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Proud Mary

Fri Jan 21 2011, 10:11AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The random star-like points of light are probably direct X-ray photon strikes on the CCD pixels.

The optimized tube angle suggests to me that the sharp edge of the anode bell is the source of field emission electrons which are impacting on the circular screening plate - though probably there are multiple sources of X-ray emission, some larger than others.

You can image the source directly with an X-ray pinhole camera, but I'd guess that your source is too weak to produce an image in this way

You may be able to improve resolution by means of a hole in a metal plate between the tube and the screen. You could try a hole of 10mm placed directly on the tube glass to start with.

Two or more holes spaced apart would make the simplest form of X-ray collimator.

radhoo

Fri Jan 21 2011, 11:29AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

08.Soft vs. Hard X-rays
Note: A 2X2 Tube in inverse polarization at 50KV. At 6cm a green fluorescent screen, with and without aluminum sheet shield.

Left picture: Fluorescent screen with Al sheet shield. Right picture: Threshold L=100

Left picture: Fluorescent screen without any shield. Right picture: Threshold L=100

Conclusion: the amount of soft x-rays seems to be negligible as compared to the hard x-rays. Possible causes: the tube's glass envelope as a blocker -or- the fluorescence produced by the soft-xrays is overwhelmed by the stronger, more intense hard-xray fluorescence.

Proud Mary

Fri Jan 21 2011, 12:01PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I think you should assume that the glass envelope blocks photons below about 15keV - with possible ranges across 12 - 18keV. So an aluminium filter will not have made much difference.

Expensive lead glass is not likely to have been used in 2X2, which was designed to rectify VRMS 5.5kV max.

The 2X2A iteration was a robust version of 2X2, "for applications critical as to severe shock and vibration" and may have had thicker, more radio-opaque glass, but I am just guessing.

How much the CCCP version followed the US design in glass technology, I have no idea.

radhoo

Fri Jan 21 2011, 01:03PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

09.Vertical emission angle
Note: A 2X2 Tube in inverse polarization at 50KV. A fluorescent screen at 6cm and then at 12cm. The tube is positioned vertically, tube's longitudinal axis is parallel to the fluorescent screen plane (see pictures)

Note: The brightness has been increased in software, at 12cm the fluorescence is much fainter than at 6cm.

Laser level for bottom and top of 2X2's bell

The measurements:

The vertical emission angle is 30Â°

Some excellent news: using the laser level marker and three pictures taken to the same setup (two with laser visible, one with x-ray fluorescence) and software to combine the three images, it can be seen that the vertical's angle bisector is perpendicular on the tube's axis! The origin of the vertical emission angle is at the same height as the center of the bell ( as pictured)

So we got a very well centered / conveniently placed x-ray emission source. Too bad I won't be using it in vertical position. The emission band is too narrow (only 3cm wide at 6 cm away from the tube's center) - good only for tiny objects. See the next post.

radhoo

Fri Jan 21 2011, 01:10PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Proud Mary wrote ...

The random star-like points of light are probably direct X-ray photon strikes on the CCD pixels.
The optimized tube angle suggests to me that the sharp edge of the anode bell is the source of field emission electrons which are impacting on the circular screening plate - though probably there are multiple sources of X-ray emission, some larger than others.

Hard to tell , when the tube is placed in vertical position, there are strong indications that the center of emission is the center of the bell. Very round, nice, numbers.

Proud Mary wrote ...

You can image the source directly with an X-ray pinhole camera, but I'd guess that your source is too weak to produce an image in this way
You may be able to improve resolution by means of a hole in a metal plate between the tube and the screen. You could try a hole of 10mm placed directly on the tube glass to start with.
Two or more holes spaced apart would make the simplest form of X-ray collimator.

Thanks, I will try that.

radhoo

Fri Jan 21 2011, 01:37PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

09.Emission at 45Â°
Note: A 2X2 Tube in inverse polarization at 50KV. The tube is inclined, tube's longitudinal axis makes a 45Â° angle to the fluorescent screen plane (see pictures)
I already uploaded a few radiographs, underlining that the best position in terms of x-ray illuminated surface, but also uniformity of the filed intensity, is when placing the tube at 45Â°. As a comparison, here are two pictures, one with the tube in vertical stand, and the second with the tube at 45Â° (the pictures are not altered in software, they are as recorded by the camera):

To compare emission intensity, here are the images again, with Threshold (L=50) applied in software:

Placing the tube in vertical position offers a very good, strong emission, unfortunately the illuminated surface comes as a narrow band of only 3cm at 6cm away from the tube. On the other hand, placing the tube inclined at 45Â°, results in a sport-like surface, better suited for illuminating various objects. The only loss is x-ray intensity, but we still have sufficient levels for taking radiographs.
Another big advantage of placing the tube at 45Â° is the uniformity of the emission: not yet understood why, but I got sharper images with less shadows this way. Here is a comparison:

The first object is a DY86 tube. The emission tube 2x2 was placed in vertical stand.
The second radiograph shows several objects (SDCard, USB Flash, USB WLAN). The tube was placed at 45Â°.
Comments:
The first radiograph shows blurry edges and shadows. On the other hand, the second radiograph shows very sharp edges, with no shadows.
This uniformity can also be observed in the green fluorescence color - the second picture clearly comes with a smoother, more homogeneous green color - an advantage clearly reflected in the quality of the radiographs.

Pictures of the setup:

Notice the emission pictured in the last image. The bottom level corresponds to the bell position, while the upper level limit is projected by the small metal plate, under the bell. Rotating the tube produces different top projections, because of the position of the small metal plate (not quite parallel to the bell's bottom surface):

radhoo

Fri Jan 21 2011, 01:49PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

10.Other vacuum tubes
Note: I will be using several vacuum rectifier tubes or shunts, in inverse polarization at 50KV.

DY86:

Weak, or no emission.

Three other high voltage tubes 3A3, 3CZ3, 6LJ6:

No emission . These 3 tubes all come with lead-glass.

So bottom line is 2X2 is a great tube, both affordable and producing nice amounts of x-rays. Thanks to Proud Mary for the discovery:

radhoo

Fri Jan 21 2011, 02:00PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Some more images:

A remote control with blue and green fluorescent screen . I prefer the green (Kodak lanex fine):

A TV Cascade multiplier and a SD Card (from my first tests - not the best photo)

Another type of TV Cascade multiplier

In case anyone wants me to test the 2X2 with a particular target, just drop a few lines.

Proud Mary

Fri Jan 21 2011, 02:19PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Have you any minerals or crystals to test for fluorescence, Radhu?

And not forgetting your NaI(Tl) scintillator block.

radhoo

Fri Jan 21 2011, 02:55PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Proud Mary wrote ...

Have you any minerals or crystals to test for fluorescence, Radhu?

And not forgetting your NaI(Tl) scintillator block.

I got a few, from a mine near Antsirabe, Madagascar:

I'll be testing the scintillator soon.

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