Radioactive recoil

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Radioactive recoil (English Radioactive Recoil ) denotes the recoil that a nucleus during radioactive decay due to the conservation of momentum undergoes.

For example, the lead- 206 core, which is formed from a polonium 210 core through alpha decay ( i.e. the release of a helium-4 core), receives a kinetic energy of around 2% of the energy released by the alpha decay of 5 through the recoil , 3 MeV , i.e. around 100 keV. This energy is sufficient to destroy molecular bonds and, under suitable conditions, to separate the daughter atoms from their parent atoms.

The radioactive recoil was first noticed by Harriet Brooks in 1904 when she brought non-radioactive plates near radioactive sources and observed them develop activity. But it was not until the end of 1908 that Otto Hahn actually demonstrated and explained the radioactive recoil experimentally. Hahn's work was published in the Physikalische Zeitschrift in early 1909 under the title About a new phenomenon in activation with actinium . It says, among other things:

“As is well known, the decay of a radioactive atom happens like an explosion, the alpha rays reach a speed of up to 1/10, the electrons almost full speed of light. If such a radioactive atom bursts, the remaining atom will be recoiled by the ejection of electrons or even more alpha rays, similar to a cannon when the projectile leaves the barrel. The speed of the residual atom is therefore determined by the principle of the center of gravity. "

Practically the same effect (although no radioactivity is involved) is used in the Szilard-Chalmers reaction to separate the product atoms from (n, γ) nuclear reactions ; Here, the recoil causes the emission of the gamma quantum to release the newly created atom from its chemical bond.

When measuring gamma spectra , the recoil, which leads to a broadening of the spectral lines, is undesirable and can be greatly reduced by incorporating the atoms in a crystal lattice ( Mössbauer effect ).

literature

  • Otto Hahn: About a new phenomenon in the activation of actinium , Physikalische Zeitschrift, 10th year, No. 3, pp. 81–88, 1909
  • BW Sargent: Nuclear Physics in Canada . In: William R. Shea (Ed.): Otto Hahn and the Rise of Nuclear Physics , pp. 221-240. D. Reidel: Dordrecht, Boston, Lancaster 1983
  • Walther Gerlach , Dietrich Hahn: Otto Hahn - A Researcher Life of Our Time , Wissenschaftliche Verlagsgesellschaft, pp. 39–41, Stuttgart 1984
  • M. Mladjenovic: History of early nuclear physics , 1992