross section in a horizontal pipe. In general, the measurements are performed with two spectral gamma radiation detectors placed on top and bottom of the pipe respectively. 

The size of the leakage was determined as follows. Radiation detectors were mounted on the inlet of the first side, and the outlet of the second side of the heat exchanger and at additional locations for control. A short pulse of Kr-85 tracer (<0.1 sec) was injected into the feed stream, which gave rise to detector responses shown in figure 3. 

Lead sesquioxide is used as an oxidation catalyst for carbon monoxide ia exhaust gases (44,45) (see Exhaust control), as a catalyst for the preparation of lactams (46) (see Antibiotics, P-lactams), ia the manufacture of high purity diamonds (47) (see Carbon, diamond-natural), ia fireproofing compositions for poly(ethylene terephthalate) plastics (48), ia radiation detectors for x-rays and nuclear particles (49), and ia vulcanization accelerators for neoprene mbber (50). 

Electronic. Diamonds have been used as thermistors and radiation detectors, but inhomogeneities within the crystals have seriously limited these appHcations where diamond is an active device. This situation is rapidly changing with the availabiHty of mote perfect stones of controUed chemistry from modem synthesis methods. The defect stmcture also affects thermal conductivity, but cost and size are more serious limitations on the use of diamond as a heat sink material for electronic devices. 

A radioactive source was transferred from one container to another by remote operation in a shielded cell. A radiation detector, interlocked with the cell door, prevented anyone from opening the cell door when radiation could be detected inside it. To make sure the interlock was working, an operator tried to open the cell door, by remote control, during a transfer. He found he could open it. He then found that the closing mechanism would not work. Fortunately he had not opened the door very far. 

Fay and Lewis (1977) used spherical gas samples inside soap bubbles whose volumes ranged from 20 to 190 cm. Typically, a sphere was ignited with resistance wire, and the combustion process was then filmed with a high-speed camera. The fireball s maximum height and diameter, as well as the time needed to complete combustion, were evaluated. The fireball s thermal radiation was sensed by a radiation detector. Figure 6.3 relates fireball burning time and size to initial propane... 

Collecting optics, radiation detectors and some form of indicator are the basic elements of an industrial infrared instrument. The optical system collects radiant energy and focuses it upon a detector, which converts it into an electrical signal. The instrument s electronics amplifies the output signal and process it into a form which can be displayed. There are three general types of instruments that can be used for predictive maintenance infrared thermometers or spot radiometers line scanners and imaging systems. 

Most physicians do not test for americium in their offices, but they can collect samples and send them to special laboratories. Since americium is radioactive, it is normally measured by its radiation emissions. These emissions are used to tell the amount of americium (in curies or Becquerels) and the radiation dose it gives to your body (in Sieverts or rem). Radiation detectors measure the radiation that is released from objects or materials, including the whole body. If... 

This module describes the principles of radiation detection, detector operation, circuit operation, and specific radiation detector applications. 

SUMMARIZE the principles of operation of various types of radiation detectors. 

The pulsed operation of the gas-filled detector illustrates the principles of basic radiation detection. Gases are used in radiation detectors since their ionized particles can travel more freely than those of a liquid or a solid. Typical gases used in detectors are argon and helium, although boron-triflouride is utilized when the detector is to be used to measure neutrons. Figure 5 shows a schematic diagram of a gas-filled chamber with a central electrode. 

The alpha curve is higher than the beta curve from Region I to part of Region IV due to the larger number of ion pairs produced by the initial reaction of the incident radiation. Detector voltage principles are summarized below. 

The Geiger-Muller detector is a radiation detector which operates in the G-M region. 

The scintillation counter is a solid state radiation detector. 

The scintillation counter is a solid state radiation detector which uses a scintillation crystal (phosphor) to detect radiation and produce light pulses. Figure 24 is important in the explanation of scintillation counter operation. 

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