Author Archives: Dr. Zoomie

Thorium – From Lenses to Fuels

A little over a decade ago I got a phone call asking me what I knew about thorium. Not much as it turned out – that part of the call didn’t last long. But it led to an interesting consulting project that let me delve into the manufacture of high-quality optical glass and the Second World War (among other things).

Some older photographic lenses were produced with glass elements containing small amounts of thorium. If stored in the dark for prolonged periods of time, these lenses can undergo what is commonly called “yellowing”.

In the first part of the 20th century the highest-quality optics were made in Germany, and even American military suppliers were buying their optical glass from the Germans – lenses that went into periscopes, telescopes, and pretty much anything else that depended on lenses. Part of what made German glass so good was its clarity and its refractive index, both of which were enhanced by adding materials to the glass. Just as dissolving lead into molten glass gives it the clarity, shine, and sparkle of lead crystal, the addition of thorium does the same, making it possible to fabricate thinner and lighter lenses. At the same time, the properties of thorium help to reduce the dispersion of different wavelengths of light (the different colors) as they pass through the glass. The first patents for thoriated glass lenses were issued in 1939 or so with additional patents issued through the 1940s and 1950s. And that led to my phone call, albeit a half-century later.

In the 1930s, when Germany was starting to get a little frisky the American military realized that they might need to find a more reliable supplier for their high-quality optics, so they began contracting with American lens-makers. This led to our becoming self-sufficient in this area. And, in the case of my client, it required a bit of cleanup about 15 years ago.

See, in order to make a lens the manufacturer starts off by pouring glass to form a blank – a piece of glass with the general shape of a lens, just as baseball bat starts with a piece of cylindrical wood of roughly the correct dimensions. And, just as the excess wood is removed by a lathe, the extra glass is ground off using a sort of slurry that contains the grinding compound. The glass that was removed, though, contains thorium. In the 1940s this wasn’t much of a problem – the regulations pertaining to thorium were not very strict. But in the last few decades of the 20th century this began to change and places that hadn’t required much attention earlier were now a potential concern. Which meant that my client needed to have their site surveyed and some subsurface tanks checked to see if they contained any thoriated glass residue (to cut to the chase, they did).

Of course, any lens could benefit from the addition of thorium, and after the war ended it started finding its way in to consumer products – primarily into lenses for high-end cameras. Over the years a number of manufacturers began making thoriated lenses, a practice that continued into the 1980s. And, while such lenses are no longer being made, there are still some around for those who are lucky enough to find them.

My client’s thorium-contaminated site needed to be cleaned up, even though the thorium posed no health risk to anybody. Similarly, while it’s easy enough to get radiation measurements from a thoriated camera or periscope lens from that era, the radiation dose rates are not high enough to cause harm to those using them – with the possible exception of workers who spend many hours weekly looking through thoriated glass eyepieces on microscopes, telescopes, and the like.

It also turns out that thorium is fairly versatile. I have a small container of thoriated welding electrodes that I use for demonstrations when I teach radiation safety classes – the thorium is used for its metallurgical properties just as it used to be alloyed in the metal from which jet turbine blades were made. I also have some gas lantern mantles that contain thorium; these aren’t made much in the US today, although there are still some overseas manufacturers. And then there’s the thoriated toothpaste that I wrote about in an earlier posting. These have all led to lengthy cleanups around the world, including a number in the US.

My last contact with thorium came about 7 or 8 years ago when I was characterizing a thorium-contaminated site for the NYC Health Department – this time working for the City. In this case the thorium was an afterthought – the facility used to produce rare earth elements (back in the 1930s and 1940s), the ores of which were contaminated with thorium. It turns out that thorium is very similar geochemically to rare earths so most rare earth ores also have some thorium in them. Interestingly, in this case the company began producing thorium to sell to the Atomic Energy Commission – thorium went from being waste to being a product. For awhile the government was looking into using thorium for nuclear reactor fuel. That idea was never really pursued vigorously in the US, although I’ve heard rumors that India and China might be looking into it.

Thorium reactors, though, start to get a little complicated and this piece has already covered enough ground – from Germany to the US; from military optics to cameras, welding rods, and jet engines; and from additive to waste to fuel.

If the shoe fits….

When I was younger I remember my father telling me about when my grandparents took him to get shoes when he was a kid – one of the things that really made an impression on him was this device that he could stand on and push a button and he could see an x-ray image of his feet inside the shoes – not only was it a good way to see if his feet were going to be cramped inside his new shoes, but he could wiggle his toes and see his toes and toe bones move in the image he was looking at. I got the impression he’d sometimes hit the button a few times in a row because the image was so neat to look at. The way he described it, it sounded pretty cool – it made me wish I had something like that to play with myself. Alas, I was born too late and these shoe-fitting fluoroscopes were no longer in use.

