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Scintillation Detectors
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
The sensitivity of the photocathode as a function of wavelength is very important. Some scintillators have a very strong light emission but, if not matched with a suitable light sensor, the advantage of the scintillator is lost. A typical example is CsI(Tl), which often is described as yielding a lower pulse-amplitude per MeV than the corresponding NaI(Tl) when connected to a standard bialkali PM tube. The total photon emission from CsI(Tl) is, however, more abundant than the NaI(Tl) emission, but it has a proportionally larger part occurring in the red/infrared not energetic enough to produce photoelectrons. At higher wavelengths the energy of the photon is not enough to create and eject a photoelectron from the photocathode. At lower wavelengths, around 350 nm, the glass obstructs the light. In some cases, glass can be substituted with quartz which enables transmission even in the UV-region, which is important, for instance for Xe.
Principles of Radiation Detection and Image Formation
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
X-ray and gamma radiation detection is essentially a three-stage process:A solid scintillation crystal captures and converts X-rays into light.Light is then converted into a small electrical signal by the photocathode.Finally, a photomultiplier is used to amplify the signal into a much larger useful electronic signal.
Scintillation Fiber Optic Dosimetry
Published in Arash Darafsheh, Radiation Therapy Dosimetry: A Practical Handbook, 2021
PMTs are manufactured for working in ultraviolet, visible, and infrared wavelengths. Important parameters that should be considered in identifying a PMT are their spectral response, quantum efficiency, sensitivity, and dark current. These parameters are determined by the composition of the photocathode. Generally, the long-wavelength cutoff is determined by the photocathode, while the short-wavelength cutoff is determined by the window material. The quantum efficiency of the photon–electron conversion process in the photocathode is low, typically ∼20–30% that implies ∼80–70% of the scintillation photons are wasted. For optimized results, the spectrum of the scintillator should match the sensitivity of the photocathode. The dark current consists mainly of the thermionic emission of electrons from the photocathode and the first few dynodes, with much smaller contribution from cosmic rays. For example a 5-cm-diameter photocathode may release ∼105 electrons per second in the dark at room temperature. Cooling of the photocathode greatly reduces the dark current, e.g., by a factor of ∼10 for temperature reduction from 20°C to 0°C. However, caution must be exercised to avoid condensation at the PMT window since the moisture will reduce the amount of light incident on the photocathode. In addition, excessive cooling can cause voltage drop across the photocathode. Other ambient conditions influencing the performance of the PMT are changes in the humidity, presence of vibrations and magnetic field.
Quantitative analysis of sarcosine with special emphasis on biosensors: a review
Published in Biomarkers, 2019
C.S. Pundir, Ritu Deswal, Parveen Kumar
A Photoelectrochemical (PEC) sensor is fabricated on photoactive electrodes, which can convert photoirradiation to electrical signal. Various photoactive materials were metal-contained semiconductors, such as TiO2, Graphitic carbon nitride (g-C3N4), CdSe, CdTe, ZnO and ZnS, etc (Zang et al.2017). A novel photoelectrochemical sensing platform based on CuInS2 based photocathodic enzyme sensing was formulated for sarcosine determination. The heterostructure copper indium disulfide (CuInS2) microspheres, 3 D NiO nanofilm and indim tin oxide (ITO) were successfully synthesized as a photoelectrode material. This resulted (CuInS2/NiO/ITO) complex was then coupled to SOx. The O2 dependent cathodic photocurrent was suppressed due to the competition between the O2 sensitive photocathode and SOx towards O2 reduction. The sensor had a wide linear range from 0.01–1.00 mM, with a LOD of 0.008 mM (S/N = 3) and correlation coefficient of 0.995 using linear regression equation I = 3.814e−8c–1.122e−8. Ascorbic acid, dopamine, lysine, histidine, urea and glucose at 0.1 mM concentration show no interference (Jiang et al.2018).