Radiation targeting

Nuclear science in particular obtains from laser-driven electron sources a brand new input to perform interesting measurements in the context of many laboratories equipped with ultrashort powerful lasers. The ultrashort duration of these particle bunches represent a further attractive feature for these kinds of studies. In the following, we will focus on nuclear reaction induced by gamma radiation produced by bremsstrahlung of laser-produced electrons in suitable radiator targets. This way is usually mentioned as photo-activation and is particularly efficient for photons of energy close to the Giant Dipole Resonance of many nuclei. 

Tzeng, C.M. Kornberg, A. The multiple activities of polyphosphate kinase of Escherichia coli and their subunit structure determined by radiation target analysis. J. Biol. Chem., 275, 3977-3983 (2000)... 

Radiation therapy is an integral part of treatment and can be used alone for selected patients with early-stage disease, although most patients wiU receive chemotherapy and radiation. Involved-field radiation therapy targets a single field of HL. Extended-field or subtotal nodal radiation targets the involved field and an uninvolved area. Total nodal radiation therapy targets aU areas. 

Radiation targeting involved exposing proteins to (OH/e g) or exclusively OH radical attack and then correlating activity loss with radiation dose. This correlation, using a set of empirically designed relationships, allowed a determination of protein size. It was, however, dependent upon a number of parameters such as temperature and protein concentration. Recent research carried out by Houee-Levin and co-workers as well as other groups have shown this technique to be dependent upon the judicious choice of protein and the empirical correlations fail in a wide number of systems. 

Kempner ES. (1999) Advances in radiation target analysis. Anal Biochem 113-123. 

For a freely radiating target (i.e., with cold black surroundings), the exitent spectral radiance is due only to the emission by the target (see Figure 7.17), therefore. 

Effects of ionizing radiation on DNA have been widely studied for many years (1), although previous radiation target analyses were only reported before well-defined preparations and advanced techniques became available. It was reported that radiation damage in RNA occurred only locally in that molecule (2), in distinction with the well-established spread of radiation damage throughout polypeptides (3). 

Radiation target theory predicts an exponential loss of molecules as a function of radiation exposure the rate of this loss is directly proportional to the mass of the molecule. The supercoiled form was observed to decay in this manner. The double-stranded GFP plasmid has a mass of 3300 kDa. In three independent experiments, the amount of supercoiled DNA decreased exponentially with radiation dose (Fig. 2), yielding a target size of 3059 kDa (Table 1), indicating that a single radiation interaction anywhere in the plasmid... 

A simple exponential decrease of measured properties as a function of radiation dose indicates that die effect is due to a single radiation interaction. Radiation target theory predicts that the rate of this decrease is directly proportional to the mass of the structure responsible for that property. Thus the disappearance of supercoiled plasmids is caused by a single radiation interaction anywhere in a mass of 3059 kDa - close to the known mass of the entire molecule. This result does not indicate the fate(s) of the hit supercoiled DNA molecules. 

The average is taken over the initial states of the radiation-target system. Consequently, the cross-section appears as the sum of two well-defined contributions, called coherent and incoherent. 

Figure 8. Radiation target analyses of thylakoids. High energy y-radiation was provided by a Co-source of a dose rate at the sample position of0.803 Mrad/h. The membrane temperature was maintained at -18 1 C. Initial PSII activity of the control Fv/Fm averaged 0.856 0.005.

Kempnet ES. Novel predictions from radiation target analysis. Trends Biochem Sci 1993 18(7) 236-9. 

Miller JH, Bolger G, Kempner E. Radiation target analysis of enzymes with stable free radicals. Radiat Phys Chem 2001 62 33-38. 

Schubach (1995) provides a review of thermal radiation targets for risk analysis. He concludes that (1) the method of assuming a fixed intensity of 12.6 kW/m to represent fatahty is inappropriate due to an inconsistency with probit functions and (2) a thermal radiation intensity of 4.7 kW/m is a more generally accepted value to represent injury. This value is considered high enough to trigger the possibility of injiuy for people who are unable to be evacuated or seek shelter. That level of heat radiation would cause injury after 30 s of exposure. 

Schubach, S. (1995). Thermal Radiation Targets Use in Risk Analysis. Trans. IChemE, Vol. 73, Part B. 

The vast majority of evidence implicates DNA as the primary radiation target and so the situation above can be summarized ... 

A scattering cross-section, a, is a quantity proportional to the rate at which a particular radiation-target interaction occurs. More specifically, if the incoming radiation is considered as being composed of quanta or particles (for example, photons or neutrons), a cross-section is a scattering rate (number of scattering events per unit... 

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