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. John From: John De Armond Subject: Re: Trijicon Sights Organization: Dixie Communications Public Access. The Mouth of the South. walter@kaiwan.com (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 officials. #these #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. John From: John De Armond Subject: Re: Lifespan of Trijicon Sights Organization: Dixie Communications Public Access. The Mouth of the South. okuyama@lexor.arc.nasa.gov (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. John From: John De Armond Subject: Re: Lifespan of Trijicon Sights Organization: Dixie Communications Public Access. The Mouth of the South. SHICKLEY@vm.temple.edu 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. John From: John De Armond Subject: Re: Tritium decay series/containment? Organization: Dixie Communications Public Access. The Mouth of the South. deety@airdata.socal.com (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. John 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 bagley@hc.ti.com (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- #sights. 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> :-) John |
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