Gthe radioactive isotope americium-241 is used in smoke detectors. it has a rate constant for radioactive decay of 1.6 × 10-3 yr-1 . by contrast, iodine-125, which is used to test for thyroid functioning, has a rate constant for radioactive decay of 1.1 × 10-2 day-1 . (i) what are the half-lives of these two isotopes ? (ii) which one decays at a faster rate ? (iii) how much of a 1.00 mg sample of each isotope remains after three half-lives ?

Asheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200oc and is permitted to achieve a steady-state diffusion condition. the diffusion coefficient for nitrogen in steel at this temperature is 6 x 10- 11 m2 /s, and the diffusion flux is found to be 1.2 x 10-7 kg/m2 -s. also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3 . how far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3 ? assume a linear concentration profile.

Which of the following is the phase that results when the moon is on the opposite side of the earth from the sun? a. quarter moon b. crescent moon c. new moon d. full moon

Which levels of government establish and implement educational requirements for minors