Radiation protection in the nuclear industry
Alan Martin, Sam Harbison, Karen Beach, Peter Cole in An Introduction to Radiation Protection, 2018
The neutrons emitted after fission may themselves cause further fission with the emission of more neutrons, thus making possible a chain reaction. In practice, some of the neutrons escape from the system and others are captured in non-fission reactions. In a reactor, wastage of neutrons by capture reactions is minimized by taking care to exclude materials of high neutron capture cross-section (i.e. materials that are strong absorbers of neutrons) from the core. Some loss is inevitable since even the fuel material can capture neutrons without fission. By increasing the size of the core, the fraction of neutrons escaping can be reduced to a sufficiently low level to permit a chain reaction. If a core is very small, neutrons can easily escape, but in larger cores they would be required to travel farther and are, therefore, more likely to cause fission. Another method of reducing neutron loss is to put a reflector of some light material around the core to reflect escaping neutrons back into the core.
Radionuclide Sources
Michael Pöschl, Leo M. L. Nollet in Radionuclide Concentrations in Food and the Environment, 2006
Nuclear fission is the process by which neutrons produce chain reactions in a nuclear reactor. When a fissionable nucleus is hit by a thermal or slow neutron, the nucleus can interact with the neutron and divide (fission) into two smaller nuclei, releasing neutrons and energy that initiate the splitting of more fissionable atoms, leading to a chain reaction. 235U is the most abundant naturally available isotope that can undergo fission. Gaseous diffusion and other methods are used to enrich and separate the small amount of 235U (0.72% natural abundance) from the predominantly 238U found in nature. For most nuclear reactors, such as the light-water reactors, the enrichment required for a sustained nuclear reaction is approximately 10-fold. The more significant enrichment of 235U required for atomic weapons is a difficult and expensive task.
Wellbeing, empowerment and oppression
Lucy Maynard, Kaz Stuart in Promoting Young People’s Wellbeing through Empowerment and Agency, 2017
Coleman (2007) identified the need to provide positive experiences to ‘interrupt’ the chain reaction of negative events. This in turn is a catalyst, sparking a different chain of events. Similarly, Henderson et al. (2007) worked with the concept of ‘critical moments’. They drew from Denzin’s (1989) discussion of ‘epiphanies’, Mandlebaum’s (1973) discussion of ‘turning points’, Humphrey’s (1993) discussion of ‘breaks’, and Giddens’s (1991) discussion of ‘fateful moments’. Giddens (1991: 143) defined these moments as “times when events come together in such a way that an individual stands at a crossroads in their existence or where a person learns of information with fateful consequences”. Henderson et al. state that these fateful moments can potentially be empowering experiences.
Biosynthesis of antioxidative enzymes and polyphenolics content in calli cultures of Prunella vulgaris L. in response to auxins and cytokinins
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2020
Hina Fazal, Bilal Haider Abbasi, Nisar Ahmad, Bushra Noureen, Jahangir Shah, Dan Ma, Liu Chuanliang, Fazal Akbar, Muhammad Nazir Uddin, Haji Khan, Mohammad Ali
During unusual conditions, a chain reaction is initiated due to the released of toxic free radicals in larger quantities which inhibit cells or tissues. The active member of natural antioxidants such as phenols is release by different plant species [20]. Hence scavengers of toxic free radicals and singlet O2 formation are the plant-based antioxidants. The ROS modified DNA molecule and stop manufacturing of proteins and lipids [21]. The plant-based antioxidants are most efficient because of the existence of flavonoid and particularly phenolic compounds. Through a shikimic pathway and through carboxylic acid or benzoic acid, the polyphenolics are synthesised in intact plant or in vitro cultures. Polyphenols such as lignans, xanthones, caffeic acid derivatives, ellegitannins, gallotannins, and stilbenes are produced under in vitro cultures and utilised as antioxidants [21].
Patenting Foundational Technologies: Lessons From CRISPR and Other Core Biotechnologies
Published in The American Journal of Bioethics, 2018
Oliver Feeney, Julian Cockbain, Michael Morrison, Lisa Diependaele, Kristof Van Assche, Sigrid Sterckx
DNA is made up of paired strands of bases (nucleic acids denoted by the letters C, A, G, and T), where each base pairs with one other, T binding to A, and G to C, linking the two strands in the famous double helix structure. If natural DNA is chopped up with nucleases, and if short DNA sequences (primers) are added to the mixture, then one has a mixture containing cut fragments bound to the added primers. Adding nucleic acids and an enzyme (DNA polymerase), which causes the ragged ends of these bound fragments to be extended with the appropriate nucleic acids to become blunt-ended, yields a mixture of short, paired DNA molecules. Repeatedly separating and regrowing the paired sections yields multiple copies of the short paired molecules: Starting with one combination of GGAGCTTAG bound to its complementary sequence CCTCGAATC yields two versions of each in the first replication, four in the second, and so on. The increase of copies is exponential and, by analogy with nuclear fission in a reactor or bomb, is called a chain reaction—the “polymerase chain reaction” or PCR. In this way, enough copies of the short paired molecules can be produced relatively cheaply and quickly to enable detection and characterization.
Application of next-generation sequencing in the diagnosis of gastric cancer
Published in Scandinavian Journal of Gastroenterology, 2022
Narges Moradi, Solmaz Ohadian Moghadam, Siamak Heidarzadeh
Roche 454 sequencing system functions in exclusive steps including library preparation, DNA amplification and pyrosequencing. While constructing the library, different DNA samples are broken into 300–800bp fragments. Specific primers are used to amplify denaturized DNA and clonal amplifications take place and eventually, library of single stranded DNA is constructed. The amplification system in Roche 454 fixes DNA strands in emulsion overwhelmed beads. This emulsion PCR approach is beneficiary due to its capacity for independent reactions and various beats are separated using emulsion characteristics. The system amplifies all of the fragments about one million times. The last step of pyrosequencing is based on identifying the emitted light of a chain reaction. Molecular mechanism of pyrosequencing is depicted in Figure 4. A high average read length of 400 bp and inaccuracy in assessing homopolymer length are relatively the significant advantage and disadvantage of Roche 454 sequencing system (www.creative-biogene.com). New molecular markers can lead us to develop personal treatments and faster and more accurate diagnosis of GC.
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