Wilhelm Röntgen discovered X-rays. He was doing research with the discharge tube he observed that fluorescence was produced when cathode rays were incident on barium platino-cyanide sheet placed on the side of the tube. He observed fluorescence on the sheet covering the discharge tube with a thick red paper. Then by placing a thick metallic plate between the sheet and the tube he noticed the exact thing. Röntgen came to a conclusion that those rays were not the cathode rays. Rather after incident of the cathode rays on the surface of the discharge tube a special type of rays were emitted due to which fluorescence was produced. He named it X-rays. Generally we define unknown term as X. Röntgen did the same thing.
Figure: Wilhelm Röntgen (Photo by wikimedia)
In 1895 Wilhelm Röntgen observed that if high velocity electron hits on a metal a high penetrating unknown radiation is produced. That unknown radiation is called X-ray. For the honor of the discovery these rays also called Röntgen rays. The nature and property of X-rays became know later.
There are two types of x-ray viz. soft X-rays and hard X-rays. Soft X-rays is produced with low voltage application; hard x-ray is produced by high voltage application.
- Soft X-rays: Soft X-rays is produced with comparatively high pressure inside the gas tube and low voltage application. Soft X-rays has low penetrating power. It is used extensively in medical science.
- Hard X-rays: If the pressure of gas is low inside the tube and voltage is high it produces hard X-rays. Hard X-rays has high penetrating power. These types of X-rays are used in laboratory purpose such as the determination of structure of the material.
Unit of X-rays: Unit of X-rays is Röntgen according to inventor’s name. At normal temperature and pressure one Röntgen amount of X-ray radiation can produce 3.33×10-10C charge at 1×10-3m of air.
Penetration power of X-rays compared to other rays:
X-rays have a high penetration power compared to other rays. Gamma rays have most high penetration power then second penetrating powerful ray is X-rays.
Figure: Penetration power of some rays (photo by wikimedia)
Following chart shows the penetration power of some familiar rays. We can see that Gamma is the higher power, secondly X-rays, third Ultraviolet (UV) ray, fourth infrared, fifth micro wave, sixth radio wave. High power means high frequency Gamma rays have most high frequency; second high frequencier wave is X-rays. Radio wave caries very low frequency compared to Gamma, X-rays, UV, Microwave and infra red. But Radio has most high wave length compared to all rays and Gamma has very short wave length.
Figure: X-ray production in Coolidge tube
A piece of metal is taken on side in a tube. Another side a tungsten filament is placed connecting with battery. We know flowing of current through tungsten electron emits as light energy. Those electrons hit on the other side metal at high speed. A voltage applied between two terminal metal and negative terminal of the battery connected to the tungsten. The applied voltage energized the electron to gain high velocity. Hence electrons hit the metal plate with high velocity and take another electron from atomic structure of the metal. That means one electron makes one free space to the atom. From nearest orbit another electron takes place to fill the gap and one type of ray is emitted which is X-ray. For getting Soft X-rays lower voltage applied and high voltage is applied getting hard X-rays.
A Coolidge X-ray tube is shown on figure. On this process metal plate is anode and tungsten is cathode. Electron hits from cathode to anode with kinetic energy Emax = eV.
Where, e = charge of electron. When the electron hits on the metal plate some of its kinetic energy converts on heat energy which is very low hence negligible. Assuming total kinetic energy of electrons used to produce X-ray. Total energy of electron generating X-ray photon and the energy of X-ray photon is maximum during strike. So the frequency of the photon also maximum.
Properties of X-rays:
- X-ray is invisible. When normal light is incident on people retina, it creates the sensation of vision. But X-rays does not create sensation
- It travels in straight line
- X-rays is electromagnetic transverse wave
- X-rays can destroy living cells
- Its penetrating power is extremely high
- Its wave is very low about 10-10m
- It is charge neutral
- X-rays can travel at 3×108ms-1 speed
- It effects on photographic plate
- X-rays are not deflected by magnetic field and electric field
- It ionizes gas passing through the gas
- Like ordinary light X-ray have reflection, refraction, polarization and diffraction
- It creates fluorescence
Use of X-rays
In modern science X-rays are used extensively in different purposes such in medical science, industry, commerce, laboratory, detective department etc. Some of uses are discussed below.
i) In medical Science:
- X-ray can pass through blood but can’t pass bones of human body. It is used to detect of fracture of bones, displacement of bones. Identify decay of teeth or identify decay in the root of the teeth
- It is used to determination of diseases like tumor, ulcer, tuberculosis etc
- X-rays is used to treatment of cancer and also used to destroy cells for less infection
- ii) In industry and commerce:
- To determine the presence of any poisonous chemical in toffee or chocolate or checking the quality
- To detect any defect or hole inside the metal sheet
- To identify real diamond
- To locate the presence of pearls in oysters
iii) In detective departments:
- To detect the smuggling of precious metals like silver, gold, diamond etc. at the custom posts
- X-rays are also used to detect explosives and other contraband goods like heroine, opium etc. in the container.