Roent Lec 1 NATURE OF THE ATOMHistorical Background - Matter is a physical manifestation possessing mass (occupies space and has weight) and having form or - X-rays were discovered in Nov. 8, 1895 by William shape. Konrad Roentgen (pronounced as “rentken”) - Elements are simple substances that cannot be - He pioneered 3 keys areas of x-ray imaging: decomposed by ordinary means. 1. An x-ray photograph of his closed wooden box - There are 105 known elements at present. of weights clearly revealed its contents, thus - The atom is the smallest particle of an element that presaging the security application found at has characteristic properties of that element. every airport check-in. - Each atom consists of a small nucleus, which has a 2. An x-ray image of his hunting rifle revealed a positive charge and a number of lighter particles flaw inside the metal of the gun. This was the with negative charges called electrons, which move first time a hidden structural flaw had been around the nucleus in definite orbits. exposed without destroying the object. - The atom is said to be neutral when the net number 3. of positive charges of the nucleus (protons) equals 4. He took a permanent x-ray photograph of his the negative charges of the orbital electrons. wife Bertha’s left hand, revealing the bones and - The closer of the electrons to the nucleus, the higher the rings that she was wearing. energy level. - The electrons are kept in their orbits by the balance between: 1. The electrostatic attraction of unlike charges. 2. The centrifugal forces of the fast moving electrons. ATOMIC NUMBER - The atomic number, or Z number, is the no. of …(taken: January 1896 by Roentgen) protons in the nucleus or the no. of electrons outside the nucleus. - Z number range from 1 for the simplest atom -The hand of the cadaver, they injected (Hydrogen) to 105 for the most complex atom yet mercury that reveals the architecture of discovered (Hahnium). the hand. Orbital Electrons - Electrons are very small particles carrying 1 unit of Amputated negative charge. hand after - They revolve around the nucleus in well-defined exposure to shells that exist at varying distances from the too much radiation nucleus. for 5 years.- - A maximum no. of seven potential electron- containing orbits or shells are designated as K,L,M,N,O,P and Q in order of increasing distance from the nucleus.- Roentgen was awarded the first Nobel Prize for Physics in - Electrons in the 1901. most outermost- Roentgen announced to the word the discovery of the shell are termed new kind of ray in 1895; he called it the “X-ray” after the valence electrons algebraic symbol for unknown. and determine the- Otto Walkhoff, DDS, MD completed the first dental chemical radiograph ever med in January 14, 1896. properties of the- Dr. Otto Walkhoff- first dental radiograph 25minute atom. exposure (< 0.5 seconds today).
electron has a negative charge (-1) thus, an ion pairELECTRON ORBITS OR SHELLS has been formed. - The electrons in an atom do not spontaneously fly off from the nucleus by centrifugal force or, on the IONIZING RADIATION other hand, drop into the nucleus by electrostatic Types of Ionizing Radiation attraction (unlike charges attract), because in the -Corpuscular or Particulate radiation normal atom there is a balance between centrifugal - Electromagnetic radiation and electrostatic force. - This balance results in a definite electron path or PARTICULATE RADIATION orbit for each electron around the nucleus. - Particulate radiations are actually minute particles of - Each shell has a different energy level which is matter that travel in straight lines at high speeds dependent on the atomic no. of the atom and from their sources. distances the electron from the nucleus. - Although incredibly small, they possess mass. - The attractions force is greater when the electron - All are charge electrically, except neutrons, and they shell is nearer the nucleus. all move extremely fast- sometimes as fast as light. - Thus, it would require more work (energy) to - Alpha Particles are composed of a combination of remove an electron from the K shell and out of range two protons and two neutrons. of the nuclear electric field than to remove an - It is the helium nucleus without orbital electrons. electron from one of the outer shells. - Alpha particles are emitted only from the nuclei of BINDING ENERGIES heavy metals. - The energy required to remove an electron from a - Compared with the other particles, the alpha particle particular shell is designated as binding energy of is enormous and exerts a large electrostatic that shell. attraction. - The binding energy is characteristic of a given - They have little ability to penetrate tissues and give element and shell. up their large energies within a very short distance in - This is the kinetic energy of an electron accelerated air (5cm) and in soft tissue (100 um). through a potential difference of 1 volt. - Beta Particles (Negatrons) are emitted from the - Larger