Radiation post #3- Exposure to Airborne Radioactivity
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May 30, 2017 at 9:54 pm #82659
NOTE- There are two Figures that go with this post. I will make the figures into JPGs or some image format and put them in this thread, as soon as I get that done.
Radiological Rules of Thumb and Exposure to Airborne Radioactivity
In the first post in this series, we reviewed “How much radiation” causes various acute effects and injuries and what some radiation units are. The second post reviewed some techniques for using a Geiger counter survey meter to measure radiation levels around you and how to survey items for radioactive contamination. The purpose of this post is to provide you with information and techniques to estimate your radiation exposure from being exposed to radioactivity in the air you’re breathing. Please note that in the interests of conveying this information to an audience with varying levels of math and science comfort, this has been simplified quite a bit. However, even over-simplified, the information here should still be accurate and useful.
For additional information, see NAVSEA document “APPLIED ENGINEERING PRINCIPLES MANUAL” section 7.3 “Radiological Controls”
If you are not familiar yet with units of radiation, and how much radiation dose will lead to various levels of injury, please read the first post in this series (“How much radiation”) before reading this post.
After an SHTF event, say a nuclear attack or a nuclear power station accident, you may be exposed to radioactivity and thereby radiation from particles of radioactive fallout being carried your way by the prevailing winds. The purpose of this post is to describe to you how to measure the amount of radioactive particulates in the air around you, and how to estimate the radiation dose you will receive from breathing air containing that amount of radioactive particulates.
The radiation dose you receive from a plume of fallout is both external, and internal. The external radiation exposure is what you’re body receives due to beta and gamma rays being emitted from particles in the air around you. External exposure is fairly simple to estimate, if you have a radiation survey meter (see post 2 in this series for how to use a Geiger counter) that can tell you what the (external) radiation level is around you.
However, you will also receive “internal radiation dose” from a plume of fallout, if you breathe in air containing radioactivity. The particles of radioactivity become lodged inside your lungs as you breathe them in, and give your lungs radiation dose. The rest of your body can also receive some radiation dose from the beta/gamma rays being emitted from inside your lungs, as well. Calculating the dose to your “whole body”, or figuring out the effective dose that your whole body receives combined from different doses to your lungs and other body parts, is a very complex subject. However, some “rules of thumb” are available which will give you an idea of what your radiation dose, and what your effective dose, is for situations where you’re immersed in a radioactive fallout plume. For preppers post-SHTF, the main take-home here is to be able to quickly estimate your radiation exposure based on measurements you take at your location, and use that to quickly tell if it’s safe to go outside.
Airborne Radioactivity – What is it? And how do you measure it?
Fallout consists of small particles of radioactive dust/dirt, which can be carried long distances by prevailing winds. Breathing air that contains radioactivity can cause radiation-emitting particles to become lodged in your lungs, where they will give radiation dose to your lungs and to the rest of your body. This dose is in addition to the radiation dose you receive from outside your body- your lungs will collect much of the radioactive particles that you might breathe in, where they will stay.
Most techniques for measuring the amount of airborne radioactivity involve passing air through a filter paper, and catching the particulates on the paper. A radiation detector, such as a Geiger counter, can then be used to detect the presence of radioactivity on the paper filter, and to measure how much there is. The concentration of airborne radioactivity is the amount of radioactivity (Curies) divided by the volume of air that was passed through the filter paper (cubic meters).
Radiation professionals generally make this measurement with an instrument called a portable air sampler (PAS). The PAS passes air through a filter paper, which is then counted with a measurement instrument. See Figure 1 below for a picture of a typical PAS.
Figure 1 – Portable Air Sampler (PAS)
The PAS has a flow totalizer to accurately pass a precise amount of air through the filter paper, for example, 1 cubic meter. The user sets the PAS to collect a certain volume of air, turns it on, and lets it run. The PAS turns itself off once the set volume of air has been collected through the filter paper. Typical PAS sample volumes are either 1 m3 or 0.3 m3.
A typical air sampler has to run for several minutes to run 1 m3 of air through a filter paper.
