Saturday, November 21, 2015

Testing the DY87 Thermionic Diode for X-Rays and looking forward to future Radiography

I've been wanting to get a simple X-Ray source together for years now, but never quite was able to source the crucial component; an X-Ray Diode (vacuum tube). The official/correct tubes are extremely expensive and hard to acquire, as modern ones are illegal to own/operate without a license and credentials. This means that only old/vintage/used tubes are acquirable, and they tend to be very expensive and hard to come by given their rarity and fragility. Fortunately, many old general purpose vacuum tubes (thermionic valves) are capable of producing x-rays when operated in cold cathode mode.

Years ago I had purchased an old medium power vacuum diode in hopes that I could get some results, but sadly it lost its hard vacuum before I acquired it. It still had a decent vacuum inside, but not enough to allow electron acceleration sufficient for x-ray production via anode bremsstrahlung. I put the project as a whole on the back burner for quite some time having such a sour experience of wasting money on an expensive tube.

Recently it came to my attention that a very easy to source and inexpensive tube, the DY87 / 1S2A HV vacuum diode, could produce x-rays reliably from even lower voltage HV supplies. I quickly sourced such a tube and gave it a test:

Here you can see my quickly assembled test rigging...

Given that <50kV was the HV source and thus <50KeV is the maximum photon energy, the thin 1.2mm steel plate and short distance is all that was needed for shielding of such a short duration test.

An important note is to use an RFI-shielded Geiger Counter for detection of these xrays, as the HV pulses will create copious RFI which causes false triggers in standard geiger counter circuits. Shown on the left is a Kvarts DRSB-01 that I repaired and enclosed in a 1mm thick Aluminium case which functions as a soft-beta shield and RFI blocking Faraday Cage. The DRSB-01 doesn't use a regulated HV supply so it cannot be used for measurements of radiation, but it functions well for detection of radiation.

Here you can see where I stood in relation to the tube, and the HV source I used...
Even with the low sensitivity to soft X-rays of my 1mm-Al shielded SBM-20 Geiger Tube I am quite confident that my X-ray exposure was quite minimal. That being said I won't be moving forward with this project until my remotely triggered relay arrives in the mail. I plan on doing some radiography tests with an X-Ray Intensifier Screen I purchased many years ago from George Dowell. I will operate the HV remotely from out of the room this way, and take several long exposure shots to maximize safety and image throughput.

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