multiple units of the electron volt are nucleus of radioactive atoms and possess 1 unit of frequently used: kcV for 1000 or kiloelectron volts, negative charge. and McV for 1 million or megaelectron volts. - They have very small atomic masses. - Beta particles more penetrating that alpha particlesIONIZATION and may penetrate 10- 100 cm of air and - Ionization is the process by which a neutral atom or approximately 1-2 cm of the soft tissue. molecule acquires either a positive or a negative - Cathode Rays (Electrons) are streams of electrons charge. passing from the hot filament of the cathode to the - When an atom losses or gains an electron, it is said target of the anode in an x-ray tube. to be ionized. - Beta particles come from the nucleus of radioactive - An ionized atom (called an ion) is not electrically atoms, whereas the cathode rays originated from neutral but carries a charge equal to the difference the orbital electrons of the atoms of the filament between the number of protons and electrons. material for an x-ray tube. - An atom that is not electrically balanced is called an - Protons are accelerated hydrogen nuclei. ion. - Because protons are heavy, charged particles, the - In any ionization process, ion pairs are formed; it is lose kinetic energy as they penetrate matter. this process that elicits chemical changes in matter. - Neutrons carry no electron- charge and have nearly - When an x-ray transfers its energy to an orbital the same mass as a proton. electron, it ejects it from the atom, and an ion pair is - The characteristic if being electrically neutral has formed. proved of great importance in nuclear physics - The atom becomes a positive ion (=1 charges because such a particle can penetrate into the because it has lost an electron and the ejected nucleus of an atom without being subjected to e
enormous forces of a positively charged particle. 9. They cause fluorescence of certain crystals. 10. They affect photographic film (producing a latent image which can be developed chemically). ELECTROMAGNETIC RADIATION 11. They produce chemical and biologic changes (this is - X-rays and gamma rays belong to a group of essential biologic cell damage and treatment of radiation called electromagnetic radiations. malignancies, these biologic changes depend o n - Electromagnetic radiation is the propagation of ionizations). energy through space accompanied by electric and magnetic force fields. WAVE CONCPET OF ELECTROMAGNETIC RADIATION - X-rays and gamma rays belong to a group of radiation called electromagnetic radiation. - Electromagnetic radiation is the propagation of - X-rays are produced outside the nucleus in the wave-like energy through space or mass at the speed 4 electron orbital system. of light (186, 000 miles per second or 3 x 10 m/sec). - Gamma rays are emitted from the nucleus of a - It is called electromagnetic radiation because the radionuclide. energy that is radiated is accompanied by oscillating electric and magnetic fields. PARTICULATE and ELECTROMAGNETIC RADIATION EXAMPLES OF ELECTROMAGNETIC RADIATION - The radio wave that we hear. - The light waves we see. - The infrared waves that can take pictures in the dark. - The ultraviolet rays that cause sunburn. - The x-rays. - The gamma rays of the atomic bombs. - The cosmic rays that hinder travel in space. NATURE OF X-RAYS Electromagnetic waves need no such medium as - The wave concept of electromagnetic radiation they can be propagated within and transmitted explains why it may be reflected, refracted, through a vacuum. diffracted and polarized. All waves have an associated wavelength and - The particle concept is used to describe the frequency. interaction between radiation and matter. The wavelength of a wave is the distance between two successive crests or valley, and is given theX-RAY PROPERTIES symbol λ (the Greek letter lambda, the symbol for 1. They are weightless packages of pure energy length). (photons) without an electrical charge which travel in waves with specific frequency at speed of 186, - The 000 miles per second (speed of light). no. of waves 2. Invisible, highly penetrating waves (electromagnetic passing a waves). particular 3. Electrically neutral (cannot be deflected by electrical point during or magnetic fields). a specific 4. Wide useful range of wavelengths in medicine and period is dentistry = 0.01 is equal to 1 billionth of a meter). called the 5. Most beams of x-rays are heterogeneous (consisting frequency of rays of many different wavelengths). and I given 6. They emerge from the tube in straight lines, the symbol λ diverging form the focus of the target of the anode. (the Greek 7. They are capable of ionizing gases because of their letter nu, the symbol for number). ability to remove orbital electrons from atoms. - It is usually identified as oscillations per second or 8. They travel as the same speed as light (1866, 000 cycles per second. miles per second in a vacuum). - The unit of frequency measurement is the hertz (Hz).
