Applications & Explore Online ആറ്റത്തിന്റെ ഘടന

The discharge tube of 1875 still lights up the neon signboards of a Kerala town at night. Cathode rays drew the pictures on the old TV at grandma's house. The isotopes ഐസോടോപ്പുകൾ of this chapter treat cancer at the Regional Cancer Centre in Thiruvananthapuram, tell archaeologists how old a piece of charcoal is, run nuclear power stations and find leaks in buried pipes. Every lab below uses only the ideas of this chapter. The page ends with radiation safety and a hub of links to explore online.

1. Glowing signboards, street lamps and tube lights

At night, the shops in a Kerala town light up with red-orange neon signs. A neon sign is a discharge tube ഡിസ്ചാർജ് ട്യൂബ്: a glass tube with an electrode at each end, filled with a little neon gas at low pressure, and run on a high voltage, just like Crookes’ tube. Electrons rush from the cathode and crash into the gas atoms. Each collision lifts an electron of the atom to a higher energy level (it absorbs energy). When the electron falls back, it gives out that energy as light. Every gas gives its own colour: neon is red-orange and sodium vapour is yellow-orange, like the old street lamps. In a tube light or CFL, mercury vapour gives out invisible ultraviolet light, which makes the white coating on the inside of the glass glow go further.

2. The old CRT television at grandma's house

Before flat screens, every TV and computer monitor had a big glass cathode ray tube (CRT) at the back, which is why the old TV at grandma's house is so deep. At the narrow end, a hot cathode gives out electrons, and an anode at high voltage speeds them into a thin beam: these are cathode rays. Just as in Fig 1.4, electric plates (or magnetic coils) bend the beam up and down and from side to side, so that it sweeps the screen line by line. The inside of the screen is coated with a substance that glows where the electrons hit it, like the zinc sulphide in Crookes’ tube. The beam paints the whole picture many times every second, so your eyes see a steady picture.

3. Radioactive isotopes in hospitals

Table 1.6 lists three medical uses. Iodine-131 is used to study and treat the thyroid gland. The thyroid in the neck collects iodine from the blood, so after a patient swallows a tiny dose, a detector outside the neck “sees” how much the gland has taken up. A larger dose destroys an overactive gland or thyroid cancer from the inside. Cobalt-60 gives out powerful gamma rays that are used to treat cancer. The machine turns around the patient, so the tumour receives the rays from every side while the healthy skin gets only a little from each direction. Cancer hospitals such as the Regional Cancer Centre (RCC), Thiruvananthapuram have used cobalt-60 machines for many years. Iron-59 helps to diagnose anaemia: doctors follow how fast the body takes iron into new red blood cells.

4. Carbon-14: how old is this fossil?

Plants take in carbon dioxide, and animals eat plants. So every living thing contains carbon, and a tiny, fixed share of it is radioactive carbon-14, 146C (8 neutrons). While the plant or animal is alive, the share stays the same, because it keeps taking in fresh carbon. After death no new carbon comes in, and the carbon-14 slowly breaks down. Every 5730 years about half of what is left is gone go further. By measuring how much carbon-14 is left in a bone, a piece of wood or charcoal, scientists find its age ഫോസിലുകളുടെ കാലപ്പഴക്കം. Archaeologists use this at excavation sites such as Pattanam in Ernakulam district, where charcoal and wood help to date the remains of an ancient port.

5. Uranium-235 and heavy water in nuclear power stations

Uranium-235, 23592U (92 protons, 143 neutrons), is the fuel in nuclear power stations (Table 1.6). When a slow neutron hits a uranium-235 nucleus, the nucleus splits into two smaller nuclei, gives out two or three new neutrons and releases a huge amount of heat. This is called nuclear fission go further. The heat boils water, and the steam turns a turbine that makes electricity. Heavy water ഘനജലം is D₂O, the oxide of deuterium (hydrogen with 1 proton and 1 neutron). It slows the neutrons down so that they can split the next uranium nuclei, and control rods soak up the extra neutrons to keep the reaction steady. Most of India’s nuclear power stations, for example at Tarapur, Rawatbhata and Kaiga, use heavy water in this way go further. Kudankulam in Tamil Nadu uses ordinary water. Kerala has no nuclear power station.

6. Sodium-24: finding a leak in a buried pipe

Factories and cities carry oil, water and chemicals in pipes buried under the ground. To find a leak without digging up the whole road, engineers add a very small amount of a liquid containing radioactive sodium-24 to the pipe. Where the pipe leaks, the liquid soaks into the soil and the sodium-24 collects there. A worker walks along the road with a radiation detector, and the reading jumps right above the leak. Sodium-24 loses half of its radioactivity in about 15 hours, so within a few days almost none is left go further.

7. Radiation safety – the ☢ symbol

The radiation from radioactive isotopes can damage the cells of living things, which is why the same gamma rays that kill a tumour must be kept away from healthy people. Radioactive isotopes are therefore handled only by trained people, in special laboratories, with shielding. The warning sign is a black trefoil on a yellow background. Wherever you see it, it means: radiation, keep away. Of the three radiations in the radioactivity box (α, β, γ), alpha is stopped by a sheet of paper, beta by a few millimetres of aluminium, and gamma only by thick lead or concrete go further.

✅ Check yourself

🌐 Explore online – resources hub

Everything in this guide works offline. The links below are extras: simulations and websites from trusted sources (PhET, the Nobel Prize, the Science History Institute, India’s Department of Atomic Energy and others), grouped by topic. They need internet and open in a new tab, so you will not lose your place here. Ask a parent or teacher before you go online. The PhET simulations Build an Atom, Rutherford Scattering and Isotopes and Atomic Mass run directly in the browser, with nothing to install.

Atom models: Thomson, Rutherford and Bohr

Discharge tubes and cathode rays

Electrons, protons and neutrons

Atomic number and mass number

Electron configuration and shells

Isotopes and isobars

Uses of radioactive isotopes

More to explore