Date: Thu, 26 May 2011 10:14:01

Author: Cliff Bettis

Subject: Re: Crookes Tube (was Re: Demo health hazards)

Post:

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Paul.



I was confused (wondering what sort of tube he was talking about) by Ed's
question as I don't think the cold cathode discharge tubes will light at 5
kV. There are electron beam tubes with a hot filament that do work at that
voltage and they are safe as far radiation is concerned.



I did measure the radiation from tubes excited by a hand held Tesla coil and
found substantial emission from some of them. All it takes is HV, a hard
vacuum, and a high Z target.



As far as safety goes, as long as you limit the time and aren't too close
the risk is not great. On the other hand, the demo guy gets a dose every
time the equipment is set up, so it's a good idea to wear a badge so you're
not left guessing. This is a moot point if your institution doesn't allow
the use of such sources in the first place.



Cliff



From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of Paul Nord
Sent: Thursday, May 26, 2011 9:19 AM
To: tap-l@lists.ncsu.edu
Cc: Paul Nord
Subject: Re: [tap-l] Crookes Tube (was Re: Demo health hazards)



Cliff,



Can you get it to light with just 5kV?



A "tradition" has developed here, and I think many other places as well, of
powering these with a little hand-held tesla coil. (High-Frequency Coil
) Or the old
spark timer power supply.



It works great. And it produces very bright beam of "cathode rays" in the
tubes.



The voltage is very high. Has anyone measured one of these? Perhaps 50kV?
100kV? If that produces x-rays of similar energy, those are very
penetrating; chest x-ray range.



Adolf Cortel's video demonstrates this very clearly: YouTube - Cathode-ray
tubes: be aware of X-Rays!
He shows those penetrating paper, exposing film, and going through aluminum
foil to his geiger counter. I don't know if there is additional material in
the geiger counter but the x-rays have clearly traveled through air, metal
foil, and the plastic housing of the geiger counter. That should be enough
energy to penetrate your skin and then some.



I'm thinking that it would be fun to measure an energy spectrum at various
positions around the tube.



The guidelines from the PIRT site might be very reasonable: "ARRA
regulations require that the voltage on the Tenma power supply be less than
6 volts. All operators must be trained and wear a dosimetry. All spectators
must be at least 10 feet away. A radiation sign must be displayed. Lucite
boxes should be placed over tube and power supply." Though I'd like a
better description of the voltage and current output from the power supply
in a guideline. (source here:Deflection of an electron beam
) And perhaps a radiation survey should
be done before the tube is operated with spectators.



All that said... I keep coming back to the standard for radiation safety,
"A.L.A.R.A. As Low As Reasonably Attainable." This suggests planning any
work to minimize radiation exposure to the lowest reasonable dose. For a
very "reasonable" price, you can make the radiation does from this demo go
to zero by replacing it with a tube that uses a much lower voltage and a hot
cathode: Nakamura Crookes Tube - NADA Scientific
. This device (or a
similar one) will do everything that the old tube will do. Zero is a nice
low radiation dose. And the price, though it is a lot of money, seems very
"reasonable" for being able to say to your students, "No, we did not expose
you to any radiation in the classroom."



Paul





On May 26, 2011, at 7:30 AM, Cliff Bettis wrote:





Ed,



I am not sure what kind of tube you're talking about. The cold discharge,
evacuated tubes that can emit X-rays operate at higher voltages than that.
If it is only 5kV, X-rays of that energy don't travel very far in air.



Cliff



From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of Edward Sabol
Sent: Wednesday, May 25, 2011 8:09 AM
To: new tapl
Subject: Re: [tap-l] Crookes Tube (was Re: Demo health hazards)



The demo was powered with the spectrum tube power supplies. Not sure but it
appears to be 5000 V with tube in place.

_____

From: cbettis@unlserve.unl.edu
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] Crookes Tube (was Re: Demo health hazards)
Date: Wed, 25 May 2011 07:55:33 -0500

Ed,



The TV manufacturers, back when they used CRTs, limited the accelerating
voltage below 30 kV (I suppose figuring that X-rays of energies less than
that wouldn't go through the glass or very far in air). The voltage you
place on one of these tubes will determine the X-ray energy; the current
through the tube will determine its intensity. The individual tube
properties vary from time to time so it's hard to predict what you'll get
from a particular tube. Our (University of Nebraska) radiation safety rules
prohibit the use of powered X-ray sources with unregulated power supplies
(like an induction coil). You can control the potential of an induction coil
by the spacing of discharge points connected in parallel to it but not the
current.



One of our local high school teachers actually used a demonstration Crooke's
tube to take an X-ray picture. He was very careful about it, using a remote
on/off switch.



If you do use these things I suggest you have adequate dosimetry and talk
with your safety people first.



