Gamma Rays – X-Rays – Difference – Distinction

The distinction between X-rays and gamma rays is not so simple and has changed in recent decades. Both are high-energy photons (electromagnetic radiation) with very short wavelengths and thus very high frequency. Yes, X-rays are being said to have lower energies, but this is not the rule and the main difference. According to the currently valid definition, X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus.

NASA - Electromagnetic spectrum
Source: Tour of the Electromagnetic Spectrum www.nasa.gov

Characteristics of X-rays

Key features of X-rays are summarized in following few points:

  • X-rays are high-energy photons (about 100 – 1 000 times as much energy as the visible photons), the same photons as the photons forming the visible range of the electromagnetic spectrum – light.
  • X-rays are usually described by their maximum energy, which is determined by the voltage between the electrodes. It may range from about 20 kV up to 300 kV. Radiation with low voltage is called “soft” – and radiation with high voltage is called “hard”.
  • Photons have no mass and no electrical charge, therefore they cannot directly ionize matter, neither X-rays.
  • X-rays ionize matter via indirect ionization.
  • Although a large number of possible interactions are known, there are three key interaction mechanisms  with matter.
  • X-rays travel at the speed of light and they can travel hundreds of meters in air before spending their energy.
  • Since the hard X-rays are very penetrating matter, it must be shielded by very dense materials, such as lead or uranium.
  • The distinction between X-rays and gamma rays is not so simple and has changed in recent decades.  According to the currently valid definition, X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus.
  • For X-rays generated by X-ray tube, there are two different types of X-rays spectra:
  • Characteristic X-rays frequently accompany some types of nuclear decays, such as internal conversion and electron capture.

Characteristics of Gamma Rays

Key features of gamma rays are summarized in following few points:

  • Gamma rays are high-energy photons (about 10 000 times as much energy as the visible photons), the same photons as the photons forming the visible range of the electromagnetic spectrum – light.
  • Photons have no mass and no electrical charge, therefore they cannot directly ionize matter, neither gamma rays.
  • Despite this fact, gamma rays ionize matter via indirect ionization.
  • Although a large number of possible interactions are known, there are three key interaction mechanisms  with matter.
  • Gamma rays travel at the speed of light and they can travel thousands of meters in air before spending their energy.
  • Since the gamma radiation is very penetrating matter, it must be shielded by very dense materials, such as lead or uranium.
  • The distinction between X-rays and gamma rays is not so simple and has changed in recent decades.  According to the currently valid definition, X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus.
  • Gamma rays frequently accompany the emission of alpha and beta radiation.
References:

Radiation Protection:

  1. Knoll, Glenn F., Radiation Detection and Measurement 4th Edition, Wiley, 8/2010. ISBN-13: 978-0470131480.
  2. Stabin, Michael G., Radiation Protection and Dosimetry: An Introduction to Health Physics, Springer, 10/2010. ISBN-13: 978-1441923912.
  3. Martin, James E., Physics for Radiation Protection 3rd Edition, Wiley-VCH, 4/2013. ISBN-13: 978-3527411764.
  4. U.S.NRC, NUCLEAR REACTOR CONCEPTS
  5. U.S. Department of Energy, Instrumantation and Control. DOE Fundamentals Handbook, Volume 2 of 2. June 1992.

Nuclear and Reactor Physics:

  1. J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
  2. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. W.S.C. Williams. Nuclear and Particle Physics. Clarendon Press; 1 edition, 1991, ISBN: 978-0198520467
  6. G.R.Keepin. Physics of Nuclear Kinetics. Addison-Wesley Pub. Co; 1st edition, 1965
  7. Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.
  8. U.S. Department of Energy, Nuclear Physics and Reactor Theory. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  9. Paul Reuss, Neutron Physics. EDP Sciences, 2008. ISBN: 978-2759800414.

See above:

Gamma Rays