Module content PHYS1004 Environmental: Module 3 - Radiation Hecht Physics: Calculus 2nd Ed Radiant Energy; Light Evolution of Quantum Theory • Chapter 29: Quantum Mechanics • HRW Ch 40: More about Matter Waves • Chapter 29: Atomic Structure • Chapter 30: Nuclear Physics • Chapter 27: Biological Effects of Radiation • Chapter 22: • Chapter 28: 14 lectures Dr Stephen Bosi Room 444; ph: 9351-4862 Press buzzer by door to Applied Lab room 404 opposite LT1 s.bosi@physics.usyd.edu.au Overheads available @ Copy Centre, WebCT & See module handout for details & suggested problems http://www.physics.usyd.edu.au/~sgb Environmental: Radiation Module 2 What is radiation? • “Radiation” means a disturbance that propagates outwards from a source • Examples of radiation: • Sound • Electromagnetic Radiation RADIANT ENERGY: LIGHT radio, microwaves, IR, visible light, UV, X-rays, #-rays Chapter 22 Hecht: Calculus 2nd ed. • Ionising Radiation high energy EM; X-rays, #-rays (again!?) energetic charged particles; $-rays, %-rays energetic uncharged; neutrons (not directly ionising) Environmental: Radiation Module 3 Electromagnetic radiation Electromagnetic radiation • EM waves predicted by Maxwell (Maxwell’s equations) • EM waves travel at c = 3 ! 108 m/s (in vacuum) The wavelength-frequency relation: c = f " Is light waves or particles? • EM waves produced by non-uniform motion of charges “Photons” are particles or EM radiation each with an energy E given by; • E field & B field are perpendicular Hecht §22.3 & 22.5 • Wavelike: When spread out in space & time • Particle-like: When confined to small spaces or times e.g. when being absorbed or emitted by particles E=hf (f = frequency, h = 6.63 ! 10-34 J/Hz Planck’s constant) More on this later! Environmental: Radiation Module 5 Hecht §22.6 Environmental: Radiation Module 6 How an atom produces light Continuum vs Line spectra Atom absorbs energy from outside world (e.g. through collisions or by absorbing light from elsewhere) • Previous mechanism is the simplest & yields "line spectra" • This raises e- to an “orbit” of higher • More complicated mechanisms involving many atoms can lead to "continuum spectra" • "Absorption spectrum" e.g. discovery of helium energy E2 (picture a) • e- drops back to “orbit” of lower energy E1. The excess energy is converted to a photon of light (picture b) Photon energy &E = h f where &E = E2 - E1 Same thing happens in reverse when photon is absorbed by an atom. Hecht §22.7 Environmental: Radiation Module 8 The Electromagnetic Spectrum Continuum vs Line spectra Continuum emission Environmental: Radiation Module 7 Line emission Line absorption Environmental: Radiation Module 9 Hecht §22.7 Environmental: Radiation Module 10 Quick overview of EM spectrum... Radio waves ~0.3m < " < ' • Produced by oscillating e- currents Quick overview of EM spectrum... Microwaves ~1mm < " < ~0.3m • Produced by e circulating in mag field. • Used for communication; Radio broadcast, TV, mobile phones etc. Longer wavelengths reflect off ionosphere. • 2 ways to send information using radio waves • Penetrates atmosphere so used for radio astronomy & satellite communication. Mobile phones and radar AM - amplitude modulation Hecht §22.8 FM - frequency modulation Environmental: Radiation Module 11 • Radio waves and microwaves detected by an "antenna" or "aerial" • Can heat up water molecules by causing them to rotate rapidly therefore reheating your moist & juicy meat pie.. mmm.. 2.45GHz Hecht §22.9 Environmental: Radiation Module 12 Quick overview of EM spectrum... Infrared 780nm < " < ~1mm • Produced by vibrating and rotating molecules • Emitted by warm bodies. e.g. Nightvision goggles • Detected by some semiconductors, bolometers, thermopiles and skin • TV remote controls use IR • Most of the energy in sunlight is in the IR Hecht §22.10 Environmental: Radiation Module 13 • Produced by very hot bodies, plasmas, lasers. • Detected by semiconductors, photoelectric cells, photomultipliers, fluorescent dyes, photographic film & bird or insect eyes • Energetic enough to ionise some atoms and break bonds - damages proteins and DNA (skin cancer) • Forms O3 (ozone) from O2 (ozone layer) • Forms Vitamin D in human skin Environmental: Radiation Module 15 Quick overview of EM spectrum... Gamma (#) rays 0 < " < ~10pm • Produced by nuclear reactions and matter+antimatter • Radioactive sources (e.g. Cobalt 60), particle accelerators • Detected by geiger tube, photographic film or scintillation • Penetrates most materials • Severely damages proteins & DNA (leukaemia, bone cancer) • Sometimes used to sterilise medical apparatus • Gamma & X-ray both used to treat cancer (radiotherapy) • Overlaps with X-rays, arbitrary boundary Hecht §22.14 Environmental: Radiation Module • Produced by hot bodies, semiconductors, plasmas, lasers, fluorescence etc. • Detected by semiconductors, photoelectric cells, photomultipliers, photographic film and eyes • Energy source of almost all biology • Eyes have one non-colour receptor cells (rods) & three different coloursensitive cells (cones) hence only 3 primary colours needed Quick overview of EM spectrum... Ultraviolet ~10nm < " < 390nm • Produced by outer/inner e- dropping to lower E orbits Hecht §22.12 Quick overview of EM spectrum... Visible Light 390nm < " < 780nm • Produced by outer e- dropping to lower E orbits X-ray therapy Gamma therapy 17 Hecht §22.11 Environmental: Radiation Module 14 Quick overview of EM spectrum... X-rays ~10pm < " < ~10nm • Produced by innermost e- dropping orbits & rapid braking or acceleration of fast e• X-ray tube, synchrotron & accelerator sources • Detected by geiger tube, photographic film or scintillation • Penetrates low density material • Damages proteins & DNA (leukaemia, bone cancer) but also kills cancer cells • Small "; X-ray diffraction "sees" structure of crystals (atom spacing ~10-10m) • Can be used to identify elements in electron microscopes Hecht §22.13 Environmental: Radiation Module 16