Awhile later – actually, a few decades later – I found out a little more about the things; in particular, that they’d been outlawed sometime between my father’s childhood and my own. But as I started working in health physics I started hearing occasional tales of the shoe-fitting fluoroscopes, usually with an undercurrent of “Whatever were they thinking?”

When I was in my 30s I worked in radiation safety at two hospitals, one in Ohio and one in Upstate New York. Here, I started learning more about medical fluoroscopes and learned more about how high the dose rate can be in the beam with the machine turned on. In fact, as I found out, people working regularly with fluoroscopes tend to get more radiation exposure than even most nuclear power plant workers, and fluoroscopes cause more radiation injuries than any other device of which I’m aware.

Shoe-fitting fluoroscope
A decommissioned Adrian Fluoroscope showing operator’s controls and three viewing screens on the top of the device. On the opposite side is a low platform with two half-circle holes cut into the vertical back surface for inserting the fronts of the shoes.

At one hospital I worked at there was an older fluoroscopy machine that had a dose rate of 90 rem per minute in the beam. Think about that – it takes about 300 rem to cause skin burns, so leaving that machine turned on for just a little more than three minutes could start to cause burns to the patient. Interestingly, the dose rate from the shoe-fitting fluoroscopes was to be limited to 2 rem to the feet for a five-second exposure, or 24 rem per minute, which is comparable to the dose rate from medical fluoroscopy machines in the 1990s and 2000s (newer machines have lower dose rates). On the other hand, a lot of machines didn’t comply with the guidelines – some were measured as having dose rates of up to 75 rem per minute. On one of those machines, every time my father wiggled his toes, he was getting several rem to his feet. If he used one monthly, he’d have been close to today’s annual 50-rem dose limit to the extremities.

In the 1950s there were also concerns that irradiating the feet and legs of children might affect the growth plates in their leg bones, affecting their future height – given the fact that my father is above-average in height, however, it seems that he didn’t suffer from this. Although, I guess I should add that I was about four inches taller than him, so who knows how tall he might have been….

I suppose that’s what a little more personally interesting to me is the waist-level dose – the estimate there was anywhere from about 30-170 mrem to the pelvis for each 20-second exposure. So if my father had spent 20 seconds wiggling his toes each month he’d have received as much as 2 rem of gonad dose every year. And it’s reasonable to wonder if this might have had any effect.

It turns out it didn’t. And I’m not basing this on what I see in the mirror every day (as impressive as that view might be!) but, rather, on the understanding we’ve accumulated over the years on the reproductive effects of ionizing radiation. And it turns out that there’s no evidence that pre-conception radiation exposure is linked to any sort of health effects at all in children conceived later. So none of the kids who were wiggling their toes back in the 1930s, 1940s, and 1950s had to worry about their future kids.

In fact, it turns out that the kids (and adults) who were playing with the shoe-fitting fluoroscopes don’t appear to have been affected at all – but some of the sales staff were because they might be using the machines repeatedly every day, with their hands in the beam as they squeezed the shoes (and the feet within) to show how the shoes might fit under different circumstances. One saleswoman, for example, developed a case of dermatitis from having her hands in the fluoroscope beam so often; there was also an incident in which a shoe model had her feet in the machine so often that she developed skin burns and other radiation damage – her lower leg eventually had to be amputated.

As we learned more about the effects of radiation on health, as public concerns about radiation grew, and as regulations started ratcheting down these devices eventually went away – by 1960 or so they were pretty much extinct in the US. The consensus is that the health effect on the customers was negligible; likely because even kids don’t get new shoes all that often.


From the Chest to the Cosmos

A solid chunk of plutonium-238 (Pu-238) is so hot that it glows red-hot. Where the heat comes from is the radioactive decay of the plutonium – every time a plutonium atom decays it gives off a high-energy (5.6 MeV) alpha particle and all of this energy is deposited in the chunk of plutonium. A single alpha doesn’t have enough energy to make plutonium glow – but every single gram of Pu-238 undergoes enough radioactive decays to produce slightly more than a half watt of heat; one kilogram will generate more than 500 watts – in two hours this piece of plutonium will produce 1 kilowatt-hour of energy, enough to light a small home. Incidentally, 1 kg of Pu-238 will fit inside a typical shot glass. This isn’t the place to go through the detailed calculations, but it’s fairly easy to see that it doesn’t take much plutonium to produce a fair amount of energy – if we can figure out how to use it.

Luckily, there are these things called thermocouples! It turns out that if a thermocouple is heated on one side and cooled on the other – more specifically, if there is a temperature differential from one end of the thermocouple to the other – it will generate electricity. Which means that if we simply let the plutonium do what it wants to do – undergo radioactive decay and heat up – we can use thermocouples to extract some of that energy to produce electricity. Then the question is what to do with it.

