X Ray Definition
On 8 November, 1895, X-rays were discovered by a German Physicist named Wilhelm Conrad Röentgen.
X-ray is an electromagnetic radiation with very short wavelength, and very high energy. X rays have a frequency ranging from 30 petahertz to 30 exahertz.
The wavelength of X-rays is shorter than the Ultraviolet rays, and longer than Gamma rays.
So, what is the wavelength of X rays?
X Rays have a wavelength ranging from 10-12 m (picometers) to 10-9 (nanometers).
X-rays have many applications and in this page, we will cover the top 5 uses of X rays with other uses of X Rays in Physics and X-ray characteristics.
X-Rays
X-Ray is also called the Roentgen radiation. It is an electromagnetic radiation with the energy ranging from 124 eV to 124 keV. Where this energy can be written in the form of Joules. However, a wave with this much energy can easily pass from transparent to opaque objects.
X-rays were discovered accidentally by German scientist Roentgen in 1895. In 1901, Roentgen was awarded for his great work in this regard.
X-rays are highly penetrating electromagnetic radiation and have proved to be a very powerful tool to study the crystal structure, in material research, in the radiography of metals and in the field of medical sciences.
How are X-Rays Produced?
Roentgen discovered that when X-rays are passed through arms and hands or any other body part, they create crystal clear and detailed images of the inner bones.
Whenever a doctor performs an X-ray of a patient, an x-ray sensitive film is put on one side of his body and then the x-rays are shot through him. While the skin is transparent, the bones are dense and absorb more x-rays (because of the nature of X-rays to cross the opaque object). This is why the impression of bones is left on the x-ray film while the skin remains invisible in the x-ray. Below figure shows the wavelength of different electromagnetic spectrum including the X-ray wavelength:
[Image will be uploaded soon]
What is the Wavelength of X Rays?
X-rays possess very short wavelengths that vary between 0.03 and 3 nanometers or between 0.02 Å and 100 Å; however, some x-rays are small like a single atom of an element.
Properties of X-Rays
X-rays with short wavelengths with high penetrating ability are highly destructive, that’s why they are called hard x-rays.
The uses of X rays in medicinal purposes possess less penetrating power and have longer wavelengths and are called soft x-rays. X ray waves have a dual nature. We will now discuss the following properties of these radiations:
They can cross the materials with more or unchanged.
They are not easily refracted.
These rays do not get affected by the electromagnetic field.
X-rays ionize the surrounding air by discharging electrified bodies.
They have very short wavelengths ranging from 0.1 A° to 1 A°. The velocity of X rays are similar to that of visible light, i.e., 186,000 miles/second or 300,000 kilometers/sec.
X-rays are produced when a metallic anode is bombarded/broken by very high energy electrons.
They can propagate independently, i.e., without any need of a medium.
X-rays are diverging rays, i.e., they cannot be focused on a single point
These radiations ar invisible, i.e., they cannot be heard or smelt
They make a linear path in a free space but they do not carry an electric charge with them.
They can cause photoelectric emissions.
Intensity of X - rays rely on the number of electrons hitting the target.
Continuous spectrum appears because of the retardation of electrons.
What are the Characteristics of X Rays?
Below are the characteristics of X-rays:
1. The characteristics equation for an X-ray is:
eV = hfm
Where,
e = electron charge;
V = accelerating potential
fm = maximum frequency of X radiation
2. The Characteristic Spectrum due to transition of electron from higher to lower state:
𝜈 = a (z-b)2 (Moseley's Law)
Where
𝜈 = wavenumber
b = shielding factor, whose values vary accordingly:
b = 1 or ka and 7.4 for La
3. Bragg’s Law
2d Sinθ = nλ
Here, θ= angle for a maximum intensity
4. Binding energy or the total mechanical energy
\[\frac{1}{\lambda }=R(z-b)^{2}[\frac{1}{n1^{2}}-\frac{1}{n2^{2}}]\]
Here,
\[v=\frac{1}{\lambda }\] = wave number
R = Rydberg’s constant, whose value is 1.0973731568508 × 10 7 per metre.
5. Cut off wavelength or minimum wavelength, where v (in volts) is the potential difference applied to the tube λmin = 12400 / V A°.
5 Uses of X Rays
X-rays are used to analyze alloys through the diffraction pattern.
X-rays enable doctors to easily detect things such as a bone fracture or sprain in the body.
X-rays are used to identify manufacturing defects in tyres.
Doctors use X-rays to check flaws in welding joints and insulating materials.
Doctors use X-ray to capture the human skeleton defects.
