Radiation damage mechanism

The examples of hydroxyl radical addition products identified in single crystals of adenine and guanine base derivatives confirm that water can play an important role in the radiation damage mechanism. It should be noted that the new mechanism has attracted some criticism [38]. The main objection is that nonplanar geometries were calculated for the gas phase radicals whereas planar structures are expected experimentally due to the hydrogen-bonding scheme... 

Besides direct damage of the DNA strand, it is also possible for the surrounding water molecules to be involved in radiation damage mechanisms. The hydration layer of DNA consists of a primary layer (approximately 20 or 21 water molecules per nucleotide), which possesses properties different from crystalline ice upon freezing, and a secondary layer, which cannot be distinguished from bulk water upon crystallization. Upon irradiation of water, many different products can be formed ... 

MODELS OF RADIATION DAMAGE MECHANISMS Direct impact vs. defect accnlnnlation models A modified model of direct impact amorphization Temperatnre-dependence of the amorphization dose The effects of ion mass and energy... 

To observe thse initially unstable or primary radicals requires low temperatures (77 K) and sometimes as low as 1.5 K ( ). Based on such studies, it has been possible to give a reasonably complete radiation damage mechanism for crystals consisting of C, N,... 

Clarification of the role of enzymes and proteins in repair of radiation-damaged cellular DNA and of mechanisms of enzymatic reactions leading to altered nucleotide sequences (Hagen 1990)... 

There are two other methods in which computers can be used to give information about defects in solids, often setting out from atomistic simulations or quantum mechanical foundations. Statistical methods, which can be applied to the generation of random walks, of relevance to diffusion of defects in solids or over surfaces, are well suited to a small computer. Similarly, the generation of patterns, such as the aggregation of atoms by diffusion, or superlattice arrays of defects, or defects formed by radiation damage, can be depicted visually, which leads to a better understanding of atomic processes. 

Electron irradiation causes chain scission and crosslinking in polymers. Both of these phenomena directly affect the glass transition temperature (Tg) of the materials. Thermomechanical (TMA) and dynamic-mechanical analysis (DMA) provide information about the Tg region and its changes due to radiation damage. Therefore, DMA and TMA were performed on all irradiated materials. 

The mechanisms of interaction between fluorouracil and radiation are not clearly understood. Different hypotheses have been postulated to explain the synergistic or potentiated effect of 5-FU with radiation including redistribution of cells to a more radiosensitive cell cycle phase, deranged pyrimidine pools with reduced capacity for repair of DNA damage, and activation of apoptosis. The effect of 5-FU on radiation damage also appears to vary in different cell lines, thus complicating the extrapolation of laboratory results into clinical practice. 

As with other radioactive substances, exposure to its ionizing radiation can cause cancer. When ingested it tends to accumulate in the liver, kidney, and spleen causing radiation damage from the alpha particles. All operations and handling must be carried out in leak-proof boxes by mechanical means behind thick neutron shields. 

---