This article aims to answer a very simple question; Is the Geiger counter a reliable tool in the evaluation of radiation on a watch dial? It is a very simple question, yet the answer is anything but simple. I will give two versions of the answer; a short one and a more detailed one.
The short answer is that the Geiger counter is most unlikely to be able to offer any reliable insight into the evaluation of the radiation on a watch’s dial. It is not a question of experience or of having tested many watches. The answer is that there are simply too many variables that can affect the use of a Geiger counter to provide anything reliable. This article will explain why the Geiger counter has no place in the process of evaluating a watch.
Evaluating pre-1960 dials
Given the enormity of the subject matter, this article will focus specifically on the use of Geiger counters in evaluating pre-Tritium Rolex dials. It is in this area where there is most contention and as such more value in making the picture clearer. Although the Atomic Energy Commission (AEC) ruled on 13th December 1960 that Tritium would replace the use of Radium in timepieces, one cannot identify a specific time-line for when Radium was stopped in the manufacture of watch dials. The US military were notably patchy in their replacement of radium dials. The US army still used Radium-226 in its dials well into the late 1960s. Furthermore, the 1967 International Standard on luminous materials still permitted the use of Radium in watches, albeit recommending the use of Tritium or Promethium-147. Realistically, one could argue that some watches from the early 1960s will have had Tritium, yet at the same time other watches - even from the same reference - from the late 1960s could well have still been produced with Radium. It is known that some US motor manufacturers started using Tritium on its instrument dials from 1959. As ever with Rolex, there is no definitive truth. Having said this, it seems a reasonable first conclusion to draw that pre-1960, dials are unlikely to have contained Tritium .
Rolex didn’t just use Radium-226 - they used all sorts of different radioactive materials
The second conclusion, however, is that just because Tritium was probably not in use before 1960 does not mean that Radium-226 was the only other possible luminous material being used. In fact, it is known that a whole range of different possible radioactive materials were being used. For example, as mentioned above, the use of Promethium-147 was still permitted under the 1967 International Standard. It is similarly documented that the US Navy responded to the 1960 AEC ruling by replacing Radium with Strontium-90. The Strontium-90 scare with the Rolex GMT 6542 originated in the late-1950s. The 6542 GMT was, of course, being sold before this scare, which begs the question of how far back was Strontium being used? Finally, not all Radium is the same. Most typically, when one reads about the use of Radium on watch dials, what is being referred to is Radium-226. It is now known that other Radium variants (for example. Mesothorium) were also in use. So, to clarify, the second conclusion that can be drawn is that a wide range of radioactive materials were in use in the pre-Tritium era.
So if different radioactive materials were used, why is that important for Geiger counter usage?
Why is this relevant with respect to the use of a Geiger counter? Well, different radioactive materials give off different types of emission. Further, the amount of radioactive decay from one material to the next can be very different. Since a whole range of different radioactive materials have been used, this makes identification using a tool as blunt as the Geiger counter fraught with problems. Put simply, a Geiger counter cannot differentiate between various radioactive materials.
For example, Radium-226 has a half-life of 1600 years, meaning that after 1600 years its emission rate will be halved. Compare that with, for example, Strontium-90, which has a half-life of just 29 years. For a watch dating from 1950, the emission rate from Strontium-90 would today be around 20% of its original level whereas for Radium-226, its emission rate would be just 3% less than its starting point in the 1950s. Mesothorium has a half-life of 5.8 years while Promethium-147 has a half-life of 2.6 years. Emission rates will, then, vary dramatically depending on what radioactive material was used. For some materials that were used, radioactive emissions today would be close to zero. Yet, even for materials with long half-lives, like Radium-226, emission rates may have fallen dramatically. How?
Does anyone know how much decay had already occurred in the radioactive materials used by Rolex in the 1950s?
