Voice Sensitivity 20.00 15.00 10.00 5.00 0.00 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 1000 Time (yrs) Scientists found plant specimens in a cave in Siberia which had been preserved by the cold. Samples taken from one of the specimens have carbon-14 activities of 20.0 counts/min. A reference sample of the same size from a plant alive today has a carbon-14 activity of 160.0 counts/min. What is the age of the specimen in years? (3) 4. The half life of arsenic-74 is 18 days. If the initial amount of arsenic-74 is 24.0 mg, how much arsenic- 74 is left in the body after 72 days? (5) ). If a pregnant woman should be exposed to no more than 20.0 rad, and a radiation source gives 38.0 rad at 195 cm, what is the minimum distance she should stand from the radiation source? s: On cessibility: Unavailable Focus Q O