Tritium (³H) is used in glowing "EXIT" signs located where there is no electricity for lightbulbs. If the half-life of tritium is 12.26 years, what percentage of the original quantity of the isotope is left in the sign after 18.5 years?

Question

Quizplus · Accepted Answer

To solve this problem we use the radioactive decay equation: 
N = N0 (1/2)^(t/h)
where
N = final quantity of tritium remaining after time t
N0 = initial quantity of tritium present
t = time in years
h = half-life of tritium in years

Substituting the given values we get:
N = N0 (1/2)^(18.5/12.26)
N/N0 = (1/2)^(18.5/12.26)
N/N0 = 0.3506 or 35.1%

Therefore, the percentage of the original quantity of tritium remaining in the sign after 18.5 years is 35.1% (Option C).

Tritium (3H) Is Used in Glowing "EXIT" Signs Located Where

Tritium (³H) Is Used in Glowing "EXIT" Signs Located Where