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RE: The need for geiger counters for high voltage vacuum experiments

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  • Vaughn Mcdowell
    I have experimented with low to medium vacuum systems occasionally since the early 1960 s when I was in early high school. I have always been fascinated
    Message 1 of 2 , Sep 17, 2012
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      I have experimented with low to medium vacuum systems occasionally since the early 1960's when I was in early high school. I have always been fascinated watching gas discharge tubes glow; watching the Faraday disks and the dark space. Recently I decided to get back into vacuum systems because of some experiments I wanted to try out. Being on a beer budget I purchased items from Ebay such a thermocouple gauges and vacuum pumps on the cheap. The question being on the cheap what could I use for my reference; the best I could come up with is a home brew gas discharge tube. There is a lot of reference material regarding the degree of vacuum achieved verses what is being observed in the discharge. About two years ago when I decided to do my vacuum experiments I realized that high voltage and vacuum systems can be a recipe for X-Rays; so I purchased in advance from E bay Geiger counters ( for gamma => X ray) ; and radiation surveillance equipment; just in case.

      Here is the interesting part, I hope someone can help me on this one: 1) I wanted to get a rough idea as to the degree of the vacuum being achieved, on a beer budget, using the discharge tube as an indicator ( I cleaned the glass; polished the metal, rinsed with acetone and alcohol , . This is all I have for doing a rough calibration of my thermocouple gauges. Testing my good Welch 1400 and 1405 roughing pumps; this is what I have observed; 2) the electrodes were spaced about 11" connected to a low power 35KV power supply; as the vacuum progressed I observed that described in the text books; The tube had a valve connected to its input so that after pumping for hours and heating the tube with a heat gun to out gas;sealing it off when I was finished; opening it up again pumping it again;repeating this several times. I believe I finally got close to the pump's rated value maybe?? below a micron.

      When the dark space increased and started to disappear the glow became faint; !! my Geiger counters sounded off!! X-Rays; at first they were in the mil-radian region ; the glass had glowing streaks; as the pumping progressed the faint glow disappeared; then random gas pockets of discharge in pulses; !! the Geiger counter sounded off across the room now more powerfully!! I stayed in another room; then finally everything became silent except for an occasional discharge. I is at this point that I believe I am somewhere in the micron region or slightly less; I have abandoned this until I can do this safely. Any ways I have sense used these pumps to do a very rough calibration for my thermocouple gauges. Can anyone confirm the gas discharge and degree of vacuum?? The other thing I like about using a gas discharge is its color; water is a giveaway if I got the color correct.
    • Vaughn Mcdowell
      OOPS should be mR/hr instead of mil-radian; after the discoverer of X-Rays ________________________________ From: Vaughn Mcdowell
      Message 2 of 2 , Sep 17, 2012
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        OOPS should be mR/hr instead of mil-radian; after the discoverer of X-Rays


        ________________________________
        From: Vaughn Mcdowell <vaughn.mcdowell@...>
        To: mad_scientist@yahoogroups.com
        Sent: Monday, September 17, 2012 8:50 AM
        Subject: [mad_scientist] RE: The need for geiger counters for high voltage vacuum experiments


         
        I have experimented with low to medium vacuum systems occasionally since the early 1960's when I was in early high school. I have always been fascinated watching gas discharge tubes glow; watching the Faraday disks and the dark space. Recently I decided to get back into vacuum systems because of some experiments I wanted to try out. Being on a beer budget I purchased items from Ebay such a thermocouple gauges and vacuum pumps on the cheap. The question being on the cheap what could I use for my reference; the best I could come up with is a home brew gas discharge tube. There is a lot of reference material regarding the degree of vacuum achieved verses what is being observed in the discharge. About two years ago when I decided to do my vacuum experiments I realized that high voltage and vacuum systems can be a recipe for X-Rays; so I purchased in advance from E bay Geiger counters ( for gamma => X ray) ; and radiation surveillance equipment; just in case.

        Here is the interesting part, I hope someone can help me on this one: 1) I wanted to get a rough idea as to the degree of the vacuum being achieved, on a beer budget, using the discharge tube as an indicator ( I cleaned the glass; polished the metal, rinsed with acetone and alcohol , . This is all I have for doing a rough calibration of my thermocouple gauges. Testing my good Welch 1400 and 1405 roughing pumps; this is what I have observed; 2) the electrodes were spaced about 11" connected to a low power 35KV power supply; as the vacuum progressed I observed that described in the text books; The tube had a valve connected to its input so that after pumping for hours and heating the tube with a heat gun to out gas;sealing it off when I was finished; opening it up again pumping it again;repeating this several times. I believe I finally got close to the pump's rated value maybe?? below a micron.

        When the dark space increased and started to disappear the glow became faint; !! my Geiger counters sounded off!! X-Rays; at first they were in the mil-radian region ; the glass had glowing streaks; as the pumping progressed the faint glow disappeared; then random gas pockets of discharge in pulses; !! the Geiger counter sounded off across the room now more powerfully!! I stayed in another room; then finally everything became silent except for an occasional discharge. I is at this point that I believe I am somewhere in the micron region or slightly less; I have abandoned this until I can do this safely. Any ways I have sense used these pumps to do a very rough calibration for my thermocouple gauges. Can anyone confirm the gas discharge and degree of vacuum?? The other thing I like about using a gas discharge is its color; water is a giveaway if I got the color correct.




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