Index Home About Blog
From: John De Armond
Subject: Re: Opinions wanted: Trijicon vs. Meprolight
Organization: Dixie Communications Public Access.  The Mouth of the South.

grl@drutx.ATT.COM (Randy Lyman) writes:

#Do any of you have first-hand experience with night sights such
#as those made by Meprolight or Trijicon?  These are the tritium
#(radioactive) sights described in an article by Charles Petty
#featured in the February "American Rifleman."

A friend I quite often shoot with had a Glock with Trijicon sights.
That's the only part of the gun I'm impressed with. (Yep I'm a
glock hater)  They are extremely bright and the three dots line
up very easily.

#This article mentions that the Trijicon sights can be damaged
#by acetone or ethanol, whereas Meprolight claims that their
#sights are "impervious to solvents."  I'm wondering if there are
#any other significant differences between the two brands.

Don't know.  Peering through a 10X loupe, the Trijicon sight appears to have
small glass capsules full of tritium gas and phosphor for each dot.  They
appear to be held in with some kind of epoxee or other cement.  The only
comment I can make regarding solvent sensitivity is that these sights have
demonstrated no problems in a year or so of use.


From: John De Armond
Subject: Re: Trijicon Sights
Organization: Dixie Communications Public Access.  The Mouth of the South. (WALTER EMIL TEAGUE III) writes:

#I was wondering if anybody has any info. on the effects to long term
#exposure to Trijicon sights.

No effects.

#Like the cancer caused by radar guns,

No effects, other than in the minds of some overly-cautious police

#things may be causing problems which we currently know nothing about.  I
#would like some input.

Very little about the effects of ionizing radiation we don't know about.

To the subject of tritium specifically, the decay of tritium releases
one very low energy beta (electron) with insufficient energy to escape
a solution or solid matrix nor to penetrate more than a millimeter or so in a
gas cloud.  No beta radiation escapes the illumination capsule.  Even
when ingested, tritium is considered by the government to be a trivial
hazard and objectively speaking, presents no hazard.  The biological
half-life of tritium (how long it stays in the body) is only a few days
because its tritium oxide, the most common form, is chemically almost
identical to water.

There is NO radiation exposure associated with an intact tritium
sight.  And even if you remove the capsule and eat it, the risk
is vanishingly small to nonexistent.


From: John De Armond
Subject: Re: Lifespan of Trijicon Sights
Organization: Dixie Communications Public Access.  The Mouth of the South. (Darin Okuyama) writes:

#Does anyone know how long the Trijicon nights
#sights will last?  Also, how long before they
#start to dim?

Tritium's half-life is a touch over 12 years.  Theoretically the
sight would be at half its original brightness in 12 years.  In reality,
the life is shorter than that.  The rather intense radiation bombardment
damages the phosphors.  While there appears to have been advances in
phosphor technology in the last few years, tritium light tubes I've
owned for about a decade are very dim.  These are backlight tubes for
displays on military equipment so I'd expect it to be of high quality.
I think 10 years would be a good estimate for planning purposes.


From: John De Armond
Subject: Re: Lifespan of Trijicon Sights
Organization: Dixie Communications Public Access.  The Mouth of the South. writes:

#This means that there will always radioactivity in the sights.
#It is important to know : (1) when the original material of the
#sights were made; (2) when the sights were made; (3) how long they
#were in stock before you bought them. Then you can do some head-
#scratching and arithmetic. The important question is how much of the
#original beta-emiiting energy is required to maintain luminosity
#sufficient for your eyes (aging?) to see in the dark.

Only partially true and not for the reason cited.  Half-life is
a relative term.  In 12.6 years from a reference time, half of whatever
there was will remain.  That means if you look at you sight now,
all else being equal (which it isn't), the sight would be at half
intensity in 12.6 years.   Then it another 12.6 years it will be at
half THAT intensity.  It doesn't matter when it was made.  The
radioactivity falloff is relative to whatever time reference you choose.
Say, from the date you open the package.

Knowing the approximate age is still important, however, because phosphor
degradation is the dominent failure mechanism.  The phosphor will
be hammered into darkness by the beta bombardment much faster than
the tritium decays.


From: John De Armond
Subject: Re: Tritium decay series/containment?
Organization: Dixie Communications Public Access.  The Mouth of the South. (D. T. Burroughs) writes:

#	With all the discussion of the half-life of tritium, I became
#curious about the actual decay of the isotope.  What is the radiation
#emitted during the decay?  Is it just a beta particle (electron), or
#is there also a gamma photon emitted during the decay?  What is the
#decay series i.e. what does the tritium atom become after emitting
#the radiation?  Anyone know the energies (eV) of the particle(s)?

Tritium decays with a single 18.6 KEV beta to helium.  This is
a very low energy beta, the lowest of any common isotope.
To put this in perspective, Stronium-90 (actually the immediate
decay product Yr-90) decays with a 2282 KEV beta.  The beta is
too weak to escape a solution of H-3 or a solid compound involving
H-3 bound in the molecular structure.  That's what makes it so nice
for luminous purposes.  It is radiologically harmless and yet the
beta has enough energy to stimulate a phosphor.

#	Also, how is the tritium contained in the Trijicon sights?
#Is it in a gaseous form inside a container, or somehow combined in a
#crystalline or amorphous solid carrier similar to the glass method of
#radioactive waste disposal?

