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Scintillation Detectors
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
In the avalanche photodiode a higher voltage (a few hundred volts) is applied over the p and n contacts of the diode, sufficient to create an avalanche of electrons through the collisions of electrons accelerated through the diode. This results in a collected charge much larger than what is obtained through the PIN photodiode. The gain may reach a factor of hundred thus enabling better signal-to-noise ratios than for PIN photodiodes. The main disadvantage is the strong sensitivity of the gain to fluctuations in temperature and applied voltage. Analogy is often drawn to gas detectors operating as ion chambers, proportional counters, or in Geiger-Müller mode. The ordinary PIN photodiode is analogous to the ionization chamber while the avalanche photodiode mimics the behaviour in the proportional counter provided the voltage is not so high as to produce continuous avalanches, which would be the GM-mode of operation.
Scintillation Fiber Optic Dosimetry
Published in Arash Darafsheh, Radiation Therapy Dosimetry: A Practical Handbook, 2021
A photodiode detector is made of a semiconductor material with appropriate doping optimized to work around the visible spectrum. The scintillation photons produce electron–hole pairs instead of just electrons as in a PMT photocathode. The quantum efficiency of a photodiode can be as high as ∼80% which makes it attractive for use in low-level radiation detection. PMTs generally have higher sensitivity than photodiodes. Photodiodes produce more electrical noise than PMTs do but they are smaller and less expensive. Most photodiodes do not amplify the signal. A special kind of photodiodes is avalanche photodiode (APD) where electron–hole pairs produced are multiplied through avalanche process. The process is analogous to the electron multiplication in a PMT except that in this case there are no dynode-like mechanical structures involved. The end result of the electron–hole multiplication is the transformation of a very low-level signal into a pulse having measureable amplitude [37]. The signal amplification in APD is not as much as that in a PMT.
III-Nitrides–Based Biosensing
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
Manijeh Razeghi, Ryan McClintock
By using the same template that allowed for the realization of back-illuminated p–i–n photodiodes it is possible to realize back-illuminated III-nitride-based APDs. Back-illumination maximizes the injection of holes into the multiplication region making it a better approach for III-nitride-based avalanche photodiodes yielding higher gain and significantly reduced excess multiplication noise performance (Figure 28.20).
Development of nanodispersion-based sildenafil metered-dose inhalers stabilized by poloxamer 188: a potential candidate for the treatment of pulmonary arterial hypertension
Published in Pharmaceutical Development and Technology, 2019
Charisopon Chunhachaichana, Rutthapol Sritharadol, Somchai Sawatdee, Paul Wan Sia Heng, Teerapol Srichana
The dynamic light scattering (DLS) technique was used to evaluate the hydrodynamic particle size of the content of nanodispersion-based sildenafil MDIs. The Zetasizer instrument (Zetasizer Nano-ZS; Malvern Instruments, Worcestershire, UK) was used in this study. The light scattered by the sample was detected by an avalanche photodiode at a backscattering angle of 173° according to Mie theory. The measurements were performed at 25 °C in an air-tight sealed microcuvette (Type 46 Semi-Micro Cuvette with Screw Cap; FireflySci, Staten Island, NY). The samples were prepared by discharging the content of the MDI in an inverted position into the cuvette; then the cuvette was immediately sealed to prevent the excessive evaporation of co-solvent and propellant. The refractive index used for sildenafil was 1.683. The data were recorded and analyzed using the Zetasizer software (v6.34; Malvern Instruments, Worcestershire, UK). The sample was equilibrated for 120 s at 25 °C before the measurement. The experiment was repeated at least 3 times. The sample was freshly prepared for each experiment.
In vitro characterization of tofacitinib loaded novel nanoemulgel for topical delivery for the management of rheumatic arthritis
Published in Drug Development and Industrial Pharmacy, 2022
Suchitra Nishal, Vikas Jhawat, Parmita Phaugat, Rohit Dutt
The particle size and PDI of TFB-NEs were observed in triplicate by zetasizer ver. 7.13 (Malvern Instruments Ltd., Malvern, UK) working on the principles of dynamic light scattering (DLS) at temperature 25 °C and angle 90°. The sample is lit with a laser beam in DLS, and the intensity of the scattered light emitted by the particles varies at a frequency that has been proportional to particle size. The particle diffusion coefficients, and indeed the particle size, are determined by measuring the variations in intensity. Avalanche photo-diode detector and He–Ne laser around 633 nm were employed for the measurement by using the polystyrene cuvette. All the formulations were diluted with water (1:10, v/v) before analysis [19,28].
Quality and efficiency assessment of six extracellular vesicle isolation methods by nano-flow cytometry
Published in Journal of Extracellular Vesicles, 2020
Ye Tian, Manfei Gong, Yunyun Hu, Haisheng Liu, Wenqiang Zhang, Miaomiao Zhang, Xiuxiu Hu, Dimitri Aubert, Shaobin Zhu, Lina Wu, Xiaomei Yan
The laboratory-built nFCM reported before was used in the present study, and Figure 1(a) shows the schematic diagram of the instrument design [43,47]. Briefly, two single-photon counting avalanche photodiodes (APDs) were used for the simultaneous detection of the side scatter (SSC) (bandpass filter: FF01 − 524/24) and orange fluorescence (bandpass filter: FF01 − 579/34) of individual EVs, respectively. Unless stated otherwise, each distribution histogram or dot-plot was derived from data collected 1 min unless stated otherwise. Ultrapure water supplied by an ultrapure water system (PURELAB Ultra FLC00006307, ELGA) served as the sheath fluid via gravity feed.