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
____________________________________________________________________
_____
David A.
Katz
Chemist, Educator, Expert Demonstrator, Science Communicator,
and
Consultant
Programs and workshops for teachers,
schools,
museums, and the public
133 N. Desert Stream Dr. * Tucson, AZ
85745-2277 * USA
voice/fax: (520) 624-2207 * email:
dakatz45**At_Symbol_Here**msn.com
Visit my web site:
http://www.chymist.com___________
______________________________________________________________
----- Original Message -----
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
