Cathode Ray Tube and X-ray Generation Course

Introduction to Cathode Ray Tubes (CRT)

A Cathode Ray Tube (CRT) is a device used in traditional television and computer monitors, and also in the generation of X-rays. It consists of a sealed glass tube containing a cathode (negative electrode) and an anode (positive electrode), and is used to produce electrons that are accelerated and directed towards a target. The collision of these high-energy electrons with the target material results in the emission of X-rays.

Basic Components of a Cathode Ray Tube

Cathode: The negative electrode, where electrons are emitted. It's heated to produce electrons.
Anode: The positive electrode that attracts electrons from the cathode. This can have a small hole to allow the electron beam to pass through.
Electron Beam: Electrons accelerated from the cathode towards the anode and eventually toward the target material.
Target (e.g., Tungsten): The material at which the high-energy electrons are directed, resulting in the emission of X-rays.

Principles of X-ray Generation

When electrons accelerated by the cathode in the tube strike a target material like tungsten, the interaction produces two types of radiation: Bremsstrahlung radiation and Characteristic X-rays.

Bremsstrahlung Radiation

This is the primary type of X-ray produced when electrons are decelerated by the atomic nuclei in the target material. The sudden deceleration causes the electrons to lose energy in the form of X-ray radiation.

E = eV

Where: E is the energy of the electron, e is the charge of the electron (1.6 × 10⁻¹⁹ C), and V is the voltage applied to accelerate the electrons.

Characteristic X-rays

When the accelerated electrons strike the target material, they can knock inner-shell electrons from atoms of the target material, creating vacancies. Electrons from outer shells then fall into these vacancies, releasing energy as X-rays. This energy is characteristic of the material's atomic structure.

E = h * f

Where: E is the energy of the X-ray photon, h is Planck’s constant (6.626 × 10⁻³⁴ J·s), and f is the frequency of the emitted X-ray.

Applications of X-ray Tubes

X-ray tubes are used in a variety of fields, including:

Medical Imaging: X-rays are used in radiography to create images of the internal structures of the body.
Security: X-ray machines are used in airports and other facilities to scan baggage and cargo.
Industrial Testing: X-rays are used in non-destructive testing to inspect the internal integrity of materials and structures.

Example of Tungsten Target and X-ray Emission

Tungsten is commonly used as a target material in X-ray tubes due to its high atomic number (Z = 74), which increases the efficiency of X-ray production. The high melting point (around 3422°C) of tungsten allows it to withstand the extreme heat produced during electron bombardment.

Key Data for Tungsten:

Atomic Number: 74
Melting Point: 3422°C
Density: 19.25 g/cm³

Formulas for Calculating X-ray Energy

To calculate the energy of X-ray photons produced by an X-ray tube, you can use the following formulas:

Energy of Accelerated Electrons:
E = e * V
where E is the energy of the electron (in joules), e is the elementary charge, and V is the accelerating voltage.
Energy of X-ray Photon:
E = h * f
where h is Planck’s constant and f is the frequency of the emitted X-ray.
Wavelength of X-ray Photon:
λ = c / f
where λ is the wavelength, c is the speed of light, and f is the frequency.

Example Calculation: If the tube is operating at a potential of 100 kV (100,000 volts), the energy of the electrons is:

E = e * V = (1.6 × 10⁻¹⁹ C) * (100,000 V) = 1.6 × 10⁻¹⁴ J

This energy is transferred to the target material, producing X-rays.