# Problem: Some watch dials are coated with a phosphor, like ZnS, and a polymer in which some of the 1H atoms have been replaced by 3H atoms, tritium. The phosphor emits light when struck by the beta particle from the tritium decay, causing the dials to glow in the dark. The half-life of tritium is 12.3 yr. If the light given off is assumed to be directly proportional to the amount of tritium, by how many percents will a dial be dimmed in a watch that is 85 years old?Express your answer to two significant figures and include the appropriate units.

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###### Problem Details

Some watch dials are coated with a phosphor, like ZnS, and a polymer in which some of the 1H atoms have been replaced by 3H atoms, tritium. The phosphor emits light when struck by the beta particle from the tritium decay, causing the dials to glow in the dark. The half-life of tritium is 12.3 yr.

If the light given off is assumed to be directly proportional to the amount of tritium, by how many percents will a dial be dimmed in a watch that is 85 years old?

Express your answer to two significant figures and include the appropriate units.