1. What happens to the amount of ‘mother’ nuclei as time passes? = As time passes, they will decay causing the amount of the 'mother nuclei' to decrease. 2. What sort of radioisotope will decay the fastest - one with a long half life or one with a short half life? = The one with a short half life will decay the fastest.
3. Does half life tell us exactly when a particular nucleus in a radioisotope will decay? = No it does not. They will randomly decay.
4. What are the two definitions of half life? = 1. It is the time taken for the activity of a sample to half or 2. It is the time taken for the number of radioactive atoms in a sample to halve.
5. What does the activity of a source mean? = the activity of a source means the amount of atoms in a sample that decays per second.
6. What is the unit of activity? = Bq (Becquerel)
7. What will happen to the number of ‘mother’ nuclei after two half lives? = After two half lives, it will decrease to a quater of the original number.
8. What will happen to the activity of a source after two half lives? = Similarly, after two half lives, the activity will decrease to a quarter of the original number. 7.10 to 7.12 calculation questions 12 January 2012 10:24
1. A radioisotope has a half life of 12 years. What fraction of the radioisotope will be left after 60 years? = (1/2)^5 = 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? = 120 / 6 = 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? = (119 - 7)/4 = 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? =
3. Does half life tell us exactly when a particular nucleus in a radioisotope will decay? = No it does not. They will randomly decay.
4. What are the two definitions of half life? = 1. It is the time taken for the activity of a sample to half or 2. It is the time taken for the number of radioactive atoms in a sample to halve.
5. What does the activity of a source mean? = the activity of a source means the amount of atoms in a sample that decays per second.
6. What is the unit of activity? = Bq (Becquerel)
7. What will happen to the number of ‘mother’ nuclei after two half lives? = After two half lives, it will decrease to a quater of the original number.
8. What will happen to the activity of a source after two half lives? = Similarly, after two half lives, the activity will decrease to a quarter of the original number. 7.10 to 7.12 calculation questions 12 January 2012 10:24
1. A radioisotope has a half life of 12 years. What fraction of the radioisotope will be left after 60 years? = (1/2)^5 = 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? = 120 / 6 = 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? = (119 - 7)/4 = 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? =
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