C-14 Dating

A very old specimen of wood contains 10^12 atoms of carbon: a) How many C-14 atoms did it contain in the year of 9474 B.C.? b) How many C-14 atoms did it contain in 2004 A.D.?

Radioactivity

A radioactive sample consists of a mixture of S-35 and P-32. Initially, 5% of the activity is due to the S-35 and 95% due to the P-32. At what subsequent time will the activities of the two radionuclides in the sample be equal?

Specific Activity

a) Tritium (H-3) has a radiological half-life of 12.3 years. What is its specific activity in units of Bq/g and Ci/g? b) A 0.2 gram sample of Kr-85 gas, which decays into stable Rb-85, is accidentally broken and escapes into a sealed warehouse measuring 40 x 30 x 20 m. What is the specific activity of the air inside in Bq/cm^3? (This is the airborne concentration)

Radioactive decay as a power source

Strontium-90 is to be used in a radioisotopic thermoelectric generator (RTG) for powering a navigation beacon located in the arctic. a) How much of the Sr-90 activity is required to generate 50 W of electric power if the conversion efficiency from heat to electricity is 30%? Tip: You must take into account the fact that Sr-90 is in equilibrium with its daughter, Y-90. b) What is the mass of Sr-90 required? c) Weight is an important factor in the design of a portable, isotopic heat source. If weight is to be kept at a minimum and if the source is to generate 50 W after 1 year of operation, would there be an advantage to using Po-210 compared to Sr-90?

Activity and activation cross section.

A cobalt foil, 1 cm diameter x 0.1 mm thick, is irradiated in a mean thermal flux of 10^11 n/cm^2-s for a period of 7 days. If the activation cross section is 36 barns and if the density of cobalt is 8.9 g/cm^3, what is the activity (Bq) at the end of the irradiation period?