Many radioisotopes have important industrial, medical, and research applications. one such radioisotope is 60co, which has a half-life of 5.2 yr and decays by the emission of a beta particle (energy 0.31 mev) and two gamma photons (energies 1.17 mev and 1.33 mev). a scientist wishes to prepare a 60co sealed source that will have an activity of at least 10 ci after 30 months of use. what is the minimum initial mass of 60co required?

Air enters a gas turbine with two stages of compression and two stages of expansion at 100 kpa and 17°c. this system uses a regenerator as well as reheating and intercooling – the intercooler returns the air to the inlet temperature. the pressure ratio across each compressor is 4 ; 300 kj/kg of heat are added to the air in each combustion chamber; and the regenerator operates perfectly while increasing the temperature of the cold air by 20°c. determine the system’s thermal efficiency. assume isentropic operations for all compressor and the turbine stages and use constant specific heats at room temperature. (0.378)