Tritium (^3H) is used in glowing \"EXIT\" signs located where there is no electr

Question

Tritium (^3H) is used in glowing "EXIT" signs located where there is no electricity for light bulbs. 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? A. 0.632% B. 25.0% C. 35.1 D. 63.2 Radiation seed therapy is a common method for treating some prostate cancers and brain turmors. Palladium - 103, with a half-life of 17 days, is one isotope used for this treatment. How long does it take for the activity of palladium - 103 to decrease to 1.0% of its initial value and essentially cease to be effective?

Explanation / Answer

Q18

the half life equation

A = A0 *(1/2)^(t/HL)

A/A0 = (0.5)^(18.5/12.26)

A/A0 = 0.351361

0.351361*100% = 35.1%

meaning that only 35% is left

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