Isotope

An **__isotope__** is a form of an element which contains a different number of neutrons then normal, but has the same number of protons and electrons. Therefore, isotopes have different mass numbers. Isotopes are specified by the name of the particuluar element followed by a hyphen and the mass number (e.g. carbon-12, iodine-131, helium-3), or by placing them as a superscripted prefix to the chemical symbol (e.g. ¹²C, ¹³¹I, ³He).

A __**radioactive Isotope**__ is an isotope whose nucleus decays spontaneously, giving off particles and energy. They can be very harmful, but are also very useful for medical technology. The energy given off can be tracked in the human body and can show what processes the body is going through.

One way that radioactive isotopes are used in medicine is PET (Positron Emission Tomography) scans. In a PET scan, a small dose of a radioactive isotope mixed with sugar is given to a patient. The patient's brain needs the sugar, so the radioactive isotope travels up with the sugar to the brain. While it moves along, it emits particles called positrons. These positrons collide with electrons, and the energy from these collisions can be detected to determine which parts of the brain are active.