ASNT Industrial Radiography Radiation Safety Practice Test

What is the composition of an alpha particle?

1. One proton and one neutron

2. Two protons, two neutrons, and two electrons

3. Two protons and two neutrons

4. One proton and two electrons

The correct answer is: Two protons and two neutrons

An alpha particle is composed of two protons and two neutrons, making it identical to the nucleus of a helium atom. This specific composition is significant because it defines the alpha particle's properties in terms of charge and mass. The presence of two protons gives the alpha particle a positive charge, while the two neutrons contribute to its overall mass but do not affect the charge. This uniqueness means that alpha particles are relatively heavy compared to other forms of radiation and have a limited range in air and materials, often only traveling a few centimeters before losing energy and ceasing to be ionizing. This composition is fundamental to understanding the behavior of alpha radiation in the context of industrial radiography and radiation safety.