Just because Radium-226 has a half-life of 1600 years, it does not mean that any watch that had Radium-226 applied will still have high radioactive readings today. Radium-226 is a naturally occurring substance. What if the Radium-226 applied to a watch in the 1950s had already been decaying for 10,000 years? The fact is, nobody knows how much decay had already been experienced in batches of Radium-226 applied in the 1950s. Varying degrees of prior decay will result in varying degrees of radioactive emission today. This leads to the third conclusion. Since it is not known how much decay a radioactive substance had already experienced when applied in the 1940s and 1950s, it is theoretically possible that a dial that had Radium-226 applied might have negligible radioactive readings today if the original Radium had already experienced significant decay. Given this theoretical variance, can a Geiger counter reading, on its own, provide definitive evidence either for or against the existence of Radium-266 on a dial? I posed this question to Cambridge University physicist. His answer was very simple. He argues that the only way to be definitive would be to undertake a direct examination of the radioactive material. A Geiger counter reading would be expected to vary from one decayed Radium-226 type to the next and thus quite useless in identifying the type of radioactive material on a dial. Quite useless.
As a radioactive material decays, it breaks down into different substances that, in turn, break down further and further. Each process involves emission of different types of radioactivity, with varying half-lives
The situation becomes more complex yet, as once a radioactive material decays, it breaks down into different types of radioactivity that can emit different types of particle. For example, Radium-226 is primarily an alpha-wave emitter with some gamma. However, once Radium-226 decays (albeit slowly) it also starts to emit beta particles. At the end of its decay, it actually turns into lead, which of course acts as a shield against radioactivity emission! Strontium-90 is a pure beta-emitter, and it decays relatively quickly into a compound that is also a beta-emitter. Mesothorium is primarily a beta emitter, but on decay breaks down into a multiple range of different compounds emitting alpha, beta and gamma. Promethium-147 is a pure beta emitter and it decays primarily into beta-emitting compounds, though the end of its decay does see some alpha emission. With varying rates of decay and with varying particle emissions, an instrument as blunt as a Geiger counter simply cannot differentiate what type of radioactive material is present on a dial. Radioactive material becomes a soup of different compound emitters.
Geiger counters cannot detect alpha waves
So, where does this leave us? Most Geiger counters cannot measure alpha waves. So, when a typical Geiger counter measures radiation emission from a watch dial, one thing it is NOT doing is measuring alpha particles. Alpha particles would not pass through a sheet of paper let alone a plexi or a watch case! But, most importantly, the vast majority of Geiger counters do not have the capacity to measure alpha. If there are beta or gamma particles that are being emitted, then the typical Geiger counter will supposedly pick those up. It takes about 8mm of aluminium to stop beta particles, so beta will make its way through plexi. Yet, the most commonly used radioactive material is thought to have been Radium-226, which is an alpha emitter. If one tested a watch known to have had Radium-226 applied, then what the Geiger will pick up will most likely be the beta and gamma emissions that have emerged following Radium-226 decay. In reality, this is what the Geiger counter is most likely measuring. Would one expect Radium-226 to produce large amounts of beta and gamma particles given that it is an alpha producer? The answer is …. maybe. The “maybe” depends on how much decay the Radium-226 had already endured and how much Radium-226 had been originally applied. Is there any recorded evidence from Rolex of this from the 1940s or 1950s? No. So, theoretically, a dial that had Radium-226 applied might emit almost pure alpha (which would record nothing on a Geiger counter), or it might record high levels of beta and gamma (which would be detected by a Geiger counter), or alternatively it might produce no alpha, beta or gamma at all, depending on how decayed the Radium-226 was to begin with. From a scientific perspective, it is impossible to be definitive using just a Geiger.
The radioactive emissions on a dial will also be impacted by what Rolex decided used as binders
Regrettably, it gets yet even more complicated because not only were Rolex experimenting with different radioactive materials, but in addition they were also experimenting with different artificial binders for the radioactive materials. Typically, a substance like zinc sulphide would be applied to a dial along with Radium. The zinc sulphide would glow when it was hit by the radiation emitted by the radium. However, after a period of time (around 3-4 years), the zinc sulphide would break down as a result of the radiation bombardment. The “glow” from the lume came not from the Radium but from the fluorescent compound with which it was bound - typically zinc sulphide. The Radium would also often degrade the varnish in the paint that held it in place, resulting in flakes of Radium breaking away…flakes that can be in dust form that can easily work free of the dial (and watch). Different binding compounds, of course, can break down into substances which can also emit different types of radiation. It has been shown that one of Rolex’s trade secrets was the addition of the radioactive substance, Mesothorium, to a dial. This would elongate the light intensity for the first five years. Thereafter, the zinc sulphide deterioration would kick-in. When exactly did Mesothorium start to be used? There is evidence to suggest its use as far back as the 1920s. It was certainly still in use in the late 1950s. Do we know which dials used Mesothorium and which used Radium-226? No. Can a Geiger counter differentiate between them? No.
