68815 revisited

Remeasurement of the particle track density as a function of depth in lunar breccia 68815 has yielded galactic cosmic-ray track densities consistent with a 2 m.y. surface exposure, in good agreement with results by other authors. The empirical track-production spectrum of Walker and Yuhas (1973) is confirmed. The solar-flare track profile is typical and shows no evidence of large-scale chipping. Radionuclide profiles (Mn-53) investigated by the Arnold group should thus be undisturbed and should provide a test of the Reedy-Arnold model and of the constancy of solar and galactic cosmic rays.