Re: [TCML] current limit system and X-rays

[Jim Lux <jimlux@xxxxxxxxxxxxx>]

I don't think it depends on mfp in the tube. Xray tubes are hard vacuum (1e-9 torr?) with mfp probably measured in meters or km. 

On Sep 27, 2010, at 7:55 AM, Chan Jeremy <jeremy_runescape@xxxxxxxxxxx> wrote:

> 
> It depends on the mean free path of electrons in the tube, hence the high vacuum. If the mean free path is 1/4 the distance between the 2 electrodes in a tube rated 120KV then you will get mostly 30KeV X rays. you might get some X ray production with an AC power supply at TC frequencies, but I think that output will be minimal. These tubes were designed to operate on HVDC.
> 
>> Date: Mon, 27 Sep 2010 07:10:10 -0700
>> From: jimlux@xxxxxxxxxxxxx
>> To: tesla@xxxxxxxxxx
>> Subject: Re: [TCML] current limit system and X-rays
>> 
>> David Rieben wrote:
>>> Hi,
>>> 
>>> snipperzz:
>>> 
>>> ----- Original Message ----- From: "Frank" <fxrays@xxxxxxxxxx>
>>> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
>>> Sent: Sunday, September 26, 2010 6:00 PM
>>> Subject: Re: [TCML] current limit system and X-rays
>>> 
>>> 
>>> 
>>>> Almost the universal voltage for most X ray work is 40-60 KV.
>>>> 
>>>> Using an NST will not work unless you can series them, even a 15KV 
>>>> transformer will be pushed.
>>>> 
>>> 
>>> Actually, dental x-rays typically run 60 to 70 kV at only
>>> a few mAs. However, medical x-rays can run >100 kV at hundreds of mAs, 
>>> depending on how much soft tissue that
>>> must be pentrated to get a clear image of the target "innards".
>>> Of course, exposure time is nearly always in the fractions of
>>> a second.
>>> 
>> 
>> and it gets trickier than that, because a standard accelerating voltage 
>> for medical x-rays is 110kV.. BUT, the actual energy of the xrays coming 
>> out is quite a bit less  ( peaking at around 30keV), but a typical x-ray 
>> machine will use an aluminum "hardening" filter that filters out the 
>> lower energy photons, leaving the remainder averaging up around 50-60 keV.
>> 
>> But.. it would be unusual to get significant xray production from NST 
>> voltages, even in a hard vacuum.  After all, the maximum energy would be 
>> the 21kV peak voltage from a 15kVrms NST, and just as with the 110kVp 
>> xrays, the vast majority of photons will be much lower energy, and not 
>> even make it out of the tube.
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