α-particle

Examples of α-particle in the following topics:

• Nuclear Size and Density

  • The famous Rutherford gold foil experiment involved the scattering of α-particles by gold foil, with some of the particles being scattered through angles of more than 90°, that is coming back to the same side of the foil as the α-source, as shown in Figure 1.
  • Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed.Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.

• 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.
  • An alpha particle (α\alpha) is made up of two protons and two neutrons bound together.
  • Their massive size (compared to beta particles, for instance) means alpha particles have very low penetration power.
  • To reduce this repulsion, the nucleus emits an α particle.

• Balancing Nuclear Equations

  • To balance a nuclear equation, the mass number and atomic numbers of all particles on either side of the arrow must be equal.
  • 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.
  • The reaction in our example above would be written as Li-6(d,α)α.
  • 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?

• Replication of Herpes Simplex Virus

  • On entering the cell, an α-TIF protein joins the viral particle and aids in immediate-early transcription.
  • Packaging of the viral particles — including the genome, core and the capsid - occurs in the nucleus of the cell.
  • The envelope covering the virus particle, when bound to specific receptors on the cell surface, will fuse with the host cell membrane and create an opening, or pore, through which the virus enters the host cell.

• Scattering of Light by the Atmosphere

  • Rayleigh scattering is the elastic scattering of waves by particles that are much smaller than the wavelengths of those waves.
  • The particles that scatter the light also need to have a refractive index close to 1.
  • The formula to calculate the intensity of the scattering for a single particle is as follows:
  • where I is the resulting intensity, I0 is the original intensity, α is the polarizability, λ is the wavelength, R is the distance to the particle, and θ is the scattering angle.
  • Describe wave-particle relationship that leads to Rayleigh scattering and apply it to explain common phenomena

• Summary of Formulas

  • α is preconceived.
  • α = probability of a Type I error = P(Type I error) = probability of rejecting the null hypothesis when the null hypothesis is true.
  • If there is no given preconceived α, then use α = 0.05.

• Alpha Decay

  • In alpha decay an atomic nucleus emits an alpha particle and transforms into an atom with smaller mass (by four) and atomic number (by two).
  • Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle that consists of two protons and two neutrons, as shown in .
  • Because an alpha particle is the same as a helium-4 nucleus, which has mass number 4 and atomic number 2, this can also be written as:
  • The alpha particle also has charge +2, but the charge is usually not written in nuclear equations, which describe nuclear reactions without considering the electrons.
  • Alpha particles have a typical kinetic energy of 5 MeV (approximately 0.13 percent of their total energy, i.e., 110 TJ/kg) and a speed of 15,000 km/s.

• Decision and Conclusion

  • A systematic way to make a decision of whether to reject or not reject the null hypothesis is to compare the p-value and a preset or preconceived α (also called a "significance level").
  • A preset α is the probability of a Type I error (rejecting the null hypothesis when the null hypothesis is true).
  • If α > p-value, reject Ho.
  • If α ≤ p-value, do not reject Ho.

• Diastereoselection in Reactions with Chiral Enolates

  • These Z-enolates are expected to favor 1,2-syn diastereoselectivity of the newly created α & β chiral centers, as noted earlier.
  • However, the 1,4-diastereoselectivity (α':β) is not consistent.
  • The 1,4-anti-selectivity shown in reactions 6 and 7 is predicted by the transition state model, but the 1,4-syn-selectivity and 1,3-anti selectivity (α':α) in reaction 5 is anomalous.
  • Again, strong facial selectivity is displayed for bonding at the re-face of the enolate as drawn, with both the new 1,2- (α:β) and 1,4- (α':β) diastereoselectivities being syn, as expected.
  • The exceptional and unusual 1,3-anti selectivity (α':α) shown by the Z-enolate is noteworthy.

• The Favorskii Rearrangement

  • Treatment of α-halogenated ketones, having acidic α'-hydrogens, with nucleophilic bases often leads to a skeletal rearrangement known as the Favorskii rearrangement.
  • Here the unsymmetrical cyclopropanone opens to favor the less substituted α-carbon, reflecting the carbanion stability order: 1º > 2º > 3º .
  • In this case cleavage of the cyclopropanol at the more substituted α-carbon probably reflects the inductive effect of the THPO substituent.