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Detection Technology
Published in Rick Houghton, William Bennett, Emergency Characterization of Unknown Materials, 2020
Rick Houghton, William Bennett
A portable multichannel analyzer is an electronic multichannel analyzer unit that is combined with an instrument that detects gamma radiation. When programmed with a gamma ray library and analysis scheme, gamma emitting radioisotopes can be identified by their signature.
Photo/Electromagnetic Sources
Published in Peter E. J. Flewitt, Robert K. Wild, Physical Methods for Materials Characterisation, 2017
Peter E. J. Flewitt, Robert K. Wild
The Raman effect is an interaction between monochromatic light, generally from a laser source, and the chemical bonds within a specimen, which produces a result similar to infrared absorption (see Section 2.5.1) (Baranska et al. 1987, Colthup et al. 1990). When a laser beam impinges on a material, most of the light is scattered at the same wavelength (Rayleigh scattering), but a small number of photons may excite molecular vibrations in the specimen. These photons will lose an amount of energy equal to that imparted to the specimen and, therefore, will be scattered with a slightly longer wavelength. This difference in wavelength is known as the ‘Stokes shift’. When the excited atoms in the specimen subsequently relax, they release energy back to the incident beam which is scattered with a slightly shorter wavelength (anti-Stokes). Since the change in wavelength of the Stokes and anti-Stokes lines is extremely small (~λ/100) and the intensity is considerably reduced compared with the incident laser beam, it is necessary to use extremely sophisticated spectrometers to detect these photons. The depth of material sampled depends upon the wavelength of the incident beam but generally is of the order of a fraction of the wavelength. Figure 4.34a shows schematically the arrangement used in a commercial laser Raman imaging microscope. Considerable effort has gone into making these instruments compact, and instruments that are capable of fitting onto a small benchtop are available. The laser can be either argon (λ = 514 nm), helium neon (λ = 633 nm) or a semiconductor (λ = 780 nm). Monochromatic light from the laser passes through focusing optics and a dichroic beam splitter to the specimen in the optical microscope. The scattered light then passes through the beam splitter and filters to a cooled camera detector (CCD). The detector can be an optical multichannel analyser, an intensified photodiode array or a charge-coupled device. A personal computer is used to scan, collect and process the data. Such an instrument will have high sensitivity so that spectra can be recorded in seconds with an overall wavelength resolution of less than a wave number. The specimen is mounted on a microscope stage so that a conventional image can be obtained, and in the particular instrument illustrated, a Raman image can also be recorded with a spatial resolution of 1 mm.
Neutron Depth Profiling Study on 6Lithium and 10Boron Contents of Nuclear Graphite
Published in Journal of Nuclear Science and Technology, 2021
Shasha Lv, Jie Gao, Yuanyuan Liu, Yumeng Zhao, Jianping Cheng, Zhengcao Li
As shown in Figure 1(a), the energy of ions produced in the sample is measured using an implanted Si detector (i.e. the passivated implanted planar silicon (PIPS) detector, a kind of solid-state detectors based on high purity silicon crystals) with a resolution of 3.26 keV (the channel width of MCA which is considered to be the resolution of the energy measured). The pulses from the detector pass through a pre-amplifier and a spectroscopy amplifier. The energy spectrum is then collected in a Multi-Channel Analyzer (MCA).