One of the things we can do with this energy is to power spacecraft. We’ve sent plutonium-powered RTGs to Mars to help search for evidence of past or present life. Other RTGs are currently orbiting Jupiter, RTG-powered spacecraft have explored Saturn, zipped past Uranus, Neptune, and Pluto, and the RTG-powered Voyager craft are currently humanity’s first probes to enter interstellar space. Plutonium power has carried, if not humans, then our robot explorers throughout the Solar System – the heat from Pu-238 alpha radiation, even after a half-century of decay, is still powering our most-distant probes.

Interestingly, we’ve used plutonium to power things much closer to home.

Over a century ago, in 1889 Scottish physiologist John Alexander MacWilliam realized that applying electrical current to the heart could help to keep it beating regularly. Over the next 50 years his observations were refined and provided the foundation for what evolved into the modern pacemaker.

The beating of our hearts, something that happens tens of thousands of times daily from before we are born and through the entirety of our lives, is triggered by a tiny electrical impulse to a small cluster of cells called the sinoatrial node, this propagates through the heart, causing the four chambers to contract in the proper sequence to send blood flowing through our bodies. The problem is that this system can malfunction, causing erratic patterns that can range from annoying to life-threatening. What MacWilliam discovered was that a stable heartbeat could be triggered by electrical signals from outside the body as well as through the natural system. Over the years the equipment needed to produce this regular current has become increasingly smaller, to the point where it can now be carried inside the body; the devices have also become increasingly sophisticated and able to not just produce a regular series of electrical pulses, but to adjust to different levels of physical activity and even to recognize and respond to unanticipated arrythmia as they arise.

The problem is that it takes energy to produce this electrical signal and even more energy to power the electronics that give modern pacemakers so much capability. Early pacemakers had to be wired into an external power supply because batteries didn’t hold enough energy to power a pacemaker for an entire day. But in the 1960s and 1970s engineers realized that the heat of radioactive decay could be used to power pacemakers just as easily as they could power spacecraft. This led to the development of a plutonium RTG-powered pacemaker that could be implanted into the body, requiring no battery changes, no recharging, and that would last for decades.

Pictured here is a Medtronic plutonium-powered pacemaker from 1974.

Using plutonium raised some concerns of course, because most people aren’t quite comfortable with the idea of implanting radioactivity into their bodies. But it turns out that the 2-5 curies of plutonium they used doesn’t emit high levels of radiation – the radiation dose rates at the surface of the pacemaker were only about 5-15 mrem/hr and the patient would only receive about 100 mrem annually to their whole body – even over a lifetime this is not enough radiation dose to cause problems.

Plutonium-powered pacemakers were only used for a short time before being replaced with rechargeable lithium batteries; at present there’s still a small number of them in the chests of patients here and there, but only a handful. Like so much other technology, they had their time, but that time has passed. But it’s sort of cool to think that, for awhile, there were people walking around with the same technology implanted in their chests that was also roaming the outer reaches of the Solar System.

A Glowing Smile

About a decade ago I was reading an account of Allied activities in Germany at the tail end of World War 2. The Allies knew that Germany was working on a nuclear program of some sort – there was evidence that it was a nuclear weapons program – and we were trying to find out how far along they were since a Nazi nuclear weapon would have been able to turn the war back in Germany’s favor. Consider, for example, the effect of a nuclear attack against the landing forces on D-Day, or against Russia’s forces as they advanced towards Berlin – or a nuclear weapon arriving over London and Moscow, delivered by V2 rockets with the attacks ordered by a leader with no compunctions about visiting utter destruction upon his foes.

As part of their operations, the Allies came to realize that Germany seemed to be buying up the world’s supply of thorium and they grew concerned that Germany might have found a way to make nuclear weapons out of thorium. It’s not out of the question – the primary isotope of thorium is Th-232 which, if it captures a neutron, will end up as U-233, an artificial isotope of uranium that fissions as easily as the U-235 used in the Little Boy nuclear weapon dropped at Hiroshima. So when Leslie Groves, the general overseeing the Manhattan Project, learned about German thorium purchases, he launched an investigation to find out if the focus on uranium and plutonium had somehow overlooked another viable path to nuclear weapons.

If thorium really did provide such a path then it could be important to the American effort as well. The main reason – and one of the reasons that there are so many proponents of thorium as a fuel for nuclear reactors – is that there is four times as much thorium on Earth as there is uranium and, unlike uranium (in which only one atom in 139 is fissionable), every single atom of natural thorium can become an atom of fissionable U-233. So instead of having to laboriously separate U-235 from U-238, a thorium weapon would only have to bombard Th-232 with neutrons and then chemically separate the resulting U-233. That being said, there were some difficulties in working with this process but if Germany has mastered them, perhaps we could as well. So an investigation was launched.

What they found had nothing to do with nuclear weapons – not even with nuclear energy. Rather, it had to do with cosmetics.

