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Author Topic: Background Radiation - Could It Be a Vexation ?  (Read 41417 times)
AG6K
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« on: October 22, 2011, 04:28:30 PM »

Background radiation came to my attention after a friend in Ojai gave me a Geiger counter.  When I was on 40m in the daytime chatting with friends I'd turn it on to see what was going on in the background in this corner of the universe.  My 1959 high-school graduation wrist-watch with a glow in the dark radium dial was a good source source of radiation.   Most of the time the Geiger counter would indicate a low count but occasionally there would be a burst that would send the count soaring.   Later I read that our sun emits x-rays and gamma-rays - plus supernovas emit large bursts of gamma-rays and that there about 60 supernovas per year.
  A Geiger-tube is basically a gas-filled chamber with HV on two electrodes with not quite enough volts on them to ionize the gas and cause conduction.  Thus, when an x-ray or gamma ray photon sails through the Geiger tube and strikes a gas atom, it can add enough extra energy to knock an electron loose, thereby causing conduction - which is then counted on the digital display.   This started me wondering whether or not an x-ray of gamma-ray photon could knock an electron loose inside a 3-500Z or 572B and cause conduction to take place? 
  Does this sound reasonable or not reasonable?  tnx
Rich, ag6k
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N6JP
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« Reply #1 on: October 22, 2011, 06:42:46 PM »

Well I don't know about affecting a tube, but I remember various families of digital logic being sold way back in the late 60's and 70's that were radiation hardened for use in outer space.  A ordinary logic chip was subject to all sorts of problems when it was bombarded by radiation.  They would change logic states and such, and crash computers and/or the devices they were installed inside. 

I remember an ordinary TTL chip that costs around  .25 cents ran around 5-10 bucks if it were radiation hardened.  Unbelievable the extra cost involved to harden the logic chips.  I can only imagine what it could do to a tube being used in a critical application.  I'm not sure how one would harden a tube?

Jer n6jp
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W8JI
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« Reply #2 on: October 22, 2011, 07:56:41 PM »

.   This started me wondering whether or not an x-ray of gamma-ray photon could knock an electron loose inside a 3-500Z or 572B and cause conduction to take place? 
  Does this sound reasonable or not reasonable?  tnx
Rich, ag6k

Years ago I remember reading your proposals, where horrible arcs were started by a photon or gamma ray striking a tube biased-off on standby, and the gamma burst making the antenna relay arc when the tube was thrown violently into conduction by the x-ray.

I often think of your photon-bombardment-causing-relay-contact-arc and catastrophic HV failure theory when I turn the light on in my family room. I keep waiting for the neon bulb near the dog food bowl to explode, and kill an innocent puppy with shards of glass or molten metal, but nothing happens. :-)

That's really a very bizarre theory, that even argues against itself. For the tube to avalanche, it would have to be worse than a Geiger tube. It would have to be worse than a neon bulb.  I wouldn't spend much money shielding a tube that gassy from photons, unless it was in the warp drives on the USS Enterprise.

I also shine flashlights in my amplifiers on the tubes, and so far none have blown up.

73 Tom
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AG6K
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« Reply #3 on: October 22, 2011, 10:12:04 PM »

Quote
Well I don't know about affecting a tube, but I remember various families of digital logic being sold way back in the late 60's and 70's that were radiation hardened for use in outer space.  A ordinary logic chip was subject to all sorts of problems when it was bombarded by radiation.  They would change logic states and such, and crash computers and/or the devices they were installed inside.

I remember an ordinary TTL chip that costs around  .25 cents ran around 5-10 bucks if it were radiation hardened.  Unbelievable the extra cost involved to harden the logic chips.  I can only imagine what it could do to a tube being used in a critical application.  I'm not sure how one would harden a tube?

Jer n6jp

  Interesting Jer.  I have motion detectors on this property and sometimes they go off when there's nothing coming up the driveway.  Perhaps it's an errant photon from who knows where ?   Since gamma-rays can penetrate lead, I don't think there's a practical way to keep them out.  Probably the best way to protect a tube from damage is a glitch-R to limit peak discharge-I from the filter C?
Rich, ag6k
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N3JBH
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« Reply #4 on: October 22, 2011, 10:23:09 PM »

Actually Tom your statement is bizarre, There would not be shards of glass or molten metal from the neon bulb. that is just plain silliness on your part speaking there. The heat generated by the neon gases would cause a rapid instantaneous combustion that actually send molten glass  to be expelled from the bulb with both the force and destructive power of a high powered shape charge, Oh the poor puppy  Sad   Jeff
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KB4QAA
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« Reply #5 on: October 23, 2011, 04:14:18 AM »

