Monthly Archives: November 2015


How Do I Protect Myself from Background Radiation?

Dear Dr. Zoomie – I just heard that we’re always exposed to radiation and it sort of scares me. And on top of that, there’s the radiation from Fukushima. Can I just line my walls with lead? And how much lead do I need to cut down this radiation to something safe?

Well…I think you might be overly concerned here. First, you’ve got to remember that radiation from natural sources has been a part of life on Earth since it first formed – it’s safe to say that every single organism that has ever lived on Earth has been exposed to radiation. Not only that, but there’s ample evidence that these natural background radiation levels today are the lowest they have ever been. This means that today we are being exposed to less radiation (from natural sources) than were our distant ancestors.

It’s also important to realize that natural radiation varies considerably from place to place on Earth. Some places – the American Gulf Coast, for example, most of Hawaii, Japan, and so forth – have unusually low levels of natural radiation (more on this in a moment) while other places (Ramsar Iran, the American Colorado Plateau, Guapari Brazil, and others) have elevated levels of natural radiation. Interestingly, cancer rates don’t seem to be at all correlated with natural radiation levels. For example, the parts of the US with the highest natural radiation levels also have among the lowest cancer rates in the country. Some people have actually used this fact to suggest that low levels of radiation might make us healthier – I’m not sure I can agree with that, though, because there are so many other things that can affect cancer rates. For example, the population along the Gulf Coast is generally older than in the Rocky Mountains, there are more people who smoke, and the area has a significant petrochemical industry – all of these could serve to increase cancer rates compared to the Rocky Mountain states. The most we can say is that the effects of these different radiation levels is fairly low – low enough to be swamped by the other factors.

Did you know Bananas contain naturally occurring radioactive material in the form of Potassium-40?

Did you know Bananas contain naturally occurring radioactive material in the form of Potassium-40?

As far as where this natural radiation comes from, there are four main sources, and these all change from place to place. They are:

  • Radiation from the rocks and soils. All rocks and soil contain potassium (about 0.01% of potassium is naturally radioactive) along with trace amounts of uranium and thorium. Uranium and thorium, in turn, decay through a number of radioactive progeny until they reach stable lead – these progeny include radium, radon, and polonium. So any rock or soil that you analyze is going to have radioactivity in it and we’re all exposed to radiation from this. On average, we receive 20-30 mrem annually from radioactivity in the rocks and soils as well as from building materials made from them (for example, bricks are made of clay that an contain radioactive potassium).
  • Radon in our homes and buildings. Radon comes from the decay of uranium in the rocks and soils. Radon is a gas; once it forms it will seep through the soil and into our homes – since it’s heavier than air it collects in basements, subway tunnels, caves, and so forth. Places with higher levels of uranium and thorium in the rocks and soils will have higher concentrations of radon in the air. On the other hand, since radon is such a heavy gas it’s not a concern above the first floor of any building. We receive about 150-250 mrem annually from radon, depending on the local geology and the amount of time we spend in areas where the radon might collect.
  • Radiation from our own bodies. As mentioned earlier, a tiny fraction of potassium is naturally radioactive, including the potassium in our own bodies. In addition, we’re always exposed to radioactive carbon (carbon-14) and hydrogen (H-3, also called tritium) that’s formed in the atmosphere from interactions with cosmic rays. Finally, we’re always ingesting or inhaling trace amounts of dust that can contain uranium or thorium. All told, we receive about 40 mrem each year from all of these sources of radiation in our own bodies.
  • Cosmic radiation from the sun and stars. The sun gives off high-energy particles as the solar wind. In addition, distant stars give off their own stellar winds and some of those particles escape into space as well – some of these stars, by the way, are far more active and energetic than our sun and the particles they give off have far more energy than what our own sun emits. As if that weren’t enough, every few decades a massive star explodes in our galaxy in one of the most energetic events in the universe – a supernova. The particles from these explosions also permeate space. When any of these particles – whether from our sun or from elsewhere in the galaxy – slam into our atmosphere they can generate what are called cosmic ray air showers; cascades of particles and gamma rays that percolate down to the ground to expose us to radiation. In general we receive from 20-40 mrem each year from cosmic radiation.