During the first part of the previous century, radium was all the rage, and radium was added to patent medicines, toothpaste, and there was even a line of condoms named “Radium” (although it doesn’t look as though the condoms were impregnated with radium!). A German cosmetics company, understanding that the war was coming to an end, was trying to figure out how to increase their business in peacetime and they hit upon a variation of this trend – if radium could be added toothpaste, why not thorium? So they set out to stock up on thorium for their post-war toothpaste line.

Doramad Advertisement for Doramad Radioactive Toothpaste

Doramad Radioactive Toothpaste (Doramad Radioaktive Zahncreme) was produced in Germany by Auergesellschaft of Berlin from the 1920s through World War II.

In hindsight, it seems their idea and their imagined product line were both somewhat overly optimistic. Oh – and as far as using the Th-232 → U-233 method for making nuclear weapons…the US (1955), Soviet Union (1955), and India (1998) have all detonated weapons that used U-233 for some or all of the fissionable mass. However, for a number of reasons, U-235 and Pu-239 continue to be the materials of choice for nuclear weapons.

Image reference:

Title: “Doramad Advertisement”, Creator:, Source:, License: This file is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.

How Dangerous is 100 Micro Roentgen/hour?

There are actually two issues here – one is about the safety of the dose rate (1 microGy or 100 microR per hour); the other is whether or not that dose rate is accurate.

Let’s tackle the first one first. A dose rate of 100 microR/hr (1 microGy/hr) is not dangerous. If this dose rate is accurate, living in it continuously (8760 hours per year) will give you a radiation dose of about 0.9 R/hr (9 mGy/yr). This is not a trivial dose – it’s about three times as much as what we’re normally exposed to in a year from natural sources (on average). At the same time, it’s less than 20% as much as nuclear workers in the US are permitted to receive in a year and a little less than half of what radiation workers in Europe are permitted to receive in a year. In addition, it’s less than half the radiation dose rate I measured in Ramsar Iran, which has the highest natural radiation levels of any inhabited place in the world. The residents in Ramsar do not appear to be suffering any ill health effects from their exposure there – it seems unlikely that the dose rate you mention will cause any harm to you.

Now – on to the second question!

One thing that you have to determine is whether or not the readings you note are accurate, and a lot of that depends on the exact kind of radiation instrument you’re using. I used a GM instrument in the Navy and I continue to use them today – they’re incredibly useful. But I also recognize their limitations; one of which is that they’re not very accurate at measuring radiation dose rate – especially from low-energy gamma radiation and even more so at low dose rates. One of the first questions I’d have to ask is whether it’s a digital display, or an electro-mechanical one with a needle pointing at the dose rate. If it’s the latter, I’d also be interested in knowing if the meter is on the very lowest scale with the needle pointing at the very lowest tick mark on the meter face – if this is the case then I would take that reading with a considerable grain of salt; in general, I try to use a meter only when the reading is somewhere between about 20–80% of the range of the scale.
Another question to ask is the size of the GM tube – a larger (and more expensive) tube is more accurate than a smaller, cheaper one.

But the main factor is that GM tubes – unless they are a type of tube called “energy-compensated” – are not accurate at measuring radiation from more than one specific energy. So if your GM was calibrated (for example) using Cs-137 – which has a gamma energy of 662 keV (1 keV = 1000 electron volts) then it can only accurately measure radiation dose from gammas of that exact energy. If you’re using that to measure natural background radiation – with a lower average energy – then the reading is going to be off by a factor of up to 10. This is because the meter “expects” that every bit of radiation entering it has the same energy as Cs-137; if the radiation is lower-energy then the reading will be higher than the actual dose rates.

Anyhow – my best guess is that the dose rate displayed by your instrument is likely not accurate for the reasons given here. But even if it is accurate, this level of radiation exposure should not be harmful.

How Do You Receive Radioactive Materials?

Hi, Dr. Zoomie – I’m working on a radioactive materials license application and it says I need to have a procedure for receiving radioactive materials. What are they looking for?

Virtually every radioactive materials license is going to require you to tell the regulators how you plan to receive radioactive materials at your facility – what precautions you plan to take, what checks you’re going to perform, and so forth. You might only receive radioactive materials once a month – maybe only once a year. Or, on the other hand, if you are at a nuclear pharmacy, a large hospital, or a large research university then you might be receiving multiple packages daily. However frequently you receive shipments, though, you’ve got to have a procedure to make sure it’s done correctly.

The easy way to do it is to commit to using the model procedure that your regulator has almost certainly developed. For example, one of my consulting clients (they had what’s called a broadscope radioactive materials license) had a line in their license application that simply stated “For receipt of radioactive materials we commit to using the model procedure found in Appendix I of NUREG 1556 vol. 11 (Consolidated Guidance About Licenses of Broad Scope).” And that’s all you really need. You can certainly draft your own receipt procedure, but if you do so then you have to be able to show that your procedure is at least as good as the model procedure.

There are a couple of things that have to be part of your procedure – whether you write your own or use the model procedure.

