Exercise 2: The electromagnetic spectrum and particle radiation

Transcription

1 Astronomy 102 Name: Exercise 2: The electromagnetic spectrum and particle radiation Purpose: In this exercise, you will gain perspective on the types (and amounts) of shielding necessary to provide protection against different types of radiation. This exercise has two parts, in which we will explore light as an electromagnetic radiation (and how to block various parts of the EM spectrum), as well as the characteristic behavior of other types of radiation (and shielding for these, too Needed: The sodium lamp, a Bunsen burner, a crystal of sodium chloride salt, tongs 1. Turn on the sodium lamp, and note the color that you see. Compare this color to the sodium emission shown on the chart in the classroom; what wavelength (in nm) is most likely the source of the color you see? 2. The instructor will hold a sodium chloride crystal in the Bunsen burner flame, such that the crystal is in the line of sight between you and the sodium lamp. What do you see? Why is this happening? Needed: The plasma ball, fluorescent light tube, other materials as needed The plasma ball is a small version of the Tesla coil, an invention of Nikola Tesla, a Serbian-American engineer, who, in 1891, envisioned it as a way to deliver electricity. 3. Turn on the plasma ball. Obviously, what part of the EM spectrum (shown above) is being emitted?

2 4. What happens when the fluorescent light tube is brought close to the plasma ball? Does the tube have to touch the surface of the bulb for this to occur? 5. What mechanism is allowing the phenomenon seen in question 4 to occur? In other words, how is the fluorescent tube doing what it is doing? 6. Clearly, the energy transfer is not due to magic. Therefore, the energy transferred must be located somewhere on the EM spectrum. How do you determine in what part of the EM spectrum the energy transfer is taking place? Note that there is a place for the process of elimination in this experiment.

3 Needed: Ultraviolet light box, UVA and UVB sensors, Vernier LabQuest datalogger 7. Plug in one of the sensors into the datalogger and make sure the display shows a reading. Point the sensor at the UV light, taking care to not expose yourself to the UV light, and record the measurement in the table below. Take the same reading (at the same distance) with the other UV sensor. Also record the wavelength of light the UV light is emitting. Wavelength of ultraviolet light emitted (nm) Reading from UVA sensor Reading from UVB sensor 8. While getting a positive reading on the datalogger from either of the sensors, place various transparent items between the UV light and the sensor to see what material will absorb the UV light. How can you tell if the UV light is absorbed by a material? What material absorbs UV light? How is this applicable to your life? Needed: Infrared camera, fog/smoke machine, opaque trash bag 9. Set up the IR camera such that it projects onto the screen, then turn on the fog/smoke machine. The instructor will pan the camera across the classroom (ideally, you cannot see the camera). Are you visible to the camera? How can this be; what is the camera actually seeing? How is this related to Wien s Law (use your body temperature of 310 K)? Does the smoke/fog block IR light?

4 10. Place the trash bag over the instructor s head and pan the camera at the instructor. Is the instructor s head still visible? Does the particular plastic of the trash bag block IR light? Try other materials; what transparent material blocks IR light? Needed: Cheap transistor radio, wire mesh 11. Turn on the radio and find a relatively strong station. Note the frequency of the station in the table below. Switch wavebands (AM to FM, or vice versa). Find another strong station and note its frequency. Note that the units for the two stations will be slightly different. Place the mesh around the radio and find the two stations, then note how strong their signals are, compared to before. Waveband AM Frequency of radio station (show appropriate units) What happens when mesh is placed around radio FM The mesh is called a Faraday cage. 12. Using the information from the previous parts, return to the plasma ball, and use the various shielding materials to eliminate portions of the spectrum (there should be a fairly obvious way to eliminate the visible part of the spectrum). Record the effect on the lit fluorescent light tube below.

5 13. What happens when you place the transistor radio near the plasma ball? How does this observation help determine what part of the spectrum is involved in the energy transfer between the ball and the tube? Needed: An alpha (α) particle emitter, a beta (β) particle emitter, a gamma (γ) particle emitter, nuclear radiation monitor, various shielding materials Note: even though these are weakly radioactive materials, nevertheless they should be treated with care. Do not inhale or ingest them; this means keeping the materials in their containers. 14. Using information given on the containers, or using the shielding materials, fill in the table below: Type of radiation alpha (α) Isotope that emits this radiation Minimum thickness of what type of material needed to reduce radiation by half beta (β) gamma (γ) One meter of soil/rock 15. Why is it not possible, with any thickness of the shielding materials, to reduce the detected radiation to zero? 16. Which of these particles is the most penetrating radiation? How does this impact your life?

6 17. Which one of these particle radiations is also found on the EM spectrum (radiation) chart? Why not the other two particle radiations?