Growth of helium bubbles in palladium, having different pre-irradiation sample treatments and subsequently implanted with 50 appm of helium, has been investigated by positron lifetime spectroscopy. Presence of dislocations has been found to enhance the density of nucleated bubbles. A suppression of helium bubble growth due to the presence of dislocations is established. Bubble growth is reduced by over-pressure in dislocation-containing samples.
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"Various ways have been explored, e.g. thermomechanical treatment , cold working , introduction of secondary phases  and oxide dispersion strengthening . A remarkable improvement has been achieved by the last two ways, which can be realized by doping alloying elements in metals  . "
[Show abstract][Hide abstract] ABSTRACT: The effect of Fe and C doping on the thermal release of helium from Al implanted with 10keV, 4.0×1021ion/m2 He at room temperature (RT) has been investigated by thermal helium desorption spectrometry (THDS) and transmission electron microscope (TEM). The results show that Fe and C doping have significant impact on the release of helium from Al and the extent depends on the doping fluence. Proper fluence of Fe and C doping would lead to the retardation of the release of helium from Al, while excessive fluence of Fe and C doping would result in more desorption peaks and the release of helium in lower temperature ranges. Fe and C doping have different influence on the release of helium from Al, and the difference is related with the secondary phases forming in the samples.
[Show abstract][Hide abstract] ABSTRACT: The relationships between graduation grade point average (GPA), class ranking, performance in graduate studies, employment opportunities, and locations of employment of graduates of Tennessee State University are studied on the basis of graduation GPA and employment information on 326 graduates of the B.S. in Electrical Engineering program from May 1972 until August 1989. The data on graduates and the graduation GPA was retrieved from student records in the department. The information on student employment and graduate studies was collected from annual alumni surveys, interviews with returning alumni during homecomings, and recruitment trips. The student records were compiled according to graduation dates. For the purpose of data analysis, the graduation GPA has been divided into 16 groups, with Group 1 being 2.00 to 2.125. It is found that the graduates are equally distributed in the process and utility industries and the federal service, although those with higher GPAs are pursuing graduate study and going to the electronics/computer industry. The incentives provided by corporations to pursue graduate study on a full-time basis have been most beneficial and fully utilized by the graduates and is reflected in a very high percentage of graduates pursuing graduate work
[Show abstract][Hide abstract] ABSTRACT: Positron lifetime measurements on palladium implanted with 100 appm of helium are reported as a function of annealing time for three different temperatures. An anomalous bubble growth regime is identified from the variation of helium atom density inside bubbles with annealing time, as deduced from τ2. In this growth regime, helium atom density is found to decrease sharply, indicating relaxation of pressure inside bubbles. This is explained as due to the availability of thermal vacancies which condense on to bubbles thereby reducing helium atom density. An activation energy of 0.88 eV is estimated from the experiment which matches with the reported vacancy migration energy. It is concluded that thermal vacancy migration to bubbles is the rate limiting process which triggers the anomalous bubble growth.
Materials Science Forum 01/1997; 255-257:578-580. DOI:10.4028/www.scientific.net/MSF.255-257.578