The construction of the dating apparatus started in the summer of 1960 and was completed one year later. The laboratory is located on the bottom floor of a three-story concrete-block building which has two thin concrete floors on concrete beams above the shield. The building is underlain by carbonate mud and coral rock. The geographic location is 25° 43.9′ N Lat, 80° 09.8′ W Long and only a few feet above sealevel. We use a proportional-counting tube with an active volume of 1 L, and a total

more »

... ple volume of 1.30 L, filled with purified CO2to a pressure of 225 cm Hg (3 atm) at 25°C. The tube is made of copper with brass ends and quartz insulators. The shielding consists of 20 cm of iron, 10 cm of paraffin with boric acid, 2.5 cm of selected lead (Östlund, 1961), and cosmic ray guard counters. The room is air-conditioned but no additional precautions have been taken to exclude outdoor dust.