III.

Characteristics and Behavior

Beta particles have all the characteristics of electrons found in atoms, except the electric charge of positrons is opposite that of electrons. At the time of their emission, they travel at nearly the speed of light. The high energy of beta particles enables them to travel through matter to a depth of several millimeters. They lose their energy by interacting with other atoms and by releasing a form of radiation known as bremsstrahlung (German for “braking radiation”). Bremsstrahlung occurs when negative beta particles are attracted to the positively charged nuclei of atoms. The velocity of the beta particles increases as they approach the positive nuclei then decreases abruptly as they move away from the nuclei. The rapid acceleration and deceleration of the beta particles produces radiation. Bremsstrahlung radiation is strongest in radioactive elements, which have a high atomic number, or number of protons within the nucleus. Elements with a low atomic number, such as aluminum, are used in shields to block beta radiation. Lead blocks radiation types such as gamma rays and X rays but has high atomic number, so it cannot block beta radiation. When beta particles enter materials, they can cause chemical changes, such as darkening of glass. Most beta particles lack the energy to penetrate beneath the skin, but in high doses they can cause skin damage.