  • All radioactive packages should be delivered directly to the RSO if at all possible.
  • If the RSO is not available (vacation, illness, travel, restroom, etc.) then the package should be placed in a secure location until the RSO can retrieve it.
  • Alternately, the RSO may designate qualified radiation workers to receive radioactive packages in his/her absence.
  • Each package needs to be visually inspected for damage or evidence of leaking contents, surveyed for radiation dose rates (and possibly contamination), and the contents checked against the shipping papers. Most of these checks are required to be performed within three working hours of the package delivery.
  • All of these checks and surveys must be documented and you are required to maintain these records.
  • And if any contamination limits or radiation dose rates are excessive, you need to let the carrier and your regulators know as soon as possible.

With regards to the first point (delivery directly to the RSO), this is important. I worked in radiation safety at one university where a radioactive package was somehow lost between being signed for by University Receiving and delivery to Radiation Safety. In another, a man was ordering radioactive materials to be delivered to him personally, then sending them out to colleagues of his overseas. In both cases, the problems was solved by requiring all radioactive materials to be delivered only to Radiation Safety (and in the latter case, the man was arrested).

Finally, one last thing to consider….

If you regularly receive packages of radioactive materials you should consider having a dedicated location for this purpose. For example, perhaps you can take a corner of a workbench to cover with a benchpad (e.g. plastic-backed absorbent paper). In addition, you should have a secure storage location where the packages can be stored until you can perform the receipt inspection and surveys – and where you can store the materials until they’re moved to their permanent storage or use location.

The Do’s and Don’ts of Transporting Radioactive Materials

Dear Dr. Zoomie – can you give me some good “do” and “don’t” suggestions for transporting radioactive materials? I’m sorta new to all this.

Boy – there’s an open-ended question! And so many things to choose from…hard to know where to start. So let’s see what comes to mind.

  • DO take a minute to properly secure your radioactive materials, especially if they’re in the back of a pickup or open bed truck. A company I used to work for sort of forgot to do this and a nuclear soil density gauge bounced out of the back of the truck when it was driving from a job site. Took us two years to find it again.
  • DON’T let bandits hijack your truck, especially when it contains a dangerous amount of radioactivity. This happened in Mexico a few years ago and got international attention…and not the good sort that increases your sales. One way to help with this is to make sure you have GPS tracking on any vehicles carrying dangerous levels of radioactivity.
  • DO make sure your radiation instruments have been calibrated – especially the ones you’re using to determine the Transport Index (TI) and for other surveys (more on this in a later posting).
    • DO make sure you label the packages correctly (White I, Yellow II, Yellow III) according to the radiation level you measure
    • DO make sure you remember to measure radiation dose rates on the package, outside the truck, and in the driver’s area

Labels Used on Radioactive Materials Packages

Labels Used on Radioactive Materials Packages

  • DON’T re-use Type A packages unless they are:
    • Designed to be reusable or
    • You’ve tested them and can document that they meet the criteria to be a Type A package
  • DON’T park a truck or car with radioactive materials in a sketchy place and leave it unattended – even if it is locked. Unlike a past consulting client whose driver left his locked car in San Francisco’s Tenderloin District (high drug use). The car was broken into, the radioactive materials (medicine intended to be used the next day) were stolen and were probably ingested by the thief, hoping to get high.
    • As an aside – when a cop asks you how he can tell if a drug addict has ingested radioactive iodine (which will destroy the thyroid), DON’T tell him to look for someone who looks lethargic since he will probably tell you the same thing he told me; “In this part of town, everyone looks lethargic. Got anything else?”
  • DO make sure that you and anyone else shipping or transporting radioactive materials have received proper training within the last three years.
  • DO make sure that your radioactive materials are blocked and braced so they can’t shift around in the vehicle when it starts, stops, turns corners, hits bumps, and so forth.
  • DO make sure you lock everything up so nobody can walk away with your radioactive source(s) or the equipment they’re inside
  • DO make sure you contract with a reputable company anytime you ship radioactive materials!
  • DON’T do this (please, please, please):

Punctured package containing radioactive material

Punctured package containing radioactive material

  • DO remember to fill out shipping papers and/or manifest – even when it’s your vehicle transporting your sources to a remote job site
    • And while you’re at it…DO remember to fill out the radioactivity in SI units (1 Ci = 37 GBq, 1 µCi = 37 kBq, etc.)
    • And DO remember to store the shipping papers in the door pocket, on the passenger’s seat, or another place in the driver’s compartment where responders can find them easily in case of an accident

How Do You Package Radioactive Materials for Shipment?

Yo, Dr. Z! I need to learn about how to package radioactive materials for shipment and I’ve got to admit I don’t know where to start. Can you help get me started?

Good luck, man – you’ve got your work cut out for you. I went over this a little bit a few posts ago, but there is certainly a lot of detail to fill in. So let’s get started!

