Actinium is pronounced as ak-TIN-ee-em. History and Uses: Actinium was discovered in 1899 by André-Louis Debierne, a French chemist, while experimenting with new methods of separating rare earth oxides. Friedrich Otto Giesel independently discovered actinium in 1902.
Radioactive decay (also known as nuclear decay or radioactivity) is the process by which an unstable atomic nucleus loses energy (in terms of mass in its rest frame) by emitting radiation, such as an alpha particle, beta particle with neutrino or only a neutrino in the case of electron capture, gamma ray, or electron in the case of internal conversion.
Astatine is a radioactive chemical element with symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours.
Electron capture is always an alternative decay mode for radioactive isotopes that do have sufficient energy to decay by positron emission. Electron capture is sometimes called inverse beta decay, though this term can also refer to the interaction of an electron antineutrino with a proton.
It is extremely radioactive; its most stable isotope, francium-223 (originally called actinium K after the natural decay chain it appears in), has a half-life of only 22 minutes. It is the second-least electronegative element, behind only caesium, and is the second rarest naturally occurring element (after astatine).
Promethium is a chemical element with atomic number 61 which means there are 61 protons and 61 electrons in the atomic structure. The chemical symbol for Promethium is Pm. Promethium is one of only two such elements that are followed in the periodic table by elements with stable forms. All of its isotopes are radioactive.
Radium oxide (RaO) has not been characterized well past its existence, despite oxides being common compounds for the other alkaline earth metals. Radium hydroxide (Ra(OH) 2) is the most readily soluble among the alkaline earth hydroxides and is a stronger base than its barium congener, barium hydroxide.
The decay of radon produces many other short-lived nuclides known as radon daughters, ending at stable isotopes of lead. Unlike all the other intermediate elements in the aforementioned decay chains, radon is, under normal conditions, gaseous and easily inhaled. Radon gas is considered a health hazard.
Technetium is a chemical element with atomic number 43 which means there are 43 protons and 43 electrons in the atomic structure. The chemical symbol for Technetium is Tc. Technetium is the lightest element whose isotopes are all radioactive; none are stable.