AND NOW, A FEW WORDS ABOUT RADIOACTIVE WATCHES

AN ESSAY IN PLAIN ENGLISH, FOR NON-SCIENTISTS.

I WORK IN HEALTH PHYSICS AT A UNIVERSITY, SO UNLIKE A WHOLE LOT OF CLODHOPPERS OUT THERE, I ACTUALLY KNOW WHAT I’M TALKING ABOUT. I am really tired of all the bad information out there on watch forums, blogs, and retail web sites.



I. What you need to know about radiation

II. Why some—but not all—watches are radioactive

III. A brief history of radioactive watches

IV. Radioactive watches today



I. WHAT YOU NEED TO KNOW ABOUT RADIATION.

     a. Radiation is the emission of energetic particles and/or photons from inside, or near the nucleus of the atom. Some—but not all—of the “bad” radiation that you hear about are alpha particles,

beta particles,

gamma photons, x-ray, and ultraviolet photons. There are other weird things that come out of the nucleus during various exotic types of radioactive decay, and like they say in the movie Airplane!, “But that’s not important right now.” What makes these particular particles and photons troublesome is that they can penetrate through our bodies, and while they are doing so, they ionize our living tissues. Ionization is the process of knocking electrons out of orbit. When you knock enough electrons out of orbit, all kinds of weird chemical reactions take place inside your cells, and they either die, or mutate. Picture somebody shooting you with a machine gun that shoots very tiny bullets through your body. The bullets are so small, that instead of visible wounds, you get chemical changes. Because of the ionization that these forms of radiation cause, the term radiation when used by biologists really means ionizing radiation i.e. radiation that can ionize you.

     b. Visible light, radio waves, microwaves, and the signal coming out of your cell phone are radiation, but they are not ionizing radiation. They don’t have enough energy to knock electrons out of orbit. So, the next time somebody heads for the microwave oven, and tells you that they are going to nuke their food, slap them. You have my permission.

    c. When you get x-rayed in the hospital, the x-rays are produced by an x-ray machine (which is basically a gigantic light bulb that is so powerful that instead of a 110 volt wimpy table lamp emitting visible light photons, it gives off 70,000 volt x-ray photons). The x-rays fly out of the glass tube, go through your body, and hit the image receptor (a cassette), forming an image. You only got ionized while the x-rays passed through you. You got ionized (chemical changes in your cells), but you did not become radioactive. Next time someone gets an x-ray, and then says, “I’m glowing!” slap them. You have my permission. The same is true when you hold something radioactive in your hand. Say you’re out hiking on Navajo territory, and find a piece of uranium ore. During the time that you hold it in your hands, your hands are getting ionized. As soon as you drop that rock, and wash your hands, you are no longer getting ionized. When you washed your hands, you didn’t “wash the radiation” off your hands, you washed the radioactive rock powder i.e. dust that came from the rock off your hands. So, the x-ray machine is called a Radiation Generating Device (the only kind of radiation they produce is X-ray) and the uranium ore you found is called Radioactive Material. The radioactive elements i.e. isotopes that are in the material determine what type(s) of radiation get emitted. Some isotopes emit only alpha. Others: beta, and still others: gamma. Some isotopes kick out any combination of the above.

     d. YEAH, BUT WHAT’S AN ISOTOPE? For an element to be an element, it has to have a fixed number of protons in its nucleus. EXAMPLE: Carbon.

     Any atom that has 6 protons in its nucleus is carbon. Period. Most carbon atoms also have 6 neutrons in their nucleus. That’s nice and balanced. This version of carbon, called Carbon 12, or C12, is not radioactive. However, if a carbon atom has less than, or more than 6 neutron, it starts to act weird, and will give off some sort of radiation. Let’s say a carbon atom has 8 neutrons. The 6 protons (remember, it has to have 6 protons, if it is carbon) and 8 neutrons make it radioactive Carbon 14, or C14. The same thing happens if the carbon atom only has 5 neutrons. Then it’s called C11, another isotope of carbon, and it, too is radioactive. C11 and C14 emit different particles. The same is true all across the Periodic Table of Elements. IMPORTANT: C14 and C11 not only emit different particles; they are also radioactive for two different amounts of time. Their half lives are different.

