Sp Unit 3.5
Practicals
Nuclear Decay
Sp Unit 3.5PracticalsNuclear DecayLearners should be able to demonstrate and apply their knowledge and understanding of: |
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| 1. | Investigation of radioactive Decay: A Dice Analogy |
| 2. | Investigation of the variation of intensity of gamma radiation with distance |
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1. Investigation of radioactive decay: a dice analogy
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⇒ Objective:
- To model radioactive decay using dice and understand the concept of half-life and the randomness of decay.
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⇒ Apparatus Required:
- – 100 six-sided dice (or more)
- – A container (box or tray)
- – A data sheet
- – A stopwatch (optional)
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⇒ Theory:
- Radioactive decay is a random process, meaning we cannot predict when an individual nucleus will decay, but we can predict the average behavior of a large number of nuclei.
- Figure 1 Radioactive decay
- – The half-life ([math]T_{1/2}[/math]) is the time taken for half of the radioactive nuclei to decay.
- – In this model, each die represents an unstable nucleus.
- – A roll of the dice represents the passage of time.
- – A specific number (e.g., rolling a “6”) represents decay.
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⇒ Procedure:
- Start with 100 dice, representing 100 unstable nuclei.
- Roll all the dice and remove those that show a “6” (decayed nuclei).
- Count the remaining dice and record the number.
- Repeat steps 2 and 3 until all dice are removed.
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⇒ Precautions & Sources of Error:
- – Use a large number of dice for better accuracy.
- – Ensure fair rolling to avoid biases.
- – Repeat the experiment multiple times for consistent results.
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⇒ Conclusion:
- The dice model effectively simulates radioactive decay, showing that decay is random but follows a predictable pattern over a large sample. The concept of half-life is well demonstrated.
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2. Investigation of the variation of intensity of gamma radiation with distance
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⇒ Objective:
- To investigate how the intensity of gamma radiation changes with distance from a source, verifying the inverse square law.
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⇒ Apparatus Required:
- – A gamma radiation source (e.g., Cobalt-60, Cesium-137)
- – A Geiger-Müller (GM) tube and counter
- – A ruler (to measure distance)
- – A lead shield (for safety)
- – A data sheet to record readings
- Figure 2 The variation of intensity of gamma radiation with distance
- ⇒ Theory:
- Gamma rays travel in straight lines and spread out as they move away from the source. The intensity (I) follows the Inverse Square Law:
- [math]I ∝ \frac{1}{d^2} [/math]
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- [math]I = \frac{I_0}{d^2} [/math]
- Where:
- – I = intensity at distance d
- – [math]I_o[/math] = intensity at 1 unit distance
- – d = distance from the source
- This means that doubling the distance reduces the intensity to one-fourth.
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⇒ Procedure:
- Set up the Geiger-Müller tube at a fixed position.
- Place the gamma source at an initial distance (e.g., 5 cm).
- Measure the count rate (number of counts per second) using the GM counter.
- Move the source farther away (e.g., 10 cm, 15 cm, etc.) and measure the count rate again.
- Repeat for multiple distances, ensuring to record data accurately.
- Subtract the background radiation (measured without the source).
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⇒ Results & Analysis:
- – The intensity decreases as the distance increases.
- – The plot of I vs.[math]\frac{1}{d^2}[/math] is a straight line, confirming the Inverse Square Law.
- Figure 3 Inverse square law experiment
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⇒ Precautions & Safety Measures:
- – Use a small, controlled gamma source.
- – Wear protective gloves and keep exposure time minimal.
- – Do not touch the source directly.
- – Measure background radiation before starting the experiment.
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⇒ Conclusion:
- This experiment confirms that gamma radiation follows the inverse square law. The intensity decreases as [math]\frac{1}{d^2}[/math], meaning distance plays a key role in reducing exposure.