You can improvise your own PAS with a “shop vac” type vacuum cleaner and a piece of paper towel to use as a filter. Place the filter paper over the suction of the vacuum cleaner, and let it run an appropriate amount of time. If you’re really slick, you might rig up a way for the vacuum cleaner suction and discharge to be outside your house, so that you don’t have to go outside to take an air sample. I don’t know of an easily-accessible way to measure the air flow of an improvised device like this, but you can still do well with this type of setup by using a stopwatch to time the duration the vacuum is running so that your readings will be consistent. For instance, you could approximate the purpose-built PAS by running the vacuum for either three minutes exactly for about one cubic meter, or one minute for about one-third of a cubic meter. You’ll see in a minute why these air volume values are useful.
Once you’ve collected your sample, you need to measure the amount of radioactivity on the filter paper. Use the same technique for this as is described in the second post in this series “How to use a Geiger counter”. Figure 2 below shows the proper technique.
Figure 2 – Measuring the radioactivity on the filter paper with a Geiger counter.
Write down (record) your readings including the date/time the sample was taken, the background reading in counts per minute (cpm), how many counts per minute (gross) you read from your sample, and how many counts per minute (net) you obtained after subtracting the backround counts per minute from the gross counts per minute. In equation form,
n = g – b, where
n = net counts per minute above background, g = gross counts per minute, and b = background counts per minute.
In the example shown in the post on how to use a Geiger counter to measure surface contamination from a surface swipe, we were looking for levels on the order of 100 counts per minute above background. That 100 counts per minute above background is also a level of interest to us for purposes of measuring airborne radioactivity.
Using Thumbrules to Estimate Airborne Radioactivity and Radiation Dose
And now, to the meat of things, let’s convert the measurement we just took into an airborne radioactivity level, and work out how much radiation dose we’d get from breathing air containing this concentration of radioactivity.
100 counts per minute above background on a 0.3 cubic meter air sample corresponds to an airborne radioactivity concentration of about 1 x 10-9 uCi/ml. (Note- no special fonts are being used here, so “uCi/ml” should be read as “micro-Curies per milliliter”). In words, one hundred counts per minute above background from a 0.3 cubic meter paper filter means the airborne radioactivity level is ten to the minus ninth power micro-Curies per milliliter.
Thumbrule time! First thumbrule:
(Thumbrule 1) (Air sample) 100 cpm > background on a 0.3 cubic meter air sample –> 1E-9 uCi/ml.
How much radiation dose do you get from breathing in this concentration of radioactivity? We need another thumbrule. Part of the answer to this is, it depends on what the radioactivity is that you’re breathing. A particular concentration of long-lived radioactivity such as Cobalt-60, will give you a higher lung and total body radiation dose than will breathing the same concentration of shorter-lived fission products. The reason is that the fission products with short half-lives will disappear more quickly than will radioactive particles with a long half-life. The longer it stays in your lungs, the more dose you accumulate.
If there’s good news here for preppers, it’s that the radioactivity you could expect to encounter after a nuclear attack or a nuclear power accident is due to short-lived fission products. You will almost certainly not have the laboratory equipment needed to determine the source of the radioactive particulates around you, but it is a safe assumption that they will be short-lived fission products for the nuclear attack/nuclear power accident scenarios. This may not be a safe assumption for a radiological “dirty bomb” situation.
So, thumbrule time again, first in words, then as bullet points.
Thumbrule 2 below applies to preppers being exposed to fallout after a nuclear attack or a nuclear power accident, that is, exposure due to short-lived fission products. Thumbrule 2: “Breathing air for one week (168 hours) that contains 1 x 10-6 uCi/ml of short-lived fission products, will give you a dose of 100 mrem to your lungs, and a committed whole-body dose of 20 mrem.”
(Thumbrule 2) One week (168 hrs) breathing short-lived fission products at 1 E-6 uCi/ml gives you a lung dose of 100 mrem, and a total body dose of 20 mrem.
How do you use these thumbrules? Use Thumbrule 1 to convert your air sample measurement into a radioactivity concentration. Use Thumbrule 2 to determine how much dose you’d receive in one week of breathing radioactivity at that concentration.
