DL-1a is intended as a replacement for DL-1 of which the stock is exhausted. It is waste rock typical of the property of Denison Mines Limited in Elliot Lake, Ontario, and is a pale yellow arkose sandstone containing uraninite and brannerite and possibly traces of monazite and uranothorite. he bulk material was dry-ground to minus 74 µm, blended, sampled systematically for analysis by optical fluorimetric and chemical methods to demonstrate homogeneity suitable for use as a reference material, and bottled in 200-g units. Evidence is available that DL-1a is in secular equilibrium.