Beta Rays (Beta Particles) | Discovery, Uses, Applications

Definition of Beta Rays

Beta rays are made up of beta particles. A beta particle has the same mass and charges as an electron. It is emitted from the nucleus of an atom during radioactive decay. It can either be negatively charged (negatrons) or positively charged (positrons).

beta rays

Collision interactions of beta particles are somewhat different from those of alpha particles. A beta particle may collide with an orbital electron or come into proximity to it. And cause the electron to be ejected by forming an ion pair.

The probability of beta particle interactions with atomic electrons increases with the density of the absorbing material. The range of beta particles in matter is considerably greater than that of alpha particles of the same energy. Because of the lower mass, lower charge, and higher velocity of travel of the beta particle in comparison to an alpha particle of equivalent energy.

Discovery of Beta Rays

Discovery of Beta Rays

While experimenting with fluorescence, Henri Becquerel accidentally found out that uranium exposed a photographic plate, wrapped with black paper, with some unknown radiation that could not be turned off like X-rays.

Ernest Rutherford continued these experiments and discovered two different kinds of radiation: alpha particles that did not show up on the Becquerel plates because they were easily absorbed by the black wrapping paper beta particles, which are 100 times more penetrating than alpha particles.

He published his results in 1899. In 1900, Becquerel measured the mass-to-charge ratio (m/e) for beta particles by the method of J. J. Thomson used to study cathode rays and identify the electron.

He found that e/m for a beta particle is the same as for Thomson’s electron and therefore suggested that the beta particle is, in fact, an electron.

Beta Decay

Beta Decay

Beta-decay (β-decay) is radioactive decay. In which a beta particle (fast, energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide.

For example, the beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; conversely, a proton is converted into a neutron by the emission of a positron with a neutrino in so-called positron emission.

Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay but are created in the decay process.

By this process, unstable atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by its nuclear binding energy.

The binding energies of all existing nuclides form what is called the nuclear band or valley of stability. Electron capture is sometimes included as a type of beta decay; because the basic nuclear process, mediated by the weak force, is the same.

In electron capture, an inner atomic electron is captured by a proton in the nucleus, transforming it into a neutron, and an electron neutrino is released.

Uses of Beta Rays

Uses of Beta Rays

The medium penetrating power of beta particles provides a range of useful applications which include:

  1. Thickness detectors for the quality control of thin materials, i.e., paper.
  2. Treatment of eye and bone cancers, strontium-90 or strontium-89 are commonly used.
  3. Tritium is used in some phosphorescent lighting, typically for emergency lighting as it requires no power.
  4. Fluorine-18 is commonly used as a tracer for positron emission tomography (PET).

Applications of Beta Rays

Following are some applications of beta rays:

  • Beta particles can treat health conditions such as eye and bone cancer and are also used as tracers. Strontium-90 is the material most commonly used to produce beta particles.
  • Beta particles are also used in quality control to test the thickness of an item, such as paper, coming through a system of rollers. Some of the beta radiation is absorbed while passing through the product. If the product is made too thick or thin, a correspondingly different amount of radiation will be absorbed. A computer program monitoring the quality of the manufactured paper will then move the rollers to change the thickness of the final product.
  • An illumination device called a betalight contains tritium and a phosphor. As tritium decays, it emits beta particles; these strike the phosphor, causing it to give off photons, much like the cathode ray tube in a television. The illumination requires no external power and will continue as long as the tritium exists (and the phosphors do not chemically change); the amount of light produced will drop to half its original value in 12.32 years, the half-life of tritium.
  • Beta-plus (or positron) decay of a radioactive tracer isotope is the source of the positrons used in positron emission tomography (PET scan).

Properties of Beta Particles

Properties of Beta Particles

Beta particles, also known as beta rays, are high speed, high energy electron (β-) or positron(β+) emitted from the radioactive decay of the atomic nucleus.

This process is called beta decay. An unstable atomic nucleus with an excess of neutrons will emit electrons (β-) during the β decay. If the unstable atomic nucleus has an excess of the proton, then a positron(β+) is emitted during β decay.

  1. Beta particles (β – particles) are fast-moving electrons or positrons with high energy emitted by the radioactive decay of an atomic nucleus.
  2. Penetrating power of beta particles is higher than α-particles. They can penetrate through a thin metal foil.
  3. The ionizing power of β-particles is 100 times lesser than α-particles. Higher ionization means higher damage to the living tissue.
  4. Both the electric field and magnetic field affect the β-particles. Applying Fleming’s left-hand rule, it is observed that the direction of deflection of β-particles is opposite to that of α-particles.
  5. Their speed can go up to 9/10 times the speed of light.
  6. In a β – decay, the atomic number of the daughter nucleus increases by one. But the mass number remains the same.
  7. Beta particles have negligible mass. They are much lighter than alpha particles.
  8. β – particles can be stopped by a thin layer of aluminum or plastic.
  9. They affect the photographic plate.
  10. They lose energy fast when they interact with matter and take a haphazard path as they move through air or other materials.

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