Nuclear Energy

Assignment 3 - Half-Life

Questions

1. Compare ²³⁵₉₂U to ²³⁸₉₂U. Which has more protons? Which has more neutrons?
2. Why is the top number always larger than the bottom number when writing the symbol of a given isotope of an element?
3. Which will have a larger reading on a Geiger counter (a device that measures radioactivity)?A sample of a substance with a short half-life or an equal amount of a substance with a long half-life. Why?

Problems

1. If the half-life of an isotope of some substance is 2 years, what fraction of the substance remains after 12 years?
2. The half-life of strontium is 28 years. What fraction of the radioactive intensity remains after 280 years compared to the original amount?
3. A Geiger counter has an initial reading of 3200 counts when measuring the strength of a radioactive material. 30 hours later the reading is 100 counts. What is the half-life of this material?
4. A 1 gram sample of a radioactive substance is measured at the beginning of a lab.After 48 hours the sample is measured to be 0.25 grams. What is the half-life of this substance?