Alpha rays are streams of positively charged particles emitted from the nuclei of certain radioactive elements such as uranium, radium, and polonium. Each alpha particle consists of two protons and two neutrons, making it identical to a helium nucleus.

Because of their large mass and double positive charge, alpha particles have low penetrating power but high ionizing ability. They can be stopped by a sheet of paper or a few centimeters of air.

• They consist of helium nuclei (2 protons and 2 neutrons).
• They carry a positive charge of +2.
• They have low penetrating power — stopped by paper or skin.
• They possess high ionizing power and can ionize air strongly.
• They are deflected by electric and magnetic fields toward the negative plate.
• They travel at about 1/10 the speed of light.
• They can produce fluorescence on materials like zinc sulfide.

Beta rays are streams of high-speed electrons or positrons emitted from radioactive nuclei. They occur when a neutron changes into a proton and an electron (β⁻ decay) or when a proton changes into a neutron and a positron (β⁺ decay).

Beta particles are much lighter than alpha particles and therefore have greater penetrating power but lower ionizing power. They can be stopped by a few millimeters of aluminum.

• They consist of electrons (β⁻) or positrons (β⁺).
• They carry a single negative or positive charge.
• They have greater penetrating power than alpha rays.
• They have lower ionizing power compared to alpha rays.
• They are deflected by electric and magnetic fields in the opposite direction to alpha rays.
• They travel at speeds approaching that of light.
• They can cause fluorescence and blacken photographic plates.

Gamma rays are a form of high-energy electromagnetic radiation emitted from the nucleus of a radioactive atom, usually after the emission of an alpha or beta particle. They have no mass and no charge.

Gamma rays have very high penetrating power and can pass through several centimeters of lead or meters of concrete. They are similar to X-rays but have a higher frequency and energy.

• They are electromagnetic waves with very short wavelengths.
• They carry no electric charge and have no mass.
• They have very high penetrating power — only thick lead or concrete can stop them.
• They have low ionizing power compared to alpha and beta rays.
• They are not deflected by electric or magnetic fields.
• They travel at the speed of light (3 × 10⁸ m/s).
• They can cause fluorescence and photographic effects.

X-rays are high-energy electromagnetic waves produced when fast-moving electrons strike a metal target, usually tungsten, inside an X-ray tube. They were discovered by Wilhelm Roentgen in 1895 while studying cathode rays.

X-rays are similar to gamma rays but differ in origin — gamma rays come from the nucleus while X-rays originate from the interaction of electrons with matter.

X-rays are categorized based on their energy or wavelength into two main types:

• Soft X-rays: These have longer wavelengths and lower energy. They are less penetrating and are mostly absorbed by soft tissues. Used in studying thin materials and biological samples.
• Hard X-rays: These have shorter wavelengths and higher energy. They are highly penetrating and can pass through thick materials like metals and bones. Used in medicine and industry.

• They are electromagnetic waves with very short wavelengths (10⁻⁸ to 10⁻¹² m).
• They have no charge or mass.
• They have high penetrating power — greater for hard X-rays than soft X-rays.
• They can blacken photographic plates and cause fluorescence.
• They are not deflected by electric or magnetic fields.
• They can ionize gases and produce secondary radiations.
• They are harmful to living tissues with prolonged exposure.

X-rays have wide applications in different fields due to their ability to penetrate matter and reveal internal structures:

• Used in medical imaging to examine bones, teeth, and internal organs.
• Used in radiotherapy for the treatment of cancer and tumors.
• Applied in industrial inspection to detect cracks or defects in metal parts.
• Used in security scanning at airports to inspect luggage and packages.
• Used in crystallography to determine the structure of crystals and molecules.
• Used in astronomy to study celestial objects emitting X-rays.
• Used in quality control and testing of weld joints.