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Basic X-ray Physics for Radiographers By Teacher: Nourah M. Al-Ruwais Chapter #1 MATTER AND ENERGY Matter: It is the material of which all things including ourselves are made. It has a mass, size and occupies space. Matter is made of molecules. Molecules are made of atoms. Atoms are made of electrons (ve) and nucleus (proton +ve and neutron). Atom is the unit of matter. Matter is of three physical states: Solid- liquid- gas. Basic Uni ts/ Fundament al units: MKS SYSTEM; Mass Length Time K= kilograms m= meter s= Seconds Velocity (speed): The distance that has been crossed in a period of time. Velocity = distance/ time m/s Stationary= no motion. Acceleration: The rate of change in velocity. A= Velocity/ time m/sec Force: The tendency to cause motion. Or to move a stationary object. F= mxa (m=mass, a=acceleration) Newton = Kg.m/s Work: It is the magnitude of force that makes a body move to a distance. W=Fxd (d=distance, F=force) Joule= Newton.m Power: It is the rate of doing work. P= work/time = Fxd/t Watt= joule/sec. Law of co nservation of Matter or E nergy: (Matter/Energy) cannot be created nor destroyed but can only be changed from one form to another. Energy: It is the ability to do work. (Joule) Forms of Energy: Electrical E.- Heat E. – Light E. – Atomic E. – Sound E. – Mechanical E.(Potential or Kinetic). 2 CHA PTER #2 Heat It is a form of energy. It is the average vibration energy of the molecules. Heat motion Kinetic Energy States of matter: Solid: Kinetic Energy of the molecules heat. Ex: ice Liquid & Gases: Particles move fast kinetic energy heat. Ex: water & steam. Temperature: It is the indication of the degree of hotness or coldness. It also represents the average speed of the particles. temp. solids melt & liquid changes into gas (Substance expands). temp. liquid becomes solid & gas becomes liquid. (Substance contracts). How is temperature measured? By a Thermometer. It ranges between the melting point of ice and the boiling point of water. Thermometers are of three types: Centigrade 0c – 100c . Fahrenheit 32F - 212F . Kelvin 273K - 373K . Normal body temperature: 37c - 96F - 310K. Units of Heat: Joule and calorie. Calorie:The amount of heat required to raise the temperature of 1gm of H2O to 1c . 1 calorie = 4.2 Joules Specific Heat: The amount of heat required to raise the temperature of 1gram of a substance to 1c. The specific heat of H2O = 1. 3 Heat Capacity: It which is required by 1K. is to the heat energy raise the temp. in of joules, the body Heat law: Heat gained by one body must be equal to heat lost by another body. Heat transmission in matter: Conduction: In solids (metal “good”- wood “bad”). Convection: In liquid and gases. Radiation: In vacuum. Radiation: It is the flow of heat in a vacuum. It is the method by which energy reaches us from the sun. C HAPTER #3 Elec tricity It is an electrical energy, which is transported from one location to another by electrons. Types of electricity: Static Electricity Current Electricity “Electrostatics” o The charge is The charge is moving in stationary a conductor due to o Production of difference in potential charge by friction across its two ends. o Ex: clothes, hands, battery.. Charge: When two bodies are rubbed together there is transference of electrons from one body to another. The body that loses electrons will be +ve positively charged. The body that gains electrons will be –ve negatively charged. Two types of charge: +ve and –ve. How are they produced? 1. By friction. 2. By ionization of an atom. What are the properties of charge? 4 1. Like charge repel each other. 2. Unlike charge attract each other. 3. There is a force (F) of attraction or repulsion between the two charges. 