Radiation source

An ideal radiation source for spectroscopy should have the following characteristics  

The source must emit radiation over the entire wavelength range to be studied. 

The intensity of radiation over the entire wavelength range must be high enough so that extensive amphfication of the signal from the detector can be avoided. 

The intensity of the source should not vary significantly at different wavelengths. 

It is obviously desirable to have an intense radiation source, so that the size of sample required or the time taken to perform an experiment can be minimized. It is also important to have radiation that is as monochromatic as possible, and this can be achieved by using a broad-band source with some filtering device, or by using a narrow-band source whose output frequency can be varied. If the source is also coherent 

Lasers can be classified as either continuous or pulsed sources, depending on whether their light output is steady or intermittent. This operational difference is dependent on the nature of the pump source, as a continuous excitation source will result in a continuous output beam, and a pulsed source yields a pulsed beam. Both have advantages for particular experiments. Continuous output is useful in Raman speetroseopy, for example, but pulsed lasers can be used in experiments involving short-lived speeies as deseribed in Section 2.8.1. Another operational difference is that some lasers are tunable, so they ean be used in a conventional way to scan a spectrum, whereas others are limited to a narrow frequency range. The titanium-doped sapphire laser is an example of a highly tunable infrared laser, commonly used in vibrational spectroscopy. The low-cost gas lasers tend to operate at a fixed frequency, but with superb resolution ( 3 GHz), exactly what is needed for Raman spectroscopy. Semi-conductor (also known as diode) and 

Schematic diagram illustrating how laser light is generated. 

Schematic and aerial photograph of Diamond Light Source, the UK s national synchrotron facility located in south Oxfordshire. The circumference of the storage ring is 561.6 m. Images coiutesy of Diamond Light Source. 

One other characteristic of synchrotron radiation can be used in spectroscopic studies. If just one bunch of electrons circulates round the ring, the output radiation consists of pulses, a few hundred picoseconds in length, separated by a few hundred nanoseconds. Thus time-dependent studies of short-lived species are possible and given the wide range of energies that are output, all sorts of sophisticated multiple resonance experiments are also feasible. 

The wide diversity of radiation sources utilized in irradiation of single organisms restricts our conunents concerning such sources to referring the reader to irradiation procedures described in the many papers on the subject of biological 

plant study plots or cages of animals could be irradiated at known levels corresponding to given distances from the source. Plant communities not available within the permanent field could be studied by moving the source to the sites of these communities. 

Both large and relatively small radiation sources placed in fixed positions were utilized by ecologists in various vegetation types in the United States, in an oak-pine forest (Woodwell, 1963), a shortgrass prairie (Fraley and Whicker, 1973a,b), a desert-shrub conununity (French, 1964), and an aspen forest (Ru- 

The shortgrass-vegetation radiation field consisted of 1.2 hectares in north-central Colorado and included a 8750-Ci Cs source that was suspended 1 m above the ground surface. The radiation field was divided into six sectors a control sector shielded from radiation, two chronically irradiated sectors, and 

In southeast France at the Cadarache Nuclear Research Center, a Mediterranean-type phytocenose was subjected to chronic gamma radiation from a Cs source of 1200 Ci. The mechanical aspects of the source consisted of a vertical tube 3 m in height in which the radioactive component moved from a lead chamber in the ground to the top of the tube, which contained a lead shield to prevent the escape of radiation from the study area. (Fabries, Grauby and Tro-chain, 1972). 

The source unit for atomic absorption should emit stable, intense radiation of the analyte element, usually of a resonance line of the element. Preferably the radiation should be a sharp line, with a width no greater than the width of the absorption line. There should be no general background or other extraneous lines emitting within the band pass of the monochromator. 

