Author Topic: Where to find a "small" focal spot x-ray tube  (Read 436 times)

Offline Davide

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Where to find a "small" focal spot x-ray tube
« on: August 01, 2022, 10:21:53 PM »
Hi everyone!
I recently built my x-ray machine using a "standard" dental x-ray tube bought on Alibaba. This tube has a focal spot size of 0.4mm.
I works ok, but I would like to have higher sharpness in the images.  As sharpness is partially due to the focal spot size, I started searching for tubes with smaller spots, but the only thing I found is another Alibaba seller who charges more than 700$ for a tube with a 50um focal spot size.
The only other source of x-ray tubes was the site "sovtube", which unfortunately doesn't sell them anymore. The tube that would be great for my needs is like this: http://www.sovtube.com/x-ray-and-geiger-tubes/315-bs5-w.html

It is not necessary to have a 6um focal spot, but something under 50um would be nice ;)

So if anyone knows of some site that still sells tubes like this, please let me know :)

Thank you!

Offline Anders Mikkelsen

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Re: Where to find a "small" focal spot x-ray tube
« Reply #1 on: August 23, 2022, 12:26:52 AM »
Can you post some of your results? In my experience, the focal spot size is rarely the limitation in hobbyist systems unless you are doing significant magnification. More often than not, the imaging system is the limit. This picture was taken with a 0.7 mm focal spot tube as an example, using photographic film.




If you are at the limit of what your focal spot can provide, options to look for are microfocus tubes, which often have very limited power handling ability, and mammography tubes, which have limited operating voltage and large size due to the rotating anode construction.

Offline Davide

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Re: Where to find a "small" focal spot x-ray tube
« Reply #2 on: August 24, 2022, 11:33:00 PM »
Hi Anders, thanks for these info.

Yes also the imaging system has a strong effect on image sharpness. In my case it is the basic setup: phosphor screen + dslr. Any advice on how to improve that is welcome :)

As you said, magnification is also present in my setup, as I’m trying to perform very basic ct-scan, so the sample needs the space to rotate (I’m using roughly a magnification of 1.5 - 2). This is an example picture (camera lens):



This instead was taken with the object (a remote) close to the phosphor screen:



I think it's a little sharper, but it's also hard to compare them.

Your images look really sharp, I guess the circuit board was placed right against the film. In this case the focal spot has little effect on image sharpness as magnification is close to 1. Anyway it looks good for a 0,7mm focal spot.

I searched for used mammography tubes, but it looks like they are really hard to find on eBay, at least in Italy.

As for microfocus tubes, I believe industrial grade ones are really expensive (talking of thousands of € or $). Do cheaper microfocus tubes exist (other than the ones at the link in my previous post)?

If you know of any source of x-ray tubes other than ebay, or if you know specific ebay sellers, let me know.
Thanks :)

Offline Fijcho

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Re: Where to find a "small" focal spot x-ray tube
« Reply #3 on: September 13, 2022, 10:05:48 PM »
Hi
I am new to this forum.
In the nineties I visited Mu Inc., Oceanside, CA.
They produced microfocus X-ray tubes.
Find attached a spec.
Good luck!

High Voltage Forum

Re: Where to find a "small" focal spot x-ray tube
« Reply #3 on: September 13, 2022, 10:05:48 PM »

 


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