Search for 10¹⁵ eV Gamma-Rays from the Crab Pulsar and Surrounding Regions
Boone, J. et al.1984, Ap.J., 285,264.

Total Proton-Proton Cross Section at s^1/2=30 TeV
Baltrusaitis, R.M. et al.1984, Phys. Rev., 52,1380.