Damage by electrons

In cells, DNA is always surrounded by proteins (cf. Fig. 12.2). The attachment of proteins modifies the DNA damage by various effects hampering an easy access of free-radicals, protection by compaction and repair of some of the damage by electron/hydrogen-donation. On the other hand, it may even induce some DNA damage via reactive intermediates formed upon the reaction of free radicals with the proteins. For this reason, the structure of DNA in solution and in the cellular environment will also have to be addressed. 

The occurrence of minerals which show CL is highly dependent on the type of meteorite. Possibly the most common phase which occurs is feldspar. Because this mineral accepts very little Fe into the structure, quenching is not a problem however, because the feldspar structure is quite open, the Na- and K-rich feldspars are easily damaged by electron beams. In contrast anorthite, the Ca rich variety, is quite stable. Pyroxene and olivine are common phases in meteorites but because they both usually contain iron, most do not luminesce. Only in the primitive meteorites do nearly pure enstatite and forsterite occur and both show brilliant CL. Other minerals are rare but include ... 

Reactions of KI with Cl2 and of NaCl and KC1 with F2 have been studied [92, 93, 103, 104] and a variety of properties have been measured as a function of the extent of reaction in the conversion of CuCl to CuCl2 by reaction with Cl2 [89, 105, 106]. A consistent feature of all these studies is that, together with or sometimes preceding nucleation and growth of new solid phases, the solid reactant is damaged by electron withdrawal, leading to the formation of various types of electronic defect of the trapped-hole or V-centre type. Studies of electrical conductivity, electron spin resonance spectra and UV absorption are useful in elucidating the behaviour of these defects. 

Folkard MK, Prise M, Vojnovic B, Davies S, Roper MJ, Michael BD (1993). Measurement of DNA damage by electrons with energies between 25 and 4000 eV. Int J Radiat Biol 64 651-658. 

Madey T E ef a/1993 Structure and kinetics of electron beam damage in a chemisorbed monolayer PFjOn Ru(OOOI) Desorption Induced by Electronic Transitions DIET V vol 31, ed A R Burns, E B Stechel and D R Jennison (Berlin Springer)... 

When dried in an oven, hydrated silica loses its water and becomes a desiccant (a substance that attracts water from the air). You find little packets of silica gel crystals in containers whose contents would be damaged by condensing moisture, such as vitamin bottles, consumer electronics, pepperoni, or leather products. 

Metals are immune to radiation damage by ionization. This is also a consequence of the free electron structure. Fast charged particles and ionizing rays can knock off electrons from the atoms they encounter. In metals, the positive vacancies so formed are immediately filled up by the electron gas, leaving no sign of damage apart from a small amount of heat. 

Any problems in the setup, startup, and operation of the CBMS also were recorded in the course of the field tests. These observations are important to improving the system before it goes into production. The field tests revealed three problems. The protective screens over electronics cooling air inlets and outlets on the CBMS II housing were damaged by operator activities in the vehicles and required reinforcement. The ground probe head, which protrudes outside the vehicle hull, required more power to maintain the correct temperature under colder or wetter weather conditions. Finally the automated mass and frequency calibration procedure was not reliable in the field and required modification. These problems have been corrected and are being incorporated in the LRIP units. 

Chaudhuri S, BhattacharyyaN, BhattacharjeeB. Hydrogen peroxide-induced DNA damages in vitro revealed by electron microscopy. J Electron Microsc 1992 41 57-59. 

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