7.10 to 7.12 questions

1.              

What happens to the amount of ‘mother’ nuclei as time passes? - They will decay, possibly into another element

2.              What sort of radioisotope will decay the fastest - one with a long half life or one with a short half life? - One with short half life

3.              Does half life tell us exactly when a particular nucleus in a radioisotope will decay? - No, it is a random process. 

4.              What are the two definitions of half life? 1) Time taken for the activity of a sample to halve; 2) The time taken for the number of radioactive atoms in a sample to halve

5.              What does the activity of a source mean? - The amount of atoms in a sample that decays per second

6.              What is the unit of activity? - Becquerel (Bq)

7.              What will happen to the number of ‘mother’ nuclei after two half lives? - It will decreased to 1/4 of the original number

8.              What will happen to the activity of a source after two half lives? - It decreases to 1/4 of the original count

7.10 to 7.12 calculation questions (working in notebook)

1.  A radioisotope has a half life of 12 years. What fraction of the radioisotope will be left after 60 years? - 1/32

2.  If the activity of a sample falls to 1/64th of its original level after 2 hours, what is the half life of the sample? - 20 minutes

3.  The background radiation in a laboratory is 7 Bq. The count rate from a radioisotope is measured and it has a reading of 119 Bq. If the half life of the radioisotope is 10 minutes, what will be the reading 20 minutes later? - 28 Bq

4.  Potassium decays into argon.  The half life of potassium is 1.3 billion years.  A sample of rock from Mars is found to contain three argon atoms for every atom of potassium.  How old is the rock? 2.6 Billion Years