Positron emission is most common in lighter elements with a low neutron to proton ratio. This captured electron joins with a proton in the nucleus to form a neutron. Electron capture is common in larger elements with a low neutron to proton ratio. All elements with an atomic number over 83 are considered radioactive. Radiation ionizes the atoms in the cylinder and allows current to flow between the electrodes.
All radioactive elements disintegrate according to their specific half life .
The half life of a radioactive substance is the time required for half of the initial number of nuclei to disin tegrate. The decay rate expresses the speed at which a substance disintegrates. By using these equations, it is possible to calculate how much of a nuclear substance will be left after a certain time and how much of a substance originally existed. A common example is isotopic dating in which the ages of archeological artifacts are d etermined by measuring the activity of the isotopes. Practice Problems 1.