World Library  
Flag as Inappropriate
Email this Article

Photodisintegration

Article Id: WHEBN0011145154
Reproduction Date:

Title: Photodisintegration  
Author: World Heritage Encyclopedia
Language: English
Subject: Nucleosynthesis, Nuclear physics, P-nuclei, Nuclear binding energy, Gamma ray
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Photodisintegration

Photodisintegration (also called phototransmutation) is a physical process in which an extremely high energy gamma ray is absorbed by atomic nucleus and causes it to enter an excited state, which immediately decays by emitting a subatomic particle. A single proton, neutron or alpha particle[1] is effectively knocked out of the nucleus by the incoming gamma ray. This process is essentially the reverse of nuclear fusion, where lighter elements at high temperatures combine together forming heavier elements and releasing energy. Photodisintegration is endothermic (energy absorbing) for atomic nuclei lighter than iron and sometimes exothermic (energy releasing) for atomic nuclei heavier than iron. Photodisintegration is responsible for the nucleosynthesis of at least some heavy, proton rich elements via p-process which takes place in supernovae.

Photodisintegration of deuterium

A photodisintegration reaction

2
1
D
 
γ  →  1
1
H
 
n

was used by James Chadwick and Maurice Goldhaber to measure the proton-neutron mass difference.[2] This experiment proves that a neutron is not a bound state of a proton and an electron,[3] as had been proposed by Ernest Rutherford.

Photodisintegration of beryllium

The photodisintegration of beryllium by gamma rays emitted by antimony-124 is used as a source for thermal neutrons.[4][5]

Hypernovae

In explosions of very large stars (250 or more times the mass of Earth's Sun), photodisintegration is a major factor in the supernova event. As the star reaches the end of its life, it reaches temperatures and pressures where photodisintegration's energy-absorbing effects temporarily reduce pressure and temperature within the star's core. This causes the core to start to collapse as energy is taken away by photodisintegration, and the collapsing core leads to the formation of a black hole. A portion of mass escapes in the form of relativistic jets, which could have "sprayed" the first metals into the universe.[6][7]

Photofission

Photofission is a similar but distinct process, in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission (splits into two fragments of nearly equal mass). Very high energy gamma rays have been shown to induce fission in elements as light as tin.

References

  1. ^ Clayton, D. D. (1984). Principles of Stellar Evolution and Nucleosynthesis. University of Chicago Press. p. 519.  
  2. ^ Chadwick, J.; Goldhaber, M. (1934). "A nuclear 'photo-effect': disintegration of the diplon by γ rays". Nature 134 (3381): 237–238.  
  3. ^ Livesy, D. L. (1966). Atomic and Nuclear Physics. Waltham, MA: Blaisdell. p. 347.  
  4. ^ Lalovic, M.; Werle, H. (1970). "The energy distribution of antimonyberyllium photoneutrons". Journal of Nuclear Energy 24 (3): 123–132.  
  5. ^ Ahmed, S. N. (2007). Physics and Engineering of Radiation Detection. p. 51.  
  6. ^ Fryer, C. L.; Woosley, S. E.; Heger, A. (2001). "Pair-Instability Supernovae, Gravity Waves, and Gamma-Ray Transients". The Astrophysical Journal 550 (1): 372–382.  
  7. ^ Heger, A.; Fryer, C. L.; Woosley, S. E.; Langer, N.; Hartmann, D. H. (2003). "How Massive Single Stars End Their Life". The Astrophysical Journal 591 (1): 288–300.  
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.