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![Characteristics of Waves
Amplitude – x [m]
Wavelength – l [m]
Period -T [s]
Wave Speed – c [m/s]
Frequency – n [1/s=Hz]
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Basic physics of ionizing radiation I.pdf
- 1. Biophysics in Radiology and Nuclearmedicine dejan.zikic@med.bg.ac.rs dzikic@gmail.com
- 2. Basic physics ofionizing radiation ◼ Electromagnetic waves ◼ Atomic Structure ◼ Nuclear stability ◼ Radioactive decay 2
- 3. What is Radiation? ◼Form of energy ◼ Emitted by nucleus of atom or orbital electron ◼ Released in form of electromagnetic waves or particles 3
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- 7. Types of wavesin physics ◼ Transverse waves - particle vibration is perpendicular to the direction of wave propagation 7
- 8. Types of wavesin physics ◼ Longitudinal waves - particle vibrating parallel to the direction of wave propagation 8
- 9. Characteristics of Waves Amplitude– x [m] Wavelength – l [m] Period -T [s] Wave Speed – c [m/s] Frequency – n [1/s=Hz] 9
- 10. By the nature oforigin mechanical electromagnetic By way of creation Transverse Longitudinal Classification: 10
- 11. By way ofpropagation line plane spherical 11
- 12. Electromagnetic Waves… ◼ Donot need matter to transfer energy. ◼ Are made by vibrating electric charges and can travel through space by transferring energy between vibrating electric and magnetic fields. 12
- 13. How do movingcharges create magnetic fields? ◼ Any moving electric charge is surrounded by an electric field and a magnetic field. 13
- 14. What happens whenelectric and magnetic fields change? E 14
- 15. • Electric andmagnetic fields are perpendicular to the direction of wave propagation • The electric field is perpendicular to the magnetic field • Transversal waves 15
- 16. Properties of EMWaves ◼ All matter contains charged particles that are always moving; therefore, all objects emit EM waves. ◼ The wavelengths become shorter as the temperature of the material increases. ◼ EM waves carry radiant energy (the energy of electromagnetic radiation). 16
- 17. What is thespeed of EM waves? ◼ All EM waves travel 300,000 km/sec in space. (speed of light- nature’s limit!) ◼ EM waves usually travel slowest in solids and fastest in gases. Material Speed (km/s) Vacuum 300,000 Air <300,000 Water 226,000 Glass 200,000 Diamond 124,000 17
- 18. Can a wavebe a particle? ◼ In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected. ◼ Whether or not electrons were ejected depended upon frequency not the amplitude of the light! 18
- 19. Can a wavebe a particle? ◼ Years later, Albert Einstein explained Hertz’s discovery: EM waves can behave as a particle called a photon whose energy depends on the frequency of the waves. E=hn 19
- 20. The whole rangeof EM wave… ◼ frequencies is called the electromagnetic spectrum. ◼ EM spectrum includes all EM waves. ◼ Different parts interact with matter in different ways. 20
- 21. The whole rangeof EM wave… ◼ Nature of EM waves is the same, but their energies and frequencies are different and in a wide range. ◼ Sources of EM waves are very different, but still represent a change in the energies of charge. ◼ The frequencies that humans can see are called visible light, a small part of the whole spectrum. 21
- 22. As wavelength decreases, frequencyincreases… 22
- 23. Radio waves ◼ Radiowaves are low frequency EM waves with wavelengths 1mm - km ◼ Antenna – detects radio waves ◼ These waves must be turned into sound waves by a radio before you can hear them. 23
- 24. Microwaves ◼ Microwaves areradio waves with wavelengths 1mm – 1m ◼ Communications frequencies ◼ Cell phones and satellites use microwaves between 1 cm & 20 cm for communication. 24
- 25. Microwaves ◼ In microwaveovens, a vibrating electric field causes water molecules to rotate billions of times per second causing friction which heats the food. 25
- 26. Infrared Waves ◼ Everyobjects gives off infrared waves; 26
- 27. Infrared Waves ◼ EMwith wavelengths between 1mm & 760 nm. ◼ Used daily in remote controls 27
- 28. Visible Light ◼ Rangeof EM humans can see from 760 nm to 380 nm. 28
- 29. Ultraviolet Waves ◼ EMwaves with wavelengths from about 10nm – 380nm ◼ Have enough energy to enter skin cells Longer wavelengths – UVA Shorter wavelengths – UVB rays Both can cause skin cancer 29
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- 31. Can UV radiationbe useful? ◼ Helps body make vitamin D for healthy bones and teeth ◼ Used to sterilize medical supplies & equip ◼ Detectives use fluorescent powder (absorbs UV & glows) to find fingerprints 31
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- 33. X Rays ◼ EMwaves 0.01nm – 10nm ◼ High Energy- go through skin & muscle ◼ High level exposure causes cancer 33
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- 35. Gamma Rays ◼ EMwith wavelengths shorter than < 0,01nm ◼ Highest energy, can travel through several centimeters of lead. ◼ Both can be used in radiation therapy to kill diseased cells. ◼ The composite image shows the all sky gamma ray background. 35