Nuclear radiations such as alpha (α), beta (β), and gamma (γ) rays are invisible to the eye, but they can be detected and measured using special instruments. The most common radiation detectors include the Geiger–Müller counter, Scintillation counter, and Diffusion cloud chamber.

The Geiger–Müller (G.M.) counter is an instrument used to detect and measure ionizing radiation such as alpha, beta, and gamma rays. It consists of a metal tube filled with low-pressure gas (usually argon) and fitted with a thin mica window that allows radiation to enter. A central wire electrode runs through the tube and is connected to a high-voltage supply.

When radiation enters the tube, it ionizes the gas molecules inside. The ions and electrons produced are attracted to the electrodes, causing a brief electric pulse. Each pulse is counted electronically and can be registered by a clicking sound, a needle movement, or a digital display.

• Ionizing radiation enters the tube through the mica window.
• It ionizes the gas molecules, producing positive ions and electrons.
• The electrons move toward the central wire, creating a momentary current pulse.
• The pulse is amplified and counted, producing an audible or visible signal.

• Detects and counts radioactive emissions.
• Measures radiation intensity or activity of a radioactive sample.
• Used in nuclear laboratories and medical radiology.
• Helps in monitoring background radiation and contamination.

A scintillation counter is an instrument that detects nuclear radiation by using substances that emit flashes of light (scintillations) when struck by ionizing particles. These flashes are then converted into electrical signals that can be measured.

The device consists of a scintillator material such as sodium iodide doped with thallium, a photomultiplier tube (PMT), and an electronic counting system.

• When radiation strikes the scintillator, it produces small flashes of light (scintillations).
• The light photons are directed to the photomultiplier tube.
• The photomultiplier converts these light photons into an electric current pulse by the photoelectric effect.
• The pulses are amplified and recorded by the counting system.

• Used for detecting and measuring gamma rays and beta particles.
• Employed in medical imaging such as PET scans and radiation therapy monitoring.
• Used in nuclear research to determine radiation energy and intensity.
• Useful in environmental radiation surveys and contamination checks.

The diffusion cloud chamber is an instrument used to observe and study the paths of ionizing particles such as alpha and beta particles. It makes the invisible tracks of these particles visible by condensation of vapor along their paths.

It consists of a sealed chamber containing air saturated with alcohol vapor (usually methyl alcohol). The bottom of the chamber is cooled using solid carbon dioxide (dry ice) to maintain a temperature gradient.

• The cooling at the base causes the alcohol vapor to be supersaturated near the bottom.
• When a charged particle passes through, it ionizes the gas molecules along its path.
• The alcohol vapor condenses on these ions, forming tiny droplets that mark the path of the particle.
• These tracks can be observed directly or photographed for analysis.

• Used to visualize the tracks of alpha and beta particles.
• Helps in studying radiation paths, direction, and ionization patterns.
• Used in educational demonstrations and nuclear physics experiments.
• Provides information about the energy and type of particle based on the track’s thickness and curvature.