Alan Appleby

Imaging of radiation dose by visible color development in ferrous‐agarose‐xylenol orange gels

Imaging of radiation dose distribution in gel phantoms by magnetic resonance techniques has previously been reported. In this paper a method of producing gels in which the distributions of radiation dose can also be visualized as a color change is reported. The color developed depends qualitatively and quantitatively on the concentrations of solutes in the gel.

Radiation chemical and magnetic resonance studies of aqueous agarose gels containing ferrous ions

Aqueous agarose gels containing ferrous ions sustain a radiolytic chain reaction, producing Fe3+. G(Fe3+)-values up to 156 have been observed, independent of dose rate between 0.434 and 3.74 Gy min-1. Dissolved oxygen is needed to maintain the chain reaction, and initial ferric yields are increased if the gel is oxygen saturated, or if the Fe2+ concentration is decreased. Longitudinal proton magnetic relaxation rates are increased in proportion to ferric production, permitting visualizing of dose levels in these gels by magnetic resonance imaging techniques. There is a potential for application to radiation therapy treatment planning.

Atmospheric formation of chloroform from trichloroethylene

Abstract Chloroform has been observed as a photochemical product in simulated ambient air containing trichloroethylene, paralleling a previous observation of carbon tetrachloride formation from perchloroethylene. Some portion of the atmospheric budget of these chloromethanes may perhaps be attributed to this process. Toxic products such as phosgene and chloro‐acetylchlorides are formed. This process may well provide another source of stratospheric ozone‐destroying chlorine atoms.

Proton spin‐lattice relaxation of water molecules in ferrous–ferric/agarose gel system

Proton spin‐lattice relaxation time (T1) of water in aqueous solutions of ferrous and ferric ions and in the corresponding agarose gel systems have been studied in the light of NMR relaxation theory. The theoretical analysis of 1/T1’s has revealed that, at the microscopic level, changes in the solvation states of paramagnetic ions in aqueous or gel environment are greater than difference in the paramagnetism between ferric and ferrous ions. The former change is the primary factor for the exhibition of radiation effect. At the phenomenological level, we have confirmed and demonstrated that: (1) Radiation effect is almost exclusively exhibited through changes in 1/T1 caused by the interactions between water proton and ferrous or ferric ions; and (2) fraction of conversion of ferrous to ferric ions induced by radiation is the ‘‘true’’ representation of the spatial distribution of radiation dose.

A new approach to monitoring radon and radon progeny using a glass scintillator in a fiber bundle structure

Abstract A Ce 3+ -doped OXIDE glass possessing good thermal characteristics for fiber drawing was developed and drawn into 50 μm fibers. These fibers were close-packed to form a fiber bundle with channels between them. Radon gas was allowed to flow through these channels. The strategy was to hold radon atoms ( 222 Rn) in the sensor for an extended time period and to give the alphas an immediate access to scintillators. Scintillations were converted into electrical pulses through the use of a PM-tube (photomultiplier tube). A prototype radon gas sensor using fiber bundles with a pore volume of 0.865 cm 3 was built and tested with radon gas. The results and modeling showed that steady state count rates could be obtained after ∼ 25 h and those values were proportional to the radon concentrations. The mean residence time of radon atoms at the sensor was found to be 113.2 s.

Effects of early track structure on the radiation chemistry of water irradiated with heavy ions

Abstract The ways in which the physical structure of heavy ion tracks influences the observed radiation chemistry of water are reviewed. Hydrated electrons are produced in the same initial yield as in low LET radiolysis, but they disappear more rapidly during diffusion of the denser tracks. LET increases with increased charge and with decreased ion velocity, but radii of the core and penumbra regions of the track depend only on ion velocity. Consequently, radicals can be produced at very different spatial densities with ions of similar LET. Homogeneous radical, molecular and initial total water decomposition yields reflect these differences. The HO2 radical is produced in significant yield only in tracks, but unlike e-aq and OH its yield appears to be a unique function of core LET. Radical scavengers increase the effective radical yields by competing with recombination processes, most efficiently in the denser tracks. Nuclear fragmentation is expected to increase radical yields measured at depth in thick targets irradiated with high energy heavy ions, by contaminating the beam with secondaries that have less dense tracks. Recent evidence indicates that this effect may not be as large as had been thought previously.

Observation of the trapping of radioactive inert gas radon on oxide glass surfaces: Macroporous scintillating-glass-fiber bundler alpha detector☆

We report the observation of the trapping of radioactive inert gas radon (222Rn) on oxide glass under ambient air temperature and pressure of 300 K and 760 Torr, respectively. Radon diffuses from the source, through two macroporous scintillating-glass-fiber bundle alpha detectors in series, to the end of the linear closed system filled with ambient air. The strategy is to provide radon atoms and alphas emitted from radon and its progeny with large accessible scintillating glass surface areas for efficient trapping and detection, respectively. Diffusion-only transport mechanism could not explain the experimental observations, strongly suggesting the trapping of radioactive inert gas radon (222Rn) on oxide glass.

Measuring ambient radon using a scintillating optical fiber bundle

A new method for detecting and measuring radon and its radioactive progeny is described, involving a bundle of scintillating optical fibers. The general sensor construction is described. A preliminary field trial is described in which the fiber sensor responded in a comparable way with a commercial radon measurement instrument, to varying ambient radon levels.

Gas chromatographic methods for ambient halocarbon measurements

Abstract Gas Chromatographic procedures for the measurement of SF6, COC12 and twelve atmospheric halocarbons, including vinyl chloride, have been developed. The identities of these relatively unstudied important atmospheric constituents were established conventionally by extensive empirical cross checking of retention data and then confirmed by the novel application of electron attachment kinetics in a dual electron capture detector system. Nine packings were found useful for the measurement of one or more of the compounds under study. In an ongoing study of the fates of halocarbons, phosgene synthesis has been demonstrated in a smog chamber experiment in which a mixture of 1 ppm C2Cl4 and 0.5 ppm NO2 in air (RH=50%) was irradiated with simulated sunlight. Phosgene identity was confirmed by its ionization efficiency and retention data on a didecyl phthalate column. Gas phase coulometry can only be used for non‐reactive electron absorbers and suffers significant error for reactive compounds such as phosgen...