One further very clear conclusion comes from this and that is that without direct compound analysis, it is simply impossible to determine what type of radioactive material is present on a pre-tritium watch dial. A typical Geiger counter could plausibly detect beta or gamma emissions, but it cannot determine the source of that emission and has no hope of detecting alpha particles.
How important is the quality of the Geiger counter?
This brings the next area of uncertainty into focus. How important is the quality of the Geiger counter being used? Most commonly used hand-held Geiger counters measure the amount of micro-Sieverts emitted. A “Sievert” is a measure of the equivalent biological effect of the deposit of a joule of radiation energy in a kilogram of human tissue. In effect, what most hand-held, non-professional, Geiger counters measure is “energy”. That is VERY different to measuring radioactive emission. Most professional Geiger counters measure in terms of “Becquerel”. A Becquerel is a derived unit of radioactivity. That is what should be being measured. Some radioactive material emits small amounts of particles but these particles may have very high energy. That would record high micro-Sievert readings, but actually the amount of radioactive decay might be quite low. What needs to be measured by a Geiger counter is the amount of decay that is being experienced. Each time that radioactive material decays, it emits a particle. Counting those particles and relating them to the material is where the Geiger counter adds value. For a Geiger that can measure only energy, for example my own Geiger (see picture below), it is not especially useful at all for this purpose.
The $64,000 question
If a Geiger counter shows no beta or gamma emission, does that mean that a dial can be invalidated as containing no Radium? This is a crucial question, but thankfully I think the answer is clear. A lack of radiation detection on a dial can occur from a number of valid reasons.
Firstly , if a Geiger counter is used incorrectly or is faulty or measures the wrong objective, it will fail to measure the gamma or beta emission correctly. In the case of the Geiger counter that I bought and that is commonly used by watch collectors, there is a very specific way of measuring. At the back of the detector there is a Geiger-Muller tube. This is the part of the device that actually catches the radiation emission. If one points the Geiger-Counter at a watch in the wrong way, i.e. with the GM tube away from the watch, then expect the readings to be very distorted. As the manufacturer of the Geiger counter is very clear stating, unless it is used in the proper way, results will be affected. I am sure others may have their own stories to discuss. Here is my evidence.
The first picture is using my Geiger pointing straight at my 5512 from the early 1960s. It shows a reading of 0.34 micro-Sieverts. That is marginally above background radiation.
Secondly , since it is entirely plausible that a radioactive substance other than Radium-226 has been used on a pre-1960 dial, it is entirely plausible that the half-life of that substance is low enough to have resulted in significant decay resulting in minimal levels of radiation…possibly even zero when measured today. Since we do not know with any certainty what radioactive material was used and with what artificial binder, there is no way of deriving that source through an instrument as blunt as a Geiger-counter. We also have no idea how much decay had already been experienced by the radioactive material applied in the 1950s. Maybe it had already decayed significantly.
Thirdly , there are other very pertinent factors that can also lead to a lack of beta or gamma emissions from a watch dial. The most relevant is the fact that Rolex were not consistent in applying radioactive material amounts. In fact, they varied how much radioactive material was applied from very low to very high amounts. How do we know that the amounts varied so much? Well, Rolex documentation shows it. The following is an extract from Rolex. It shows a Rolex supplier (Universo) offering to vary the intensity of the radium lume on the hands. If you wanted your Rolex to shine like a beacon, that could be arranged. Equally, if you wanted it to have low radium content, that too was on offer. Suppliers of dials and hands offered not only different lume substances but also different lume intensities.
This represents another very clear and important conclusion. From a purely theoretical standpoint, it is very clear that pre-1960 dials could have varied enormously in terms of how much radioactive material was applied. It is not a debate, but a fact. Theoretically, two identical watches that were manufactured in the 1950s might have consecutive serial numbers and have been untouched for the last 60 years, yet one may have had high levels of radium applied and the other may have had negligible amounts of radium applied. This fact is often something that is ignored by many experts. I have seen perfectly legitimate early GMTs declared “wrong” simply because there was no radium “glow”. A little knowledge is a dangerous thing. I think it is fine to argue that science is king, but the application of that science needs to be conducted by scientists who know how to conduct it properly. Science that is mis-applied is dangerous.
