Natural Alpha Radioactivity in Medium-Heavy Elements [Dissertation]

A large internal-sample ionization chamber was constructed and used in conjunction with a 2A.-channel pulse analyzer for the purpose of studying weak natural alpha radioactivities among the medium-heavy elements. The background of the counter was reduced to a low level by a careful selection of the materials used to construct the counter and by using massive shielding and anti-coincidence. A counting gas consisting of 94% argon, 5% ethylene, and 1% nitrogen was found to give good energy resolution and drift stability. A method was developed for forming thin, uniform oxide films over a large (1200 cm) cylindrical surface area suitable for obtaining reasonably sharp alpha spectra. The following nuclides were studied for the purpose of obtaining more precise values for the alpha particle energy, specific activity and half-life: Ce-142, Sm-147, Nd-144, and Pt-190. New natural alpha activities were sought in Sm-148, 149, Gd-152, Hf-174, and Hg-196. A search was made in natural Sm for the existence of Sm-146 activity, considered to be absent in nature because of a relatively short alpha half-life. Also, a sample of W enriched in W-180 was studied in order to determine whether this was the isotope responsible for the previously observed alpha activity in natural W.