Cliff



From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of Edward Sabol
Sent: Wednesday, May 25, 2011 7:17 AM
To: new tapl
Subject: Re: [tap-l] Crookes Tube (was Re: Demo health hazards)



What level voltage would be over driving?

_____

From: tim.cook@asu.edu
To: tap-l@lists.ncsu.edu
Date: Tue, 24 May 2011 17:16:17 -0700
Subject: Re: [tap-l] Crookes Tube (was Re: Demo health hazards)

I have a pdf of it - 47 pages 3.8 mb. We got it from Cliff Bettis I think.
When we redid the PIRT website that must have stopped working. It's a
government document so there should be no problem posting it. Can someone
remind me where to do this and I'll give it a try.



Tim



From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of Paul Nord
Sent: Tuesday, May 24, 2011 12:41 PM
To: tap-l pira
Cc: Paul Nord
Subject: [tap-l] Crookes Tube (was Re: Demo health hazards)



(I think that this message did not go through. Sorry if it's a duplicate.)



There was an excellent article documenting the X-Ray intensity from one of
these tubes. Someone had placed dosimeters at various distances in a grid
around one of these and mapped the radiation flux.



I've lost my reference for that article. I think it was linked here:
Deflection of an electron beam | PIRT - Physics Instructional Resource Team




Does anyone have that?



Paul





On Apr 22, 2011, at 4:53 PM, Paul Nord wrote:



I'm picking up a very old thread to share an important video I just found.
This was made by Adolf Cortel. It's a very convincing demonstration of the
x-ray hazard from one of these old Crookes Tubes.

YouTube - Cathode-ray tubes: be aware of X-Rays!




Paul



On Feb 13, 1996, at 2:14 PM, clifford bettis wrote:



I have a letter in my files
concerning all of our crookes type tubes and I tell people who insist
on using this equipment that I will set it up but I will not test it
nor will I be responsible for the regulatory fall out if someone
complains. I show them the letter documenting what kind of exposure
you can get from something as simple as an electron beam tube and a
hand held tesla coil. I have never had anyone insist further than
that, especially since there are safe alternatives to most of the
things the want to show.










