Many radioisotopes have important industrial, medical, and research applications. one of these is 60co, which has a half-life of 5.20 years and decays by the emission of a beta particle (energy 0.310 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 13.7 ci after 24.0 months of use. if the activity is 16.0 ci, how many 60co atoms are in the source?

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?