Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Can anyone identify these tubes?
Summary: Photomultiplier tube & Hollow Cathode Lamp from AA spec
Message-ID: <3903@kitty.UUCP>
Date: 31 Jul 90 02:29:07 GMT
References: <1624@oucsace.cs.OHIOU.EDU>
Organization: Recognition Research Corp., Clarence, NY
Lines: 57

In article <1624@oucsace.cs.OHIOU.EDU>, bwhite@oucsace.cs.ohiou.edu (Bill White ) writes:
> 	I happened to end up with two tubes that had originally been for
> some sort of X-ray experiment, I think ..

	Not x-ray.  Both of these items are most likely from a Jarrell-Ash
AA (Atomic Absorption) spectrophometer.  AA is a sensitive method used in
analytical chemistry for quantitative elemental determinations.  A sample
of an unknown is atomized into a flame (typically acetylene-nitrous oxide),
with the flame being inserted in the optical path between a single-element
light source and a photomultiplier tube with a monochromator in front of
it.  The monochromator is set to a particular absorbance wavelength for
the element being determined.  A good AA has sensitivity into the ppb range.

	Jarrell-Ash is an old line company which manufactured spectrographs
for many years.  During the 1970's they were bought by Fisher Scientific,
which was in turn bought by Allied Chemical.  Several years ago, Allied
sold Jarrell-Ash to Instrumentation Laboratory, Inc.

> 1.	1P28 (or IP28, I'm not sure).  This has 11 pins, and the glass part
> 	is covered with some kind of black paint, save for a window in which
> 	I can see either a filament or a grid of some kind.

	This is a very common photomultiplier tube, originally made by RCA,
but now made by Hamamatsu and other vendors.  The 1P28 has a UV glass window
and is usable from below 200 nm to probably 650 nm.  The photocathode
material is antimony-cesium.  Of the 11 pins, 9 are dynodes, 1 is a plate,
and 1 is a cathode.  Dynodes are typically connected in series with
resistors.  Operating voltage (anode to cathode) is typically 1,000 VDC.

> 2.	Jarrell Ash Hollow Cathode Type 45439.  It also says "Cathode Na-K",
> 	"Max Current 25 ma", and "Gas NE".  And indeed, it is filled with
> 	neon, as a little experimentation shows.

	This lamp is used as a light source for an AA, and appears to
contain a two-element cathode impregnated with sodium and potassium.
When suitably excited, this lamp will provide emission lines of sodium,
potassium and neon.  Hollow cathode lamps are available with other
elements, usually one element per lamp, but multi-element lamps such as
you have also exist.

	The hollow cathode lamp does not produce great light intensity,
but it does have very narrow resonance lines - which makes it usedful for
AA.  A hollow cathode lamp typically operates from 200 to 300 volts DC
at less than 30 mA, and develops a cathode temperature of between 300 and
400 deg C (which is colder than it may look).

> So, any idea?  If worse comes to worse, I can crack open the latter one for
> the sodium-potassium alloy and drop it in the Hocking River, but I'd prefer
> to know what these are actually _for_.

	You won't get any meaningful quantity of sodium or potassium.
Why not save it for a rainy day, or to calibrate a spectrographic
instrument some day?  Or, you can build your own AA. :-)

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231   {boulder, rutgers, watmath}!ub!kitty!larry
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