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11 Cards in this Set
- Front
- Back
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What is half-life?
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The time it takes for a radioactive material to lose half its radioactivity.
THE TIME TAKEN FOR HALF OF THE RADIOACTIVE ATOMS NOW PRESENT TO DECAY. or THE TIME TAKEN FOR THE ACTIVITY TO FALL BY HALF |
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What happens to a radioactive sample over time?
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Radioactivity decreases over time.
Each time a decay happens an alpha, beta or gamma particle is given out and one more radioactive nucleus has disappeared. |
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How quickly does this happen?
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Depends. some materials hours. some millions of years
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Why is there a problem trying to measure it?
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activity never actually reaches zero, which is why we use half-life concept.
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What's a short half-life?
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activity falls quickly - lots of nuclei decay quickly
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Long half-life?
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activity falls more slowly. nuclei sit there unstable for a while
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What is radioactivity measured in?
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becquerels (Bq) 1 Bq is one decay per second
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Use a half-life diagram to answer the following: The actiovity of a radioisotope is 640Bq. Two hours later it has fallen to 40Bq. Fine half-life.
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See diagram
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How can you investigate the half-life of a sample using a graph?
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Take several readings of a sources activity over time using a Geiger-Muller detector. Plot the results on a graph with activity Y over time x
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How do you find out the half-life using the graph?
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find time interval on graph corresponding to half the activity.
MUST REMOVE BACKGROUND NOISE. SAMPLE FIRST AND REMOVE FROM EACH READING!!! |
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What is the half-life of Uranium-235
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700 milion years
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