4. The charge cannot be created nor destroyed Electrical field: It is the field around the charge which can experience a force of attraction or repulsion. Columbs law of electrostatics: The force of attraction or repulsion (F) is directly proportional to the product of the charge (Q). And inversely proportional to the square of the distance (d ). F= K. Q1 X Q d CHAPTER #4 Atomic S tructure Elements: Chemical substances that cannot be broken down into simpler chemical forms. There are 108 chemical elements in nature. Ex: Hydrogen, Carbon, Oxygen, Nitrogen… Atoms: It is the smallest part of an element which retain the chemical properties of the element. Bohr’s theory of Atoms: An Atom has two parts Nucleus (+ve) Electrons (ve) Protons Neutrons Move around the nucleus “+ve” “neutral” In a fixed orbit or shell. Protons are equal and opposite to the charge of an electron. Protons and neutrons have the same mass. 5 An electron is 2000 times lighter than a proton. Electrons have kinetic energy. The electron distribution in an Atom: K=2e L=8e M=18e N=32e Atomic number: It is the number of protons in the nucleus “Z”. Determines the chemical properties of the atom. Atomic mass: It is the total number of protons and neutrons in the nucleus “A”. Ex: H Z=1 A=1 C Z=6 A=12 O Z=8 A=16 Isotope: Atoms having the same atomic number “Z” but different atomic mass “A”. All Isotopes have the same chemical properties because they have the same number of protons. Ex: I , I , I , I . Iodine Isotopes. Types of Isotopes: Radioactive Isotopes: they emit radiation. Such as Alpha, beta and gamma rays. Non radioactive Isotopes: they do not emit radiation. Ionization: It is the process by which a pair of ions are formed. When the force of attraction between the electron and the nucleus of an atom is balanced then the atom is neutral. When an electron is removed from a neutral atom it becomes positively charged. Ionization is lost by heat, friction or by radiation. Binding Energy: It remove an electron Depends on: is the energy required to from the shell. 6 1. The type of shell. Inner shell electrons have higher binding energy than outer shell electrons. 2. The atomic number “z” the number of protons in the nucleus. Z binding energy. Ionizing Radiation: It is the process of removing an electron from an atom by exposing it to a certain type of radiation. Such as: x-ray, gamma ray, cosmic ray… CH APTER# 5 Electrical Charge and Potential Energy o When there are excessive electrons -ve charge o When there is deficiency of electrons+ve . Charge. o Unit of charge is Coulomb. o 1coulomb= 6x10 e . Electric Potential Energy: The amount of work done in bringing a unit positive charge from infinity to that point. Potential difference: The potential difference between 2points is the work done in moving a unit positive charge from one point to another. Work done= electrical charge x potential difference 1coulomb x 100volt = 100Joule o unit of potential difference is Volt. o Volt= joule / coulmb Electro volt (ev): It is the work done in moving an electron when the potential difference is 1volt. ev . Kev= 1000ev , Mev= 1000000ev. 1ev= 16x 10 joule ex: light= 3.5ev, x-ray= 20kev- 500kev, gamma ray=100kev- 2Mev. Earth Potential: It is the baseline from which an electric potential is measured. o Earths potential is constant. 7 o o o Earth potential equals zero. Electrons travel from high to Any leakage of charge will go earth because earth has lower low potential. immediately to potential. CHAPTER#6 Capacity Movement of charge in a material: 1. Conductor: The movement of charge is fast when potential difference is applied. Ex: silver, iron, copper, aluminum. The electrons in the conductor are free. 2. Insulator: (bad conductor) the movement of charge is minimum even if there is potential difference. Ex: wood, plastic, paper, glass, rubber… The electrons are tightly bonded. Not free. 3. Semiconductor: they allow flow of charge when the potential difference is very high. Ex: silicon, germanium… Used in x-ray equipment. 