SSC
Which rays are used in medicine to destroy cancer cells?
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Answer: Option A — Gamma rays
Detailed Solution
Gamma rays are a form of electromagnetic radiation with the shortest wavelength (less than about 0.01 nanometre) and the highest frequency and energy in the electromagnetic spectrum. They are emitted from the nuclei of radioactive atoms during radioactive decay, and in nuclear reactions such as fission and fusion. They were discovered by the French scientist Paul Villard in 1900 and named by Ernest Rutherford in 1903.
Because gamma rays carry very high energy, they can penetrate deep into the body and damage the DNA of living cells. Cancer cells divide rapidly and are less able than normal cells to repair such damage. This property is used in radiotherapy (radiation therapy) to kill cancer cells and shrink tumours. Commonly used sources include:
Cobalt-60: used in cobalt therapy machines ("teletherapy") for many decades.
Gamma Knife: a device that focuses many beams of gamma rays from cobalt-60 sources precisely on a small target in the brain, used to treat brain tumours without surgery.
Modern hospitals often use linear accelerators (LINACs), which produce high-energy X-rays for the same purpose.
Other uses of gamma rays:
- Sterilising medical instruments, such as syringes and surgical tools.
- Food irradiation, to kill bacteria and insects and increase shelf life.
- Industrial radiography, to detect cracks and flaws in metal structures and welds.
- Gamma ray astronomy.
- Because gamma rays are so penetrating and harmful, protection requires thick shielding of lead or concrete.
- The electromagnetic spectrum, in order of increasing wavelength, is: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves.
- In India, cancer treatment and radiation safety are supported by the Department of Atomic Energy, including the Tata Memorial Centre, Mumbai, and the Board of Radiation and Isotope Technology (BRIT).
Why not the other options?
- ✗Infrared rays are heat radiation, used in remote controls and night vision.
- ✗Ultraviolet rays are used to sterilise water and air, and cause sunburn.
- ✗Radio waves are used in communication and broadcasting.
Quick tip
Remember: Gamma rays = shortest wavelength, highest energy, used in cancer radiotherapy (cobalt-60, Gamma Knife) and sterilisation; spectrum order: gamma, X-ray, UV, visible, IR, microwave, radio.
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Modern Physics & Nuclear Energy — Preparation
This question tests your understanding of Modern Physics & Nuclear Energy, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers atomic and nuclear physics: the discovery of the electron, proton and neutron, radioactivity and its types, nuclear fission and fusion, nuclear reactors, X-rays, semiconductors, and important laws and theories, such as Einstein's mass-energy relation. Questions usually ask who discovered a particle (J. J. Thomson discovered the electron, and James Chadwick the neutron), what powers the Sun (nuclear fusion), what happens in a nuclear reactor (controlled fission), and what moderators and control rods do. Learn the three types of radioactive radiation (alpha, beta and gamma) and how they differ. Practise the modern physics questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.