Etude par la méthode des traces nucléaires du sol de la Mer de la Fécondité (Luna 16)

Minimum track-density values have been determined in 278 feldspars (83–500 μ dia.) taken from five layers of the Luna 16 core sample. Feldspars in basaltic fragments appear to have been much less shocked than single feldspar crystals in the fines, of which 40 per cent were lost during the chemical etching. For the five layers the percentage of track-rich (solar flare irradiated) fragments, with densities > 10⁸/cm², is 98 per cent. However, for 60 per cent of the crystals (anorthite for the most) only lower limits of track-density were obtained. Single anorthites appear more highly irradiated than the feldspars in basaltic fragments, the former having a median track-density value of about 1 × 10⁹/cm² and the latter only ~2 × 10⁸/cm².Assuming an age for the basalts of Mare Fecunditatis of ~3.45 × 10⁹ yr (papanastassiou and Wasserburg, 1972), the track-density levels observed in the basaltic fragments can well be explained according to the model of Comstocket al. (1971). On the other hand, in order to account for the very high track densities observed in the Luna 16 anorthites and those reported for the Apollo 15 long drill stem by crozazet al. (1972) the model would require a rate of solar flare activity much higher during the period 4.6-3.5 × 10⁹yr than that observed today.