I'm a dental nurse studying for my radiography qualification and have been struggling with understanding some areas of physics. Just wanted to say how amazing this video is, and I'll be watching on repeat and taking revision notes from this ( aswell as my textbook of course!). Thanks so much
In general ionisation means that an electron has been knocked out of an atom so that the atom is positively charged (ionized). Excitation means that the electron has been pushed up to a higher energy level (but still within the atom). The atom still has all its electrons and is not ionised. But the excited electron will soon fall back to a lower energy level emitting a photon.
Hi Jake - Thanks for your kind comments. I would be very happy to do the videos you suggest but I'm afraid I cant do them in time for Monday and probably not for another week or so. But good luck in your exam. I hope it goes well.
Yes. There is the braking radiation. But the main X rays come from high energy electrons knocking electrons from the inner shells of the anode. Outer shell electrons can then fall down the energy level to take the space vacated by the electron. This fall in energy is released as a photon - in this case in the X ray wavelength range.
My A Level Physics revision playlist has videos on Gravitation and Electricity, both of which refer to the inverse square law for Newton's or Coulomb's laws.
Good simple explanation and useful practical/clinical tips. Just to correct one mistake DrPhysicsA in your explanation from 14:15 to 14:35, when x-rays strike the radiographic film it is blackened, not whitened or grayed. That is why the shadow of bone on the radiograph appears white or grey because the x-rays are attenuated by the dense bone. However the soft tissues do not stop the x-rays at all from penetrating hence that part of the radiographic film appears black.
Where x-rays are produced as a result of electrons falling from outer energy levels to inner energy levels then this will be a constant process because energy is constantly being given to the atom to enable electrons to jump up to the higher energy levels in the first place.
Ionisation is where the energy given to the electron (eg from a photon) is sufficient to kick the electron completely out of the atom. The atom therefore has a residual positive charge. Excitation is where the photon gives enough energy to promote the electron to a higher energy level but still in the atom.
Hi I'm an A Level student and I have my AQA unit 5 exam on Monday, I find your videos so helpful. I learn more after watching them than I've learnt in all my lessons on those topics. If you have time would you be able to do some videos on other Medical Physics topics? such as the eye, ear, and heart? This is the stuff on my syllabus, if you could make a video on anything on here it would be extremely helpful!
Thankyou for the great video, it really did help! I am just slightly confused with the graph. You said that were the minimum wavelength are seen high energy x-rays occur. On the y-axis there is intensity, so does that mean the x-rays produced on the left side of the graph have an high energy but low intensity?
watched a ton of videos on x rays and sorry to say their are a ton of really bad Physics teachers out there, BUT your videos was awesome. Thank you I HIGHLY recommend.
Thanks. In my efforts to show where the X rays would penetrate and where they wouldn't I didn't properly cover their impact on the photographic plate. I've added an annotation.
Thanks. HIgh and low energy photons will enter the body but low energy X rays will be wholly absorbed and not appear on the photographic plate. High energy will be attenuated but will still pass thro the body. So low energy X rays add to the overall dose but for no worthwhile effect.
Tungsten has a high electron density and, when hit by the electrons coming from the cathode, emits a characteristic x-ray, in that the waves have a high enough frequency and therefore, enough energy to penetrate the aluminium plate covering the tube and thus, enough energy to penetrate the bone etc to reach the lead (less penetrable material to absorb the photons)...
No i searched for linear attenuation coefficient for X-ray but didn't get what I was looking for. But with attenuation coefficient i got it on wikipedia. Thanks Sir.
My videos certainly cover the OCR syllabus but they all so cover material in the AQA and Edexcel syllabus as well as some material in the Cambridge syllabus.
You can add this correction as tag to your video for those minutes. [Reference: 'Nature of the radiographic image', pg. 3, Essentials of Dental Radiography and Radiology by Eric Whaites, 4th edition.]
I'm stumped on that one I'm afraid. I guess the answer has to do with the technology and which element best provides the Xrays which are most suitable for medical purposes. But I could be wrong. Anyone else know?
Thank you very much DrPhysicsA. It was very beneficial for me to learn physics in conceptual way. I think it would have been better if we can get your video in HD too.
that last part got me thinking about orthographic projection. is that grating essentially creating an ortho look? if it does then, is it possible to create an ortho-lens in that manner to attach to a regular (visible-light) camera? btw, great video, thank you!
it would be good if you can explain in further details of the use of the materials alongside with the description of the x-ray tube , e.g.why is tungsten used. Just a suggestion to your future videos (maybe?)
Your welcome. I understand this but I assume there's a deeper reason to this. I'm guessing that low energy photons 'frequency' causes some interaction (resonace?) with molecules more easily that high 'frequency' does. Or is it just explain cause high freuquency photons pass due to having more energy(as some being absorbed but even few which pass leave a mark on plate) or even some other way? Thanks a lot!
@14:25. The resultant image would be WHITE not BLACK. If x-rays are NOT penetrating the bone it means they are instead being absorbed. So then there is no 'exposure ' to the photographic plate/film behind the bone so it remains white. .. The 'black' in an image shows where the x-rays HAVE penetrated the object thus have exposed the medium (film) behind it. - Other than that great video - thanks.
Hello awesome video that complemented my textbook and brought life to the application section of my physics course. Is there a video about the attenuation of X-rays? Like where we use the formula to fine resultant intensity and so on? thanks
Hi, Thanks for all your wonderful videos, been a big help in simplifying some topics in Physics. Do you have any lessons on the Inverse Square law? Thanks! Keep up the good work.
Dear DrPhysicsA: From the video, are you meaning the x-ray generation from the acceleration of electron beams is equivalent to that from the energy transition of the outer shell back into the inner shell. They are of the same, but different pictures. right ?
Dear DrPhysicsA, this is a great presentation. But something worrying me ,The lead gratings at 17.00, will also be shown in the Films? that will obstruct with the image of interest. ? kindly clarify
I am sort of confused. So the braking radiation and inner shell electron transition are two different mechanisms. The latter is the usual way to generate x-ray. Right? and does the electron acceleration inside the CRT(cathode ray tube) create some long-wavelength x-ray or just the ultra-violet radiation ?
Sir, I would like to ask.Like what you mentioned, high speed electron will hit the electron from the tungsten atom. And then the outer electron will jump into the inner shell to replace it. Energy lost is the X-Ray. After outer electron fall into the inner shell, The more outer electron, I mean will others electron replace the jumping electron? will X -ray produce also?
I just have a few questions, does the rotor part of the anode also rotate along with the disc? Which part of the mechanism actually controls the tube current, is it the tube part of the cathode or the thermionic filament? Also, the anode is the positive part but does this refer specifically to the disc of the anode or the rotor that's positive to attract the electrons?
if you cover an alu plate to filter out the "weak" photons, the rest of the photons would also get attenuated by the plate, right, thus "strong" photons will become "weak" and the problem is still there???