There is a semi formal paper that was published fifteen or twenty years ago discussing cosmic radiation and its effect on semiconductors in personal computers.  It provided estimates of the chance of an individual being affected.   The numbers were small, but possible.
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KA0HCP, ex-KB4QAA Relocated to Ks. April 2019.
G3RZP
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« Reply #6 on: October 23, 2011, 05:26:00 AM »

Quite a lot has been published about semi conductors and radiation. The effects are very dependent on the process and the geometry: at Plessey Semiconductors, we had some logarithmic amplifier ICs in a bipolar process. These were irradiated to such an extent the white alumina substrate turned brown, and yet the change in performance of the three dual amplifier chips couldn't be measured.

But considering the vast number of vacuum tubes of one sort or another - TWTs, magnetrons, klystrodes as well as 'conventional' transmitting tubes in daily use, if it was an effect, it would appear far more frequently than the odd flashover.
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KA5N
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« Reply #7 on: October 23, 2011, 05:28:55 AM »

I think it is all due to etherial drift which seems to have veered this Forum off course in
recent weeks.  I can't wait until it gets back on track.

Allen
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M0HCN
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« Reply #8 on: October 23, 2011, 08:51:15 AM »

The GM tubes have a ***very*** fine wire used for the anode, so there is a very high electric field in the vicinity.

Thus an electron released at the cathode by the photoelectric effect or just a beta wondering into the tube at low energy will have a high probability of being accelerated to an energy sufficient to trigger an avalanche in the tube. Incidentally this is why GM tubes are poor for spectrographic studies, the pulse height is largely independent of the energy of the particle.

A 3-500Z or whatever by contrast has a heated cathode that runs (normally) in a permanent cloud of electrons, with the grid screening them from reaching the anode. There is nothing like the electric field strength and nothing like enough gas (except in some modern tubes Sad ) to cause avalanche breakdown. 

Consider a electron being knocked off the grid by a cosmic ray, well given the grid capacitance and the size of the charge on the electron you can work out the change in voltage on the grid (hint is is small). The same applies to an electron knocked off a gas molecule as long as there is insufficient gas and electric field strength to cause an avalanche discharge (Which is a tube design consideration).

Tube breakdown in a sufficiently gassy tube might be triggered by a cosmic ray I suppose, but realistically that tube would fail in short order anyway if it is that gassy..
 
I don't really buy it as a significant effect.

Regards, Dan.
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AG6K
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« Reply #9 on: October 23, 2011, 09:01:50 AM »

Quote
Years ago I remember reading your proposals, where horrible arcs were started by a photon or gamma ray striking a tube biased-off on standby, and the gamma burst making the antenna relay arc when the tube was thrown violently into conduction by the x-ray.

I often think of your photon-bombardment-causing-relay-contact-arc and catastrophic HV failure theory when I turn the light on in my family room. I keep waiting for the neon bulb near the dog food bowl to explode, and kill an innocent puppy with shards of glass or molten metal, but nothing happens. :-)

That's really a very bizarre theory, that even argues against itself. For the tube to avalanche, it would have to be worse than a Geiger tube. It would have to be worse than a neon bulb.  I wouldn't spend much money shielding a tube that gassy from photons, unless it was in the warp drives on the USS Enterprise.

I also shine flashlights in my amplifiers on the tubes, and so far none have blown up.

73 Tom

  bizarre
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AG6K
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« Reply #10 on: October 23, 2011, 09:48:14 AM »

Quote
The GM tubes have a ***very*** fine wire used for the anode, so there is a very high electric field in the vicinity.

Thus an electron released at the cathode by the photoelectric effect or just a beta wondering into the tube at low energy will have a high probability of being accelerated to an energy sufficient to trigger an avalanche in the tube. Incidentally this is why GM tubes are poor for spectrographic studies, the pulse height is largely independent of the energy of the particle.

A 3-500Z or whatever by contrast has a heated cathode that runs (normally) in a permanent cloud of electrons, with the grid screening them from reaching the anode. There is nothing like the electric field strength and nothing like enough gas (except in some modern tubes Sad ) to cause avalanche breakdown.

