alpha particle

(noun)

A particle consisting of two protons and two neutrons bound together, identical to a helium nucleus.

Related Terms

  • beta particle
  • isotope
  • gamma ray

Examples of alpha particle in the following topics:

  • Modes of Radioactive Decay

    • Alpha particles carry a positive charge, beta particles carry a negative charge, and gamma rays are neutral.
    • Alpha particles have greater mass 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 (He) nuclei.
    • An alpha particle (α\alpha) is made up of two protons and two neutrons bound together.
    • Alpha particles can be completely stopped by a sheet of paper.
  • Balancing Nuclear Equations

    • Common light particles are often abbreviated in this shorthand, typically p for proton, n for neutron, d for deuteron, α representing an alpha particle or helium-4, β for beta particle or electron, γ for gamma photon, etc.
    • This fits the description of an alpha particle.
    • This could also be written out as polonium-214, plus two alpha particles, plus two electrons, give what?
    • In order to solve this equation, we simply add the mass numbers, 214 for polonium, plus 8 (two times four) for helium (two alpha particles), plus zero for the electrons, to give a mass number of 222.
    • Describes how to write the nuclear equations for alpha and beta decay.
  • Isotopes

    • Unstable isotopes most commonly emit alpha particles (He2+) and electrons.
  • Indoor Pollution: Radon

    • Radon and its daughters continue to decay in the lungs, releasing alpha and beta particles that can damage cellular DNA and result in lung cancer.
  • Reactions at the α-Carbon

    • Many aldehydes and ketones undergo substitution reactions at an alpha carbon, as shown in the following diagram (alpha-carbon atoms are colored blue).
    • If the alpha-carbon is a chiral center, as in the second example, the products of halogenation and isotopic exchange are racemic.
    • First, these substitutions are limited to carbon atoms alpha to the carbonyl group.
    • Cyclohexanone (the first ketone) has two alpha-carbons and four potential substitutions (the alpha-hydrogens).
    • This is demonstrated convincingly by the third ketone, which is structurally similar to the second but has no alpha-hydrogen.
  • Allotropes of Carbon

    • Amorphous graphite: fine particles, the result of thermal metamorphism of coal; sometimes called meta-anthracite
    • The two known forms of graphite, alpha (hexagonal) and beta (rhombohedral), have very similar physical properties (except that the layers stack slightly differently).
    • The alpha form can be converted to the beta form through mechanical treatment, and the beta form reverts to the alpha form when it is heated above 1300 °C.
  • Particle Accelerator

    • A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds within well-defined beams.
    • A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams.
    • While current particle accelerators are focused on smashing subatomic particles together, early particle accelerators would smash entire atoms together, inducing nuclear fusion and thus nuclear transmutation.
    • This occurs either through nuclear reactions in which an outside particle reacts with a nucleus, which can be supplied by a particle accelerator, or through radioactive decay, where no outside particle is needed.
    • Electrostatic accelerators use static electric fields to accelerate particles.
  • Root-Mean-Square Speed

    • The root-mean-square speed measures the average speed of particles in a gas, defined as $v_{rms}=\sqrt{\frac{3RT}{M}}$ .
    • According to Kinetic Molecular Theory, gaseous particles are in a state of constant random motion; individual particles move at different speeds, constantly colliding and changing directions.
    • We cannot gauge the velocity of each individual particle, so we often reason in terms of the particles' average behavior.
    • Particles moving in opposite directions have velocities of opposite signs.
    • Since the value excludes the particles' direction, we now refer to the value as the average speed.
  • Distribution of Molecular Speeds and Collision Frequency

    • The movement of gaseous particles is characterized by straight-line trajectories interrupted by collisions with other particles or with a physical boundary.
    • Consider a closed system of gaseous particles with a fixed amount of energy.
    • In theory, this energy can be distributed among the gaseous particles in many ways, and the distribution constantly changes as the particles collide with each other and with their boundaries.
    • By understanding the nature of the particle movement, however, we can predict the probability that a particle will have a certain velocity at a given temperature.
    • As the temperature increases, the particles acquire more kinetic energy.
  • Enolate Intermediates

    • Many of the most useful alpha-substitution reactions of ketones proceeded by way of enolate anion conjugate bases.
    • Esters and nitriles are even weaker alpha-carbon acids than ketones (by over ten thousand times), nevertheless their enolate anions may be prepared and used in a similar fashion.
    • The presence of additional activating carbonyl functions increases the acidity of the alpha-hydrogens substantially, so that less stringent conditions may be used for enolate anion formation.
    • The influence of various carbonyl and related functional groups on the equilibrium acidity of alpha-hydrogen atoms (colored red) is summarized in the following table.
    • Note that each of these compounds has two acidic alpha-hydrogen atoms (colored red).
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