Proefschrift--Utrecht. / Bibliography: p. 62-64.

Thesis (Ph. D.)--Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 1986. / Includes bibliographical references (p. 193-207).

Compounds labelled with deuterium and tritium are widely used in the life sciences. Consequently there is always a need for improved methods - better incorporation, higher specificity, reduced reaction time etc. and in the case of tritium, less radioactive waste. This thesis is concerned with such aspects. Chapter 1 is a review of the background to tritium and current methods of labelling and analysis of hydrogen isotopes. In chapter 2 the possible use of an organometallic compound - the ruthenium dihydro complex, RuH2CO(PPh3)3, which is known to catalyse the insertion of olefins into the ortho position of aromatic ketones, is explored. Solid deuterated formates e.g. 2-naphthy methyl-d-formate and d-formanilide were prepared and these were used to make the deuterated complex, RuD2CO(PPh3)3 which was used to exchange deuterium into the ortho position of aromatic ketones. Aromatic compounds with other functionalities, however were not so amenable to labelling, aromatic amides were the only other compounds successfully labelled. The method is therefore more restrictive than was hoped. A method to prepare tritiated formates by ozonolysis of 2-[T]-5-phenyloxazole to a mixed anhydride followed by nucleophillic attack was discovered. [T]-formanilide was prepared in this way but only at low levels of radioactivity (0.1 Ci/mmol, 3.67 GBq/mmol) which prevented the tritiated complex being prepared. In chapter 3 the use of zeolites as strong acid catalysts for hydrogen isotope exchange reactions was explored. Isotope exchange was carried out on simple organic molecules using hydrogen, platinum and palladium exchanged zeolite-Y with D2O and HTO as isotope source. Some studies were also carried out using solid deuterium sources with the metal exchanged zeolites. Exchange occurred using 2-naphthgyl methyl-d-formate, tetrabutyl ammonium-d-formate and potassium-d-formate. In addition, microwave activation was used in order to reduce reaction times and improve isotopic incorporation.

Radiations from Zn⁶⁵ have been studied by means of a thin lens beta ray spectrometer. A spiral baffle was used to separate positrons from negatrons. The gamma ray spectrum in the energy range above 100 kev was found to consist of one gamma ray at 1.11 mev and annihilation radiation at 0.51 mev. One positron group was found with maximum energy at 0.327 mev. No internal conversion electrons were found. A decay scheme has been proposed in which Zn⁶⁵ decays either by K-capture to a 1.11 mev excited state of Cu⁶⁵ or bypositron emission to the ground state of Cu⁶⁵. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The radiation from Zn⁶⁵ has been investigated in a thin lens beta ray spectrometer. A spiral baffle was used to discriminate between positrons and negatrons. Gamma ray energies of 1.12 and 1.4 mev have been measured as well as annihilation radiation of .51 mev. A positron end point at .32 mev has also been measured. Fairly intense internal conversion was found. A decay scheme has been proposed in which Zn⁶⁵ decays by K-capture to a 1.4 mev excited state from which it proceeds to an Intermediary state by emission of a gamma ray. The alternative positron emission is to the intermediary stage from which both paths descend to the 65 ground state of Cu⁶⁵ with the emission of a 1.1 mev gamma ray. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The Environmental Radioactivity Laboratory (ERL) of iThemba LABS conducts research into levels of natural and anthropogenic radioactivity in the environment. The laboratory-based measurements are conducted using a low-background Hyper Pure Germanium (HPGe) detector system. A critical aspect of such measurements involves calibrating the detector about energy and detection efficiency. The present study details experiment that were carried to determine both energy and efficiency calibrations for various sample geometries using gamma-ray spectrometry. The measurements using reference sources of known activity were carried out using two sample holders (Marinelli Beaker (1000 ml) and, a cylindrical pill bottle (100 ml)), and a point source. The IAEA reference materials (RGU-1, RGTh-1 ore and RGK-1) were prepared and used to fill the Marinelli beaker and pill bottles. Certified reference point sources (⁶⁰Co, ¹⁵²Eu, ¹³⁷Cs, ²²Na, ²⁴¹Am and ¹³³Ba) were obtained from the National Metrology Institute of South Africa (NMISA). Experiments consisted of exposing the HPGe detector to various gamma-ray sources prepared using various sample holders and the point source geometry. The counting time for each measurement was 24 hours. Each spectrum was analysed by inserting region of interests around suitably selected photo-peaks and the counts associated with these photo-peaks were automatically determined and corrected for background by the software. The full energy peak detection efficiency was then determined from the background corrected counts, the known activity of the source and the implicit in measurement (solid angle). The experimental and simulated spectra using point sources and volume sources were compared. Both experimental and simulated spectra presented showed a good agreement in terms of shape and varying intensities as expected. Additional photo-peaks were observed from ²²Na, ⁶⁰Co, ¹³³Ba and ¹⁵²Eu (point sources) and ²³²Th and ²³⁸U (volume sources) experimental spectra these effects were not observed in the simulated spectra. These additional peaks observed are the result of coincidence summing in some of gamma emitting radionuclides. Efficiencies that were experimentally determined, were compared with the calculated efficiencies from Monte Carlo simulations using MCNPX. Efficiency calibration parameters (power fit function) for the volume sources were determined from experimental and simulated data; a = 2.58; b = -0.75 experimental and a = 1.01; b = 0.65 simulated (100 mL pill bottle) and a = 2.07; b = -0.75 experimental and a = 1.61; b = 0.66 simulated (1 L Marinelli beaker). The simulated parameters for the efficiency as determined can be used for future calculations of activity concentrations when the 100 mL pill bottle or 1 L Marinelli Beaker sample holder is used. Further improvement in these calculations can be achieved by considering the sample density. The simulation input files used to generate these values is available and can be modified to match any sample holder geometry, as well as any density that might be required in future counting.

No description available.

No description available.

No description available.

No description available.