Putting all of this together, we receive about 250-300 mrem each year from natural radiation, with some variability depending on where we live and what we eat. And remember – first, there’s no way to get away from this and second, we’ve been exposed to this radiation for as long as there has been life on Earth.

Background Radiation Pie Chart

Background Radiation Pie Chart

So – as far as your questions go – lining your walls with lead might help to shield you from cosmic rays, but that’s only a minor source of radiation. You might also line your floors with lead to reduce dose from the rocks and soils, but that’s also somewhat minor. Sealing your basement might remove radon as a source – but there’s no way to eliminate the radiation exposure from the radionuclides in your own body. But really, this doesn’t matter – again, this is radiation that our bodies have the ability to deal with. The bottom line is that I really don’t see a reason to try to shield your home from natural radiation. Ah (I hear you say) but what about the radiation from Fukushima? For that, read on!

There’s no denying that the Fukushima meltdowns put a lot of radioactivity into the environment. A lot of it ended up in the Pacific Ocean and a lot settled out on the ground in Japan, but a lot of radioactivity ended up in the atmosphere. This was measurable in the US – just as fallout from the Chernobyl nuclear accident could be measured in the US. In fact, after the Chernobyl accident I was on a nuclear submarine that was stationed off the coast of the Soviet Union and we could measure the radioactivity in the air whenever we came up to ventilate. But what I learned then – and what is important to realize now – is that just because we can measure the radioactivity doesn’t mean that it’s a threat. With the right equipment, for example, I can measure the radioactivity in my own body, in the granite countertop in my kitchen, or in a bunch of bananas. That’s because we’re really good at measuring radioactivity. But, again, just because we can measure it doesn’t mean that it’s dangerous. Consider – I can measure the weight of a single grain of sand or a single particle of dust. But does that make it dangerous to have a grain of sand land on my head? Not really – because the weight of the sand grain is so small that, although measurable, it’s insignificant. Similarly, while we could measure radioactivity in the air after the Fukushima accident, the radiation dose to anyone in the US was trivial – even in Alaska and Hawaii. Some of the Fukushima radioactivity undoubtedly settled on the ground here, but the majority of that was relatively short-lived iodine (I-131 to be precise) and the remainder was present in such low quantities that it simply poses no more threat than the natural potassium that’s already in the soil.

Finally, I wanted to mention something else briefly – about environmental sampling. Every now and again you’ll read a report that somebody has, say, sampled rainwater or soil, or even made radioactivity measurements on a beach and they’ve found elevated readings. To be honest with you, I always take these with a grain of salt because making these measurements isn’t as easy as one might think. It’s not uncommon to take a quick reading and to get counts that are higher than background readings. But just because you get a reading above background doesn’t necessarily mean anything. To get into a full discussion would require talking about counting statistics, and I won’t subject you to that! For now, let it suffice to say that radiation is random – if you take a radiation detector and push the button to record every count that comes in during the next minute you’re going to get a number. Push it again and you’ll get a different number; push it a third time and you’ll get something else. Over time you’ll notice that the readings are all clustered together a shape that’s called a bell curve. Sixty-eight percent of the time the readings will fall within one standard deviation of the average value and 95% of the time the readings will be within two standard deviations. As long as particular reading is within two standard deviations of the average then you probably don’t have anything unusual. But there are a lot of people who think that any reading that’s above background is significant, when it could simply be that your detector was hit by a cosmic ray air shower while you were counting.

Another mistake that people make is taking too small a sample and counting it for too short a period of time. If you have elevated readings after counting, say, a 1 liter sample of rainwater for an hour, it’s a lot more compelling than having an elevated reading following a 1-minute count of a one-milliliter sample. This is another problem that people run into – they’ll take a small sample, count it for a minute, and if the count rate is a little higher than background then they start worrying about contamination. Most of the time, though, counting a larger sample for a longer period of time (many environmental samples are counted for over 12 hours) will show us that there’s really no contamination. OK – so let me put all of this together!

