l 36 — modern physics [2]
DESCRIPTION
L 36 — Modern Physics [2]. X-rays & gamma rays How lasers work Medical applications of lasers Applications of high power lasers Medical imaging techniques CAT scans MRI’s. The Photon Concept. a beam of light waves also behaves like a beam of light particles called PHOTONS - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/1.jpg)
L 36 — Modern Physics [2]
• X-rays & gamma rays• How lasers work
– Medical applications of lasers– Applications of high power lasers
• Medical imaging techniques– CAT scans– MRI’s
![Page 2: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/2.jpg)
The Photon Concept• a beam of light waves also behaves like a beam
of light particles called PHOTONS• Photons are little packets of electro-magnetic
energy • The energy is proportional to the frequency or
inversely proportional to the wavelength• Ephoton = h f, but c = f so Ephoton = h c/,• where h is a constant called Planck’s constant,
and c is the speed of light• blue photons have more energy than red
photons
![Page 3: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/3.jpg)
X-ray and gamma ray photons• x-rays are very short wavelength photons• gamma rays are have even shorter wavelengths
![Page 4: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/4.jpg)
How are x-rays produced?
electron gun
coppertarget
x-rays
• when electrons that have been accelerated through about 50,000 volts slam into a piece of copper, some of the electron energy is converted to x-rays• x-rays are energetic enough to penetrate through soft tissue and thin metal foils
x-ray tube
![Page 5: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/5.jpg)
Gamma rays
• extremely energetic photons• constantly bombard the earth• cosmic rays • emitted by radioactive materials• x ray photons are a 1000 times more
energetic than visible light photons• gamma ray photons are 1,000,000 more
energetic than visible light photons
![Page 6: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/6.jpg)
Lasers a device that controls the way that energized atoms release photons.
• First we must understand the difference between incoherent and coherent radiation
• Ordinary light sources (light bulbs, fluorescent lights, etc) produce incoherent light
• lasers produce coherent light all atoms radiate in the same manner
![Page 7: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/7.jpg)
Spontaneous vs Stimulated Emission • Coherent radiation is
produced when an atom undergoes stimulated emission.
• Spontaneous emission occurs when an electron makes an unprovoked transition to a lower energy level
• Stimulated emission occurs when an incoming photon induces the electron to change energy levels amplification
Ei (larger energy)
Ef (smaller energy)Spontaneous emission
Stimulated emission
Incomingphoton
photon
![Page 8: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/8.jpg)
A Helium-Neon (HeNe) Laser
![Page 9: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/9.jpg)
Medical Applications of Lasers
Laser surgery to correct for(a) nearsightedness, and(b) farsightedness
![Page 10: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/10.jpg)
Applications of High Power Lasers
Using lasers toCut metals
![Page 11: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/11.jpg)
Multiple beams of a powerful laser are focusedon a tiny pellet containing fusion fuel. The laser energy compresses the pellet producing a mini-hydrogen bomb that produces energy
Laser Fusion Energy
fuel pellet1 mm diameter
![Page 12: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/12.jpg)
pellet
500 Trillion Watts of light power
5000 times average US power
as much energy on a 1 mmtarget as a 2000 lb carmoving at 60 mph.
![Page 13: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/13.jpg)
Solid State Laser Diodes
small
Come in a variety ofdifferent colors
![Page 14: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/14.jpg)
Lasers Diodes• Diode lasers use semiconductor materials
(tiny chips of silicon) as the lasing media• When current flows through the silicon
chip it emits an intense beam of coherent light.
• Diode lasers are used to read the information embedded in the pits in CD’s and DVD’s, and also to read UPC’s in bar code scanners and in laser pointers!
![Page 15: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/15.jpg)
Laser speed guns
• these are replacing “radar” guns• the gun sends out a series of pulses of
infrared laser light that bounce off the car and return to the gun.