The first thing you need to know is where to find the rules – that’s in the transportation regs. Specifically, you need to look at Subpart I of 49 CFR 173 (49 CFR 173.401 – 477). And right away you’re going to notice a lot of terms with definitions that are not really intuitive. But you have to be able to understand them if you’re going to be able to do this correctly.

So here goes….

First, there are two “forms” of radioactive materials:

Special form means that the radioactivity is in a sealed source or something similar. Specifically, it means that the radioactivity is sealed up inside a welded metal capsule of some sort. Unless they develop leaks, special form materials are unlikely to cause contamination. The A1 limit (more on this shortly) applies to special form radioactive materials.

Special Form

An example of a capsule used for Special Form

Normal form (also called “other than special form”) is everything else. These are unsealed radioactive materials – it could be contaminated soil from a remediation project, radiopharmaceuticals intended to be injected into patients to diagnose disease, or radio-labeled chemicals intended for use in research. The A2 limit applies to normal form radioactive materials.

Normal Form

Example of containers used for Normal Form

OK – so now we get to types of packages. The most common types are Type A and Type B – these will cover all of your packaging needs unless you’re shipping something fairly esoteric (fissile materials, for example, or radioactive materials that are pyrophoric). Virtually all radioactive materials travel inside of Type A packages – these can be as simple as a sturdy cardboard box, metal ammo cans that you get at an Army-Navy surplus store, or something similar (more on this in a moment). Type A packages are used to transport A1 or A2 quantities of radioactivity, so let’s take a brief detour to figure out what in the world this means. And I know this is starting to get confusing – but bear with me for a minute and hopefully it will be a little more clear.

Type A packaging

An example of a container used to meet Type A packaging requirements

There’s a table in 49 CFR 173.435 that gives A1 and A2 quantities for a bunch of radionuclides. If the amount of radioactivity you’re trying to ship is less than the A1 activity (for special form radioactive material) or less than the A2 activity (for normal form) then you can ship the radioactive material in a Type A container. If you’ve got more than that then you have to use a Type B container.

OK – so how does this work in practice? Well…say you’re trying to ship a Cs-137 source with an activity of 20 Ci. What sort of package do you need to ship it in?

So – start off by going to the table I just mentioned. If you scroll down to Cs-137, it lists the A1 limit of 54 Ci. Since your source is 20 Ci, and 20 Ci is less than 54 Ci, it means that you can ship your radioactive source in a Type A package – easy peasy! And if your Cs-137 is not in a sealed source? Well, go a couple of columns to the right to see the A2 (normal form) column and you see that the A2 value for Cs-137 is only 16 Ci. So your 20 Ci of normal form Cs-137 has to be shipped in a Type B container, which is another kettle of fish entirely.

This helps you to figure out how your radioactivity has to be packaged, but we still need to figure out exactly what is meant by a Type A or Type B package. For this, you have to go to another part of the regs – 49 CFR 173.410 is where they start (for typical industrial packages) with additional information given in 49 CFR 173.411-412 and 415. In addition, if you’re going to certify a package yourself, 49 CFR 173.465-466 goes into all of the tests that you have to perform (and that the package has to pass – and that have to be documented) to show the package will be acceptable. For example, you have to show that the package can maintain its integrity when it’s sprayed with water, when it’s dropped onto a hard surface, when it’s dropped onto a corner of the package, when it’s stacked 5 high in a warehouse, and so forth.

So a reasonable question is “Where do I get these packages?”

One answer is that you can do it yourself. To do this, take whatever box you want to ship your radioactive materials in, outfit it the way you plan to use it, and test it. So, for example, if you’re going to have a Styrofoam insert, put that inside the box. If you plan to have your source inside a 25-pound lead shield, put the lead shield inside the box and the Styrofoam insert. If you’re going to seal the box up with strapping tape, buy some of the tape and tape up the box. And then you put it through all of the tests and document that it’s passed them all. Alternately, you can buy a Type A package (make sure it comes with a certificate that confirms it’s been tested). There are also reusable Type A containers – a metal box, for example, that can be locked with a padlock and that’s been tested to make sure it meets the Type A package criteria.

Package Types

Package Types

One last thing, and then I’ll try to put all of this together. If your source comes in higher than the A1 or A2 limits then you have to ship them in a Type B container. If what you have is an industrial radiography source then the camera itself is going to be an acceptable Type B container. But for the most part, Type B containers are fairly large contraptions that can weigh several thousand pounds and take up a fair amount of space – they’re usually transported by highly qualified companies that specialize in shipping high levels of radioactivity. And if you’re shipping some of the more esoteric types of radioactive materials (fissile materials, for example) then you’ve got to meet other criteria. But the people who are shipping things like this are also going to have to go through a LOT of training and they’ll know the requirements very well.

Type B Containers

Type B Containers being hauled on a semi truck

OK – so let’s try to summarize all of this.