     e. WHAT IS A HALF LIFE? A Half-Life is the amount of time it takes something to be half as radioactive as it is today. Carbon 11’s half life is 20.4 minutes, and it decays (turns into) Boron 11. Carbon 14’s half-life is 5730 years, and it decays into Nitrogen 14. Pretty weird, huh?

     f. WILL I DIE IF I GET EXPOSED TO RADIATION? GET CANCER?
A little radiation? No. A lot of radiation? Depends on what the isotope is, and how much you were exposed to. Radiation has existed before there was life on Earth. Every cell in your body has repair mechanisms that spend all day long 24/7 fixing the damage from ionizing radiation. The threshold for how much is too much varies from person to person, and even changes for the same person, depending on their age and health status. This is why doctors and scientists won’t give clear, yes-or-no answers to questions about exposure.

II. WHY SOME WATCHES ARE RADIOACTIVE, AND OTHERS AREN’T

     a. First of all, why should any watch be radioactive? Surprise #1: Things that are radioactive do not glow. Period. There are lots of watches out there with “glow-in-the-dark paint” on the hands. The paint is nothing but a chemical that is luminescent. It gets energized by the sunlight, or some lamp in your house, and when you go into a dark room, the watch glows because the energized paint is slowly losing energy in the form of visible light. This is analogous to charging up a cell phone battery. If you have a watch with tons of luminescent paint on it—like a Seiko Monster—then it will grow longer and brighter: merely because it has more paint on the hands and dial than other watches (Seiko has a really good quality luminescent chemical that they developed, patented, and named Lumibrite, but it, too, will fade to complete darkness, given enough time). The solution to the problem of luminescent paint losing its energy, and no longer glowing is to mix something into the paint that will keep exciting it 24/7. Radioactive materials are mixed into the bottle of luminescent paint. What you don’t realize while you’re wearing the radioactive watch is that it is glowing with the same brightness all day long. During the day, your eyes are adjusted to the sun light, or the lights on in the room, so you have no way of seeing that your Luminox or Traser is glowing fiercely. AGAIN: WHEN YOUR TRASER RADIOACTIVE WATCH IS GLOWING, WHAT YOU SEE IS NOT THE RADIOACTIVITY; YOU SEE THE PAINT THAT IS BEING STIMULATED BY THE RADIOACTIVE MATERIAL.

b. IMPORTANT POINT:
     If you look at the luminescent paint on any older watch, you might have no way of knowing whether it is just luminescent paint, or luminescent paint mixed with some isotope, unless (1) the watch has the a marking somewhere on the dial that lets you know. If you look at older Swiss watches, you will see some of them say “T Swiss Made T”. That means that they mixed Tritium (a radioactive isotope of Hydrogen) into the glow-in-the-dark paint. Old watches and clocks where they used Radium might not have anything painted on them, but you can easily detect the radioactivity with a Geiger counter. I use an old electric alarm clock with a radioactive radium dial when I teach the Radiation Safety class for new lab workers. We keep that old clock in a plastic zip-lock bag. Why? Because the old Radium paint can crumble, and get on your hands.

c. So why are Rolexes, Omegas, etc no longer radioactive, while Luminox, Praetorian, and Snoon are? Here’s why:

III. A BRIEF HISTORY OF RADIOACTIVE WATCHES.

     a. Originally, and for the first half of the 20th Century, the radioactive material mixed into the luminescent paint was Radium. The four isotopes of Radium: Ra 223, Ra 224, Ra 226, and Ra 228 are all nasty. The first three are alpha emitters, and the last is a beta emitter. Here’s the thing about alpha particles: you can pour a bottle of some alpha emitter—let’s say a bottle of Ra 226 labeled luminescent paint—onto your hand in the lab, and the alpha particles are not able to penetrate your skin. The bottle of radioactive paint is called an open source. Take that same bottle and drink it (pretend that the glow-in-the-dark paint is harmless), and it could kill you. The people who hand-painted the mixture of Ra 226 and glow-in-the-dark paint onto watch and clock dials in the factory were women. They used little horse hair brushes (remember when you were in school, and used to make models?), and would lick the brush tip, to make it sharp and pointy. Each time they did that, they swallowed some Ra 226 that went into their intestines, where it got absorbed into the blood stream, and went to all kinds of undesirable organs. They all died of cancer.

