Proton emission

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The proton emission ( English emission proton , including proton conversion proton activity, proton radioactivity or proton decay called) is a very rare phenomenon in the nuclear physics , in which an atomic nucleus with the emission of a single proton is converted into the element with the next lower ordinal number. Proton emission must not be confused with proton decay , namely the hypothetical decay of the proton.

History

A proton emission was first observed in 1970 by K. Jackson from the nuclide Co-53m. This decayed directly to Fe-52 with splitting off of a proton instead of, as expected, by β + decay to Fe-53. It is therefore subject to a dual nuclear decay with the probabilities of 1.5% (proton emission) and 98.5% (β + decay) for the respective decays.

In 1981, S. Hofmann observed another proton emission from the nuclide Lu-151, which was produced at UNILAC in Darmstadt.

In the following years further observations followed: The nuclides Tm-147, Tm-147m and Lu-150, as well as Cs-113 and I-109 were identified as proton emitters, whereby their main type of decay remains the β + decay. 95 such proton emitters have now been discovered.

One proton emission

Proton emission only occurs with nuclides that have a very high proton -to- neutron ratio. Because of this large ratio, the protons can only be bound very poorly, the binding energy of the protons even drops so much that they can leave the nucleus. Such “proton-rich” nuclei usually get rid of their “positive excess” by means of β + decay, ie the emission of a positron, but in rare cases a proton can be split off instead.

The following reaction scheme illustrates the decay of the nuclide Co-53m already mentioned above:

Types of decay of the cobalt isotope Co-53m

In almost all cases the nuclide will transform through the β + decay, but there is a low probability that proton emission will take place.

In this case, the starting nuclide is a nuclide in the metastable state, a nuclear isomer . Usually such nuclei decay via an isomerism transition ; with Co-53m this is suppressed by a high angular momentum barrier (nuclear spin 19/2) and has not yet been observed.

With most nuclides, however, proton emission occurs from the ground state, as with the nuclide Lu-151 mentioned above.

Two proton emission

The occurrence of a two-proton decay, which was first considered by Witali Iossifowitsch Goldanski in 1960 and later by B. Alex Brown, is even rarer . Not just one but two protons are ejected at the same time. This only happens with nuclides where the proton-to-neutron ratio is even greater than with single-proton emitters. Such a decay was observed for the first time in 2002, again at UNILAC, on the nuclide Fe-45.

and at the same time on the GANIL ( Bertram Blank and others).

To date, 13 two-proton emitters are known.

See also

Individual evidence

  1. ↑ KP Jackson et al .: Phys. Lett. 33B, p. 281 (1970).
  2. ↑ a b c d J. Magill, J. Galy: Radioactivity, Radionuclides, Radiation. 2005, ISBN 3-540-21116-0 , pp. 77-79, 168-169.
  3. ↑ H. Krieger: Fundamentals of radiation physics and radiation protection. 2nd edition (2007), ISBN 978-3-8351-0199-9 , p. 121.
  4. ^ KH Lieser: Nuclear and Radiochemistry. 2001, ISBN 3-527-30317-0 , p. 66.
  5. ↑ S. Hofmann et al., In: Proc. 4th Int. Conf. on Nuclei Far from Stability , CERN 81-09, Geneva, 111 (1982).
  6. ^ S. Hofmann: Proton Radioactivity. Radiochimica Acta 70/71, pp. 93-105 (1995).
  7. ^ BA Brown: Phys. Rev. C 43, pp. 1513-17 (1991)
  8. ↑ M. Pfützner u. a., European Physical Journal A, Volume 14, 2002, p. 279
  9. ↑ Jérôme Giovinazzo, Bertram Blank a. a., Two-Proton Radioactivity of 45 Fe, Physical Review Letters, Volume 89, 2002, p. 102501
  10. ^ Nuclei reveal novel decay , Physics World, September 16, 2002
  11. ↑ Bertram Blank, Researchers observe two proton radioactivity , CERN Courier, December 1, 2002