Alpha Radiation
Alpha radiation is a type of ionizing radiation emitted during the process of alpha decay, in which an unstable atomic nucleus ejects an alpha particle composed of two protons and two neutrons. This radiation is characterized by its positive charge and relatively low penetration capabilities, making it easily shielded by materials such as paper or skin. Alpha radiation plays a significant role in various applications, including targeted cancer therapies using isotopes like radium-226 and in smoke detectors, which utilize americium-241 to generate an electric current.
The phenomenon of radioactivity involves the spontaneous decay of unstable isotopes, resulting in the release of energy in the form of radiation, which can potentially cause chemical changes in living organisms, leading to health risks like cancer. The concept of half-life is crucial in understanding how long it takes for half of a radioactive substance to decay, influencing both safety measures and medical applications. Historical figures such as Ernest Rutherford contributed significantly to the understanding of alpha radiation, paving the way for advancements in nuclear physics and technology. Overall, alpha radiation, while less penetrating than other forms of radiation, has essential applications and implications in both medical and scientific fields.
Alpha Radiation
FIELDS OF STUDY: Electromagnetism; Atomic Physics; Nuclear Physics
ABSTRACT: Alpha radiation is generated by the release of alpha particles, which are two protons and two neutrons bound together. Alpha radiation is typically emitted by radioactive materials undergoing alpha decay, especially nuclear fission. Alpha radiation was discovered by Ernest Rutherford in 1899.
PRINCIPAL TERMS
- alpha decay: a form of radioactive decay in which a radioactive atom’s nucleus splits and discharges an alpha particle, made up of two protons and two neutrons.
- Geiger-Müller probe: a device that can be used to detect alpha radiation as well as beta radiation, gamma radiation, and x-rays.
- half-life: the average time it takes for half of the unstable nuclei in a radioactive element to undergo radioactive decay, transforming into a lighter element and giving off radiation.
- isotopes: variants of a chemical element with differing numbers of neutrons; they are often unstable and radioactive.
- neutrons: subatomic particles that, with protons, make up the mass of an atom’s nucleus; they have functionally the same weight as protons but no electric charge.
- protons: subatomic particles that, with neutrons, make up the mass of an atom’s nucleus; they have functionally the same weight as neutrons but hold a positive electric charge.
- radiation: energy being transmitted via electromagnetic waves (e.g., light, heat, x-rays) or subatomic particles (e.g. alpha particles, beta particles).
- revolution: describes circular motion wherein an object circles an internal axis (e.g. the moon spinning about its axis); contrast to rotation, wherein the axis is external (e.g. the moon orbiting the earth).
Alpha and Beta: Radiation without Waves
"Radiation" often refers to electromagnetic radiation (EMR), which includes visible light, x-rays, and ultraviolet rays. Alpha radiation, however, is different. It is transmitted by subatomic particles ejected at high speed when a radioactive atom’s nucleus undergoes alpha decay. The alpha particle and the beta particle, which transmits beta radiation, were detected and described by British physicist Ernest Rutherford in 1899. Alpha radiation can be used in a variety of applications, including cancer treatment and smoke detection.
An alpha particle is made up of four subatomic particles: two protons and two neutrons. Because protons have a positive charge and neutrons are neutral, alpha particles are positively charged. They have an atomic weight of four, and are equivalent to a helium nucleus stripped of its electrons.
Radioactivity and Isotopes
An atom is said to be radioactive if it gives off ionizing radiation. This radiation is the result of an unstable nucleus ejecting energy in the form of subatomic particles in order to reach a more stable configuration. The half-life of a radioactive material is the average time it takes for half of a given sample of the material to undergo decay.
The three main forms of radiation emitted during radioactive decay are alpha, beta, and gamma radiation. All three are considered ionizing radiation. They possess enough energy to change the electrical charge of atoms they pass through. This can in turn lead to chemical changes. Through interaction with the atomic structure of living molecules, ionizing radiation can cause cancer, sickness, and increased mutation rates.
The number of protons in an atom’s nucleus determines which element it is. This number is known as the atomic number and is used to sort elements in the periodic table. The nucleus of any one atom of a given element will always have the same number of protons as every other atom of that element. However, the number of neutrons may vary. This variation in number of neutrons creates isotopes. Isotopes have more or less total atomic weight because of the addition or subtraction of neutrons. Normal carbon has 6 protons and 6 neutrons, adding up to a total atomic weight of 12. Carbon occurs in isotopes known as carbon-13 (one extra neutron) and carbon-14 (two extra neutrons). Isotopes can occur naturally or can be created artificially. Some isotopes are stable. Some, called radioisotopes, are inherently unstable and subject to spontaneous radioactive decay. All elements with atomic numbers of 83 or above are inherently unstable and radioactive. Most below that number have at least one radioisotope.
Rutherford, Villard, Geiger, and Müller
In 1899 Ernest Rutherford (1871–1937) performed radiation experiments using samples of uranium, thin sheets of metal foil, and a detection screen coated in zinc sulfide. The screen gave off light when exposed to the radiation given off by uranium. Rutherford found that one type of radiation, alpha radiation, could be stopped by an ultrathin sheet of metal. Another type, beta radiation, could penetrate 100 times as much metal before being absorbed. The following year, French physicist Paul Villard (1860–1934) discovered an even more penetrating form of radiation. Rutherford would later dub these gamma rays.
Almost a decade later, Rutherford and his assistant, German physicist Hans Geiger (1882–1945), used beams of alpha particles as a method of probing the structure of atoms. In 1908, during his tenure with Rutherford, Geiger came up with the idea for a tube filled with gas that would produce an electric pulse in response to the presence of ionizing radiation. Twenty years later, Geiger and Walther Müller (1905–79) worked together to produce a functional Geiger-Müller tube. This tube is the basis of the Geiger-Müller probe (often called a "Geiger counter"), a device that is used to detect ionizing radiation.
Uses of Alpha Particles
The positive charge and relatively low penetration of alpha particles make them suitable for a variety of applications. Tiny amounts of radium-226 may be used as a targeted form of radiation therapy for cancer, because the alpha particles will not penetrate far beyond the tumorous tissue they are intended to kill. Some smoke detectors use the positive charge of alpha particles emitted by americium-241 to generate an electric current in a sensing chamber. When smoke enters this chamber, it disrupts the current and sets off the alarm. Far and away the biggest impact alpha particles have had on everyday life, however, is through their discovery and use in establishing the basis of modern nuclear physics and with it nuclear energy and weapons technology.
Bibliography
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