Core Practical 15: Nuclear Radiation: Edexcel A-level Physics

Summary

This video covers the core practical of investigating gamma ray absorption by lead, focusing on determining how the thickness of lead affects radiation absorption. The experiment involves measuring the count rate at different lead thicknesses, subtracting background radiation, and processing data to identify the half thickness — the lead thickness that halves the gamma radiation. The relationship between lead thickness and gamma absorption follows an exponential decay, which is linearized by taking the natural log of the count data. The video highlights important safety procedures and the significance of accurate data processing for precise results.

Takeaways

• 😀 The core practical focuses on investigating how the thickness of lead affects gamma ray absorption.
• 😀 The key concept is finding the 'half thickness,' which is the thickness of lead that absorbs half of the gamma radiation.
• 😀 The experiment involves using a Geiger-Müller tube connected to a counter to measure gamma radiation at varying lead thicknesses.
• 😀 Accurate setup is crucial: Ensure the distance between the source and GM tube remains constant to avoid variability in results.
• 😀 Always measure the background radiation before starting the experiment to correct for it in the data analysis.
• 😀 For accurate results, take background measurements for five minutes and use the average value to adjust the count rates.
• 😀 Safety when handling radioactive sources is a priority: always use tongs, never pick up sources by hand, and keep them pointed away from you.
• 😀 Data consistency is important: raw data should be reported with consistent significant figures and decimal places.
• 😀 Logarithmic data processing is required: after collecting raw counts, the natural logarithm (ln) of the count values is calculated.
• 😀 The relationship between lead thickness and gamma radiation follows an exponential decrease, which can be represented with a logarithmic equation.
• 😀 From the log graph, the absorption constant (mu) can be determined from the slope, and the half thickness is calculated as 0.693 divided by the absorption constant (mu).

Q & A

What is the purpose of the core practical in the video?

The purpose of the core practical is to investigate the absorption of gamma rays by lead and determine how the thickness of lead affects the amount of gamma radiation absorbed.

What is meant by 'half thickness' in the context of this experiment?

Half thickness refers to the thickness of lead that absorbs half of the original gamma radiation being detected by the Geiger-Müller tube.

What type of graph is commonly used in this experiment, and why is it important?

A log graph is commonly used in this experiment to process data. It helps analyze the exponential decrease in radiation counts as lead thickness increases, which is important for understanding the relationship between lead thickness and gamma radiation absorption.

How should the Geiger-Müller tube and radiation source be set up in the experiment?

The Geiger-Müller tube should be connected to its counter and positioned at a fixed distance from the radiation source. This distance should remain constant throughout the experiment to avoid variability in the measurements.

Why is it necessary to measure the background radiation before starting the experiment?

Measuring the background radiation is necessary to ensure that the detected radiation is not just due to natural environmental radiation. It allows for the correction of the count rate by subtracting the background radiation.

What safety precautions should be followed when using radioactive sources in a laboratory?

Safety precautions include using tongs or tweezers to handle the radioactive source (never using hands), ensuring the source is pointed away from you and others, and keeping a record of its usage. The source must also be stored in a lead-lined container when not in use.

How is the raw data processed in this experiment?

The raw data, which consists of the count rates at different lead thicknesses, is corrected by subtracting the background radiation. Then, the natural logarithm (ln) of the corrected count rate is taken to prepare the data for plotting on a log graph.

What does the equation derived from the experiment represent, and how is it used?

The equation represents the exponential relationship between lead thickness and count rate. It is rearranged into a linear form, where the natural log of the count rate (ln C) is plotted against lead thickness, allowing for the determination of the absorption constant and the half thickness.

How is the 'half thickness' calculated from the experimental data?

The half thickness is calculated by setting the count rate to half of the initial count rate and solving the logarithmic equation. The natural log of 0.5 is divided by the absorption constant (mu) to find the half thickness.

Why is it important to use consistent significant figures in the experiment?

It is important to use consistent significant figures to ensure the accuracy and precision of the data. For example, when processing log data, using too few significant figures could result in misleading or indistinguishable values.