Did you know we receive anywhere from 20 to 40 mrem each year from cosmic radiation?

Did you know we receive anywhere from 20 to 40 mrem each year from cosmic radiation? – Graphic by W. Kent Tobiska

First, every creature that has ever lived on Earth has been exposed to background radiation and we’ve evolved to cope with this level of exposure. Background radiation comes from radionuclides in the rocks and soils, in our own bodies, from radon, and from cosmic rays. Cosmic radiation varies around the world, but these variations don’t seem to be correlated with health or cancer risks. That being the case, you really don’t need to worry about shielding your home to reduce exposure from background radiation. And with regards to radiation from Fukushima, some of that was detected in the air shortly after the accident and some might even have settled to the ground in the US. But radiation dose from this fallout was so low that it’s not worth worrying about – less exposure than if you were to move from the Gulf Coast to the Rocky Mountains. Finally, there are a number of people who have reported measuring higher levels of radioactivity at various times. But unless the samples were obtained and analyzed by someone with experience in environmental sampling they’re likely to be small samples counted for a short period of time – as such, the results are likely to be meaningless. And even if an increase was seen, unless it’s more than a few standard deviations higher than background levels, the results are most likely nothing more than a statistical anomaly rather than an indication of contamination.

What Should Be Included in a Training Program for Radiation Workers?

Hello, Dr. Z – I’m a Radiation Safety Officer (RSO). I am putting together a training program for my radiation workers. What do I need to include to make sure I cover all the bases? Thanks!

Wow – great question! And very near and dear to my heart – I’ve been teaching in one way or another since the early 1980s. So let’s see how much I can tackle here.

First, let’s start off with who is considered to be a radiation worker. And the fact is that there is no regulatory definition of what a radiation workers is – this is something that you will have to define for yourself based on your understanding of your facility. The bottom line is that anybody who is NOT a radiation worker is limited to 100 mrem of exposure annually, so if you have anybody who you can reasonably expect to reach or exceed this level of exposure then you need to designate them as a rad worker and give them appropriate training. You might do this based on radiation dose rate measurements (if a person works for 2000 hours a year in a radiation field of 0.05 mrem/hr they’ll receive 100 mrem in a year).

Alternately, you might decide to designate everyone who works in a particular area or who performs specific tasks as a rad worker – everyone who operates an x-ray cabinet for QA/QC measurements for example, or everyone who works in a veterinary x-ray suite. Something else to consider is that some types of workers are likely never going to receive 100 mrem in a year – but they should be considered rad workers nevertheless. Think, for example, of laboratory technicians who handle radionuclides every day – even though these workers almost never receive any measureable dose at all (at most universities, anyhow) they’re working directly with radioactive materials in a form that can easily cause contamination.

Pictured here, an RSO gives a short demonstration on how to properly use a survey meter.

Pictured here, a Radiation Safety Officer (RSO) gives a short demonstration on how to properly use a survey meter.

OK – moving on…training is a regulatory requirement, in addition to being simple good sense. Think about it – if you’re going to ask someone to work with anything potentially hazardous, you owe it to them to teach them how to do so safely. So we have, say, electrical safety training for those working with electrical gear, we give driver’s training before we can operate vehicles…and we give radiation safety training to people before they’re allowed to work with radiation or radioactivity. And if that’s not enough of a reason for you, radiation safety regulations (specifically 10 CFR 19.12) require training for “all individuals who… are likely to receive in a year an occupational dose in excess of 100 mrem (1 mSv)….” Not only that, but all of your radiation workers are required to receive annual refresher training.

Oh – I should also point out that you might need to give training to non-radiation workers if they routinely work around radiation or radioactivity. For example – your maintenance or housekeeping staff might regularly enter radiological areas to clean up, empty the trash, or fix equipment. Even though these people might never receive any appreciable exposure they’re still working around radioactive materials and they deserve to know how to do so safely. These are called ancillary workers and of course they should receive training! Luckily, this training need not be very in-depth – mine would usually only last about 10 minutes and I’d briefly make sure they could recognize the radiation symbol, that they knew not to remove radioactive waste, I’d make sure to let them know that the health effects were minimal (given the very low exposure they were receiving), and would let them know how to get in touch with Radiation Safety or Security if they ran into any problems.

