Photofission

Nuclear physics
Models of the nucleus
Nuclides' classification
Nuclear stability
Radioactive decay
Nuclear fission
Capturing processes
High-energy processes
Nucleosynthesis and
nuclear astrophysics
High-energy nuclear physics
Scientists

Photofission is a process in which a nucleus, after absorbing a gamma ray, undergoes nuclear fission and splits into two or more fragments.

The reaction was discovered in 1940 by a small team of engineers and scientists operating the Westinghouse Atom Smasher at the company's Research Laboratories in Forest Hills, Pennsylvania.[1] They used a 5 MeV proton beam to bombard fluorine and generate high-energy photons, which then irradiated samples of uranium and thorium.[2]

Gamma radiation of modest energies, in the low tens of MeV, can induce fission in traditionally fissile elements such as the actinides thorium, uranium,[3] plutonium, and neptunium.[4] Experiments have been conducted with much higher energy gamma rays, finding that the photofission cross section varies little within ranges in the low GeV range.[5]

Baldwin et al made measurements of the yields of photo-fission in uranium and thorium together with a search for photo-fission in other heavy elements, using continuous x-rays from a 100-MeV betatron. Fission was detected in the presence of an intense background of x-rays by a differential ionization chamber and linear amplifier, the substance investigated being coated on an electrode of one chamber. They deduced the maximum cross section being of the order of 5×10−26 cm2 for uranium and half that for thorium. In the other elements studied, the cross section must be below 10−29 cm2.[6]

  1. ^ Walter, Marni Blake (2015-09-01). "An Unlikely Atomic Landscape: Forest Hills and the Westinghouse Atom Smasher". Western Pennsylvania History Magazine. 98 (3). Senator John Heinz History Center: 36–49. Retrieved 2019-12-03.
  2. ^ Haxby, R.O.; Shoupp, W.E.; Stephens, W.E.; Wells, W.H. (1941-01-01). "Photo-Fission of Uranium and Thorium". Physical Review. 59 (1): 57–62. Bibcode:1941PhRv...59...57H. doi:10.1103/PhysRev.59.57.
  3. ^ Silano, J.A.; Karwowski, H.J. (2018-11-19). "Near-barrier Photofission in 232Th and 238U". Physical Review C. 98 (5): 054609. arXiv:1807.03900. Bibcode:2018PhRvC..98e4609S. doi:10.1103/PhysRevC.98.054609.
  4. ^ Doré, D; David, J-C; Giacri, M-L; Laborie, J-M; Ledoux, X; Petit, M; Ridikas, D; Lauwe, A Van (2006-05-01). "Delayed neutron yields and spectra from photofission of actinides with bremsstrahlung photons below 20 MeV". Journal of Physics: Conference Series. 41 (1). IOP Publishing: 241–247. Bibcode:2006JPhCS..41..241D. doi:10.1088/1742-6596/41/1/025. ISSN 1742-6588.
  5. ^ Cetina, C.; Berman, B. L.; Briscoe, W. J.; Cole, P. L.; Feldman, G.; et al. (2000-06-19). "Photofission of Heavy Nuclei at Energies up to 4 GeV". Physical Review Letters. 84 (25): 5740–5743. arXiv:nucl-ex/0004004. Bibcode:2000PhRvL..84.5740C. doi:10.1103/physrevlett.84.5740. ISSN 0031-9007. PMID 10991043. S2CID 206326581.
  6. ^ Baldwin, G. C.; Klaiber, G. S. (1947-01-01). "Photo-Fission in Heavy Elements". Physical Review. 71 (1). American Physical Society (APS): 3–10. Bibcode:1947PhRv...71....3B. doi:10.1103/physrev.71.3. ISSN 0031-899X.