Laser is an acronym for light amplification by simulated emission of radiation. In SERS, as well as in other types of Raman scattering experiments, a continuous-wave (CW) gaseous ion laser is normally used, e.g., an argon-or krypton-ion laser. It is also possible to use a pulsed laser, such as a neodymium, Nd , in yttrium-aluminum garnet (YAG) laser however, a much 

FIGURE 4. Side view of laser plasma tube. 

TABLE I. Some Lasing Lines for Continuous-Wave Lasers  

FIGURE 5. Optical setup about the electrochemical cell in a 90° collection geometry. 

In the region beyond 5000 em (2 pm), blackbody sourees without envelopes are commonly used. The same spectral characteristics cited for the tungsten incandescent lamp apply to these as well. Unfortunately, the emission maximum lies in the near infrared. A fraetion of the shorter wavelength radiation is present as stray light, whieh is particularly serious for long-wavelength measurements. 

A elosely wound Niehrome helix ean be raised to ineandeseenee by resistive heating. A black oxide forms on the wire, whieh gives aeeeptable 

In the very far infrared beyond 200 cm (50 pm), blackbody-tyrpe sources lose effectiveness, since their radiation decreases with the fourth power of wavelength. High-pressure mercury arcs, with an extra quartz jaeket to reduee thermal loss, give intense radiation in this region. Output is similar to that from blackbody sources, but additional radiation is emitted from a plasma, whieh enhances the long-wavelength output. 

Monochromators employing prisms for dispersion use a Littrow 60° prism plane mirror mount. Midinfrared instruments employ a sodium ehloride prism for the region from 4000-650 cm (2.5-15.4 pm), a potassium bromide or cesium iodide prism and optics extend the useful speetrum to 400 em (25 pm) or 270 em (37 pm), respectively. Quartz monochromators, designed for the ultraviolet visible region, extend their eoverage into the near infrared to 2500 cm (4 pm). 

Plane-reflectance-grating monochromators dominate today s instruments. To eover the wide wavelength range, several gratings with different ruling 

Truly incoherent white light sources convenient for cw and transient absorption spectroscopy include cw, high pressure arc lamps ( 2 kW, spectral irradiance 3 mW/ (cm l cm2 sr)) and flashlamps ( 1 /, 10 ns). Note that the spectral irradiance of a 1 mW He-Ne laser (Av 1 MHz, dQ = 10-6sr, beam waist w 0.1 cm) is 3 x 109 W/(cm-1 cm2- sr), approximately 1012 times larger than that of the most robust incoherent cw radiation source. 

Continuously tunable laser systems are complex, many-component systems. In a typical research laboratory, far more time is often spent aligning and trouble-shooting the laser system than in recording spectra. 

If two beams of radiation with frequencies bj and u 2 are to be combined to generate radiation at u z, then momentum conservation requires 

In some nonlinear wave-mixing schemes, all energy and momentum remains in the radiation field, but in others (e.g., Stokes Raman shifting, optically pumped lasers) some energy and momentum is exchanged between the radiation field and the material medium. 

Certain crystals (those in which the unit cell lacks inversion symmetry) enable a variety of useful three-wave mixing processes Second Harmonic Generation (SHG), u 3 = uq + uq Sum Frequency Generation (SFG), uz = uq + w2 Difference Frequency Generation (DFG), u z — uq — w2 and Optical Parametric Oscillation (OPO), uq = uq + W3. In SHG, for example, energy and momentum (wavevector) conservation requires, for colinear propagation, 

In summary, Ti02 or modified forms of Ti02 are cui rently the materials with the highest prospects for photocatalytic reactors. It is expected that new photocatalysts in the neai future may considerably help increase the utilization of visible light. 

The radiation source, ultraviolet (UV) radiation or more specifically near-ultraviolet radiation, is a very important ingredient of the photocatalytic process. Ultraviolet radiation refers to electromagnetic radiation in the 200-400 nm wavelength range. UVA covers from 315 to 400 nm, UVB from 280 to 315 nm and UVC from 200 to 280 nm. 

