Particle

A particle is a minute fragment or quantity of matter. In the physical sciences, the word is used to describe a small localized object to which can be ascribed several physical or chemical properties such as volume or mass; subatomic particles such as protons or neutrons; and other elementary particles. The word is rather general in meaning, and is refined as needed by various scientific fields. Something that is composed of particles may be referred to as being particulate. However, the term particulate is most frequently used to refer to pollutants in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.

Conceptual properties

The concept of particles is particularly useful when modelling nature, as the full treatment of many phenomena is complex. It can be used to make simplifying assumptions concerning the processes involved. Francis Sears and Mark Zemansky, in University Physics, give the example of calculating the landing location and speed of a baseball thrown in the air. They gradually strip the baseball of most of its properties, by first idealizing it as a rigid smooth sphere, then by neglecting rotation, buoyancy and friction, ultimately reducing the problem to the ballistics of a classical point particle. The treatment of large numbers of particles is the realm of statistical physics.

Alpha particle

Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α²⁺. Because they are identical to helium nuclei, they are also sometimes written as He2+
or 4
2He2+
indicating a helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) helium atom 4
2He.

Some science authors may use doubly ionized helium nuclei (He2+
) and alpha particles as interchangeable terms. The nomenclature is not well defined, and thus not all high-velocity helium nuclei are considered by all authors to be alpha particles. As with beta and gamma rays/particles, the name used for the particle carries some mild connotations about its production process and energy, but these are not rigorously applied. Thus, alpha particles may be loosely used as a term when referring to stellar helium nuclei reactions (for example the alpha processes), and even when they occur as components of cosmic rays. A higher energy version of alphas than produced in alpha decay is a common product of an uncommon nuclear fission result called ternary fission. However, helium nuclei produced by particle accelerators (cyclotrons, synchrotrons, and the like) are less likely to be referred to as "alpha particles".