The founder of Nevada Technical Associates, Inc., the late Dr. Robert Holloway, frequently conducted Radiation Safety Officer Training courses, and other short courses on Radiation Safety.

The founder of Nevada Technical Associates, Inc., the late Dr. Robert Holloway, frequently conducted Radiation Safety Officer Training courses, and other short courses on Radiation Safety.

How the training (both initial and refresher) is given is not specified in the regs – I will always give the initial training in person, but I’ve found a number of ways to give the refresher training. I’ve required rad workers to watch instructional DVDs, to read the refresher training materials, I’ve had on-line refresher training, and also given annual classes. I’ll also accept (only for refresher training) certificates from related radiation training – for example, if a person attends a class on responding to radiation emergencies. Whenever possible I prefer to give all training in person, but sometimes this just isn’t possible. The bottom line is to make sure that you can document that all of your rad workers have received the training and that the training meets the regulatory requirements. As to what those requirement are…keep reading!

The same regulation mentioned earlier also tells us what has to be included in the training:

  • Kept informed of the storage, transfer, or use of radiation and/or radioactive material;
  • Instructed in the health protection problems associated with exposure to radiation and/or radioactive material, in precautions or procedures to minimize exposure, and in the purposes and functions of protective devices employed;
  • Instructed in, and required to observe, to the extent within the workers control, the applicable provisions of Commission regulations and licenses for the protection of personnel from exposure to radiation and/or radioactive material;
  • Instructed of their responsibility to report promptly to the licensee any condition which may lead to or cause a violation of Commission regulations and licenses or unnecessary exposure to radiation and/or radioactive material;
  • Instructed in the appropriate response to warnings made in the event of any unusual occurrence or malfunction that may involve exposure to radiation and/or radioactive material; and
  • Advised as to the radiation exposure reports which workers may request

In addition to these, you should also consider discussing program-specific topics; what these are is up to you. For example, I would include a discussion of the most common problems we found when we inspected our radiation laboratories, I’d go over a few instructive case studies, and would also show the rad workers (most of them were laboratory technicians or graduate students) how to work safely with radioactivity in their labs. Oh – and at the end of the rad worker training you should give an exam to the students to confirm that they’ve been paying attention. Typically your regulators will be looking to make sure that they receive a score of 70% or higher – anyone who can’t get this score should be required to re-take the training, hoping the information will stick a little better the second time around.

Now a few odds and ends….

  • You need to keep records of everything. Students should sign in for the training (keep the sign-in sheets) and their exam grades should be recorded; these records should be kept for at least a year, until they take their refresher training (and pass the exam for that).
  • You, as Radiation Safety Officer (RSO), also need to have periodic refresher training, presumably to keep you from just talking to yourself for a half hour or so every year. And since you have to have a far higher level of knowledge than any of your rad workers, you should seriously consider taking a 2-3 day class for your refresher training, but this class need not be called “RSO refresher training.” Many regulators will accept any radiation-related class you find – I’ve had RSO refresher students in classes I’ve taught on radiological terrorism, radiation instruments, Naturally-Occurring Radioactive Materials, and more.
  • You might also have to receive more specialized training. For example, if you’re transporting or shipping radioactive materials then you have to receive training in this every three years. If you have (for example) an irradiator then you’ll probably have to teach people how to safely use the irradiator before they’re allowed to do so. And so forth….
  • And there’s no specific requirement as to how long the training should last – I’ve been to rad worker training that lasted as little as a half hour and to training that took three full days – you’re going to have to balance what the regulations require, the site-specific materials you’d like to go over, as well as the amount of time you’re able to pry your workers away from their normal duties.

That’s about it on training – I can go into more details but, really, from here it gets to be very program-specific. I hope it helps – and good luck!