• by measuring the time for the pulse to return the distance to the car can be measured
• the speed of the car is determined by two consecutive measurements of the distance
![Page 16: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/16.jpg)
time t1
position x1
time t2
position x2
2 1
2 1
x xspeedt t
![Page 17: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/17.jpg)
How does a CD burner Work?• http://computer.howstuffworks.com/cd-burner4.htm • infrared laser light is applied to a layer of
photosensitive dye on top of the plastic• this causes the dye to darken (no burning!)• by selectively darkening particular points
along the CD track, and leaving other areas of dye translucent, a digital pattern is created that can be read by a standard CD player
![Page 18: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/18.jpg)
Medical Imaging Techniques
• x-rays• CT and CAT scans (Computerized
Tomography)• MRI’s (Magnetic Resonance Imaging)
![Page 19: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/19.jpg)
X-rays• very short wavelength
(0.01 – 0.1 nm) electromagnetic waves
• produced when energetic electrons slam into a metal target
• able to penetrate soft tissue, but not bone
• produces a two dimensional shadow imagex-ray of Homer’s head
![Page 20: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/20.jpg)
A pineapple and a banana• A shadow image can be
misleading• two shadows taken from
different angles provides a better picture
• shadows taken at multiple angles gives a more complete picture
• this is what a CT or CAT scan does
![Page 21: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/21.jpg)
CAT Scans
X ray images are taken at many different anglespassing through the patient. Some of the cuts overlap. A full three dimensional image can be reconstructed using computers. this procedure is called tomography.
![Page 22: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/22.jpg)
Computerized Tomography• A computerized tomography
or CT scan image is formed by analyzing x-ray shadow images taken at many different angles and positions
• an x-ray source and an array of electronic detectors rotates around the patient as the patient slowly moves through the ring.
![Page 23: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/23.jpg)
![Page 24: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/24.jpg)
Is there a better medical diagnostic?• A CAT scan does a good job of imaging
bones, but it does not provide as good an image of soft tissue
• Also, it requires that the patient receives a big dose of x-rays, which can be harmful in themselves it is an invasive diagnostic
• Magnetic resonance imaging (MRI) is a better method of imaging soft tissue
![Page 25: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/25.jpg)
MRI- how does it work?• MRI works by locating the hydrogen atoms
inside the body. Since the body is mostly water, there are lots of hydrogen atoms
• the nucleus of a hydrogen atom is a single proton. Protons behave like tiny bar magnets with a north pole at one end and a south pole at the other end.
• If you put a bar magnet in a magnetic field, it will try to align itself with the field.
![Page 26: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/26.jpg)
A bar magnet in a magnetic field
N
S
magnetic field
NS
Solenoid for producing a strong magnetic field by passing a large current
through a set of coils
![Page 27: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/27.jpg)
Magnetic Resonance Imaging• The rules of atomic physics (quantum
mechanics) require that the atomic hydrogen bar magnets can only have 2 orientations when placed in a magnetic field either parallel or antiparallel to it, we call this spin-up or spin-down
spin-up spin-down
magneticfield
protons
![Page 28: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/28.jpg)
Magnetic Resonance• Protons have a “spin” that can be either
“up” or “down” relative to the direction of the magnetic field
• If radio waves (FM) hit the protons, it can cause it them to flip from one spin state to the other at a frequency that depends on the strength of the magnetic field
• These spin flips result in the absorption or release of radio wave energy that can be detected electronically
![Page 29: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/29.jpg)
Magnetic Resonance Imaging• In effect, the magnetic field makes the
protons act like tiny radio transmitters that only broadcast their signal when the value of the magnetic field is just right
• By varying the strength of the magnetic field as a function of position in the body, the spin flips can be detected in various parts of the body
• A computer is used to combine the signals from various parts of the body to generate detailed cross-sectional images
![Page 30: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/30.jpg)
MRI DEVICE
![Page 31: L 36 — Modern Physics [2]](https://reader035.vdocument.in/reader035/viewer/2022062305/56816388550346895dd47608/html5/thumbnails/31.jpg)
MRI safety considerations• The magnetic field used in MRI are very
strong – 30,000 times the strength of the earth’s magnetic field.
• Because the magnet coils are cooled to liquid helium temperatures, they are usually kept on all the time
• Because the magnetic field is on, all iron and steel objects must not be allowed to enter the room. http://www.mercola.com/2001/aug/15/mri.htm