Chapters 9 & 10

Photon Emission
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Terms in this set (23)
Photon Emission
Photons are emitted when an atom (or molecule or nucleus) lose energy. Seen in transparent gasses (usually hot). Example—fluorescent light
Thermal Radiation
Light is emitted by warm/hot opaque objects.
Example—incandescent bulb
Emitted by opaque objects. The emission lines
broaden into each other, resulting in a continuous
spectrum. The overall emission carries a signature of
the temperature of the object
Thermal Radiation Laws
Wien's Law (microns, kelvin)
Power (total) = A fancy o T^4
Artificial Lighting (Visable)
Thermal radiation:
Hot = bluer; cool = redder
•Lighting: Incandescent = continuous spectrum, usually "warmer". Most energy is in the infrared and is "wasted".
• Fluorescent = Discrete spectrum, typically 5 color bands
• LED (light emitting diode)—different "color temperatures";
- 7000K = brighter and bluer
- 2700 K = redder (often called "warmer"
Public Lighting Concerns
Street lighting = 30% of all outdoor lighting, so it's important.
LED's are more efficient than sodium vapor lights that have been in use, so municipalities are switchig
Bluer LED's
• Early LED's
• More efficient
• Cheaper
• More glare
•More biological impact; AMA statement
• Impacts Astronomy viewing
Infrared "Night Vision"
"Image enhancers"—enhance visible light
• Long wavelength IR (10 microns)—"thermal imaging"
• Short wavelength IR (0.65-2 microns)—sees reflected
light from IR flashlights— "active illumination"
Military uses: Stinger missiles
Remote controls for TV use IR
Ultraviolet
Reminder: Our atmosphere absorbs a lot of UV, but not all
• Sunburn/Windburn (cell damage)
• Skin cancer (DNA damage)
UV Applications
"Black Light" is another word for an ultraviolet light.
They can be dangerous to look at, depending on the strength and the frequency (UV-A is safer than UV-C)
Fluorescence: UV light is absorbed and induces the
emission of visible light
"Whiter than White" - Laundry detergent has fluorescent dyes—excuse me—optical brightener
Clothes under black light
UV Application Clean Water
Clean water: UV can damage DNA, and prevent bacteria from reproducing. UV Waterworks was inspired by a cholera outbreak in Bangladesh in 1993. It was developed at Lawrence Berkeley National Lab
UV Destroys Viruses
• It probably destroys the novel coronavirus (2019).
• It destroys other coronaviruses.
• It can be used to disinfect surfaces.
• It cannot be injected into the body, nor is the body
transparent to UV
UV - Atmospheric Blocking/Ozone LayerUV from the sun creates Ozone (O3) . • Lower stratosphere, 12-19 miles altitude • Ozone absorbs UV. So, sunlight creates ozone high in the atmosphere, and then the ozone absorbs UV and it doesn't reach the ground. This is good and healthy for peopleThe Ozone Hole and CFCsCFC's, used in aerosol sprays and as refrigerants, began destroying the Ozone in the 1970's, especially Antarctica (cold). • Montreal Protocol 1989 • Mid-latitude recovery will take until 2050 • Antarctic recovery will take until 2075CFCs replaced by HFCs• Current aerosol propellants are mainly hydrocarbons. • CFC's were replaced by HFC's (Hydrofluorocarbons) for refrigeration. Both are greenhouse gasses, 5000/1400 times stronger than CO2. This helps the Ozone levels, but they are not good for climate change. • Note: Concentrations are in parts/trillion, rather than parts/millionKigali Amendment (Rwanda)Kigali Amendment, Oct. 2016: • 197 countries agreed to curb the use of HFC's. • Replacements include •HFO's (hydrofluoroolefins) • "Natural Refrigerants"- CO2, Ammonia, Propane •Which is best depends on the application: •As of 9/21/2020, it has been ratified by 104 countries, but not the USImaging - Medical and OtherIonizing Radiation: - X-ray/Fluoroscopy • CAT Scans/CT Scans • Molecular Imaging: PET/SPECT Scans Non-Ionizing Radiation: • MRI • Thermography (done) • Ultrasound -X-Ray backscatterImaging: X-RaysConventional x-rays = radiography Note: Digital x-rays have improved significantly since the text was written and are now preferred to photographic x-rays. Medical images: Bones, teeth, mammograms, bone density scans Other uses: Aerospace—used to detect tiny cracks and defects Security—used to inspect packages, especially for heavy elementsImaging: FluoroscopyX-ray "movie" • Track the movement of an instrument: e.g., placing a stent or catheter) • Track the movement of a contrast agent (or dye) • The dye is denser and absorbs more x-rays • Angiograms use iodine to view blood vessels and blood flow • Barium is used to view the intestinal tractImaging: CAT Scans• CAT Scan: Computer Aided Tomography • X-rays are taken from many different directions, and a 3-D image is constructed • Contrast can be enhanced in regions with no bone • Dose can be high • With or without contrastImaging: PET ScansPET scans: Positron Emission Tomography • Uses radioactive material that emits positrons (anti electrons) —falls under Nuclear Medicine • Each positron annihilates with an electron, and two gamma rays are emitted • The gammas are detected • The distribution of the radioactive material is constructedImaging: MRIMRI—Magnetic Resonance Imaging (Nuclear Magnetic Resonance) • Protons have a magnetic property—they behave like tiny magnets. • Strong magnet aligns the protons • A perpendicular field causes the spins to rotate • A detector picks up the rotationImaging: UltrasoundReally doesn't belong in this chapter—it uses high frequency sound, not light. Ultrasound of breast malignancy— note the indistinct boundary and invasion into surrounding tissue, which are typical of a malignancy. (cancer : crab-like)Imaging: X-Ray BackscatterWhen x-rays do not penetrate, they can be absorbed, or they can bounce back (reflect, kind of like a mirror). We can detect the x-rays that bounce back and create an imageClimate ChangeGreenhouse Effect - the effect of our atmosphere on the temperature of the earth Global Warming - temperature change due the change in Greenhouse Effect (direct and indirect) Climate Change -secondary effects of warming, and other non-temperature effects