4. Superconductor: substances, which offer no resistance to the flow of current. Capacitance: It is the storage ability of the conductor at a fixed potential. Or how much charge it can store. Capacitance of conductor=storage of charge/ potential Q=C.V “C has constant capacity” Q is directly proportional to the potential. Unit of capacitance is “FARAD”. FARAD= coulomb/ volt. mF, F, nF, pF. Capacitor: It is a device which stores charge. Two types: 1. Spherical capacitor 8 2. Parallel plate capacitors Charging the capacitor: The time taken to charge the capacitor. Charge is added in an Exponential rate. “Exponential growth” Discharging the capacitor: Time taken to empty the charge from the capacitor. Charge is removed from The capacitor at an Exponential rate. “exponential decay” Capacity symbol: Law of capacitance in series: When the capacitors are connected in series, the total capacity (c) is increased. c1 c2 c3 c4 C=c1+c+c3+c4… Law of capacitance in parallel: When the capacitors are connected in parallel, the total capacity (c) is decreased. C=1/c1+1/c+1/c3+1/c4… Capacitors in Radiography: 1. Capacitor discharge in mobile units. 2. Electronic timer. 3. Voltage stabilizer. 4. Induction motor. Symbols: Mains kev Battery Ammeter 9 Voltammeter Coil Resistance Variable resistance Ohmmeter Ohm Transformer Conductor Earth c hapter# 7 Elec tric current What is a circuit? It is a simple wiring diagram, where varies electrical components are connected represented by there symbols. Simple circuit Current: It is the movement of an electrical charge in a conductor. Or, it is the flow of electrons from higher to lower potential. Current (I)= flow of charge (Q)/ time (t) Ampere= coulomb/ sec. 6x10 electrons/1 sec. charge (Q)= I X T. Ex: How much charge is there if the current is 20mA, in 1sec.? Coulomb= mAs Resistance: (R) It is the opposition to the flow of current in a conductor. When the current passes through the resistance it loses its energy and is converted into heat. The unit of resistance is ohm ( ). Ohms law: The current (I) flowing in the conductor is directly proportional to the potential difference (v) across the two ends 10 while the temperature and pressure are constant. I v R=v/I ohm( )=volt/ampere Ohm: If the current flowing in a conductor is 1A and the P.D. is 1v then the resistance of the conductor is 1ohm. What are the factors effecting resistance? RL (length), R1/a (area of cross section) R=k.L/a (k=constant of a material, called resistivity) resistivity is opposite to conductivity. What causes resistance? The interaction of electrons with the electrons in the conductor causing opposition in the flow. Material which has large number of free electrons has less resistance. More heat more resistance. Law of resistance in series: When 2 or more resistances are connected in series then the total resistances are equal to the sum of individual resistances. R= r1 + r2 + r3 + … R= 1+2+3+… Law of resistance in parallel: When 2 or more resistances are connected in parallel then the reciprocal of the total resistances is equal to the reciprocal of individual resistances. 1/R= 1/r+1/r2+1/r3+… = 1/1+1/2+1/3+… Resistances connected in parallel is always less than any of the individual resistances. Electromotive force (e.m.f): It is the force that moves electrons in a conductor. Electrical energy: It is the amount of work done by electricity. EE= P.D. X charge EE= v x Q (joule) 11 Q= I x t , EE= v x I x t , joule= watt x sec. If the current given in an x-ray tube is 2mA in 1sec and the P.D. is 100kv . then calculate the electrical energy in the xray tube? Electrical power: It is the rate of doing work by electricity. EP= EE/time EP= vxIxt/t EP= Ixv Watt = ampere x volt Electrical energy is used in the production of x-ray. In each chest x-ray, 100watt is required of electrical power. Electricity is also required for heating of the filament for thermion emission of electros. CH APTER# 8 Magne ts Properties of magnets: 1. Always point in a north – south direction. 2. Has 2poles (north and south poles). 3. It attracts faro magnetic substances such as iron, nickel, cobalt… 4. Like poles repel each other, unlike poles attract each other. 5. There is a force of attraction or repultion between two poles. 6. No separation between north and south poles. 7. Pole strength is always equal. 8. Magnetism is produced by magnetic induction or by electrical current flowing in a coil. 9. The force of attraction or repulsion (f) between 2poles is directly proportional to the pole strength (m). 