Uses of X Rays in Physics
Restoration
Medical Science
Security
Astronomy
Industry
FAQs on X Ray
1. What are X-rays as defined in Physics, and who is credited with their discovery?
X-rays are a form of high-energy electromagnetic radiation with wavelengths ranging from about 0.01 to 10 nanometers. They fall between ultraviolet (UV) light and gamma rays in the electromagnetic spectrum. Due to their short wavelength and high energy, they possess significant penetrating power through materials that are opaque to visible light. The discovery of X-rays is credited to German physicist Wilhelm Conrad Röntgen in 1895.
2. How are X-rays produced in a standard Coolidge tube?
In a Coolidge tube, X-rays are generated through a multi-step process based on fundamental physics principles:
- Thermionic Emission: A tungsten filament (cathode) is heated to a high temperature, causing it to release electrons.
- Acceleration: A very high potential difference (accelerating voltage) is applied between the cathode and a heavy metal target (anode), such as tungsten or molybdenum. This high voltage accelerates the electrons towards the anode at immense speeds.
- Deceleration (Bremsstrahlung): When these high-energy electrons strike the anode, they are abruptly stopped or deflected. Their kinetic energy is converted into electromagnetic radiation in the form of X-ray photons. This radiation, caused by the 'braking' of electrons, is called Bremsstrahlung or continuous X-rays.
3. What is the fundamental difference between continuous and characteristic X-rays?
While both are generated from electron interactions within the anode, their physical origins are distinct:
- Continuous X-rays: These are produced when a high-speed electron from the cathode is slowed down by the electric field of a target atom's nucleus. The energy lost during this deceleration is emitted as an X-ray photon. Since the amount of deceleration can vary, it results in a continuous spectrum of X-ray energies.
- Characteristic X-rays: These are produced when an incident electron collides with and ejects an electron from an inner shell (like the K or L shell) of a target atom. To stabilize, an electron from a higher energy shell drops down to fill this vacancy, emitting an X-ray photon with a specific, discrete energy. This energy is unique to the element of the target material, making it a 'characteristic' property.
4. How does changing the accelerating voltage in an X-ray tube impact the resulting X-ray beam?
The accelerating voltage is a crucial parameter that directly influences the quality and energy of the X-rays produced. A higher accelerating voltage gives the electrons more kinetic energy before they strike the target. This leads to two main effects:
- Increased Hardness: The maximum energy of the produced X-rays increases, resulting in a more penetrating or 'harder' X-ray beam.
- Lower Cutoff Wavelength: The minimum possible wavelength of the X-rays (the cutoff wavelength) decreases, as it is inversely proportional to the maximum kinetic energy of the electrons (λmin = hc/eV).
Essentially, a higher voltage produces more energetic and penetrating X-rays.
5. What are the key physical properties of X-rays?
X-rays exhibit several important physical properties that are central to their applications:
- High Penetrating Power: They can travel through materials like soft tissue and plastic but are absorbed or scattered by denser materials like bone and metal.
- Ionising Effect: They carry enough energy to eject electrons from atoms, creating ions. This is the basis of their biological effects and their use in radiation therapy.
- No Deflection in Fields: Being uncharged, X-rays are not deflected by electric or magnetic fields.
- Photographic Effect: They can expose photographic plates, creating images based on the differential absorption of materials.
- Induce Fluorescence: They can cause certain materials (phosphors) to emit visible light, a property used in fluoroscopy and detector screens.
6. Why are X-rays the preferred choice for medical imaging of bone fractures over other types of radiation?
X-rays are ideal for imaging the skeletal system due to the principle of differential absorption. Bones, being rich in calcium, are much denser than the surrounding soft tissues (like muscle and skin). This high density causes bones to absorb X-rays much more effectively. In contrast, the less dense soft tissues allow most of the X-rays to pass through them. When captured on a detector, this difference creates a high-contrast image where bones appear white (as they block the rays) and soft tissues appear in shades of grey or black, making fractures and bone structures clearly visible.
7. Given their use in medicine, are X-rays considered harmful, and why are safety measures necessary?
Yes, X-rays are a form of ionising radiation and can be harmful to living cells, especially with high or repeated doses. Their high energy allows them to knock electrons from atoms in biological molecules, including DNA. This can lead to cell damage, mutations, or an increased long-term risk of cancer. Therefore, strict safety protocols are essential. These include using the lowest possible dose for diagnosis, focusing the beam only on the target area, and using lead shielding (like lead aprons) to protect other parts of the patient's body and medical personnel from unnecessary exposure.
