X-rays- Discovery and Production, Coolidge Tube, Practice Problems, FAQs

When you have an accident while participating in any activity, you should contact a doctor. They recommend that you have an X-ray. The doctor can determine whether or not there is a fracture in the bone using X-ray images. Have you ever wondered how X-rays assist us in detecting a bone fracture? This is due to the fact that X-rays do not penetrate through bone, thus they cast a shadow on it. So, if a fracture exists, we can see it on the X-ray picture. Wilhelm Roentgen, a German scientist, discovered a new kind of radiation in 1895. Because he didn't know what it was, he named it X-radiation. That's all there is to it.

Table of Contents

• X-rays
• Discovery of X-ray
• Production of X-ray
• Practice Problems
• FAQs

X-rays

X-rays are high-energy electromagnetic radiations with very small wavelengths () generated when rapidly moving electrons or cathode rays collide with an object with a high atomic mass. These rays are imperceptible to the naked eye. In a vacuum, they are electromagnetic waves with a speed of . Its photons have 1000 times the energy of visible light. The following diagram depicts the increasing order of electromagnetic waves as frequency increases.

X-rays are created when rapidly moving electrons with energies on the order of several KeV collide with a metallic object.

Discovery of X-ray

Roentgen discovered X-rays when he observed that a discharge tube running at low pressure and high voltage generated radiation that caused a nearby fluorescent screen to flash brilliantly. Fluorescence was seen in crystals of barium platinocyanide. If the discharge tube was covered in black paper to block out the light, the results were the same. This suggested that fluorescence was caused by an unknown radiation (eventually referred to as X-rays). When cathode rays (electrons) collide with the discharge tube's wall, Roentgen proved that X-rays are produced.

Production of X-ray (Coolidge Tube)

When energetic (rapid moving) electrons collide with a target, such as a metal piece, X-rays are created. When electrons collide with solid atoms, their kinetic energy is lost, and this is transformed into radiant energy in the form of X-rays. The diagram below depicts the key characteristics of a contemporary X-ray tube invented by Coolidge.

A glass chamber is drained to a near-perfect vacuum in Coolidge's X-ray tube. The cathode generates electrons by heating a filament that receives power from the battery. A solid copper bar serves as the anode. The end of a copper rod is implanted with a high melting metal such as platinum or tungsten, which acts as a target. Between the cathode and the anode, a high voltage DC is maintained.

The target's melting point, specific heat capacity, and atomic number should be high. When a voltage is put across the filament, the filament releases electrons as it heats up. When electrons collide with a target, X-rays are created.

When electrons collide with a target, a portion of their energy is lost and transformed to heat. The melting point and specific heat of the target should be high because the target should not melt or absorb heat.

The accelerating voltage is raised for higher energetic electrons. The voltage across the filament grew as the number of photons increased. Only roughly 1 to 10% of the energy of electrons is transferred to X-rays, with the remainder being converted to heat.

The nature of the emitted X-rays depends on:

• The current in the filament.
• The voltage between the filament and the anode.

Note:

• The number of electrons emitted by the filament grows as the current of the filament increases. A larger number of electrons results in a more powerful X-ray beam. We can manage the number of X-rays, as well as the intensity of X-rays, in this way.
• The kinetic energy of the electrons grows as the tube's voltage rises. An intense beam of X-rays is created when a very energetic beam of electrons is abruptly halted by the target. We can regulate the quality of X-rays, i.e. their penetrating strength, in this way.
• X-rays are divided into two varieties based on their penetrating power: HARD X-rays, which have a high energy and high penetration power, and SOFT X-rays, which have a low energy and low penetration power.

Practice Problems

Q. Electrons accelerated by a potential difference of 17,000 volts impact a copper target in an X-ray tube. What is the speed of the X-ray that is emitted within a tube?

A. As X-rays is electromagnetic radiation its speed is equal to speed of light i.e. .

Q. A 5kV potential difference is supplied to an X-ray tube, with a current of 3.2 mA flowing through it. Then how many electrons strike the target per second?

A. As we know,

Number of electrons striking the target per second,

electrons strike per second on target.

Q. Can an electric or magnetic field be used to deflect an X-ray beam?

A. No. We can't use electric or magnetic forces to deflect an X-ray beam since X-rays have no charge and are neutral.

Q. The voltage of an X-ray tube is 20 kV. At the initial collision, an electron loses 5% of its kinetic energy and emits an X-ray photon. What wavelength does this collision belong to?

A. Kinetic energy acquired by the electron is

The energy of the photon is =

Thus,

FAQs

Q. What's the difference between a soft and a hard X-ray?
A. Soft X-rays have a lower frequency and hence lower energy than hard X-rays.

Q. When X-rays pass through a powerful electromagnetic field, what happens?
A. Because X-rays have no charge, they are not deflected by electromagnetic fields.

Q. How does doubling the voltage of an X-ray tube impact the intensity of the X-rays?
A. The intensity of X-rays is unaffected by the voltage of the X-ray tube. It will improve the X-ray penetration power.

Q. What is the location of the X-ray region in the spectrum?
A. The X-ray region is located between the gamma and ultraviolet radiation.