10. The force of attraction or repulsion(f) between 2poles is inversely proportional to the square of the distance (d ). 12 11. F= 1/ m1 x m2 / d = constant Any magnetic substance consists of domains. In an unmagnetized material the domains are bipolar. In a magnetized material the domains are arranged. The north pole pointing in one direction and the south pole pointing in the opposite direction. Types of magnets: 1. Bar magnet (permanent magnet) 2. Horse shoe magnet (permanent magnet) 3. Electromagnet (temporary magnet) Horse shoe magnet is the type used in x-ray equipment. Magnetic field: It is the field around the magnet which attracts or repels other magnets. Magnetic field strength increases with the increase in number of coil turns. Magnetic field strength increases with incretion of iron core. Magnetic field strength increases with increase in current in the coil. But only to a certain level. Application of electromagnets in radiology: 1. Breaks. To hold the x-ray tube & table. 2. Relays. A switch which controls the pass of electrical current. 3. Meter (voltameter, ammeter) a device which measures the mA, s & kv on the control panel. Types of meters: I. Moving iron meter II. Moving coil meter CHAPTER #9 13 Current electricity Alternating current Direct current -The direction changes -one direction for for the flow of current. The flow of current number of cycles/sec. one cycle is one complete waveform. Frequency: it is the number of cycles/sec. unit is Hertz (Hz). 1Hz= 1cycle/sec. Frequency of current is (50Hz or60Hz). Transformer: A device or an equipment which can increase or decrease the voltage and current. Types of transformers used in x-ray units: 1. Autotransformer. 2. Voltage stabilizer. 3. High tension transformers. 4. Filament transformer. CHAPTER #10 Electromagnetic Radiation A steam of photons traveling at the speed of light in an electrostatic and magnetic field. Properties of EMR: 1. Cosmic rays: stars, high energy, background radiation. 2. Gamma rays: radioactive isotopes, NM, high energy, coblat60… 3. X-ray: (soft=low energy), (hard= high energy). 4. Ultraviolet: Sun, causes cancer. 5. Light: sun, fire, lamps. 14 6. 7. 8. Infrared: sun, hot objects , used for muscular pain. Microwave: communication, oven. Radio waves: radar, radio,TV. Intensity: Amount of x-ray in a unit time or a unit area. Factors affecting Intensity: 1. mA Intensity. 2. time “. 3. Kv “. 4. Distance “. 5. filtration “. 6. Atomic number (z) of target “. Factors effecting quality of x-ray: 1. mA No effect on quality. 2. time “. 3. distance “. 4. Kv quality. 5. Filtration quality. Inverse square law: Intensity: amount of x-ray in a unit time or a unit time. Law: The intensity from a source is inversely proportional to the square of the distance. I (intensity) 1/d (distance) I 15 =1/4 I CHAPTER #11 Mechanism of X-ray Production Interaction of electrons at the target (the target is made of ---------. MECHANISM 1: When an incoming electron hits the electron of the tungsten atom, It will give energy to the tungsten electron which will go into higher energy state. When it goes back to its normal energy level ,It will release heat and x-ray. MECHANISM 2: When an incoming electron hits the bound electron in the tungsten atom, It gives some of the energy to the bound electron and will change in direction and interact with another bond electron until it loses all its energy as heat. MECHANISM 3: (Formation of Characteristic x-ray) When an incoming electron hits a bond electron of the tungsten atom, it losses all its energy and produces PHOTOELECTRON. If the bound electron is knocked out of the inner shell then an electron from an outer shell will move to fill the space. In doing so it losses energy as CHARACTERISTIC X-RAY… 16 MECHANISM 4: (Bremsstrahlung Radiation) When an incoming electron interacts with the tungsten atom and has sufficient energy and passes next to the nucleus (which has a +ve charge), it will attract the electron and change its direction without hitting the nucleus. In doing so the energy is converted into heat and xray. 17