A search for "structure" in the energy spectra of cosmic ray protons and He-nuclei above 104 GeV

The energy spectra of nuclei heavier than helium all show a flattening above about 10(3)-10(4) GeV/nucleon. Here we search for a possibly similar structure in the proton and He-spectra at energies above those where direct measurements are available. One possible explanation of the flattening of the spectra of nuclei is the model advanced by us [J. Phys. G 23 (1997) 979; Astropart. Phys. 7 (1997) 1, 203; 8 (1998) 265, 283; (in press)] in which a local, recent supernova was invoked, but there may be others too. The problem is examined in a number of ways but most of the paper is devoted to the establishment of a method that can be used with extensive air shower data in order to examine the proton and He-nuclei spectra. Although present experimental data are still not very accurate in the shower size region in question, we apply the method to these data. The result is that, taking our single source model as the datum, the fraction of protons and He-nuclei taken together is 20 +/- 10%. The astrophysical significance of these tentative results is discussed. (C) 1999 Elsevier Science B.V.