PubMed · 8416648
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R L Eisenberg. 1993. Cathode rays and controversy.. https://doi.org/10.2214/ajr.160.1.8416648
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We report that high energy beta particles may function as a means for mapping the surface of a protein. Comparable to Fe-EDTA in the presence of ascorbate and peroxide, 90Y-EDTA alone can break polypeptide backbone bonds on the surface of E. coli RNA polymerase. The two methods give very similar fragmentation patterns, although some unique fragments are produced by each. Radiolytic footprinting may prove useful for mapping proteins inside living cells, since beta-radiolysis produces reactive species up to approximately 1 cm away from the emitting 90Y.
The analysis of depth-dose distributions in bricks sampled from walls in areas with nuclear waste or accident contamination has the potential of providing information on the energy and source configuration of the gamma-radiation that had been incident on the brick. In this study, a brick from a mill facing a shallow water reservoir of the contaminated Techa river in the South Ural region is investigated. Thermoluminescence (TL) methods were used to measure the accumulated dose at several depths in the brick. The accidental external gamma-dose is obtained by subtracting the natural radiation background dose from the total accumulated dose. In the first segment of the brick, at a depth of about 1.5 cm, the accident dose was found to be roughly 3.5 Gy. Monte-Carlo simulations of the photon transport from the reservoir bed contaminated with 137Cs were calculated for different depths in the brick. The calculations were made assuming different attenuating water levels. It is found that the depth-dose distribution determined by measurements corresponds to a water level between 20 and 50 cm. The results indicate that TL measurements combined with Monte-Carlo modelling calculations are highly promising for external gamma-dose reconstruction applications.
The various approaches in radionuclide dosimetry depend on the size and spatial relation of the sources and targets considered in conjunction with the emission range of the radionuclide used. We present some of the frequently reported computational techniques on the basis of the source/target size. For whole organs, or for sources of targets bigger than some centimetres, the acknowledged standard was introduced 30 years ago by the MIRD committee and is still being updated. That approach, based on the absorbed fraction concept, is mainly used for radioprotection purposes but has been updated to take into account the dosimetric challenge raised by therapeutic use of vectored radiopharmaceuticals. At this level, the most important computational effort is in the field of photon dosimetry. On the millimetre scale, photons can often be disregarded, and beta or electron dosimetry is generally reported. Heterogeneities at this level are mainly above the cell level, involving groups of cell or a part of an organ. The dose distribution pattern is often calculated by generalizing a point source dose distribution, but direct calculation by Monte Carlo techniques is also frequently reported because it allows media of inhomogeneous density to be considered. At the cell level, alpha and electron (low-range beta or Auger) are the predominant emissions examined. Heterogeneities in the dose distribution are taken into account, mainly to determine the mean dose at the nucleus. At the DNA level, Auger electrons or alpha-particles are considered from a microdosimetric point of view. These studies are often connected with radiobiological experiments on radionuclide toxicity.