Radioactivity and Geiger-Müller Tubes

Radioactivity

• Radioactivity is the process where unstable atomic nuclei release energetic subatomic particles.
• The SI unit for radiation is Becquerel (Bq).
• Radiation cannot be detected by the five senses; special detectors are needed.
• Several devices have been developed to detect radiation across generations.
• Examples include cloud chambers, electroscopes, and Geiger-Müller tubes.

Geiger-Müller Tube

• The Geiger-Müller (GM) tube is a useful and sensitive radiation detection device.
• Radiation enters the tube through a thin mica window.
• Argon atoms become ionized into electrons and argon ions.
• Free electrons accelerate towards the central wire (anode).
• These accelerated electrons collide with other argon atoms, causing further ionization (an "avalanche" of electrons).
• This enhances the current pulse.
• The amplifier measures and rates the count rate.

Three types of radioactive emissions

• Unstable nuclei release tiny particles randomly.
• Alpha particles:
  • Highest ionizing power, but low penetration.
  • Composed of two protons and two neutrons.
  • Identical to a helium nucleus (He2+ or α).
  • Can be blocked by paper.
• Beta particles:
  • Moderate ionizing and penetration power.
  • High-speed electrons.
  • Released by radioactive isotopes like potassium-40.
  • Represented as β⁻¹ or β.
• Gamma rays:
  • Lowest ionizing power and highest penetration.
  • Electromagnetic waves similar to X-rays.
  • Cannot be considered particles.
  • Represented as γ⁰.
  • Most harmful.
  • Lead and thick concrete reduce penetration.

Deflection of Radioactive Emissions

• Alpha particles are positively charged, deflecting towards the negative cathode in an electric field.
• Beta particles are negatively charged, deflecting towards the positive anode in an electric field. Gamma rays have no charge and aren't deflected.
• In a magnetic field, alpha particles show a small deviation, beta particles a larger deviation, and gamma rays show no deviation.

Radioactive Decay

• Radioactive decay is the spontaneous and random emission of radiation from unstable nuclei.
• Each decay of radioactive nuclei reduces the radioactive activity.
• The rate of decay is described by half-life.

Nuclear Equations

• The numbers for atomic number and mass must balance.
• Alpha decay represents a helium nucleus (He2+).
• Alpha decay increases the atomic mass by 4 and decreases the atomic number by 2.

Beta Decay

• One proton is subtracted from the atomic number when a neutron decays into a proton.
• This explains the increase in atomic number and no change in atomic mass.

Gamma Emission

• Even after alpha and beta decay, the nucleus can be in an excited state.
• Energy is released in the form of a gamma ray to lower the energy status,.

Nuclear Fission and Fusion

• Nuclear fission is the splitting of an atom's nucleus into two or more smaller atoms, along with some by-products.
• Nuclear fusion is the joining of multiple atomic nuclei to create a heavier nucleus, releasing or absorbing energy.

Uses of Radioactive Isotopes

• Radioactive isotopes are used in medical tracers, detecting leaks, and carbon dating.

Precautions

• Wearing protective clothing (e.g., lead-lined suits).
• Maintaining distance from radioactive materials.
• Enclosing radioactive materials (in lead containers).
• Limiting exposure time.

Detecting Leaks

• Use a short-lived radioisotope, releasing it into the pipe, and using a Geiger-Müller (GM) tube to detect its movement and signal leaks.

Carbon dating

• Carbon-14, with a long half-life, is present in living organisms.
• The amount of Carbon-14 decreases after death at a predictable rate, allowing estimation of the organism's age.
• Carbon dating is not suitable for non-living materials.

Astrophysics

• Weight is the force acting on an object due to gravity.
• Planets have strong gravitational fields.
• Gravitational field strength is the force acting on a unit of mass.
• The Solar System is composed of the Sun, planets, and other celestial bodies.
• Rocky planets include Mars, Earth, Venus, and Mercury; gas planets include Jupiter, Saturn, Uranus, and Neptune.
• An asteroid belt lies between the rocky and gas planets.
• Satellites are celestial objects orbiting larger celestial objects: Natural (e.g., the Moon) and Artificial (e.g., communication satellites).
• Asteroids are small rocky objects orbiting the Sun; comets are made of dust and ice; the ice melts to form a tail when they approach the Sun.