Positron
. Positron, elementary particle identical to the electron except for its electric charge and its magnetic moment (a property that determines how it behaves in a magnetic field). Positrons are elementary particles , which are fundamental constituents of matter—that is, they cannot be divided into smaller units. Positrons have uses in medicine and in industry, particularly in a form of imaging known as positron emission tomography (PET). CHARACTERISTICS AND BEHAVIOR All elementary particles have basic characteristics called mass, charge, and spin (a property analogous to angular momentum). The positron has the same mass—amount of matter—as the electron, and the same spin. The two particles also have the same amount of electric charge, but the positron’s charge is positive and the electron’s is negative. For this reason, the positron is sometimes called a positive electron. Although positrons and electrons have a measurable mass, charge, and spin, they have no measurable size, shape, or