A sample of river water was found to contain 8 x 10-18 tritium atoms h per atoms of ordinary hydrogen. tritium decomposes radioactively, with a half-life of 12.

A sample of river water was found to contain 8 x 10-18 tritium atoms H per atoms of ordinary hydrogen. Tritium decomposes radioactively, with a half-life of 12.3 yr. What will be the ratio of tritium to normal hydrogen atoms (in terms of 10-19), after 49 yr. the original sample was taken, if the sample is stored in a place where additional tritium atoms cannot be formed ?