Friday, August 15, 2008

Backscattering of Antiprotons

The figure shows the energy and number backscattering coefficients of hydrogen ions incident on thick layer of aluminum as a function of incident kinetic energy [1], and can be used to estimate the backscattering coefficients of antiprotons. (You can see the real size image by clicking on the image).
In the previous essay I wrote about the backscattering (also called reflection) of antiprotons from aluminum wall found by Italian physicists. The ratio of the number of backscattered particles to the number of particles incident on a layer of material is called number backscattering coefficient RN.

RN of antiprotons are almost the same as that of protons, because the basic formula of the phenomena related to the passage of particles through matter, i.e., the energy loss per unit pass length and the Rutherford scattering cross section, are independent of the sign of the incident particles. Therefore, RN of antiprotons can be estimated by the use of a universal empirical equation we published for RN of light ions, which include the hydrogen ion, i.e., the proton, incident on different absorber materials [1].

The equation for the hydrogen ion incident on the thick aluminum layer is given by the upper curve in the above figure. The energies of the antiprotons referred to by the Italian physicists are from 1 to 10 keV. For these energies, RN of the hydrogen ion and accordingly that of the antiproton can be seen to decrease from about 13%, a considerable fraction, at 1 keV to 2.5% at 10 keV.

  1. R. Ito, T. Tabata, N. Itoh, K. Morita, T. Kato and H. Tawara, Data on the backscattering coefficients of light ions from solids (A revision), Institute of Plasma Physics Nagoya University Report IPPJ-AM-41 (1985).

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