- One hertz equals 1 cycle/ sec and 80 Hz is the long waves are in the radio region of the standard 60 cycle/ sec. electromagnetic spectrum. Dangers: THE ELECTROMAGNETIC SPECTRUM - Large doses of radio wavesare believed to cause cancer, leukaemia and other disorders. What are electromagnetic waves? - Some people claim that the very low frequency field - All forms of electromagnetic radiation are grouped from overhead power cables near their homes has according to their wavelengths in what is called the affected their health. electromagnetic spectrum. - All have no mass, no electrical charge and travel with MICROWAVES wave motion. - Microwaves are basically extremely high frequency - Electricity can be static like what a balloon to the wall or radio waves, and are made by various types of makes your hair stand on end. Magnetism can also be transmitter in a mobile phone, they’re made by static like a refrigerator magnet. But when they change or move together, they make waves electromagnetic a transmitter chip and an antenna, in a waves. microwave oven they’re made by a - Electromagnetic waves are formed when an electric “magnetron”. Their wavelength is usually a field (blue arrows) couples with a magnetic field (red couple of centimetres. Stars also give off arrows). Magnetic and electric fields of an microwaves. electromagnetic wave are perpendicular to each other Uses: and to the direction of the wave. - Microwaves cause water and fat molecules to vibrate which makes the substances hot. Thus we can use microwaves to cook many types of food. - Microwaves have wavelengths that can be measured in centimetres. The longer microwaves, those closer to a foot in length, are the waves which heat our food in a microwave oven. - Microwaves are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, THE ELECTROMAGNETIC SPECTRUM clouds and smoke. Rabbits Radio - Shorter microwaves are used in remote sensing. Mate Microwaves These microwaves are used for radar like the In Infra-Red doppler radar used in weather forecasts. Very Visible light - Microwaves, used for radar, are just a few inches Unusual Ultra-violet long. This microwave tower can transmit information eXpensive X-rays like telephone and computer data from one city to Gardens Gamma rays another. - Because microwaves can penetrate haze, light rain,RADIO WAVES snow, clouds and smoke, these waves are good for - Radio waves are made by various types of viewing the earth from space. transmitter depending on the wavelength. They are - Mobile phones use microwaves as they can be also given off by stars sparks and lightning which is generated by asmall antenna which means that the why you hear interference on your radio in a phone doesn’t need to be very big. The drawback is thunderstorm. that, being small, they can’t put out much power and - Objects in space, such as planets and comets, giant they also need a line of sight to the transmitter. Thus clouds of gas and dust, and stars and galaxies, emit means that mobile phone companies need to have light at many different wavelengths. many … - Some of the light they emit has very large wavelengths (sometimes as long as a mile). These
Dangers: - Each color has a different wavelength. - Prolonged exposure to microwaves is known to - Red has the longest wavelength and violet has the cause “cataracts” in your eyes which is a clouding of shortest wavelength. lens preventing you from seeing clearly (if at all!). So - When all the waves are seen together they make don’t make a habit of pressing your face against the white light. microwave oven door to see if your food’s ready! - When the white light shines through a prism or - People work on aircraft carnet decks wears special through water vapour like the rainbow, the white suits which reflect microwaves to avoid being light is broken apart into the colors of the visible “cooked” by the powerful radar units in modern light spectrum. military planes. - The light which our eyes can detect as part of the visible spectrum (small).INFRA-RED - There is a lot of radiation around us which is - Infra-red waves are just below visible red light in the “invisible” in our eyes but can be detected by other electromagnetic spectrum (“intra” means “below”). remote sensing? instruments and used to our - You probably think of infra-red waves as heat advantage. because they’re given off by hot objects and you can - The visible wavelengths cover a range from feel them as warmth in your skin. approximately 0.4 to 0.77 mm (violet to red). - Infra-red waves are also given off by stars, lamps, flames and anything else that’s warm- including you. Uses: -Infra-red waves are called IR for short. They are used for many tasks, for example, remote controls for TVs, and video recorders and physiotherapists use heat lamps to help heal sports injuries. - Shorter, near infrared waves are not hot at all- in fact you cannot even feel them. These shorter wavelengths RADIATION are the ones used in your TV’s remote control. Dangers: The warmer the object, the more infrared radiation it - Too much light can damage the retina in your eye. emits. - This can happen when you look at something very bright, such as the sun. - Because every object gives off IR waves, we can use - Although the damage can heal, if it’s too bad, it’ll be them “to see in the dark. Night sights for weapons permanent. sometimes use a sensitive IR detector. - Gas infrared waves are thermal. In other words, we ULTRAVIOLET experience the type of infrared radiation every day in the form of heat! The heat that we feel from the -Ultra-violet sunlight, a fire, a warm sidewalk are infrared. light is made by - You’ve probably seen TV programmes in which the special lamps, police helicopter track criminals at night using for example, on cameras which can see in the dark. These cameras sun beds. use IR instead of “ordinary light” which is why -It is also given people look bright in pictures. off by the sun in largeDangers; quantities. - The danger from too much infra-red radiation is very - We call it UV. simple, overheating.VISIBLE LIGHT Uses: - Sun tan - Visible light waves are the only electromagnetic - Detecting fake money waves we can see. - Light sure composite - We see these waves as the colors of the rainbow.