     b. Somewhere along the way somebody realized that you could use Tritium, which is a lot safer. Why is Tritium safer? You’re not gonna believe this, but years ago the good folks in the U.S. Government worked out a chart called ALI: the Annual Limit of Intake. Every isotope has a stated ALI of how much you’re allowed to consume. Isn’t that nice? Tritium has a great ALI. In other words, you’re allowed to be exposed to tons of it, before the government starts to worry about you. First, watch companies started painting the mixture of Tritium and glow-in-the-dark paint right onto the hands—the same way they did with the Ra 226/glow-in-the-dark paint. Eventually, they decided to abandon Tritium altogether. Why? Well, any time you have quantities of radioactive materials in your workplace e.g. a watch factory, a research lab, a hospital etc, you have to have a radioactive materials license from the government (This is true in any modern, western industrial country), and the license requires you to follow all kinds of safety and inspection procedures. There is lots of paperwork involved. Also, regardless of what the isotope is, you have to follow all kinds of industrial hygiene procedures to avoid contaminating the work room. Last—but not least—whenever you want to ship radioactive materials from your facility to some other location, you have to perform tests for radioactive contamination, and provide documentation of these tests. The big watch companies got tired of the paperwork—especially in a world increasingly wary of radiation—and stopped using Tritium. Too bad. My Rolex Submariner with a Tritium dial glowed all night.

IV.    RADIOACTIVE WATCHES MANUFACTURED TODAY.

     As far as I know, all radioactive watches today have what is called a sealed source: the mixture of radioactive Tritium and glow-in-the-dark paint is sealed inside a glass tube. Each glow-in-the-dark marker on the hour hand, minute hand, second hand, etc is a separate, tiny sealed glass tube. What’s supposed to happen is one facility makes the glass tubes, injects the radioactive stuff, and seals the tubes (forever). They then clean the outside of the tubes, and send them to the guys at another facility where the glass tubes are glued to the watch hands and dials. Snoon, Luminox, all these guys get their tubes from MB Microtec, a Swiss company. Microtec’s glow-in-the-dark tubes are used for all sorts of applications, besides watches. For example, they are used on a lot of gun sights. Ask the next cop you see if his watch has Tritium markers.

d. TRITIUM: THE REAL SCOOP: Tritium is a heavy isotope of Hydrogen. It has one proton (it has to, if it wants to be called Hydrogen) and two neutrons. Because it has 3 particles in the nucleus, it is called Tritium. Get it? One of the neutrons breaks down (decays) becoming a proton that stays in the nucleus, and an electron that is kicked out. That’s all a neutron is: a positive proton and a negative electron who have become one, and electrically neutral (hence the name neutron). The high-energy electron that gets puked out of the nucleus is called a Beta Particle. Now that the Hydrogen atom has 2 protons—guess what? That’s right—you can’t call it Hydrogen, anymore. Now it’s a Helium atom. Here’s the cool thing about Tritium: when it decays i.e. vomits out that Beta Particle, that so-called high-energy electron isn’t all that high-energy. Tritium’s Beta Particles are so wimpy, that when you wear a Luminox, there are literally zero Beta Particles crashing into your body, ionizing you. The watch, itself, is shielding you. TRITIUM’S BETA PARTICLES ARE SO WEAK, THAT YOU CANNOT DETECT THEM WITH A GEIGER COUNTER. The only way to detect Tritium (even if you spill some liquid on the counter) is with a very sensitive test called a wipe test. You take a very clean absorbent paper (manufactured for this purpose) and wipe the area that may- or may not be contaminated. You then deposit the wipe into a very sensitive instrument that detects what you picked up.

e. HOW LONG DOES A TRITIUM WATCH LAST? Okay, here’s he deal: Tritium’s half-life is 12.33 years. What that means is that if you buy a Traser watch today, and it was made on January 1st of this year, then 12 years and 4 months from now it will have half as much Tritium as it did this year. If the watch has 25 milliCuries of Tritium, then 12.33 years from now it will have 12.5 milliCuries. In real life, that means that the watch will be half as bright as it was the year you bought it. If you’ve ever looked at a Luminox at 2:00 a.m. to read the time, you know that’s still going to be pretty good. Another 12.33 years after that i.e. 24.66 years after you bought the watch, the watch will be half as bright, again. It will be only 25% as bright as it was when you bought it brand new. The next time some dingleberry tells you that Tritium watches “only last 10 years” go ahead and slap them. You have my permission.