Large Xray tube, making weak radiation experiment - Page 1
Forum section: electronics / projects

author: oz2cpu
author_rank: Frequent Contributor
timestamp: January 18, 2023, 08:40:38 am
content: I got a very large Xray tube 81kV and 125mAand tried to see if it was possible to create very weak xray with it,the idea was to use a Geiger counter as detectorand slowly increase the anode voltage until i hear geiger clickssee all details about the experiment herehttps://youtu.be/H6Td_9pC2Vk

author: Emo
author_rank: Regular Contributor
timestamp: January 18, 2023, 09:41:46 am
content: Hi,The way this is done in flexible units is that both anode voltage as well as filament supply can be changed.So if you would like short wavelength=high voltage, than you can limit the power by lowering the filament feed or better apply the voltage at which you want the tube to operate and slowly increase the filament supply and see the anode current slowly riseEricPS. Be careful, your tube is very powerful. Take the necessary precautions and absolute lead screening (solid lead or lead plywood)

author: inse
author_rank: Super Contributor
timestamp: January 18, 2023, 08:46:41 pm
content: I wonder if the rough area on the anode is caused by wear - who knows about that?If you compare item #1 to #8 in this auction, one could imagine it.https://www.ebay.de/itm/204205964083?mkcid=16&mkevt=1&mkrid=707-127634-2357-0&ssspo=xlbjqc1cRCS&sssrc=2349624&ssuid=UJEfguXdQ76&var=&widget_ver=artemis&media=COPYHave you seen Kreosans hilarious X-ray experiments on YouTube?

author: Gyro
author_rank: Super Contributor
timestamp: January 19, 2023, 11:00:53 am
content: The path traced by the electron beam on the rotating target does certainly become pitted after long heavy use, reducing X-ray quality (poor varying spot size). It's hard to tell from that photo where the beam is intended to strike and whether that part is smooth. There is certainly far more rough area than the beam would strike so I think that is probably roughness from casting. I suspect that the electron beam target area is actually the narrow smooth turned ring between the rough areas (or maybe the smooth area at the edge).

author: Psi
author_rank: Super Contributor
timestamp: January 19, 2023, 11:17:14 am
content: A 10kW xray tube, jezz.I can understand you wanting to power it up very slowlyI've done some work around 160kV 700uA luggage scanner xrays tubes, but they're only ~100W.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 19, 2023, 11:46:31 am
content: I have used an X-ray maching with a 18 KW tube, though usually at a lower power setting (e.g.5-10 kW range). That "tube" however was more open with a continuously running pump and water cooling from inside the rotating anode.I don't see much electron optics. So chances are the source spot is not that small and it could be the 2 bands. This may not be a tube for taking pictures but more for x-ray diffraction.A rought surface would cause somehwat inconsistant and reduced power, as most radiation comes out at a shallow angle one would thus not that well come out from pits.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: January 19, 2023, 01:18:23 pm
content: yes i belive the anode rought two traces are from the two strike points the two warmed cathodes make be two beams hit,this tube was replaced and thrown out many years ago,one of my collector buddies saved it from the bin,he wanted to know if it was still vacuum tight, and if it was still possible to make xray with it,he promissed me 10 times he will never ever try to power it..i am not an xray expert, and i do not claim to be.please do not power up any type of xray tubes, no matter what size they might be,please do not recreate the high voltage generator either, even that one alone is very dangerous.

author: BrianHG
author_rank: Super Contributor
timestamp: January 19, 2023, 01:54:15 pm
content: I did not know that they rotated so fast and were so noisy, here is one rotating:I guess that's why the anode needs to be balanced.

author: inse
author_rank: Super Contributor
timestamp: January 19, 2023, 02:40:40 pm
content: In the 90‘s I did my civil service in the x-ray department of a hospital and I remember that ringing sound, now I know what it came from…

author: BrianHG
author_rank: Super Contributor
timestamp: January 19, 2023, 03:01:36 pm
content: Quote from: inse on January 19, 2023, 02:40:40 pmThanks, now I know the ringing sound in the video wasn't because of a broken bearing.I guess without any lubrication and in a vacuum mounted against a large glass frame, this is the commuted vibration sound you get through the glass.I like how after the electro-magnet is removed, that anode just keeps on spinning at the exact same speed. No slow-down.

author: Wolfram
author_rank: Frequent Contributor
timestamp: January 19, 2023, 03:20:01 pm
content: Quote from: Psi on January 19, 2023, 11:17:14 amThat might be typical operating parameters for a portable x-ray setup or other cases with limited power available. Tubes of this size would typically handle 50+ kW peak depending on focal spot size, and larger tubes up to 100 kW are not uncommon, in order to keep exposure times short and patient motion blur down. Here's an example of a tube datasheet with some relevant info:https://www.vareximaging.com/wp-content/uploads/2022/01/A-102_PDS_132852-000.pdf