- UV in discos (glow in the dark) - The amount of energy carried by each quantum photon - Sterilization depends on the frequency of the radiation. - Sunlight (vitamin D) - If the frequency (vibrations per second) is doubled, the The OZONE layer protects the earth from the heat of energy of the photon is doubled. the sun. - The unit used to measure the energy of photons is the Filters about 95% of heat. electron-volt (eV). Only 5% heat UV reaches earth’s surface. WHAT ARE X-RAYS?Dangers: - X-rays are weightless packages of pure energy - Sunburn- basal cell CA (photon) that have no electrical charge and travel in - Cataract- blindness waves with specific frequency at a speed of 3 x 108 m/sec.X-RAYS - Their energies depend on the frequency of theirUses: wavelengths. - MRI, CT-scan - The greater the frequency of their wavelength, the - Intra-oral x-rays greater the energy of the photon. - A drink of barium sulphate. This will absorb x-rays, - The greater the energy of the photon, the more and so the patient’s intestines will show up clearly readily it will penetrate matter. on an x-ray image PROPERTIES OF X-RAYSGAMMA RAYS - X-rays are invisible and weightless; they cannot be - They have the smallest wavelengths and the most seen, felt or smelled. energy of any other wave in the electromagnetic - X-rays travel in straight lines, they can be deflected spectrum. from their original direction but the new trajectory is - These waves are generated by radioactive atoms and linear. in nuclear explosions. 8. - X-rays travel at the speed to light (3 x 10 ? m/sec). - Gamma-rays can kill living cells, a fact which - X-rays have a wide range of wavelengths, 0.01- 0.05 medicine uses to its advantage using gamma rays to nm in length. kills cancerous cells. - X-rays cannot be focused to a point over distance Radioactivity is particularly damaging to rapidly the beam diverges much like a beam of light. dividing cells, such as cancer cells. - Because of their extremely hot wavelengths, they This also explains why damage is done by are able to penetrate materials that absorb and radiotherapy to other rapidly dividing cells in reflect visible light. the body such as the stomach lining (hence - X-rays cause certain substances to fluoresce, that is nausea), hair follicles (hair tends to fall out) and to emit radiation of longer wavelength (it is this a growing fetus (not because of mutations, but property that makes it possible to use intensifying simply major damage to the baby’s rapidly screens in radiography. dividing cells). - X-rays produce biological changes that are valuableDangers: in radiation therapy but necessitate caution when - Gamma rays cause cell damage and can cause a used for diagnostic purposes. variety of cancers. - X-rays can ionize gases that is remove electrons from - Cause mutations in growing foetuses, so unborn atoms to form ions, which can be used for measuring babies are especially vulnerable. the controlling exposure (ionization chambers).PARTICLE CONCEPT OF ELECTROMAGNETIC RADIATION-Short electromagnetic waves, such as x-rays, may react withmatter as if they were particles rather than waves.- These particles are actually discrete bundles of energyhaving no mass, and each of these bundles of energy is calledquantum or photon.- These photon travel at the speed of light.