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Physics 1 Unit 3
Productions and Properties of Xrays & Half-life problems
| Question | Answer |
|---|---|
| What does Electromagnetic Energy arise from? | vibrating e- |
| what is the smallest unit of EMR? | photon |
| what are two wave parameters that determine EMR? | wavelength & frequency |
| What is wave frequency? | the rate of rise & fall of the sine wave. |
| How is wave frequency measured? | Hz (hertz) |
| what is wavelength? | the distance between one crest to the next OR one trough to the next. |
| what is amplitude? | the distance between center of the wave to the crest of the wave. |
| what is wave velocity? | speed of the wave |
| As velocity increases, what happens to frequency? | velocity increases, frequency increases (directly proportional) |
| If velocity is constant what happens to wavelength as frequency increases? | velocity=constant; wavelengths get shorter as frequency increases |
| what is the wave equation? | velocity= wavelength * frequency OR c= wavelength * frequency |
| who discovered planck's quantum theory? | Max Planck |
| what does planck's quantum theory state? | photon E is directly related to frequency; this value is planck's constant (h), measured in eVs. |
| As photon E increases what happens to frequency and wavelength? | As photon E increases, frequency increases, wavelength decreases |
| What 4 things need to occur to produce xrays? | liberation of e-, acceleration of e-, focusing the stream of e- and stopping the e- suddenly |
| what does liberation of e- mean? | boiling e- off the hot filament (free supply of e-) E is added to e- to cause them to spin; the faster the e- spin, the further they get from the nucleus. |
| how does the acceleration of e- occur? | strong negative charge is applied to the filament and at the same time a positive charge is applied to the anode target. e- are propelled at the target at speeds approaching 1/2 the speed of light. |
| why is focusing the stream of e- so important? | e- need to stay together to prevent off-focus radiation (only happens in the tube); also a smaller focal spot can be achieved if the stream is focused. |
| what does stopping the e- suddenly do? | when e- strike the anode there is a lot of KE present. When e- stop the KE is coverted to 99.4% heat and .6% into xrays. |
| What are 3 interactions that can be produced from xray production? | heat production, characteristic production interactions, and Brems Production |
| How is heat produced? | interaction between projectile e- (from filament boiled off and accelerated) to vibrate around the outer shell. |
| How are characteristic xrays produced? | interaction between projectile e- and inner shell e- of the target (K or L normally). Target e- are ejected. need a minimum kV of 69.5. |
| T/F: As you get further away from the nucleus; e- E increases, binding E decreases. | true |
| Why is the emitted photon called "characteristic"? | because its energy is specific to the target element & the energy shells that are involved. |
| What is photon E? | difference between binding E of shells involved. |
| If a k shell e- of tungsten atom is replaced by an L shell e-; how much E will the photon have? K-shell binding E= 69.5 KeV L-shell binding E= 12.1 KeV | photon E= 57.4 KeV (69.5-12.1) |
| As you get further out of the nucleus what happens to the average E? | decreases |
| How are Brems xrays produced? | projectile e- approaches the nucleus of tungsten. the e- slows down, looses E & changes direction. e- may loose all or only some of the E. |
| In Brems xray production, the closer the e- gets to the nucleus the more or less it changes direction? | more it changes direction |
| In Brems xrays, the degree of the e- changing direction reflects what? | how much E is lost(converted into something else); the sharper the turn away from the nucleus = high-energy brems photon |
| what KeV is needed for Brems xrays to occur? | any KeV. no minimum amount |
| How is the average E determined on a graph? How is it calculated? | on the graph it is the highest peak. it is calculated by taking 1/3 of the kV setting. So if the kV setting was 120kV; the average energy would be 40kV. |
| name some properties of xrays | highly penetrating, invisible, dual nature; electrically neutral; polyenergetic; liberate small amounts of heat when passing thru tissue; travel in straight, diverging lines; travel at speed of light; cause florescence in some materials; cannot be focused |
| T/F: Brems interaction is an example of secondary xray production. | False; it is an example of primary xray production because it occurs inside the tube. |
| What is an example of secondary radiation? | produced by the patient when the photons interact with the tissues |
| What are some factors that affect xray production? | tube current(mA), kVp, filtration, and target material |
| What happens to the average energy and the spectrum when kVp increases? | average E increases, intensity of e- increases and the spectrum is shifted to the right |
| what happens to the average energy, amplitude, and intensity of the spectrum as filtration increases? | average/effective E increases, amplitude decreasesa and intensity decreases which moves the spectrum to the right. |
| T/F: higher atomic # of material yields higher amplitude & intensity & higher effective energy beams. | true |
| Characteristic photons that arise from ionizations in the M shell are not considered to be useful. Why? | because they are further away from the nucleus and they have lower binding E. |
| Heat is produced as a result of incident electrons interacting with inner or outer shell electrons? | outer shell electrons |
| T/F: photons with longer wavelengths travel slower. | false; all photons travel at the same speed (speed of light) |
| You are given a sample @ 8AM; the material has a 1/2 life of 2 hrs. You are given the sample in an amount that there is 1000MCi. How much will remain @8PM? | 15.6MCi; how many half lives have passed= hrs. passed/how long a 1/2 life is 12hrs./2hrs. = 6 half lives occurred. 0=1000; 1=500; 2=250 etc. |
| You are given a sample of a radioactive material @ 6PM measuring 4MCi. The sample was acquired @ 10AM with 64MCi. How long is 1 half life? | 0 half lives=64MCi; 1 half life =32MCi; 2=16MCi;3=8MCi; 4=4MCi. 4 half lives have occurred and 8 hrs have passed. 8hrs./4 half lives= 2hrs. Every 2hrs. = half life |
| a certain radioisotope has a half life of 30 min. If 250mCi are present at a given time; a) how much will remain after 2.5 hours b)how many half lives will have transpired? | a) 7.8mCi b)5.5 lives |
| A certain radioisotope has a half life of 1.5 hrs. If a sample of this nuclide is measured at 540mCi, how much will remain after 4.5 hrs? | 4.5hrs/1.5hrs(1 half life) = 3 half lives have occurred. 540mCi=0; 270=1;135=2;67.5=3 |
Created by:
mokapis
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