An [tex]$X$[/tex]-ray photon is scattered at an angle of [tex]$\theta=180.0^{\circ}$[/tex] from an electron that is initially at rest. After scattering, the electron has a speed of [tex]$4.30 \times 10^6 \, \text{m/s}$[/tex]. Find the wavelength of the incident [tex]$X$[/tex]-ray photon.



Answer :

Sure! Let's break down this problem step-by-step.

### Step 1: The Problem's Parameters

We are given the following values:
- Scattering angle, [tex]\(\theta = 180.0^\circ\)[/tex]
- Speed of light, [tex]\(c = 3.00 \times 10^8 \, m/s\)[/tex]
- Mass of the electron, [tex]\(m = 9.10938356 \times 10^{-31} \, kg\)[/tex]
- The speed of the electron after scattering, [tex]\(v = 4.30 \times 10^6 \, m/s\)[/tex]

### Step 2: Convert Scattering Angle to Radians

[tex]\[ \theta_{rad} = \theta \times \frac{\pi}{180} = 180.0^\circ \times \frac{\pi}{180} = \pi \, \text{radians} \][/tex]

### Step 3: Calculate the Relativistic Momentum of the Electron After Scattering

The momentum ([tex]\(p\)[/tex]) of the electron after scattering is given by:
[tex]\[ p = m \times v \][/tex]

Substituting the given values:
[tex]\[ p = (9.10938356 \times 10^{-31} \, kg) \times (4.30 \times 10^6 \, m/s) = 3.9170349307999995 \times 10^{-24} \, kg \cdot m/s \][/tex]

### Step 4: Compton Wavelength Shift

The Compton wavelength shift formula is:
[tex]\[ \Delta \lambda = \frac{h}{m \cdot c} \left( 1 - \cos \theta \right) \][/tex]

Where [tex]\(h\)[/tex] is Planck's constant:
[tex]\[ h = 6.62607015 \times 10^{-34} \, J \cdot s \][/tex]

Since [tex]\(\cos(180^\circ) = -1\)[/tex]:
[tex]\[ \Delta \lambda = \frac{6.62607015 \times 10^{-34}}{9.10938356 \times 10^{-31} \times 3.00 \times 10^8} \left( 1 - (-1) \right) \][/tex]

[tex]\[ \Delta \lambda = \frac{6.62607015 \times 10^{-34}}{9.10938356 \times 10^{-31} \times 3.00 \times 10^8} \times 2 \][/tex]

[tex]\[ \Delta \lambda = 4.849263477494848 \times 10^{-12} \, m \][/tex]

### Step 5: Calculate the Initial Photon Energy

To determine the initial wavelength, we utilize the energy relation for the photon and the momentum of the electron after scattering.

Energy of the photon right after scattering:
[tex]\[ E_{photon} = p \times c \][/tex]
[tex]\[ E_{photon} = 3.9170349307999995 \times 10^{-24} \, kg \cdot m/s \times 3.00 \times 10^8 \, m/s \][/tex]
[tex]\[ E_{photon} = 1.17511047924 \times 10^{-15} \, J \][/tex]

### Step 6: Calculate the Initial Photon Wavelength

The wavelength [tex]\(\lambda\)[/tex] is obtained by:
[tex]\[ \lambda = \frac{h}{p} \][/tex]
[tex]\[ \lambda_{initial} = \frac{6.62607015 \times 10^{-34}}{1.17511047924 \times 10^{-15}} \][/tex]
[tex]\[ \lambda_{initial} = 1.6916035386609936 \times 10^{-10} \, m \][/tex]

### Step 7: Find the Incident Wavelength

Finally, the incident wavelength [tex]\(\lambda_{initial}\)[/tex] can be calculated by adjusting for the Compton shift:
[tex]\[ \lambda_{incident} = \lambda_{initial} - \Delta \lambda \][/tex]
[tex]\[ \lambda_{incident} = 1.6916035386609936 \times 10^{-10} - 4.849263477494848 \times 10^{-12} \][/tex]
[tex]\[ \lambda_{incident} = 1.643110903886045 \times 10^{-10} \, m \][/tex]

So, the wavelength of the incident X-ray photon is:

[tex]\[ \lambda_{incident} = 1.643110903886045 \times 10^{-10} \, meters \][/tex]