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Re: [TCML] Homemade Crookes Tube?





Hi All,


FWIW, the attenuation length for X-rays of 20KeV in dry air is on the order of 15mm and 
2mm in glass. Since it is highly unlikely that an electron will transfer  100% of its energy 
in a collision, this may be looked at as an upper limit.


Matt D.



-----Original Message-----
From: David Rieben <drieben@xxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sat, Sep 20, 2014 5:29 pm
Subject: Re: [TCML] Homemade Crookes Tube?






On Saturday, September 20, 2014 3:46 PM, David Rieben <drieben@xxxxxxx> wrote:
 


Stefan, Dave(s),

Repeating my previous "disclaimer" - I am no authority on this subject matter 
BUT ;^)
I really don't think that just a few thousand volts applied to a hard vacuum is 
going to 
pose a significant ionizing radiation hazard. Remember the old CRT computer 
monitors 
or better yet, the 25" or 27" CRT-type color TVs? Those "big screened" colored 
TV 
picture tubes required 25 to 30 kV to operate properly and I do seem to recall 
as a 
teenager (1970s) the concern for "some" x-ray exposure if one stood with their 
face 
pressed against the TV screen "for hours" while it was on ;^) Of course, thanks 
to the 
inverse-squared law, they were considered completely safe if viewed from a 
"proper 
distance". ;^)

BTW, Cobalt 60 DOES appear to be somewhat of pro in this matter and he also 
seems 
to agree with me that such relatively low voltages are NOT going to produce 
significant 
radiation hazards with hard vacuums.

Yet another David (Rieben)


On Saturday, September 20, 2014 8:35 AM, Dave Halliday <dh@xxxxxxxxxxxxxx> 
wrote:
 


Hi Stefan

Blue glow is perfectly normal:

http://www.thetubestore.com/Resources/Matching-and-other-tube-info/Blue-Glow

Dave

Subject: Re: [TCML] Homemade Crookes Tube?
> 
> Hi Cobalt
 60,
> 
> when I was experimenting with large transmitting tubes 
> (graphite anodes) at 
> only arround 6kV anode voltage, there was a bright blue 
> glowing visible 
> arround the complete inner surface of the glas bulb.
> I'm sure, this "fluorescence" was generated by x-rays, 
> hitting the glas. 
> Although not sure, which amount of x-rays really was able to 
> go through the 
> glas and hitting me, this was the main reason, I immediately 
> canceled all my 
> further experiments with such tubes, because I was afraid of 
> x-rays, even at 
> such low voltages. So I think the dangerous level is far 
> below 30kV, as you 
> stated.
> I even have some QB5/1750 Tetrodes, which are only 5kV anode 
> voltage or so, 
> and this tubes have "Danger X-Ray radiation" warning's on it.
> 
> Regards,
> Stefan
> 
> 
Dangerous x-rays require a minimum voltage of 
> 30 kV with some 
> > tubes operating with as much as 200 kV. Tungsten is the 
> typical target and 
> > a very hot high current filament is necessary to produce 
> powerful 10 keV 
> > and higher x-rays. The super hot filament is required to 
> emit enough 
> > electrons to generate the x-rays. What you have is
> > not much different than using a fluorescent lamp to arc to 
> the secondary 
> > output.
> >
> > A Bishop
> > Principal Device Physics Tech
> >
> > Sent from my iPad
> >
> >> On Sep 18, 2014, at 7:05 PM, David Rieben <drieben@xxxxxxx> wrote:
> >>
> >> Paul,
 

> >> I am certainly no authority
 on this matter but from what I 
> have gleaned, 
> >> you are not going to produce "hard" x-rays in this manner. 
> Besides the 
> >> hard vacuum, this would also require a white-hot filament (for an 
> >> electron source) for the cathode, a heavy metal target 
> (usually tungsten) 
> >> for the anode, and well over ~50  kVDC potential between 
> the said cathode 
> >> and anode to really produce the ionizing, body penetrating 
> hard x-rays 
> >> (even dental x-ray tubes typically run about 70 kV(DC)). 
> That being said, 
> >> if you are powering your tube with say 10 to 20 kVDC, you 
> may produce 
> >> some low energy "soft" x-rays, but I don't think it's 
> going to be a 
> >> significantly ionizing radiation source. I'm not even sure 
> if you can 
> >> produce any kind
 of x-rays at all with AC? That's just 
> "my" 2 cents. ;^)
> >>
> >> David
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla

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