Consider a electron being knocked off the grid by a cosmic ray, well given the grid capacitance and the size of the charge on the electron you can work out the change in voltage on the grid (hint is is small). The same applies to an electron knocked off a gas molecule as long as there is insufficient gas and electric field strength to cause an avalanche discharge (Which is a tube design consideration).

Tube breakdown in a sufficiently gassy tube might be triggered by a cosmic ray I suppose,

  Not tube breakdown/flashover, just conduction.

Quote
but realistically that tube would fail in short order anyway if it is that gassy..

  I was not thinking of a high energy photon only striking a gas atom in a tube Dan, I was thinking about it striking any atom in a tube and knocking one or more electrons loose -- thereby causing the tube to briefly conduct due to the several kilovolts present.  When a biased off transmitting tube even briefly conducts there is enough potential to arc the NO contacts on the Tx/Rx bias relay - which could cause major mischief.   The reason I started this thread is because two days ag I received a telephone from an Ham in Idaho whose 8166/4-1000A amplifier  had an event when it was in Rx / biased off.   Rich, ag6k
 
Quote
I don't really buy it as a significant effect.

Regards, Dan.
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AG6K
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« Reply #11 on: October 23, 2011, 10:00:24 AM »

Quote
Quite a lot has been published about semi conductors and radiation. The effects are very dependent on the process and the geometry: at Plessey Semiconductors, we had some logarithmic amplifier ICs in a bipolar process. These were irradiated to such an extent the white alumina substrate turned brown, and yet the change in performance of the three dual amplifier chips couldn't be measured.

But considering the vast number of vacuum tubes of one sort or another - TWTs, magnetrons, klystrodes as well as 'conventional' transmitting tubes in daily use, if it was an effect, it would appear far more frequently than the odd flashover.

  I am not talking about a blitzy flashover, I 'm talking about momentary conduction of a tube that is biased off.  I have occasionally been getting reports of this since the first QST article on parasites appeared in Fall 1988. The last such report was from Idaho on the 20th of this month.  Rich, ag6k
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AG6K
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« Reply #12 on: October 23, 2011, 10:14:32 AM »

Quote
There is a semi formal paper that was published fifteen or twenty years ago discussing cosmic radiation and its effect on semiconductors in personal computers.  It provided estimates of the chance of an individual being affected.   The numbers were small, but possible.

  My Toyota Prius has three computers.  Occasionally when I try to accelerate hard the computer-controlled throttle backs off and  acceleration stops.   The fix is to pull over, shut it off and relaunch.  As I understand it, some Prius owners occasionally have more serious computer controlled accelerator problems.  Nissan had similar problems with their computers but they came up with a clever workaround that takes the brakes out of anti-lock mode whenever the accelerator is advanced.  This allows the driver to stop the car even if the throttle is wide open.  Rich, ag6k
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M0HCN
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« Reply #13 on: October 23, 2011, 10:38:44 AM »

I was thinking about it striking any atom in a tube and knocking one or more electrons loose -- thereby causing the tube to briefly conduct due to the several kilovolts present.  
Work the numbers, gate capacitance, charge on an electron... delta V on the gate.

Lets assume a 1pf gate/cathode capacitance (more makes the effect smaller), then knocking an electron off and having it accelerate to a large distance will change the grid voltage by delta V = delta Q /  C = 10^-19 / 10^-12 = 10^-7 V  (Working to orders of magnitude).
It takes 10^7 electrons to change the bias by a volt given a completely open circuit grid @ 1pf...... The only way you are getting that is if the tube avalanches, and if there is enough gas for that you have worse problems (Or you have a hunk of Cs137 on the shelf behind the amp in which case you also have worse problems).
Quote
 The reason I started this thread is because two days ag I received a telephone from an Ham in Idaho whose 8166/4-1000A amplifier  had an event when it was in Rx / biased off.
Interesting, but I would be looking elsewhere.

Regards, Dan.

« Last Edit: October 23, 2011, 11:24:48 AM by 2E0CHE » Logged
W8JI
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« Reply #14 on: October 23, 2011, 12:49:32 PM »

AG6K  says:
Quote
  The reason I started this thread is because two days ag I received a telephone from an Ham in Idaho whose 8166/4-1000A amplifier  had an event when it was in Rx / biased off.

Quote
Interesting, but I would be looking elsewhere.
Regards, Dan.

The common cause of a faults on standby is a gassy tube, although sometimes it can be a HV fault outside the tube. I've seen dozens of cases where a tube will arc on standby. None of it is anything more than a simple tube fault.

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