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Answer 1 · 2017-05-28T19:19:36

The half life is 10.7 h.

The integrated rate law for radioactive decay is

#ln(A_0/A_t) = kt#

where

#A_0# and #A_t# are the activities at time #t = 0# and at time #t#
#k# is the decay constant
#t# is the time

∴ #ln((9000 color(red)(cancel(color(black)("Bq"))))/(400 color(red)(cancel(color(black)("Bq"))))) = 3.114 = k × "2 days"#

#k = 3.114/"2 days" = "1.557 day"^"-1"#

#t_(1/2) = ln2/k = ln2/"1.557 day"^"-1" = "0.4453 days" = "10.7 h"#