Photon Interactions with Matter
Eric Ford in Primer on Radiation Oncology Physics, 2020
In the coherent scattering process the incident photon interacts with an electron (Figure 5.1.2). The photon causes the electron to oscillate up and down (recall that photons can be thought of as electromagnetic waves and it is the oscillating electric field that produces a force on the electron). An accelerating charged particle always produces an electromagnetic wave. This is something we will consider in more detail in a later chapter. Therefore, as the electron oscillates, a second wave (or photon) is produced. This wave emerges in some other direction. The wavelength (or energy) of the emerging wave is equal to that of the incoming wave. That is, no energy is gained or lost in this interaction. There are two flavors of coherent scattering: Thompson scattering, in which the photon scatters from a free electron, and Rayleigh scattering, in which it scatters from an electron bound in an atom. It is the wavelength-dependent process of Rayleigh scattering from molecules in the atmosphere that makes the sky appear blue on the earth.
Use of radiochromic film with synchrotron radiation
Indra J. Das in Radiochromic Film, 2017
The modern third-generation synchrotron facilities are spread around the globe and include the Advanced Photon Source (Chicago, USA), the European Synchrotron Radiation Facility or ESRF (Grenoble, France), and the Australian Synchrotron Facility (Melbourne, Australia) shown in Figure 19.1. These facilities maintain relativistic electrons in orbit around a storage ring that has a diameter comparable with a football stadium (110 × 50 m). Much of the research conducted at synchrotrons relates to X-ray diffraction and scattering mainly used for protein crystallography, small angle X-ray scattering, X-ray absorption, or X-ray fluorescence of material samples including biological samples.
Hybrid x-ray luminescence and optical imaging
Yi-Hwa Liu, Albert J. Sinusas in Hybrid Imaging in Cardiovascular Medicine, 2017
Sensors for small chemical analytes in thick tissue were demonstrated by Chen et al. using scanning x-ray excited optical luminescence (Chen et al. 2011). This study reports a high spatial resolution imaging technique to measure optical absorption and detect chemical and physical changes on surfaces embedded in thick tissue. Developing sensors to measure chemical concentrations on implanted surfaces through tissue is an important challenge for analytical chemistry and biomedical imaging. Tissue scattering dramatically reduces the resolution of optical imaging. In contrast, x-rays provide high spatial resolution imaging through tissue but do not measure chemical concentrations. It describes a hybrid technique that uses a scanning x-ray beam to irradiate Gd2O2S scintillators and detect the resulting visible luminescence through the tissue. The amount of light collected is modulated by optical absorption in close proximity to the luminescence source. By scanning the x-ray beam and measuring total amount of light collected, one can measure the local absorption near scintillators at a resolution limited by the width of luminescence source (i.e., the width of the x-ray excitation beam). For proof of principle, a rectangular 1.7-mm scanning x-ray beam was used to excite a single layer of 8-mm Gd2O2S particles and detect the absorption of 5-nm-thick silver island film through 10 mm of pork. Lifetime and spectroscopic measurements, as well as changing the refractive index of the surroundings, indicate that the silver reduces the optical signal through attenuated total internal reflection. The technique was used to image the dissolution of regions of the silver island film, which were exposed to 1 mM of H2O2 through 1 cm of pork tissue.
Self-emulsifying drug delivery systems: a novel approach to deliver drugs
Published in Drug Delivery, 2022
For the investigation of microemulsion, scattering approaches have been used. Small-angle X-ray scattering (SAXS), DLS, PCS, and small angle neutron scattering (SANS) are some of the techniques used. Structural data provided by SAXS on macromolecules vary in size from 5 to 25 nm, as well as repetition distances in partly ordered systems up to 150 nm in partially ordered systems. It is used to determine the structure of particle systems at nanoscale or at microscale, including size of particles, dispersion, morphologies, and the surface-to-volume ratio, among other things. To use SANA is to find droplet shape and size. Micelles, oil-swollen micelles, and mixed micelles, are described by the term 'droplet'. The interference effect of wavelets dispersed from diverse materials in a sample is used in small-angle neutron scattering investigations.
Structural and in vitro in vivo evaluation for taste masking
Published in Expert Opinion on Drug Delivery, 2018
Basheer Al-Kasmi, Okba Al Rahal, Hind El-Zein, Abdul-Hakim Nattouf
PXRD is one of the analytical techniques that can be used in quantification analysis of different materials. In addition, this technique can record the three dimension arrays of molecules in crystal structures of different powdered materials giving distinct diffractograms for unique crystalline materials [18]. Furthermore, this analytical technique is the definitive method to differentiate between amorphous and crystalline materials and therefore it will be the most reliable technique to confirm the formation of a solid dispersion, i.e. the structural success of a taste-masking process. The PXRD patterns of crystalline forms show strong diffraction peaks as a result of crystallinity whereas amorphous forms exhibit no peaks and only show halo diffraction patterns. Diffraction can be defined as a scattering phenomenon in which incident X-rays from an X-ray source get diffracted when they hit a solid sample in its crystalline form [19]. The diffracted beam is then detected and the final signal is shown as peaks in a diffractogram.
Solidification of hesperidin nanosuspension by spray drying optimized by design of experiment (DoE)
Published in Drug Development and Industrial Pharmacy, 2018
Qionghua Wei, Cornelia M. Keck, Rainer H. Müller
The particle size distribution of hesperidin nanosuspension was measured by using laser diffractometry (LD). A Mastersizer 2000 (Malvern Instruments, UK) was employed. The selected characterization parameters were the diameters d(v)10%, d(v)50%, d(v)90% and d(v)95%, which were calculated in volume-weighted diameters. A value of d(v)10% means that 10% of the particles in the tested samples are smaller than the given value, and this applies to the other parameters as well. Calculations were performed using the Mie theory of light scattering, which is based on the collected scattering intensity data, assuming the particles possess spherical shapes. The Mie theory has to be applied for size calculation when the particle size is below 5x the laser wavelength used in the instrument. In contrast to the Fraunhofer theory, this theory requires input of RI and IRI. The refractive index (RI) used was 1.57, and the imaginary refractive index (IRI) was 0.01 [21]. The samples were dispersed in water and measured with medium sonication.
Related Knowledge Centers
- Density
- Mean Free Path
- Particle Accelerator
- Sound
- Neutron Scattering
- Cell
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- Cross Section
- Attenuation Coefficient
- Bidirectional Scattering Distribution Function