Define these terms: (a) \(\alpha\) particle, (b) \(\beta\) particle, (c) \(\gamma\) ray, (d) X ray.

When we discuss ionizing radiation, an alpha particle is one of the types that we encounter. It comprises two protons and two neutrons, which makes it relatively heavy and positively charged. Due to these characteristics, alpha particles do not travel very far in the air and are quickly absorbed by materials; even a sheet of paper or the outer layers of human skin can halt them. However, if alpha-emitting substances are ingested or inhaled, they can cause significant damage due to the high energy they impart to surrounding tissues.

Alpha particles are typically found in the decay processes of heavy elements such as Uranium-238, which breaks down into Thorium-234 while releasing an alpha particle. This release of particles from radioactive materials is an example of alpha decay, a phenomenon that is significant both in nuclear physics and in practical applications such as medical treatments and radiometric dating.

Another form of ionizing radiation is the beta particle. Unlike alpha particles, beta particles are much smaller because they are essentially either high-energy, high-speed electrons (negatively charged) or positrons (positively charged). Due to their small mass and charge, beta particles can travel further through air than alpha particles, but they can still be stopped by a few millimeters of aluminum or plastic.

Beta particles are typically emitted in a process called beta decay. This occurs when a neutron in an atom's nucleus converts to a proton (or vice versa in the case of positron emission) and an electron or positron is ejected as a result. Beta decay is critical in fields such as nuclear medicine, where the decay processes of isotopes are utilized for imaging and treatment. Moreover, understanding beta decay is key to insights regarding the stability of atomic nuclei and the processes governing stellar nucleosynthesis.

Gamma rays represent the highest energy form of electromagnetic radiation. Unlike alpha and beta particles, which have mass, gamma rays are massless photons, traveling at the speed of light. Their high energy levels mean gamma rays can penetrate much deeper into materials than alpha or beta radiation. Lead or several inches of concrete are usually required to effectively shield gamma rays.

Gamma rays are produced by various high-energy processes in the universe, such as during radioactive decay of atomic nuclei, in nuclear explosions, and by cosmic entities like pulsars and supernova remnants. Their applications range from medical imaging and treatment (in the form of radioactive isotopes) to being used as probes in astrophysical observations to understand distant celestial events. Despite their useful applications, gamma rays can pose a significant health risk due to their penetrating power and ability to damage biological tissues and DNA.

X rays, like gamma rays, are a form of electromagnetic radiation. However, they generally have lower energy levels compared to gamma rays. These rays are produced by either bombarding a material with high-energy electrons or via electron transitions within the inner shells of an atom. When an electron jumps from a higher to a lower energy level, it can emit energy in the form of an X-ray photon.

One of the most familiar uses of X rays is in medical diagnostics, where they help in creating images of the inside of the body, such as in the case of X-ray radiography. They are also utilized in materials science for the analysis of crystal structures, inspection in industrial processes, and security scanning. While being invaluable tools across various fields, protection measures are still necessary when working with X rays due to their potential to cause harm through biological tissue and cellular damage.