I can't speak to the Trijicon in particular but the two most common
forms are tritiated water (vapor) or a tritiated polymer, typically
polyethylene.  The glass encapsulated systems such as the Trijicon
almost always use tritiated water.  The phosphor is deposited on the
inside of the capsule.  A common example of tritiated polymer are the
self-luminous EXIT signs seen in aircraft and some buildings.  The
phosphor is mixed with the polymer and the result is a solid block of
plastic that glows.


From: John De Armond
Subject: Re: Seeking glow-in-the-dark paint
Organization: Dixie Communications Public Access.  The Mouth of the South.
Date: 20 Jun 1994 17:59:56 -0400 (Ross Bagley) writes:

Let's see if we can clean this mess up.

#This isn't day-glo paint which is phosphoresent, but glow-in-the-dark
#which is luminesent.  Big difference for you lucky readers :)

Day-glo paint is fluorescent which means it absorbs photons of
light of one color (in this case ultraviolet) and then re-emits it at
a lower frequency (whatever color the paint is).  Phosphoresence (as
applied in the context of paint) is the ability of a substance to "store"
light.  That is, it glows for awhile after being exposed to visible
light.  Fluorescence and phosphoresence are quite similar mechanisms.
Phosphorescenct materials simply delay releasing its stored energy
as opposed to fluorescent materials which do so almost immediately.
Luminesence refers to the ability of a substance to emit light
without an external source of energy.  Chemical (such as lightening bugs)
and nuclear powered luminescent sources are common.

#I heard this too.  Actually, it's not too suprising.  The paint contains
#a slightly radioactive salt, radium I think (someone correct me if this is
#wrong) along with a phosphoresent dye that absorbs the higher energy quanta
#and releases them as visible light.  Light impinging on the salt somehow
#temporarily increases the rate of radioactive decay (could be electron
#orbital related) and that makes those glow-in-the-dark toys and clock hands
#really bright for a little while.  They are always dimly visible though
#(in the dark) and you are correct that this is the cheap way to get night-

First off, radium is intensely radioactive, indeed the definition of the
Curie was originally that amount of activity in a gram of radium.  Radium
was used in luminous paint in the WWII era.  It was typically a mix of
radium chloride and activated zinc sulfide.  The zinc sulfide absorbs
energy from an alpha particle emitted from the radium and is excited.
A few nanoseconds later it sheds this energy as a photon of visible
light.  Radium was a particularly poor choice as an energy source because
it emits copious amounts of highly penetrating gamma rays and because
the high energy alphas destroy the zinc sulfide over time.  As an
example, I have a luminous button designed to be worn on the lapel
with a grease-penciled code number on it.  It was issued to my dad
in France in WWII and enabled sentries identify people without
the use of a flashlight.  This button no longer glows, the radium having
long since destroyed the phosphor but it DOES emit a LOT of radiation.
About 0.1 R/Hr at a foot.  I use it as a calibration source in my lab.
It is normally stored in a lead pig.  Dad said that they got a couple
hundred of these things packed in a wooden box!

Radium is also particularly bad because it acts chemically enough like
calcium that it seeks the bone when ingested and once incorporated
into bone, it is almost impossible to get rid of.  The famous case
of the women who painted instrument dials with radium paint in the
plant in NY involved bone-related problems from the huge amount of
radium absorbed as they used their tongues to point their brushes.

These days tritium, the third isotope of hydrogen, is used as the energy
source.  It has a decent half-life, emits only a low energy
beta that does a good job of stimulating phosphors while not presenting
any health risks.  And it's cheap since it is a man-made isotope
manufactured in huge quantities by the US govt for weapons purposes.

#The only thing you can buy now is phosphoresent paint.  Hey, maybe you could
#buy some pitchblende (uranium ore), take some shavings or carefully ground
#fragments and paint them with the phosphoresent paint.  Then glue them to
#your sights.  Although hazardous to manufacture, these could work fairly
#well for night sights.

Ah, NO.  Pitchblende isn't very radioactive, containing only a few mg/ton
of radium at best.  Besides the phosphor must be activated for the
type of radiation at hand (for any decent conversion efficiency) so
bombarding just an phosphor with radiation doesn't work very well.

Now to the original question.

For luminous sights, I recommend just getting a Trijicon sight.
Because it uses a phosphor-coated capsule filled with tritium gas, it will
glow brighter than anything you can cook up at home for the simple
reason that the beta is so low in energy than any solid or liquid absorbs
most of them before they can reach the phosphor.

But let's say you want to play.  Fair enough.  You can't buy tritiated
paint.  The radiophobes have taken care of that.  But you CAN buy
tritium-activated luminous material.  Many companies sell self-activated
EXIT signs.  I'm looking at one right now in the American Hotel Register
Supply company catalog but I also know that Lab Safety Products Inc and
other similar safety products companies sell them.  They typically cost
under $300.  These look like ordinary EXIT signs except that the light
is replaced by a sheet of tritiated polyethylene plastic.  The tritium
is bound up in the polyethylene molecule and the plastic is doped with
phosphor.  When you open up the sign, you find a sheet of plastic that
glows fairly intensely.

Once you have this sheet of plastic in hand, the possibilities are
endless.  The tritium is chemically bound up in the polyethylene
molecule so there is zero possibility of releaseing it by cutting the
plastic.  Need a chunk of glow for something?  Just whack off a chunk.
Need glowing paint?  Just file the edge of the plastic with a fine file,
mix the dust in with some linseed oil and voila!  Luminous paint that
doesn't run down for over a decade.  The sheet is large enough that you
can play for years and not run out of plastic.  Of course, altering this
approved nuclear device without a license is illegal according to the
NRC so if that bothers you, ignore everything I've written about EXIT
signs.  <wink> :-)


Index Home About Blog