Heavy fragment production through electropion excitation ofFe56

Abstract

Heavy ejecta with charges ranging from $Z=3 \mathrm{to} 14$ have been observed following the collisions of 20 GeV electron with $^{56}\mathrm{Fe}$ nuclei. Crude charge and energy spectra of the fragments have been determined with track-etch detectors. For $Z\ensuremath{\le}8$, the source is found to be slowly moving ($\frac{v}{c}<0.004$) nuclear matter with a temperature of 13\ifmmode\pm\else\textpm\fi{}1 MeV, quite similar to that responsible for the evaporation of nuclei excited by high-energy protons. The total cross section for producing fragments with $Z=7 or 8 \mathrm{by} 20$ GeV electrons is about 700 times smaller than that for producing these fragments through collisions of 2 GeV protons with iron nuclei. The excitation mechanism is most likely that of electropion production, as evidenced by the similarity of calculated and measured cross sections. An additional, as yet unknown, mechanism is required to explain the observed production of fragments with $Z\ensuremath{\ge}12$, energy > 140 MeV, and cross section of the order ${10}^{\ensuremath{-}33}$-${10}^{\ensuremath{-}32}$ ${\mathrm{cm}}^{2}$.NUCLEAR REACTIONS $^{56}\mathrm{Fe}$($e$,$X$), $E=20$ GeV; Measured $\ensuremath{\sigma}({E}_{X},\ensuremath{\theta})$ for $X=\mathrm{L}\mathrm{i},\phantom{\rule{0ex}{0ex}}\mathrm{B}\mathrm{e},\phantom{\rule{0ex}{0ex}}\mathrm{B},\phantom{\rule{0ex}{0ex}}\mathrm{C},\phantom{\rule{0ex}{0ex}}\mathrm{N},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{O}$. Determined temperature and velocity of source of fragments.