Alpha-Particle Decay Measurements for Very Long - Quasi-Stable Isotopes of Neodymium, Platinum, Samarium and Uranium.

Half lives and alpha-particle energies of very long-lived (10('9) - 10('16) years) quasi-stable nuclei with A > 140 have been measured using a cylindrical gas -flow proportional counter. The source materials were deposited on the inner surface of the cathode cylinder over an area of about 1700 cm('2). Low-level counting techniques were developed with emphasis on the reduction of background from external and internal sources. External background can be reduced by shielding and rise-time discrimination. Internal background from (alpha)-contaminants in the counter materials and the source materials was a major source of background and was studied in detail. Stainless steel was found to be superior to brass and aluminum. Ultrapure source materials had to be superior to brass and aluminum. Ultrapure source materials had to be used. Half lives and energies were measured for ('144)Nd, ('147)Sm, ('190)Pt, ('234)U, ('235)U, ('238)U, and lower limit was obtained for ('148)Sm. Reduced alpha widths which describe the preformation of (alpha)-clusters in the nuclear surface were obtained for the entire region N > 82 to Z (LESSTHEQ) 84 from all available data. Systematic trends which reflect upon the nuclear structure of these nuclei make it possible to predict new short-lived proton-rich alpha emitters as well as additional very long-lived quasi-stable alpha emitters.