Re: Spinthariscopes, scintillators, etc... (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 29 Oct 2003 13:06:00 -0700
From: Kevin Christiansen <kevinc@xxxxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Spinthariscopes, scintillators, etc...

At 11:30 AM 10/27/03 -0700, you wrote:
>Original poster: Steven Roys <sroys@xxxxxxxx>
>
>
>Whilest meandering the web, I found a reference that said that the
>phosphor from a black and white TV set is a mixture of two phosphors, one
>of which is a silver-activated ZnS that responds to radiation.  I'm going
>to sacrifice one of my old B&W tv's to see for myself how it works, but
>can anyone confirm or deny this, and does anyone know how much phosphor is
>actually used in a typical portable TV picture tube?  I DO know that the
>silver-activated phosphor by itself is very expensive, and if old, dead
>B&W tv's have enough to to make it worth destroying them, they would be a
>great source of very cheap phosphor material for your scintillators or
>whatever.
>
>Steve
>

It's funny you should bring this up, because finding some radiation-
sensitive phosphors was already on my "to do" list for last night.
I checked a bunch of different phosphors with an americium source
from a smoke detector, in a dark room, after my eyes had dark-adjusted
for a few minutes.  Here is what I found - "works" means that the
americium causes it to glow, "nope" means that the americium did not
cause any glowing that I could see.

Two different x-ray screens - both work great.
An old bottle of glow-in-the-dark paint - works great.
A glow-in-the-dark plastic toy - nope.
  (The plastic probably blocks the Alpha particles.)
Some modern "rare earth" glow-in-the-dark powder - nope.
White phosphors from three different incandescent light bulbs - nope.
White phosphors from a high pressure mercury lamp (HID lamp) - nope.
Pixel phosphors from a 1993 NEC color computer monitor - works great!
"Voltarc Green" neon tube phosphors - works great!
"Voltarc Sparkling Blue" neon tube phosphors - works, medium brightness.
"Voltarc Snow White 6500" neon tube phosphors - works, very dim.

I scraped the phosphors off the back of the computer monitor screen
with a 3 x 3 inch piece of standard photocopy paper.  The phosphor
coating is in two layers. The top (silvery white) layer came
off easily in large sheets. This layer does not glow under the
americium source. The actual phosphor pixels were under that layer,
and they took a little scraping with the edge of the paper to get
them off, and when they did come off, they came off as a fine powder.
This powder glows very well under the americium source.

After spending several hours scraping and testing phosphors, I
have decided that it's probably a lot easier to take advantage
of Richard Hull's offer for his brand-spankin-new nice-and-pure
P4 phosphors...

[It's definitely easier, and for $10 you can't go wrong.  But information
like this is nice to know, particularly since not everyone is enthusiastic
or dedicated enough to spring for a $700 bottle of phosphor.  And who
knows when Richard's supply will run out.  Another thing that might need
to be considered is the phosphor's persistence.  Even if something glowed
like blazes when irradiated, you might not want it to CONTINUE glowing
like blazes after you removed the radiation.  It would depend on your
application, but I would think that in general a long persistence phosphor
would not be as good as one with a short decay time.  A long persistence
phosphor would reduce flicker at low refresh rates, but really trash any
temporal resolution you could hope for.  From what I've found, P4 has a
fairly short persistence. SRR]

 - Kevin Christiansen