  1. You’re trying to figure out how to ship, say, a 10-Ci sealed source (remember, a sealed source is considered to be special form) of Co-60
  2. You go to 49 CFR 173.435 and you see that the A1 limit (for special form) for Co-60 is 10 Ci. Whew – your source is less than this, so you can use a Type A package!
  3. You dig through your supplies and find that you have a reusable Type A package at your facility.
  4. You round up the Type A certificate to ensure that you (or someone else) tested the package properly.
  5. You stick your source in the package and ship it off to its destination.
    1. And if it’s a reusable package – don’t forget to insist that it be returned!

How Do You Label Radioactive Materials for Shipping?

Dear Dr. Zoomie: We’re a well-logging company and we ship and transport radioactive materials sometimes and I just found out we’re supposed be labeling our packages. I’m not quite sure how to figure out the right label to use. Can you help me? Thanks!

Yeah – this is a common question and a place where people make a lot of mistakes. First, the chances that your vehicle will be stopped and that you’ll get in trouble for making a mistake – pretty slim odds. On the other hand, you have to follow the rules whether you think you’re going to get caught or not – it’s the right thing to do. Not only that, but if you’re doing things the right way it doesn’t matter if you do get stopped because you’ll be doing things correctly. So here goes!

The first concept you have to learn is the Transport Index (abbreviated TI). The Transport Index is just the radiation dose rate that you measure at a distance of 1 meter from your package, in mR/hr. So if you get a reading of, say, 1.3 mR/hr a meter away from the package then the TI is 1.3; if you put some additional shielding around the same source and reduce the dose rate to 0.5 then the TI (for the exact same source) is reduced to 0.5. So the TI has nothing to do with the amount of radioactivity in the package – it only reflects the radiation dose rate you measure a meter from the package surface.

A few things to remember – alpha radiation can’t even penetrate through a sheet of paper, so if your package contains only alpha radioactivity then your TI will be zero no matter how much radioactivity is present (beta sources are similar – you might get readings from a high-energy beta emitter such as strontium-90, but might have no readings at all from a carbon-14 source). In addition, you have to remember that a neutron-emitting source (such as many well-logging sources) will be emitting radiation that might not be detected by all radiation instruments – you need to use a neutron detector to measure neutron radiation. Oh – and don’t use a Geiger counter to measure radiation dose rates unless it’s an energy-compensated GM; any other sort of GM detector is likely to give erroneous readings.

OK – so once you’ve got the TI figured out then you can get a start on figuring out how to label your package.

There are three labels you have to choose from, White 1, Yellow 2, and Yellow 3.

White 1 Radiation Label

White 1 Radiation Label

White 1 Radiation Label

The lowest level of label is a White 1. If the radiation level at the surface of the package (what you would measure by putting your radiation detector on contact with the package surface) is less than 0.5 mR/hr then it can be labeled with the White 1 label. White 1 packages don’t have a Transport Index – by the time you get to a distance of a meter there won’t be anything that you can measure.

Yellow 2 Radiation Label

Yellow 2 Radiation Label

Yellow 2 Radiation Label


Next is Yellow 2.  You will use a Yellow 2 label for packages with surface radiation dose rates of up to 50 mR/hr and that are less than 1 mR/hr (TI < 1) at a distance of 1 meter.

Yellow 3 Radiation Label

Yellow 3 Radiation Label

Yellow 3 Radiation Label

The highest level of label is the Yellow 3. These are used to label any packages with surface radiation dose rates in excess of 50 mR/hr OR for any packages with a TI greater than 1 (that is, where dose rate is higher than 1 mR/hr at a distance of 1 meter from the package).

One thing to keep in mind is that if your sources are expected to be transported a lot (soil density gauges, industrial radiography sources, and well logging sources are frequently transported from job site to job site), the carrying cases or packaging will very likely to be properly labeled by the manufacturer already. In that case, all you need to do is to check the radiation dose rates to make sure they’re what you expect to see (if the shielding is compromised somehow dose rates might be too high; if the source falls out of the shield then the dose rates will be too low).

Now that you’ve (hopefully) figured out how to label your packages, you need to know whether or not you can carry a particular package inside your vehicle – or someone else’s. Here, what matters is whether or not the vehicle is a common carrier (e.g. Federal Express) or an exclusive use vehicle (this can be your company truck or a contract carrier); it also matters whether or not the vehicle is open (a flat-bed truck or in the bed of a pickup truck that’s not covered).

If you’re shipping a radioactive package with a common carrier then the radiation dose rate has to be less than 200 mR/hr on contact with the exterior of the package and it has to have a TI of less than 10 (remember – this means that the dose rate measured 1 meter from the package can’t exceed 10 mR/hr).

If you’re transporting the radioactive materials in your own vehicle or with a contract carrier then you have a little more latitude. Here, if the vehicle is closed, you can have surface radiation dose rates up to 1 R/hr (1000 mR/hr) and up to 200 mR/hr on contact with the vehicle’s surface. For an open vehicle you’re limited to 200 mR/hr on contact with the package surface as well as at the edge of the vehicle’s bed. In both cases, you can’t exceed a dose rate of 10 mR/hr two meters from the side of the vehicle and no more than 2 mR/hr in the cab.

