Tritium is a radioactive isotope of hydrogen with two neutrons in the nucleus. It has a half life of 12.3 years. Some EXIT signs, such as those found in the High Tech Center at GBC in Elko contain tritium gas sealed in tubes which cause a phosphorus coating on the inside of the tube to glow. These tubes, only 1/4 inch in diameter are used to spell out the word EXIT. They will glow for years. Calculate in how many years these signs will have to be replaced. Assume that the end lifetime is when the emission from the tritium is down to only 37% from the initial emission when installed. Answer in years.
a. about 15 years
b. about 17.7 years
c. about 13.2 years
d. about 12.3 years
e. about 22.8 years
f. about 19.9 years