Bioengineering and Ethics
Howard Winet in Ethics for Bioengineering Scientists, 2021
While Darwin was being reborn, Newton was being redefined. Albert Einstein’s two papers (1905, 1915) replaced a mysterious Newtonian force of gravity with curvature of space in his special and general theories of relativity. In a 1905 paper on photoelectric effect, he provided crucial evidence for light quanta and quantum theory of the atom. In another paper that same year, he provided direct evidence from calculations of Brownian motion for the existence of molecules. Evidence that the atom was not indivisible was provided by J.J. Thompson (1897) and E. Rutherford (1898). The work of these pioneers led to development of the fields of the smallest, nuclear, and the largest, space, physics. We shall spend no more of our history on space physics, although BEs interested in space-related careers will want to pursue the subject. Erwin Schrödinger (1887–1961) developed wave mechanics, the mathematical equations that predict the behavior of subatomic particles using wave equations (Millar et al. 1996).
Instrumentation
Clive R. Bagshaw in Biomolecular Kinetics, 2017
Photodiodes are generally much less sensitive than photomultipliers as there is no built-in gain (i.e., one photon gives one electron), but they are sufficient for many absorption studies and can show reasonable sensitivity into the IR region. Their small physical size allows them to be assembled into arrays suitable for determining spectrally-resolved signals. Avalanche photodiodes (APDs) are a special form of diode that is subject to a bias voltage (around 100 to 200 V) just below its breakdown voltage. When a photon impinges on the surface, there is a “catastrophic” breakdown and a pulse of electrons is produced analogous to that of a photon-counting PMT (cf. Figure 7.23c). The quantum efficiency of APDs in the visible range can approach 90% (cf. 10% for PMT), but they are not very sensitive to uv light and can operate only in the photon-counting mode. Electron release is an all-or-none event and the quantum efficiency is a measure of the probability that an electron will be emitted when a photon is captured. Indeed, the photoelectric effect provided key evidence that light is quantized. An APD response time is of the order of tens of nanoseconds.
Phototherapy Using Nanomaterials
D. Sakthi Kumar, Aswathy Ravindran Girija in Bionanotechnology in Cancer, 2023
X-rays can be used as efficient energy sources for initiating effective PDT. For this, scintillation nanoparticles (ScNps) with attached photosensitizers are employed, which serves the purpose of self-lighting photodynamic therapy (SLPDT) [208]. These materials can convert X-rays to UV-visible light and this concept improved the efficiency of PDT without employing an external light source. X-rays will be irradiated to the tumor site where the nano sensitizer systems have been accumulated. Upon irradiation, the encapsulated nanoparticles will emit light and this can be collected to activate the nearby PS. The scintillation process involves the conversion of incoming radiation into a large number of electron-hole pair and transfer of this electron-hole pair energy to the luminescent ions. Upon interaction with high energy photons with the lattice of ScNPs, many electron-hole pairs will be created and thermalized in the conduction and valence band respectively. Photoelectric effect and Compton Effect account for this interaction. Afterwards, these electron-hole pairs will migrate through the materials and repeated trapping at defects of these materials cause energy losses mainly due to non-radiative recombination. This will be followed by the final stage, which is luminescence, and here the energy from the SCNPs will excite the nearby PS causing 1O2 generation [209, 210].
Advancements in the use of Auger electrons in science and medicine during the period 2015–2019
Published in International Journal of Radiation Biology, 2023
Atomic vacancies that lead to Auger and ICD processes are created by several mechanisms. One mechanism that creates an inner atomic shell vacancy is the photoelectric effect. The Auger electrons that are emitted following the photoelectric effect were observed by Pierre Auger when he irradiated a cloud chamber with X-rays (Auger 1923). Radionuclides undergoing internal conversion (IC) transitions also create inner atomic shell vacancies, as do radionuclides that decay by electron capture (EC). The shower of low energy electrons that follow was seen by Meitner when she was conducting experiments on radioactive decay (Meitner 1923). The stochastic nature of the atomic and molecular electronic relaxation process results in different yields and energies of electrons for each initial vacancy created. Most of these electrons have very low energies (∼20–500 eV) which have extremely short ranges in water (∼1–10 nm). Biological molecules near the Auger cascade are impacted by the direct effects of electron irradiation as well as indirect effects caused by radical species that are produced during the radiolysis of water by these electrons (Figure 2) (Wright et al. 1990). Other physical mechanisms such as Coulomb explosion, caused by extremely rapid charge neutralization of highly ionized atoms, can cause damage to the molecule in which electronic vacancies are created (Pomplun and Sutmann 2004).
Comparison and performance evaluation of human bio-field visualization algorithm
Published in Archives of Physiology and Biochemistry, 2022
Gunjan Chhabra, Ajay Prasad, Venkatadri Marriboyina
Further, Max Planck’s study of blackbody radiation, give rise to the quantum mechanics. According to his theory, atoms are tiny oscillators that absorb and emit electromagnetic radiations, with the crucial property that their energies can only take on a series of discrete values. Adding further, Albert Einstein anticipated a validation for the photoelectric effect, that light is composed of individual packets of energy called photons. This implied that the electromagnetic radiation, while being waves in the classical electromagnetic field, also exists in the form of particles (Bhat 2002, Heisenberg and Bond 1959). In addition to this, de Broglie, Werner Heisenberg, Max Born, Erwin Schrödinger, Paul Dirac, and Wolfgang Pauli are some of the researchers who stated various hypothesis, theories, and results on quantisation and wave-particle duality. Nevertheless, all these research was scattered, initially, but latter on these scattered ideas was united under one discipline known as quantum mechanics. In continuation, Einstein published as theory on photoelectric effect based on Maxwell’s electromagnetism as “theory of special relativity.” The Schrödinger equation, illustrated in Equation (i), underlying quantum mechanics could explain the stimulated emission of atoms, where an electron emits a new photon under the action of an external electromagnetic field.
9th international symposium on physical, molecular, cellular, and medical aspects of Auger processes: preface
Published in International Journal of Radiation Biology, 2023
Katherine A Vallis, Roger F. Martin, Nadia Falzone
Removal of an inner orbital electron through the photoelectric effect, electron capture, or internal conversion leads to a vacancy which is then filled by a cascade of electron transitions from the outer shells. These transitions are accompanied by the emission of low energy ‘Auger’ electrons or characteristic X-rays. Auger electrons have low energy (<25 keV), have a short track length and are densely ionizing. As a result, the absorbed radiation dose they deposit in biological material is extremely high but restricted to a nanoscale volume (a few nm3) around the decay site. These qualities mean that Auger electron emitting radionuclides are suited to the ultra-precise delivery of radiation to individual cells, organelles or even to specific molecular targets, and so hold promise as oncologic therapeutic agents.
Related Knowledge Centers
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