The last thing to mention is that some vehicles will have to be placarded – specifically, any vehicle carrying a Yellow 3 package as well as trucks carrying a category of radioactive materials called “low specific activity” (or LSA) material – this primarily comes from remediation of contaminated sites.

Radiation Placard Position on Trucks

Radiation Placard Position on Truck and Trailer

Remember – there’s a lot more to radioactive materials transportation than labeling the packages and placarding the trucks properly.  I’ll have some more postings on the topic, and you can also find information in a booklet published online by the Nuclear Regulatory Commission.

If you’re interested in attending a training course Nevada Technical Associates conducts courses on the topic of Transportation of Radioactive Materials and holds courses several times a year.

How Do You Transport Radioactive Materials?

Hi, Dr. Zoomie – got a question for you. We have some small radioactive sources in some soil gauges that we have to drive from job site to job site. I just took over as RSO and my boss told me to make sure we’re doing the transportation right. Can you tell me what I should be looking out for?

Wow – it might not seem like it, but there’s a LOT that goes into this; too much for a single posting. So let me give a sort of overview here and then I’ll get into some of the details later (there have been a lot of transportation questions lately, so it seems like a good topic to cover in some detail). For starters, the regulations you’ll need to follow are scattered through the Code of Federal Regulations – specifically, Title 49, Parts 171-173 (of 49 CFR 171-173).

So – first of all – if you are transporting or shipping radioactive materials (including your soil density gauges) then you or somebody else at your company is required to attend training in radioactive materials transportation every 3 years. If you don’t have any records showing anybody attending this training then this is something you need to take care of as soon as you can. Incidentally, there are a lot of hazmat transportation courses and most of them include a little bit of information on radioactive materials. But if you are driving these sources around every day then I would strongly advise taking a class that focuses on radioactive materials transportation and shipping since those classes tend to be taught by people who really know the details of radioactive shipments (and believe me, there are LOTS of details).

Second, I also need to differentiate between transportation and shipping. If you are driving the radioactive materials around yourself then you’re transporting radioactive materials. If you’re packaging them and handing them off to somebody else then you’re shipping. But either way you need to have the training every three years. On – you only have to worry about this if your radioactive materials are going to be moving by vehicle over public roads. At a university I used to work for we would transfer radioactive materials by walking them over to the appropriate building – so no need for special packaging or anything. And if you’re moving the materials over, say, an industrial campus that the public can’t access then you also don’t need to worry since these are not public roads.

packaging for transporting radioactive materials

Packaging for transporting radioactive materials

Whether you’re transporting or shipping you need to make sure that the materials are properly packaged. There are three main categories of radioactive materials – Type A, B, and C. Type A quantities of radioactive materials are to be packaged in Type A packages; Type B quantities must be transported in Type B packages, and Type C quantities are transported in (wait for it…) Type C packages – it makes an odd sort of sense. Type A packages don’t need to be very elaborate – some Type A quantities are shipped in strong cardboard boxes sealed with tough packing tape. By comparison, Type B packages are virtually indestructible – there are some videos online that show not only the size of these things, but some of the testing done to confirm that they’ll keep truly dangerous amounts of radioactivity safe, even under dire circumstances. Shown here are a stock photo of a Type A container and a photo I took of a Type B container that was used to transport a high-activity radioactive source – although the Type B container isn’t fully assembled (the two pieces shown are bolted together, one atop the other) you can get an idea of the size and ruggedness of these things.

Workers are loading an irradiated source into a Type B container for shipping.

Workers are loading an irradiated source into a Type B container for shipping.

One big thing to remember – with any package – is that it has to be certified as a Type A, B, or C package! And unless it’s certified then you can’t use it. Now, in your case, your gauge and shipping case (if it came with one) have already been certified as a Type A container so you don’t need to worry about this. But anyone reading this who is shipping or transporting, say, radioactive samples, radiopharmaceuticals, and that sort of thing…well, you might be tempted to just re-use the Type A package you received your last shipment in. And you would be wrong to do so since you haven’t certified the package the way that you normally use it, pack it, and seal it.

You also have to make sure the package is properly labeled – the categories here are White I, Yellow II, and Yellow III depending on the radiation dose rates you measure a meter away from the package (the transport index) and on the package surface. There’s some good information about all of this in a number of places online – one the most easily understandable is on a site maintained by the National Institutes of Health.

There’s a lot more than this on the topic of transportation and shipping, but this is a good place to stop for this overview. As I said, I’ve had a number of other questions so stand by for more details on labeling, packaging, transportation index, and so forth. But this should get you started. If you’re interested in attending a training course Nevada Technical Associates conducts courses on the topic of Transportation of Radioactive Materials and holds courses several times a year.