author: TurboTom
author_rank: Super Contributor
timestamp: January 19, 2023, 05:59:47 pm
content: FYI, here's what one of the larger dental X-ray heads with a stationary anode tube looks like internally. All this HV stuff is placed inside a lead-lined cavity that's filled with insulating oil. The rotating anode type of X-ray tubes are rather used in CT scanners and fluoroscopes, i.e. equipment that needs prolonged or continuous duty operation of the X-ray source at considerable power. It's not unheard of that the rotating anode of these tubes actually develops radial cracks due to the massive amount of heat cycles it's exposed to.BTW: The brownish hue of the glass envelope that can be found on virtually all X-ray tubes is the result of the formation of colour centres due to the interaction of the energetic radiation with the glass on a molecular level. It's basically the same effect that can be observed on standard electron tubes operated for prolonged time at high voltages, i.e. horizontal output tubes of "pre-historic" TV receivers, though in the latter case, electron bombardement of the glass also plays a role. I've read that this kind of discoloration can be removed by exposing the glass to elevated temperatures of some 150~200C for several hours, though I never tested that myself.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 19, 2023, 09:06:03 pm
content: Hi,I spent about 20 years involved in the design and manufacture of medical x-ray generators.oz2cpu has aninsert. The insert is combined with an oil-filledhousingto make an x-ray tube.The 150 in the part number is a 150kV max.The 50 may be the small focus power rating in kW and 101 may be the large focus power rating in kW.The 'R' may indicate that the tube can be operated at high speed.The standard for power measurement is for a 100ms exposure.The tube is operated in an emission limited mode. The filament is pre-heated and then the high-voltage is pulsed. The filament could be up to 75kV from ground. The anode current is controlled by changing the filament current. There is no grid.The high energy electrons hit the anode. 99% of the energy is converted into heat and about 1% is emitted as x-rays. To prevent the anode from melting, the anode is rotated. It essentially puts a cool(er) piece of anode into the electron beam. The power rating varies with the length of the exposure.The two rough areas on the anode are where the electrons have hit the anode. They are called the focal tracks. The focus is a virtual focus below the surface of the anode.The motor is a drag cup. A rotating magnetic field drags the cup around. The stator may be capacitor run or three-phase. The anode is rotated with line frequency or three times the line frequency.The motor drive can spin the anode to about 11,000 rpm in 1.5 seconds. The motor drive will also provide braking to reduce the speed quickly to avoid mechanical resonances.Regards,Jay_Diddy_B

author: DavidKo
author_rank: Frequent Contributor
timestamp: January 20, 2023, 06:07:03 am
content: The reason why nowadays X-rays are so small, is the development in detection area. Old X-Rays used photographic film, but with the CCDs, the power had changed dramatically and you can have these hand held devices without dosimeters needed (typical dentist X-ray).

author: elecdonia
author_rank: Frequent Contributor
timestamp: January 20, 2023, 04:11:40 pm
content: My dentist always keeps up-to-date with the latest technology. I was surprised when they recently began using ahand-held battery-powered X-ray sourcefor dental X-rays.Prior to this they had been using electronic image sensors for several years, but were still using a conventional dental X-ray machine for the X-ray source. The electronic image sensor device has a cable which connects to a PC. The image appears on the LCD monitor screen within 1 minute after the exposure. The procedure included placing a lead blanket over the patient’s torso along with the dental technician going outside the examination room to trigger the X-ray machine.The new setup with the hand-held X-ray source does not require any protection such as a lead-lined blanket for the patient. Also the dental technician is in the room and simply holds the X-ray generator in their hand to operate it. The electronic image sensor device which goes inside the patient’s mouth looks different than the previous version. I suspect it has much higher sensitivity so that it can function with an ultra-low-power X-ray source.So can anyone explain the technology inside a hand-held battery-powered dental X-ray source?I doubt that it would contain a vacuum tube. Could it possibly contain a laser diode which fires a pulsed beam of concentrated photons at some type of target which converts the energy into X-rays?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 20, 2023, 04:44:40 pm
content: In my first electronics job in the '90s they bought a used industrial x-ray machine similar to this type of setuphttps://www.balteau-ndt.com/baltospot/The scariest thing was the howl of the turbomolecular pump spooling up.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 20, 2023, 04:48:20 pm
content: The Xray tubes have not changed that much. With low power there is no need for rotating the anode and this simplifies things quite a bit. AFAIK the dental X-ray machines were fixed anode already before.Not much change from the outside, but to get better image quality they go for increasingly smaller focus points and a lower power level helps with this. With a finer focus to start with one could get a similar picture quality (but noise vs sharpness) from less energy. So it is not just getting a picture with less energy, but often also getting better resolution.The high voltage generation can get smaller by running the transformer at a higher frequency, better diodes (maybe even SiC) and capacitors. Compact size may not have been such a priority.The old sources may also very well had quite some shielding inside the unit. With some care in the desing of the tube part of the shielding may be inside the tube and thus much smaller area to cover.Even with a lower power I don't like the idea of having the x-ray source hand held. No real need to have it portable and even at the lower level one should minimize exposure if possible. The usual articulated arm is not such a problem and some distance still helps.

author: BrianHG
author_rank: Super Contributor
timestamp: January 20, 2023, 04:50:36 pm
content: Remember, every time you use a boxing tape gun, the triboluminescence effect of the separating tape produces enough X-rays to image a human finger.See here:https://www.technologyreview.com/2008/10/23/217918/x-rays-made-with-scotch-tape/Ok, the tape needs to be pulled under vacuum conditions, but are you certain...