6. If 175 markium nuclei remain from a sample of 2800 nuclei, how many half-lives have passed? Show work.

What percent of a parent isotope would remain after two half lives? 50%25%13%66

4. (Show your work) The half-life of 235U is equal to 7.1 x 108 year. What is the time constant in yr?

Macmillan l 30: F2 W S A 210.2 ng sample of an unknown radioactive substance was placed in storage and its mass measured periodically. After 47 days the amount of radioactive substance had decreased to 26.28 ng. How many half-lives of the unknown radioactive substance have occurred? number of half-lives: #3 H 80 F3 mmand E D A GA $ X C 4 OOD 886 F4 R F % от ото 5 V F5 T G ^ 6 B F6 Y & 7 H 8 F7 U N 00 * 8 DII FB J L - ( 9 M K DD F9 O . V - ... I 4 F11 { [ option + = ? 11 1 F12 } ] half-lives delete return st