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Physics 1 Unit 3

Productions and Properties of Xrays & Half-life problems

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