Yet, when experts tell us that routine testing of specific watches always results in a similar radioactive result, then one would seemingly need to think that it was typical for a specific watch to have had a similar radioactive treatment. That almost seems like scientific evidence! This is especially the case for watches that were made within very narrow production periods. An example of this is the Rolex Submariner 6200. One expert told me that having tested 20 of these models, all 20 recorded readings of around 3.0 micro-Sieverts. I spoke with another expert who told me he had tested 5, and that 3 out of the 5 had no radiation readings at all, one had a reading of 0.8 and one had a reading of 2.3. I have tested a small number and found the range of readings to vary from zero up to just over 3. What does this tell me? Well, given that we know that both the type of radioactive material and the amount used could vary, a mixed outcome seems entirely plausible. Further, one could also argue that measuring the radioactivity through micro-Sieverts was actually the wrong yardstick through which to make any judgment……
The bottom line is that it seems impossible to hold any conviction about how much or how little radioactivity a pre-Tritium Rolex dial should have. Any conclusion to the contrary is of course possible, but so far there has been no scientific evidence to that end.
Facts versus empirical observations
There is another key issue to mention. Since we don’t know the facts, experts create the facts based on empirical observations. Yet, for some watches, the number of examples is so low that it is statistically foolish to draw conclusions. Take my 6610 Red Depth, for example. I would estimate that there are probably fewer than 20-30 or so genuine versions in existence all within a narrow serial range. If I tested 10 and they all had a similar Geiger counter reading to mine, does that mean that another that appears completely authentic on all criteria would be wrong if it recorded a different level of radiation altogether? Statistically, with such small sample sizes, sampling error will be large and it would be foolhardy to draw conclusions. Sampling size is crucial. For rare watches that have very low numbers for testing, creating “facts” from such small sample sizes is very unscientific. Scientists would NOT do it. Empiricism based on a sample of 20 isn’t scientific.
My own observations
Which brings me to my own empirical testing. With the help of my Cambridge University physicist, using a professional Geiger counter as well as my own Geiger counter, I tested a number of my own watches as well as watches from friends. What I found was extremely interesting. Firstly, Geiger counters that measure just energy (ie Sieverts) are not really very good at detecting Becquerels, so not really the right tool to be using. Secondly, using a professional Geiger showed that three-quarters of the watches that I tested recorded about 80-90% beta emissions and about 10-20% gamma emissions. I asked the physicist if this meant that these three-quarter of the watches were lumed with the same material. His response was that it was absolutely impossible to determine that since the plexi was preventing any alpha particles leaving the watches. Only through full mass spectrometry would it be possible to determine the composition of the lume. So, even though I could argue that my dials were emitting beta/gamma in roughly an 85/15 ratio, it could still tell me NOTHING about what type of material was on the dials. This type of analysis was possible using a professional Geiger counter. The hand-held Geiger version, like the one I own, is essentially useless as it provides less information still. Although its fun to detect the radiation using a hand-held Geiger, my Cambridge physicist could draw no conclusions at all from the readings.
In the spirit of empirical observation, my early 1960s Submariner 5512 recorded a reading of just over 5 micro-Sieverts per hour. I challenge anyone with an early 1960s 5512 to record the emissions of their watch. I will make a guess - the variation in readings will be significant. From zero up to double-figures. Why do i suspect this? I tested 6. They were all perfectly correct. And they all had very different radioactive emission. Of course, to be scientific, I should probably need to test 100 or so. But expect a wide variance. That’s Rolex for you. Does anyone want to make a definitive claim about what radiation should be emitted by an early 5512s? I would truly hope not.
The role of science
Science has a role in the evaluation of a watch’s dial. When conducted by proper scientists and when conducted under proper laboratory conditions, it is possible to determine what has been applied to a dial. Using a Geiger counter to determine this answer is, in the view of all of the experts i asked, simply not possible. Even if one used proper science and subsequently evaluated the composition of a dial, given that Rolex provided such uncertainty on what they applied and in what quantities, could science really provide a categorical answer to whether a dial was authentic or not? Maybe…..but most likely maybe not. I think there are far better ways to evaluate a watch.
It is time that experts recognised that using cheap hand-held Geiger counters does not serve the watch collecting community. A little knowledge is a dangerous thing.