Browsing by Author "Armstrong, Timothy Robert"

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Deuterium implantation in graphite and copper
(Te Herenga Waka—Victoria University of Wellington, 1976) Armstrong, Timothy Robert
The D - D reaction has been used to depth profile deuterium implanted in graphite end copper over the temperature range 100 °K to 450 °K. The profiles are obtained using a method based on observing the energy spectrum of tritons emitted from D - D reactions initiated with a 200 KeV probing beam. Both graphite and copper, when implanted at 100 °K, are found to retain large concentrations of deuterium and the depth profiles show that the atomic loadings of deuterium (D:host atoms) in both materials are similar. However, the amount of deuterium retained within graphite is larger because of the greater number of host atoms per unit path. In graphite, the amount of deuterium retained continues to decrease with increasing temperature until at 425 °K the fetention has fallen to approximately half that at 100 °K. The profile shape is almost independent of target temperature and integrated dose. Copper targets show a greater decrease in the amount retained as the temperature is increased and a layer of deuterium is formed on the surface when the temperature is above 200 °K. Also, following prolonged bombardment at warm temperatures, the region in which the deuterium is retained begins to extend deeper into the target. The irradiated areas have been examined using a scanning electron microscope end blisters with diameters of approximately 1 to 10 microns have been seen in the copper targets but ho surface deformation has been observed on the graphite targets. The deuterium distributions within a copper target have also been measured using a 3He beam and a comparison is made between the two methods of profiling deuterium.
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Radiation Blistering and Deuterium Retention in Copper
(Te Herenga Waka—Victoria University of Wellington, 1980) Armstrong, Timothy Robert
200 keV deuteron beams from a low energy accelerator have been used to study the retention of deuterium and radiation blistering of copper samples. These studies have been conducted over a range of target temperatures, deuteron current densities and deuteron fluences. By using the D(d,p)T reaction to depth profile the implanted deuterium it has been found that approximately 100% of the deuterium implanted at target temperatures of less than 140 K is retained within the target. Increasing the target temperature above 140K.has been found to produce a steady decrease in the amount of deuterium retained until at a temperature of 380 K only ~15% of the implanted deuterium remains within the target. Some samples implanted in the temperature range 140 to 320 K have shown an increased yield of protons from the D(d,p)T reaction due to the increased retention of deuterium in the near surface regions. The deuterium depth distributions have also been examined using a 2 MeV deuteron beam. This method has been found to provide useful information about the amount of deuterium retained around the low energy deuteron projected range despite a large separation, both in time and distance, between the accelerators used for the implantation and the profiling. The radiation blistering studies have involved measuring the onset of blistering using an in-situ method based on the scattering of laser light at a non-specular angle from the irradiated area. Additional information about the blister morphology has been obtained by SEM examination of these targets following irradiation. Discrete blisters are found to form rapidly at a well defined fluence. For a target temperature of 120 K, this critical fluence required for blistering has been found to depend strongly upon the incident current density and to be a minimum at a current density of (2+-1) A.m-2. Also at 120 K, a ring of blisters surrounding the main beam spot has been observed. Irradiations at higher target temperatures are found to produce two different blister morphologies. For target temperatures in the range 120 to 190 K and 300 to 380 K, semi-spherical blisters are found to form at fluences of approx. 2 x 10 22 d m-2 and 4 x 10 22 d.m-2 respectively. In the intermediate temperature region, irregularily shaped blisters are found to form at a fluence of~6 x 10 22d.m-2. The deuterium retained within the surface regions of the target has been related to the onset of blistering.