Artificial UV lamps can power photocatalytic processes. The band gap of Ti02 anatase is 3.2 eV and the irradiation portion that can participate in the photocatalytic reaction is the one below 388 nm. 

TABLE 3.2. Artificial UV Light Sources as reported in Bolton et al. (1995) 

Parameter Low Pressure Mercury Lamp Medium Pressure Mercury Lamp High Pressure Mercury Lamp 

For absorption-based optical methods, one has to consider the linewidth of the excitation source in relation to the linewidth of the respective transition of the absorbing species. 

The half width of elemental lines is of the order of 0.002 nm when observed by emission spectroscopy with flame or electrothermal atomisation. A number of reasons can cause broadening of the linewidth, of which the most important and best understood are natural, pressure, resonance, and Doppler broadening. If a stable and sensitive detection is to be achieved, the linewidth of the excitation radiation must be narrower than the full width at half maximum (FWHM) of the analyte line. Under these conditions, the entire radiant energy produced by the excitation source will be available for absorption by the analyte. The typical line sources used for atomic absorption are element specific excitation sources such as the hollow cathode lamp or the electrodeless discharge lamp. But even continuum sources can be used with appropriate instrumental designs. 

The hollow-cathode lamp Initially described in 1916 by Paschen, the hollow cathode lamp (HCL) is probably the most versatile excitation source for atomic absorption spectrometry. A schematic of this excitation source is given in Fig. 12.4. It consists of a Pyrex glass tube in which the cathode and anode are located under an 

The boosted hollow-cathode lamp A very intense radiation source for AAS is the boosted hollow-cathode lamp. It has been developed from the regular hollow ath-ode lamp and includes a second pair of electrodes between which a boosted 

The electrodeless discharge lamp The electrodeless discharge lamp (EDL) is another atomic line source that allows one to produce a highly effective excitation source for elements that cannot be cast into hollow cathodes, such as mercury, arsenic, antimony, and some other elements. 

This section should provide a description of the operating organization s policy and the operational application of the ALARA (as low as reasonably achievable) principle. It should be in line with the conceptual description, as outlined in para. 3.51, and should demonstrate that as a minimum the recommendations for the application of the ALARA principle, as described in Refs [40,41], have been followed. 

This section should provide the estimated annual occupancy of the plant s radiation areas during normal operation and in anticipated operational occurrences. In order to reduce radiation doses to workers, the necessity of their presence in certain plant areas where radiation levels are high should be investigated (in order to limit working hours in those areas). 

This section should provide a description of all on-site radiation sources, with account taken of both contained and immobile sources and potential sources of airborne radioactive material. It should also cover the possible pathways of exposures. 

This section should provide a description of the design features of the equipment and the facility that ensure radiation protection. It should provide information on the shielding for each of the radiation sources identified, describe the features for occupational radiation protection, describe the instrumentation for fixed area monitoring of radiation and continuous monitoring of airborne radioactive material, and the criteria for their selection and placement, and address design provisions for any decontamination of equipment, if necessary. 

Where radiation dose targets are included in the design specification, these should be stated here. If relevant, this section should also include any radiation dose targets that relate to the dose levels expected for members of the public from the operation of the plant throughout its operating lifetime [23]. 

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The principles of gamma-ray radiography are the same as X-ray radiography except that a radioisotope is used as the radiation source rather than an X-ray tube. 

Recently we have made available the isotope Selenium for non-destructive testing. These sources offer technical specifications as required by industrial applications and provide various advantages when compared with other radiation sources. 

The paper presents the results from systematic comparisons of contrast and resolution obtained with different types of radiation sources on steel thicknesses from 5 to 40 mm. These results have been taken into account with the definitions of the European standard for radiographic inspection of weldments (EN 1435) that is approved since 1997. Conclusions from practical investigations on pipe line sites, in petrochcemical plants and in nuclear power stations will be discussed as well. Furthermore, the presentation will stipulate a variety of advantages obtained from the new source in terras of coUimation and radiation protection. 

