17. Radioactivity and Nuclear Chemistry

How can a nucleus emit an electron during β decay when there are no electrons present in the nucleus to begin with?

A β-emitting radiation source gives 250 units of radiation at a distance of 4.0 m. At what distance does the radiation drop to one-tenth its original value?

The red arrow in the graph (see margin) indicates the changes that occur in the nucleus of an atom during a nuclear reaction. Identify the isotopes involved as product and reactant, and name the type of decay process.