Nuclear Energy

Assignment 2 - Half-Life

1. Tritium is a radioactive isotope of hydrogen. It is ³₁H. Tritium has a half-life of 12.3 years.

1. How many protons and neutrons are in tritium?
2. If you started with a 2 gram sample of tritium, how much will be left after 24.6 years?

2. One of the isotopes of neptunium is ²³⁸₉₃Np. It has a half-life of 2 days.

1. How many protons and neutrons are in ²³⁸₉₃Np?
2. You started with a 4 gram sample on Monday. How many grams will remain on Tuesday of the next week?

3. A sample of ²¹⁰₈₄Po was purchased for a physics class on September 1 to start the school year.

1. How many protons and neutrons are in ²¹⁰₈₄Po?
2. When it was first bought the decay rate was 2million decays per second. If ²¹⁰₈₄Po has a half-life of 138 days, what will be the decay rate when the class uses it on June 1?

4. Tritium (see problem 1) used to be used to produce a fluorescent glow in wrist watches so you could see the time in the dark. If the brightness of the watch is proportional to the decay rate of tritium, how bright is the watch 6.15 years after you bought it compared to the original brightness?