Question 3: (a) What are X-rays? How are these produced?
(b) Enlist some characteristics of X-rays.
Answer
(a) X-rays are electromagnetic radiations of very high frequencies. Their range of frequencies is from 10-2 A0 to 102 A0. [Since 10 = 10-10 m ⇒ 1 × 10-2 A0 = 10-10 × 10-2 m ⇒ 10-2 A0 = 10-12 m ⇒ 10-2 A0 = 10-3 × 10-9 m = 0.001 × 10-9 m = 0.001 nm. Convert the other end 102 A0 to nano meters yourself]. The rays were discovered by the German Physicist Rontgen in 1895.
Production of X-rays
X-rays are produced in a number of methods. Here we discuss the Roentgen method of X-rays production.
Roentgen method of X-rays production
A special type of cathode rays tube for this purpose. In this tube the cathode is concave shaped which focuses the emitted electrons on a particular area of the anode. Second, the voltage applied to the cathode and anode is very high, as high as 30000 to 50000 volts, and the pressure in the tube is as low as 0.001 mm Hg.
Now under these conditions, some of the gas molecules in the tube are ionized. The heavy positive ions produced are attracted by the cathode with high velocities and due to their collisions, electrons are the high potential difference between cathode and anode. Their they knock out some inner shell electrons of the anode and consequently, some high energy level electrons jumps to the vacancy left by the ejected electron. With jumping to the lower shell, the excess of energy is emitted as X-ray radiation.
(b) Characteristics of X-rays
Following are the main characteristics of X-rays.
- X-rays travel in straight line.
- They are not deflected in the electric or magnetic fields. This shows X-rays are neutral radiations.
- They can ionize gases.
- X-rays produce fluorescence in many substances.
- X-rays are reflected as well as diffracted (showing the wave characteristics of X-rays).
- X-rays can be diffracted by crystalline substances. (Important property for investigating the structure of crystals).
- X-rays can penetrate through many substances.
- X-rays affect photographic plate.
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