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Questions and Answers
What is the primary method by which Gamma radiation undergoes attenuation in matter?
What is the primary method by which Gamma radiation undergoes attenuation in matter?
What does the variable $𝜇$ represent in the intensity equation?
What does the variable $𝜇$ represent in the intensity equation?
Which equation represents the relationship between half value thickness and the linear absorption coefficient?
Which equation represents the relationship between half value thickness and the linear absorption coefficient?
What two factors are NOT mentioned as affecting linear and mass absorption coefficients?
What two factors are NOT mentioned as affecting linear and mass absorption coefficients?
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Which of the following correctly describes the mass absorption coefficient ($µ_m$)?
Which of the following correctly describes the mass absorption coefficient ($µ_m$)?
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If the initial intensity of radiation is $I_0$, what will be the intensity after passing through a thickness of material equal to one half value layer ($X_{1/2}$)?
If the initial intensity of radiation is $I_0$, what will be the intensity after passing through a thickness of material equal to one half value layer ($X_{1/2}$)?
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What is the effect of Gamma-Ray Energy on absorption coefficients?
What is the effect of Gamma-Ray Energy on absorption coefficients?
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What is the role of the GM Tube in the experiment?
What is the role of the GM Tube in the experiment?
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Study Notes
Radiation Physics - Practical Experiment No. 1: Linear and Mass Absorption Coefficients
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Objectives:
- Verify the absorption law of Gamma radiation.
- Determine:
- Linear absorption coefficient (μ)
- Mass absorption coefficient (µm)
- Half-value thickness (X1/2) of the absorbing material
Apparatus
- GM Tube and stand (Counter box, power supply, transformer, GM Tube, shelf stand, USB cable, source holder)
- Source of radiation
- Sheets of different absorbing materials (Aluminum and Lead)
Theory
- Gamma radiation passing through matter undergoes attenuation primarily due to Compton, photoelectric, and pair production interactions.
- Intensity decreases as a function of absorber thickness
- Intensity (I) is related to the original intensity (I0), linear absorption coefficient (μ), and absorber thickness (x) by the following formula: I = I0e-μx
Half-Value Layer (HVL)
- The half-value layer (HVL, X1/2) is the thickness of absorber that reduces the initial intensity (I0) to half (I0/2)
- The formula for calculating HVL is X1/2 = ln(2)/μ or X1/2 = 0.693/μ
Factors Affecting Linear and Mass Absorption Coefficients
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Atomic Number
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Density
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Thickness
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Gamma-Ray Energy
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Mass absorption coefficient (µm) is calculated by dividing linear absorption coefficient (µ) by the density (ρ) of absorber material: µm = µ/ρ
Procedure
- Connect electric mains
- Set timer to 60s, operating voltage to 380V
- Measure background count rate (Ibg)
- Position source in front of the GM tube
- Record initial count rate (I0)
- Place Al sheet midway between source and GM tube
- Record count rate (I1 and I2) and calculate average (Iavg)
- Repeat steps for increasing thicknesses of absorbing material (Al and Pb).
- Plot graph of ln(I0/I) vs thickness (x). A straight line verifies the absorption law.
- Determine the slope of the graph, which equals the linear absorption coefficient (μ).
- Calculate the mass absorption coefficient (µm) .
- Plot a graph between Intensity (I) and thickness (x). Graphically determine X1/2
- Calculate X1/2 theoretically using the formula X1/2 = ln(2)/µ
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Description
This quiz covers Practical Experiment No. 1 in Radiation Physics, focusing on the verification of the absorption law of Gamma radiation. Students will explore key concepts such as the linear absorption coefficient, mass absorption coefficient, and half-value thickness of various absorbing materials like aluminum and lead.
