Browsing by Author "Cherry, R D"

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    Alpha-radioactive isotopes in the marine environment.
    (1975) Higgo, Jennifer Joan Wynne; Cherry, R D
    Various marine organisms collected from southern hemisphere waters around Cape Town were analysed by radiochemistry and alpha-spectrometry for Pu-239, 240. Many of these organisms were also analysed for Pu-238, Po-210 and - those isotopes of thorium and uranium that are alpha-emitters. In some samples an estimate of the Ra-226 content was also made. The Pu-239 concentrations are compared with the values reported in the literature for similar organisms found in the northern-hemisphere and an attempt is made to relate the differences in concentration to differences in the quantity of fall-out Pu-239 delivered to the sea-surface in the two hemispheres. Within the limits of experimental error it appears that the Pu-239 content of recent fall-out is reflected in the Pu-239 concentration in many marine organisms.
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    Natural alpha-radioactivity in bone, liver and blood samples from the various species
    (1969) Shay, Malcolm MacGregor; Cherry, R D
    In this thesis, samples from the various species are studied for alpha-radioactive content. The experimental technique used is one of thick source "total" alpha counting with "fast pair" scaling enabling separation of "Thorium" series contribution. A study of the change in count rate over a time period enables Po-210 activity to be determined. Additional alpha spectroscopic techniques are used to identify specific alpha emitting isotopes in the samples. Bone tissue alpha-activity levels are used as a basis for comparing levels between the species. Liver is studied as it shows interesting features, and blood is also studied. The method of sample preparation involves the removal of water from the samples at low temperatures and no additional chemical techniques are used. Thirty-six different species from four groups of animals were studied (herbivores, carnivores, omnivores and marine environment). Man shows very low levels of alpha-activity compared with other species of which the group "herbivores" show highest levels of alpha-activity, including large amounts of Po-210. The marine environment species show a large accumulation of Po-210 in liver.
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    Preliminary investigation of a possible dose rate effect on survival of cells irradiated with low energy protons
    (1989) Robinson, L P G; Cherry, R D; Jones, Dan T L; Bohm, L
    Apparatus has been developed for the irradiation of V79-379A Chinese hamster lung fibroblast cells with 3.6 MeV protons from the Van de Graaff accelerator at the National Accelerator Centre in Faure. The original intention of this work was to investigate and measure a possible dose rate effect on the survival of V79 cells, in the dose range from zero to 25 Gy, at dose rates of about 3 Gy/s and 300 Gy/s. The survival curves initially obtained were anomalous in that they showed abnormally high levels of survival and a tendency to remain at a constant survival level for doses above 10 Gy. Systematic attempts to correct this observed anomaly, involved the following; apparatus improvements were made, a means of measuring the beam profile was devised, the current measuring device and the dosimetry were improved and a possible dose rate effect on intracellular oxygen was investigated. After these improvements, the anomalous effect was much reduced, but not entirely eliminated. The final results showed no significant difference between the survival of cells irradiated at dose rates of about 3 Gy/s and 300 Gy/s; qualitative differences were however noticeable. After correction for the effect of a non-uniform beam profile, the survival curves were significantly different to published work. This difference suggested a possible dose rate effect between dose rates of about 0.1 Gy/s and dose rates above 3 Gy/s.
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    Studies of alpha-radioactivity in the marine environment
    (1970) Shannon, L V; Cherry, R D
    This dissertation deals with the alpha-radioactivity in the marine environment around South Africa, and the published literature relating to alpha-emitting nuclides in sea water and in marine organisms is surveyed in Chapter 1. As a first step in the investigation, the total alpha-activity of some 400 samples of marine life was determined using the thick-source alpha-particle detection technique. The relative contributions of the thorium series nuclides and "excess" unsupported polonium-210 were determined by using the "thorium pairs" technique and by studying the variation of the total alpha count-rate with time. This is considered in Chapter 2. The 'second phase of the investigation was to investigate the alpha-spectrum of marine life. This was done for several plankton samples using a large capacity ion-chamber. As expected several disequilibria were found to exist and the findings are discussed in Chapter 3. Unsupported polonium-210 accounted for the major proportion of the total alpha-activity in several marine groups, while radium-226 and daughters accounted for most of the long-lived radioactivity. Thorium series elements were also present. Using the ion-chamber data together with total alpha-counting data, an estimate of the radium-226 content of plankton was made.