Radioactive decay occurs when an unstable atomic nucleus loses energy by emitting particles or electromagnetic waves. These emitted particles or electromagnetic waves are called radiation. Some elements are far more radioactive than others. For example, the element radium is more radioactive than uranium. Also, isotopes tend to be less stable because they contain a larger number of neutrons than non-isotopes of the same element. Radioactive isotopes are called radioisotopes.
Types of Decay
The decay products were given the alphabetic names alpha, beta, and gamma, ordered by their ability to penetrate matter. Alpha decay is seen only in heavier elements greater than atomic number 52, tellurium. The other two types of decay are seen in all of the elements. These three modes can be broken down even further.
Alpha, Beta, Gamma Composition
Alpha particles carry a positive charge, beta particles carry a negative charge, and gamma rays are neutral. Alpha particles are more massive than beta particles. By passing alpha particles through a very thin glass window and trapping them in a discharge tube, researchers found that alpha particles are equivalent to helium nuclei. Other experiments showed the similarity between classical beta radiation and cathode rays; they are both streams of electrons. Likewise, gamma radiation and X-rays were found to be similar high-energy electromagnetic radiation.
The three types of radiation have different levels of penetrating power. Penetrating power refers to the energy with which the radiation particles are ejected from the atom. The higher the energy, the more the radioactive decay will penetrate a substance.
An alpha particle (
Alpha decay occurs because the nucleus has too many protons. A nucleus with too many protons causes repulsion between these like charges. To reduce this repulsion, the nucleus emits an α particle. Examples of this can be seen in the decay of americium (Am) to neptunium (Np).
In radioactive nuclei with too many neutrons, a neutron may be converted into a proton, an electron, and another particle, called a neutrino.
The high energy electrons that are released in this way are called beta particle.
Beta particles (
During beta decay, the number of neutrons in the atom decreases by one, and the number of protons increases by one. Since the number of protons before and after the decay is diﬀerent, the atom has changed into a diﬀerent element.
When particles inside the nucleus collide during radioactive decay, energy is released.
This energy can leave the nucleus in the form of waves of electromagnetic energy called gamma rays.
Gamma radiation (
Gamma decay occurs if the nucleus' energy level is too high. Since gamma rays are part of the electromagnetic spectrum, they can be thought of as waves or particles. In gamma decay, a ray or a particle called a photon is released, and the atomic number and atomic mass remain unchanged.