A small quantity of radioactive gold was deposited on the end of a gold cylinder After holding for 24 h at a high temperature the specimen was sectioned and the radioactivity of each slice was as follows: Distance from end of to center of slice (um) 10 20 30 40 50 bar Radioactivity (a. u.) 83.8 66.4 42.0 23.6 8.74 Use the above data to determine the diffusivity D).