Physics Fundamentals and Radiation Characteristics

Introduction to Physics

Physics is the study of the interactions between matter and energy in their various forms, emphasizing exactness and certainty in describing these interactions. It encompasses fundamental concepts, units, and the behavior of matter and energy.

Fundamental Quantities and Units

Key physical quantities are categorized into Base Quantities (Length, Mass, Time) and Derived Quantities (Energy, Power, Work, Momentum, Force, Velocity, Acceleration). These are measured using various systems, primarily the SI System (International System of Units), alongside MKS, CGS, and British systems.

Length (Meter): Originally defined by a platinum-iridium bar, now by the wavelength of orange light from Krypton-86 or distance traveled by light.
Mass (Kilogram): Originally 1000cm³ of water in a platinum-iridium cylinder, now 1000cm³ of water at 4°C.
Time (Second): Originally based on Earth's rotation, now defined by the vibration of cesium atoms.

Special quantities in radiation physics include Exposure (C/kg), Absorbed Dose (J/kg or rad), Effective Dose (J/kg or rem), and Radioactivity (Bq or curie).

Mechanics

Mechanics is the branch of physics dealing with objects at rest (statics) and in motion (dynamics).

Inertia: A body's resistance to changes in its state of motion, directly proportional to its mass.
Force: A push or pull, defined by Newton's Second Law as mass times acceleration (F=ma).
Newton's Laws of Motion:

First Law (Inertia): An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Second Law (Force): The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F=ma).
Third Law (Action/Reaction): For every action, there is an equal and opposite reaction.

Velocity/Speed: The rate of change of position with time (v=d/t).
Acceleration: The rate of change of velocity with time (a = Δv/Δt).
Weight: The force exerted on a body by gravity (Wt=mg).
Momentum: The product of mass and velocity (P=mv).
Work: Force applied over a distance (W=fd).
Power: The rate at which work is done (P=w/t), measured in Watts (Joule/second).

Energy and Heat Transfer

Energy is the ability to do work, conserved (neither created nor destroyed), and measured in Joules (J). It exists in various forms:

Kinetic Energy (KE): Energy of motion (KE = ½ mv²).
Potential Energy (PE): Stored energy due to position or configuration (PE=mgh).

Heat is the kinetic energy of random molecular motion. Its unit, the calorie, is the heat needed to raise 1g of water by 1°C. Heat transfer occurs via:

Conduction: Transfer through direct contact.
Convection: Mechanical transfer of hot molecules in a fluid or gas.
Radiation/Thermal Radiation: Transfer by emission of infrared radiation (e.g., X-ray tube cooling).

Atomic Structure and Nomenclature

An atom is the smallest part of an element retaining its properties. Early models evolved from Democritus's "atomos" (indivisible) to modern understanding:

J.J. Thomson (1890): "Plum Pudding" model, discovered the electron (negative charge).
Ernest Rutherford (1911): "Nuclear model," discovered the small, dense, positively charged nucleus.
Niels Bohr (1913): "Miniature solar system" model, with electrons orbiting the nucleus in fixed, well-defined paths.

Fundamental Particles within an atom:

Proton: Discovered by Eugene Goldstein, positively charged, found in the nucleus, composed of quarks.
Neutron: Discovered by James Chadwick (1932), uncharged, found in the nucleus, composed of quarks.
Electron: Discovered by J.J. Thomson (1897), negatively charged, orbits the nucleus, determines chemical properties.

Atomic Structure Principles:

Atoms are mostly empty space and are electrically neutral in their normal state (protons = electrons).
The number of protons (atomic number, Z) defines the chemical element.
The atomic mass number (A) is the total number of protons and neutrons.
Electron Binding Energy: The energy required to remove an electron from its orbit, higher for electrons closer to the nucleus.

Atomic Nomenclature describes variations in atomic composition:

Isotopes: Atoms of the same element (same Z) but with different numbers of neutrons (different A).
Isobars: Atoms with the same atomic mass number (same A) but different atomic numbers (different Z).
Isomers: Atoms with the same A and Z but existing in different energy states due to nucleon arrangement.
Isotones: Atoms with the same number of neutrons but different A and Z.

Atoms combine to form molecules. Chemical bonds include Ionic Bonds (electron transfer, forming ions) and Covalent Bonds (electron sharing).

Ionization and Radiation

Excitation is the addition of energy to an atom, raising electron energy levels. Ionization is the process where an atom gains or loses electrons, becoming an ion (a charged atom). A lost electron creates a positive ion (cation), while a gained electron creates a negative ion (anion). An ion pair consists of a cation and an anion.

Radiation is energy traveling through space and matter. It can be:

Electromagnetic Radiation: Includes gamma rays, X-rays, ultraviolet light, and visible light, produced by accelerating or decelerating charged particles.
Particle Radiation: Includes alpha particles, beta particles, and neutrons, emitted during radioactive decay or nuclear reactions.
Cosmic Radiation: High-energy protons and atomic nuclei from outer space.

Sources of Ionizing Radiation include natural environmental radiation (cosmic rays, terrestrial radiation, radon) and man-made sources (diagnostic X-rays).

The discovery of radiation by Henri Becquerel (1896) and the work of Marie and Pierre Curie, along with J.J. Thomson's electron discovery, laid the foundation for understanding ionization.

In radiology, ionization is crucial for diagnostic imaging (affecting image contrast), radiation therapy (damaging cancer cell DNA), and radiation detection (e.g., Geiger counters).

Electricity, Magnetism, and Electromagnetism

Electricity is the interaction of electric charges. Protons carry positive charges, electrons carry negative charges. Electrostatics studies stationary charges, which can be created by friction, contact, or induction. The unit of electric potential is the Volt (V).

Coulomb's Law describes the electric force between charged objects: like charges repel, unlike charges attract. The fundamental unit of charge is the Coulomb (C).

Materials are classified by their electrical properties:

Conductors: Allow easy electron flow (e.g., copper).
Insulators: Inhibit electron flow (e.g., glass).
Semiconductors: Behave as either depending on conditions (e.g., silicon).

Electric Current is the continuous flow of electric charge, measured in Amperes (A). It can be Direct Current (DC), flowing in one direction, or Alternating Current (AC), oscillating back and forth.

Electric Circuits involve components like resistors (oppose current flow, measured in Ohms Ω), batteries (provide potential), capacitors (store charge), ammeters (measure current), voltmeters (measure potential), and switches. Ohm's Law states that voltage equals current times resistance (V=IR).

Superconductivity is the property of some materials to exhibit zero electrical resistance below a critical temperature.

Magnetism is a fundamental property of matter, first observed in lodestones. Every magnet has a North and South pole. A moving charged particle creates a magnetic field. Materials are classified as nonmagnetic, diamagnetic (weakly repelled), paramagnetic (slightly attracted), or ferromagnetic (strongly attracted, can be permanently magnetized).

Electromagnetism is the relationship between electricity and magnetism. Hans Oersted discovered that electric currents create magnetic fields. An electromagnet is a current-carrying coil of wire around an iron core, producing a magnetic field.

Alessandro Volta developed the voltaic pile (precursor to the modern battery) by stacking different metals. Michael Faraday's work on electromagnetic induction led to the development of devices like the induction motor, used in X-ray tubes.

Transformers

A transformer is a device that uses interacting magnetic fields to change the intensity of alternating voltage and current. A step-up transformer increases voltage (turns ratio > 1), while a step-down transformer decreases voltage (turns ratio < 1). Common types include closed-core, autotransformers, and the highly efficient shell-type transformers.

Physics and Radiation Fundamentals

Physics and Radiation Fundamentals