Chemistry Standard 2, Objective 2

Title: Radioactive Review problems.

Description: These are half-life problems for the students to work out.

Time Needed: This can take up about 20 minutes in class and for those that don’t finish, it can be homework.

Prior Knowledge: These half life problems can be given the day after teaching the students about how to calculate the half life of different elements.

Safety Considerations: None.

Procedure: 1. This is an example of a table students can use for every hal- life problem. Here is an example from #4 on the Review: # Half lives Time left Amount Remaining 0 0 1 (or 100%) 1 30 years 1/2 2 60 years 1/4 3 90 years 1/8 4 120 years 1/16 2. Give them the review to practice the half-life radioactive problems.

Scoring Guide: Participation points can be awarded or make each answer worth 2 points. Here are the answers for the review: 1. Ideally you should get as far from all the rocks as possible. If you must hold one and put one in your pocket, hold the alpha emitter because the skin on your hand will shield you. Put the beta emitter in your pocket because its rays might be stopped by the combined thickness of clothing and skin. Throw away the gamma emitter because its rays would penetrate deep into your body from either of these places. 2. a)1/4, 1/8 b)The elements transmute into another, and will keep transmute until they become a more stable element. 3. 5.730 + 5,730 = 11,460 years 4. As from the example table above, it would be 120 years. Name______Period______Review

1. Pretend you are given three radioactive rocks-one an alpha emitter, one a beta emitter, and one a gamma emitter. You can throw one away, but of the remaining two you must hold one in your hand and place the other in your pocket. What can you do to minimize you exposure to radiation?

2. a) If you have a sample of a radioactive isotope that has a half-life of one day, how much of the original sample is left at the end of the second day? The third day?

b) What becomes of the atoms of the sample that decay?

3. Suppose an archeologist extracts 1.0 g of carbon from an ancient ax handle and finds that carbon to be one-fourth as radioactive as 1.0 g of carbon extracted from a freshly cut tree branch. About how old is the ax handle?

4. The isotope cesium-137, which as a half-life of 30 years, is a product of nuclear power plants. How long will it take this isotope to decay to one-sixteenth its original amount?