Date: Thu, 30 Sep 2010 17:00:43 -0700
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From: DAVID KATZ <dakatz45**At_Symbol_Here**MSN.COM>
Subject: Re: UV and gas discharge tubes
In-Reply-To: A

I have been using cathode ray tubes and spectrum tubes with my classes for approximately 40 years.
Cathode ray tubes, also called Crookes or Geissler tubes, can generate some x-rays.  These are powered by an induction coil which has a power adjustment (a potentiometer).  If the power level is kept low, duration of use is short, and the students are at a safe distance of about 10 feet or more, there should be not any x-ray problem.  The reason these were taken off the market was that individuals would use high power to get the brightest possible stream of cathode rays and were irresponsibly generating unnecessary x-rays.
Spectrum tubes, such as those for hydrogen, helium, sodium vapor, mercury vapor, etc. are designed to be used to observe visible spectra in the 400 to 800 nm region.  I don't particularly like the standard power supplies as they only have an on-off switch and appear to send a lot of power through the tubes.  I recommend using a large rheostat, such as the type used for controlling the voltage to the old heating mantles, to lower the voltage to the power supply.  That should reduce any UV or x-rays generated.  Again, students should be kept at a reasonable distance from these tubes, although I have not read any precautions about dangerous radiation from these tubes.
In my lecture classes, I pass out pieces of Flinn C-Spectra (about 1.5 cm square), a holographic diffraction grating with approximately 300 lines/mm.  Students can view the visible spectra from the back of the darkened lecture hall without any additional apparatus. You can contact Flinn to obtain a sample of the C-Spectra. 
In the lab we use those triangular shaped plastic spectroscopes which contain a small piece of holographic diffraction grating (approx. 600 lines/mm) to view visual spectra against a numerical scale.  Students can see the spectra in a slightly darkened room at a distance of several feet from the spectrum tube. This latter type of spectroscope allows for relative wavelengths to be measured (although we don't do much of that anymore).  
These tubes are only used about once each semester and generally for short duration of operating times. No one, in my experience with these tubes, has suffered any adverse effects.  That includes me, as I am usually in close proximity to the operating tubes. 
David Katz
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  David A. Katz             
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----- Original Message -----
From: Murphy, Dr. Ruth Ann
To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Sent: Thursday, September 30, 2010 10:50 AM
Subject: [DCHAS-L] UV and gas discharge tubes

Good Afternoon!

How much of a risk of UV damage to the eye is there from using spectroscopes and looking at hydrogen spectra, mercury vapor spectra, etc.? One lab text admonishes students not to =93look directly=94 at the illuminated lamps.  Do you think this - along with wearing the usually splash goggles -  is sufficient precaution?

Thank you.

Ruth Ann

Ruth Ann Murphy, Ph.D.

Professor of Chemistry

Chairperson, Department of Chemistry, Environmental Science and Geology

Chairperson, Health Professions Advisory Committee

JAMP Faculty Director

Goldwater Scholarship Faculty Representative

The University of Mary Hardin-Baylor

900 College Street

Belton, TX  76513-2599

Phone 254.295.4542

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