Even if you can’t calibrate your vacuum cleaner cum portable air sampler to know exactly how many cubic meters of air you’ve run through your filter paper, you don’t need that in order to make use of it. Relative measurements are useful, too.
Reducing Your Radiation Exposure From Airborne Radioactivity
Time, distance, and shielding are three methods for reducing your radiation exposure from any type of radiation. For exposure to airborne radioactivity, you can also reduce your radiation dose by reducing the concentration of radioactivity in the air you breathe (filter your air) and by reducing the likelihood of your body absorbing some of the radioactive material (iodine tablets).
Time, distance, and shielding are simple. Minimize the time spent being exposed to radiation, increase the distance between you and the radiation source, and increase the amount of shielding between you and the radiation source. Let’s consider a “typical” prepper SHTF scenario where either you’re downwind of a nuclear attack target, or are downwind of a nuclear power plant that’s had an accident and is releasing radioactivity into the air upwind of you. The radiation coming from the radioactive particles will be coming at you from every direction around you if you’re inside the plume, and even from the ground under your feet if much of the radioactivity has settled out of the air onto the ground.
Assuming you’re not affected by the blast or thermal effects of the attack/accident, your general plan to avoid radiation exposure from the plume of radioactive particles being blown at you and around you (and settling out onto every exposed surface) is to take cover inside. Take cover inside as deeply within the structure as you can. This maximizes the distance between you and all the radiation-emitting radioactive fallout, and also maximizes the shielding between you and the radiation. If you have to go outside for some reason, stay outside as little as possible and get back inside as soon as you can. Stay inside until the outside radioactivity levels have returned to normal, or to as close to normal as you are able to wait.
Filtering the air you breathe inside your fallout shelter will reduce the amount of radioactivity that gets inside with you and the air you’re breathing. If it’s not obvious, in such a situation you should also turn off your heating/cooling system so that you’re not circulating unfiltered air throughout your house or shelter. Any filter is better than no filter, but something like a HEPA filter would be best and is what is typically used in the radiation industry.
In the event that you’re being exposed to airborne fission product radioactivity from a nuclear attack or a nuclear power plant accident, iodine tablets have the potential to reduce the radiation dose your thyroid receives. There are several isotopes of iodine that are radioactive, but Iodine-131 (I-131) is one of the more significant threats to you. This is because as you inhale or ingest iodine, your body will concentrate iodine into your thyroid. This puts the source of radiation right up close (inside of!) your thyroid- remember, reduce radiation by time, distance, and shielding, and up close is bad! If you anticipate being exposed to fission products, taking a dose of non-radioactive iodine before the exposure will saturate your thyroid with iodine. When you later breathe air containing radioactive iodine, then, the radio-iodine will enter your body but won’t be able to collect in the thyroid, the thyroid already being “full”. Commonly-used forms of iodine are either potassium iodide (KI) pills or sodium iodide (NaI) pills. Hopefully this explanation makes it clear that taking the iodine pills in advance only protects you from having your thyroid blasted by concentrated radio-iodine. The iodine pills do not protect you from the external radiation exposure or from generally being immersed in a cloud of radioactive particles. The iodine pills only block your thyroid from absorbing radio-iodine. That’s important and useful, but it’s not the only thing.
May 30, 2017 at 10:01 pm #82660
Figure 1 – Portable Air Sampler (PAS)
May 30, 2017 at 10:04 pm #82661
Figure 2 – counting the filter paper from a portable air sample.
May 30, 2017 at 10:05 pm #82662
Here is the post as a PDF, with figures inline with text.
This is the most convenient for reading, if you don’t mind downloading the file to read it.
May 30, 2017 at 10:19 pm #82663Joe (G.W.N.S.)Moderator
I encourage everyone to download this PDF and add it to a binder of CBRD reference material.
Many of us live within the prevailing winds of Nuclear Power Plants. Far too many overlook that many “Post-Event” scenarios could lead to extremely dangerous incidents at these palnts.
Hopefully you will never need it, but if you do this type of information will be priceless!
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