sentence: Some isotopes are radioactive.
sentences_before: It is a transition metal, a group of metals. It is sometimes considered a post-transition metal. Zinc is the 30th element on the periodic table, and has an atomic number of 30. Zinc has a mass number of 65.38. It contains 30 protons and 30 electrons.
sentences_after: Their half-lives are between 40 milliseconds for 57Zn and 5x1018 years for 70Zn.
concept_name: isotope
headings: Zinc
categories: Chemical elements Transition metals