In this paper a new design for a high-energy 3D-CT scanner equipped with a linear accelerator as radiation source and an area high-energy x-ray detector is presented. This system is the extension of a 2D system which is installed at present time [3,4]. 

The setup as seen in Figure 1 mainly consists of a Varian Linatron 3000A linear accelerator (LINAC) as radiation source, a rotational stage for sample manipulation, and a two-dimensional high-energy x-ray detector array consisting of four amorphous silicon area detectors Heimann RIS 256. The source to detector distance is 3.7 m. 

Induction electron accelerators - betatrons- are widely used as radiation sources in industrial flaw detection of materials and articles of high thickness. However, relatively low radiation intensity has become the barrier for the most wider betatron use in this area. For the efficiencyincrease of radiation control method of articles, as well as for the possibility to control materials and articles of the most thickness the significant increase of betatron radiation intensity has been required. 

Evaluation of results of those photos gives radiation source dimensions with area no more than Imm what defines high contrast of roentgen photos of flaw detected objeets. 

Equations 1 and 2 shows that the distance b between the radiation source and the object has big influence on the X-ray image [8]. Therefore you have to find a compromise between a small geometrical unsharpness and a sufficient high magnification to archive an optimal... 

The GAMMASCAN 1500 HR is a combined system for two-dimensional (2D-CT) and three-dimensional (3D-CT) computed tomography, as well as digital radiography (DR). The system is equipped with two separate detector systems for the fan-beam and cone-beam CT. The sire of the objects is limited to a height of four meters, maximum diameters of 1.5 meters and a weight of up to 15 tons. The turntable which carries the test samples can be moved along and across the beam direction ( X- and Y- direction). The radiation source and the detector systems can be moved in Z- direction, both, simultaneously and independently. 

Various computed tomography CT- scanners for industrial applications have been designed and constructed) They use as radiation sources X-ray tubes or gamma emitting radioisotopes and as detectors NaI(Tl)-scintillators for gamma rays and image intensifiers for X-rays. 

New metliods appear regularly. The principal challenges to the ingenuity of the spectroscopist are availability of appropriate radiation sources, absorption or distortion of the radiation by the windows and other components of the high-pressure cells, and small samples. Lasers and synchrotron radiation sources are especially valuable, and use of beryllium gaskets for diamond-anvil cells will open new applications. Impulse-stimulated Brillouin [75], coherent anti-Stokes Raman [76, 77], picosecond kinetics of shocked materials [78], visible circular and x-ray magnetic circular dicliroism [79, 80] and x-ray emission [72] are but a few recent spectroscopic developments in static and dynamic high-pressure research. 

Ytterbium metal has possible use in improving the grain refinement, strength, and other mechanical properties of stainless steel. One isotope is reported to have been used as a radiation source substitute for a portable X-ray machine where electricity is unavailable. Few other uses have been found. 

Turbidimetry and nephelometry are two related techniques in which an incident source of radiation is elastically scattered by a suspension of colloidal particles. In turbidimetry, the detector is placed in line with the radiation source, and the... 

One instrumental limitation to Beer s law is the use of polychromatic radiation instead of monochromatic radiation. Consider a radiation source that emits two wavelengths of... 

Work on EXAFS then progressed very little until the advent of the synchrotron radiation source (storage ring), described in Section 8.1.1.1. This type of source produces X-ray radiation of the order of 10 to 10 times as intense as that of a conventional source and is continuously tunable. These properties led to the establishment of EXAFS as an important structural tool for solid materials. 

Lead bricks are generahy used as temporary shields for radiation sources at nuclear power stations, research institutes, hospitals, and fuel reprocessing plants. Plat, rectangular bricks requite a double layer with staggered seams whereas the interlocking bricks requite only one course. Lead shot can be poured into inaccessible areas like a Hquid. 

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