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Paul. I was confused (wondering what sort of tube he was talking about) by =
Edís question as I donít think the cold cathode discharge =
tubes will light at 5 kV. There are electron beam tubes with a hot =
filament that do work at that voltage and they are safe as far radiation =
is concerned. I did measure the radiation from tubes excited by a hand held Tesla =
coil and found substantial emission from some of them. All it takes is =
HV, a hard vacuum, and a high Z target. As far as safety goes, as long as you limit the time and arenít =
too close the risk is not great. On the other hand, the demo guy gets a =
dose every time the equipment is set up, so itís a good idea to =
wear a badge so youíre not left guessing. This is a moot point if =
your institution doesnít allow the use of such sources in the =
first place. Cliff From:=
=
tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On =
Behalf Of Paul NordSent: Thursday, May 26, 2011 9:19 =
AMTo: tap-l@lists.ncsu.eduCc: Paul =
NordSubject: Re: [tap-l] Crookes Tube (was Re: Demo health =
hazards) Cliff, Can you get it to light with just =
5kV? A =
"tradition" has developed here, and I think many other places =
as well, of powering these with a little hand-held tesla coil. (High-Fr=
equency Coil) Or the old spark timer power =
supply. It works great. And it produces very bright beam =
of "cathode rays" in the =
tubes. The voltage is very high. Has anyone measured =
one of these? Perhaps 50kV? 100kV? If that produces =
x-rays of similar energy, those are very penetrating; chest x-ray =
range. Adolf Cortel's video demonstrates this very clearly: =
YouTube =
- Cathode-ray tubes: be aware of X-Rays! He shows those =
penetrating paper, exposing film, and going through aluminum foil to his =
geiger counter. I don't know if there is additional material in =
the geiger counter but the x-rays have clearly traveled through air, =
metal foil, and the plastic housing of the geiger counter. That =
should be enough energy to penetrate your skin and then =
some. I'm thinking that it would be fun to measure an energy =
spectrum at various positions around the =
tube. The guidelines from the PIRT site might be very =
reasonable: "ARRA =
regulations require that the voltage on the Tenma power supply be less =
than 6 volts. All operators must be trained and wear a dosimetry. All =
spectators must be at least 10 feet away. A radiation sign must be =
displayed. Lucite boxes should be placed over tube and power =
supply." Though I'd like a better description of the voltage =
and current output from the power supply in a guideline. (source =
here:Deflection of an electron =
beam) And perhaps a radiation survey should be done =
before the tube is operated with spectators. All that said... I keep coming back to the standard =
for radiation safety, "A.L.A.R.A. As Low As Reasonably =
Attainable." This suggests planning any work to minimize =
radiation exposure to the lowest reasonable dose. For a very =
"reasonable" price, you can make the radiation does from this =
demo go to zero by replacing it with a tube that uses a much lower =
voltage and a hot cathode: Nakamura =
Crookes Tube - NADA Scientific. This device (or a similar one) will =
do everything that the old tube will do. Zero is a nice low =
radiation dose. And the price, though it is a lot of money, seems =
very "reasonable" for being able to say to your students, =
"No, we did not expose you to any radiation in the =
classroom." Paul On =
May 26, 2011, at 7:30 AM, Cliff Bettis wrote:Ed, I am not sure what kind of tube youíre talking about. The cold =
discharge, evacuated tubes that can emit X-rays operate at higher =
voltages than that. If it is only 5kV, X-rays of that energy donít =
travel very far in air. Cliff From:=
tap-l-owner@lists.ncsu.edu=
[mailto:tap-l-owner@lists.ncsu=
.edu] On Behalf =
Of Edward =
SabolSent: Wednesday, May 25, 2011 8:09 =
AMTo: new =
taplSubject: Re: [tap-l] Crookes Tube (was =
Re: Demo health hazards) The demo =
was powered with the spectrum tube power supplies. Not sure but it =
appears to be 5000 V with tube in place.From: cbettis@unlserve.unl.edu=
To: tap-l@lists.ncsu.eduSubject:=
Re: [tap-l] Crookes Tube (was Re: Demo health hazards)Date: Wed, 25 =
May 2011 07:55:33 -0500Ed, The TV manufacturers, back when they used CRTs, limited the =
accelerating voltage below 30 kV (I suppose figuring that X-rays of =
energies less than that wouldnít go through the glass or very far =
in air). The voltage you place on one of these tubes will determine the =
X-ray energy; the current through the tube will determine its intensity. =
The individual tube properties vary from time to time so itís hard =
to predict what youíll get from a particular tube. Our (University =
of Nebraska) radiation safety rules prohibit the use of powered X-ray =
sources with unregulated power supplies (like an induction coil). You =
can control the potential of an induction coil by the spacing of =
discharge points connected in parallel to it but not the =
current. One of our local high school teachers actually used a demonstration =
Crookeís tube to take an X-ray picture. He was very careful about =
it, using a remote on/off switch. If you do use these things I suggest you have adequate dosimetry and =
talk with your safety people first. Cliff From:=
tap-l-owner@lists.ncsu.edu=
[mailto:tap-l-owner@lists.ncsu=
.edu] On Behalf =
Of Edward =
SabolSent: Wednesday, May 25, 2011 7:17 =
AMTo: new =
taplSubject: Re: [tap-l] Crookes Tube (was =
Re: Demo health hazards) What level =
voltage would be over driving?From: tim.cook@asu.eduTo: tap-l@lists.ncsu.eduDate: =
Tue, 24 May 2011 17:16:17 -0700Subject: Re: [tap-l] Crookes Tube =
(was Re: Demo health hazards)I have a pdf of it Ė 47 pages 3.8 mb. We got it from Cliff =
Bettis I think. When we redid the PIRT website that must have stopped =
working. Itís a government document so there should be no problem =
posting it. Can someone remind me where to do this and Iíll give =
it a try. Tim From:=
tap-l-owner@lists.ncsu.edu=
[mailto:tap-l-owner@lists.ncsu=
.edu] On Behalf =
Of Paul =
NordSent: Tuesday, May 24, 2011 12:41 =
PMTo: tap-l =
piraCc: Paul =
NordSubject: [tap-l] Crookes Tube (was Re: =
Demo health hazards) (I think =
that this message did not go through. Sorry if it's a =
duplicate.) There was =
an excellent article documenting the X-Ray intensity from one of these =
tubes. Someone had placed dosimeters at various distances in a =
grid around one of these and mapped the radiation =
flux. I've lost =
my reference for that article. I think it was linked here: Deflection =
of an electron beam | PIRT - Physics Instructional Resource =
Team Does anyone =
have that? Paul<=
o:p> On Apr 22, =
2011, at 4:53 PM, Paul Nord wrote: I'm picking =
up a very old thread to share an important video I just found. =
This was made by Adolf Cortel. It's a very convincing =
demonstration of the x-ray hazard from one of these old Crookes =
Tubes.YouTube - Cathode-ray tubes: be aware of =
X-Rays! Paul<=
o:p> On Feb 13, =
1996, at 2:14 PM, clifford bettis =
wrote: I have a =
letter in my files concerning all of our =
crookes type tubes and I tell people who insist on using this =
equipment that I will set it up but I will not test it nor will I be =
responsible for the regulatory fall out if someone complains. I show them =
the letter documenting what kind of exposure you can get from =
something as simple as an electron beam tube and a hand held tesla coil. =
I have never had anyone insist further than that, especially since =
there are safe alternatives to most of the things the want to =
show.
------=_NextPart_000_007C_01CC1B8D.A24DFB20--


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