One of the classic doomsday scenarios, often inappropriately given way more prominence than it deserves, is some type of nuclear event that results in a massive release of radiation.
Let’s understand the nature of radiation and fallout risks – from that understanding can follow a better appreciation of what one needs to protect against and how to do so. The two terms are sometimes used interchangeably, but they are importantly different.
What is Radiation
The term ‘radiation’ covers a lot of different things. Light is a form of radiation. So are radio waves. But for our purposes, radiation can be split into two types. The first type is relatively safe, and is termed ‘non-ionizing’ radiation, and this includes radio and light waves, plus heat, sound, and various other things. Non-ionizing radiation is a type of radiation that isn’t thought to make changes to the atomic structure of things it comes into contact with, but it may cause other sorts of changes or side-effects (as you’ll know any time you stick something in a microwave oven, which uses non-ionizing radiation to cook the food you placed in it), so it is not necessarily completely safe.
Our discussion in this article however is about ionizing radiation. This is radiation that can change the make up of the individual atoms in things it comes into contact with. That is almost always a bad thing, and in particular, it can break up DNA in living tissues, which can lead to the formation of cancers.
There are five major and relevant types of ionizing radiation, termed alpha, beta, gamma, neutron and X-ray. Cosmic rays (primarily protons) are also ionizing, but they are a constant thing that does not change with a nuclear explosion, and so we can ignore them for this article’s purposes.
Let’s consider the main properties of these five types of radiation (and for the nuclear physicists reading, yes, we have simplified things somewhat, but hopefully have not compromised the overall accuracy of the article).
Alpha particles are the same as Helium-4 nuclei. They comprise two protons and two neutrons. They travel at about 5% of the speed of light (ie at a speed of about 10,000 miles in a second) but they are very short range – they typically only travel a couple of inches in air, and can be stopped by a single sheet of paper.
Because of their short-range and low penetration, alpha particles are not much of a problem.
Beta particles are typically electrons (if you wanted to be fastidious you could say there may be some anti-matter positrons briefly present too, but let’s not dwell on that). They are typically very fast-moving, and can travel greater distances than alpha particles, and will penetrate further as well (which is sort of implied by their greater range, of course). They will be blocked by about 1/10th of an inch of aluminum or other metal, or by an inch or more of plastic.
Gamma rays are ‘highly energetic photons’. In case that doesn’t explain much to you, they are fast-moving things (they travel at almost the speed of light) with no mass and no electric charge. This makes them hard to block, and they can penetrate a considerable distance through most materials. As a simplification, the more mass of material between you and the gamma rays, the better the material will act to attenuate (ie reduce) the amount of gamma radiation passing through it.
Gamma rays have an effective danger range of only a few miles, by which stage so few will remain as to no longer be harmful. Depending on the magnitude of the original explosion and the amount of gamma rays released, this danger range is anywhere from under one mile to perhaps three miles.
Neutron radiation is – as its name implies – a stream of the sub-atomic particles we call neutrons. It is also fast-moving, at a similar speed to that of alpha particles.
This type of radiation is nasty. When a neutron hits an atom, it can change the atom into a different substance, and it can change a stable substance into an unstable (and therefore radioactive) substance. Neutron radiation of a given level is generally said to be ten times more damaging than gamma or beta radiation. Oh – and did we mention that they also penetrate very well, requiring a substantial thickness of material to block them.
Water and concrete are good blocking materials.
Neutron radiation has slightly less range than gamma radiation.
X-rays are similar to gamma rays and are sometimes released as secondary radiation as part of a radiation event, but are not a primary product released by radioactive material, and so can be ignored for the purpose of this article.
The Shared and Relevant Characteristics of Radiation
The previous section looked at five different types of ionizing radiation, all of which is harmful to living creatures. They share a couple of important properties – they are all very fast-moving (even the slowest moves at a rate of about 10,000 miles per second) and they are all very small – some are so small as to have no mass or size at all (yes, we know that doesn’t sound sensible, but it is what it is).
They also have moderately short ranges – generally less than 5 miles, and sometimes less than 5 inches.
A nuclear explosion will almost instantly release lots of radiation, and in only a second or so, not only will this radiation have been released, but it will have also traveled as far as it is going to go. In other words, if you see a nuclear explosion, by the time your eyes have blinked from the bright flash, you’ve already received all the radiation you’re going to get from the immediate explosion itself.
Depending on where you are, that is either a good thing or a bad thing.
What is Fallout
So, what is fallout? Fallout is all the ‘stuff’ that was in and around the bomb. Some of this was radioactive to start with – by which we mean, it was emitting ionizing radiation. Some of the rest of it has become radioactive, as a result of neutron radiation changing the properties of the elements and making them into new radioactive elements. To be pedantic, you could term this ‘radioactive fallout’ but it seems to often be referred to merely as ‘fallout’, even though not all fallout is necessarily radioactive (but, to a greater or lesser extent, most of it is).
In the case of a bomb that is exploded in the air, most of this fallout material is simply the remains of the bomb itself. But if a bomb is exploded close to, on, or in the ground, then the neutrons from the initial explosion will react with the soil and any other materials close at hand (buildings, cars, people, whatever) and will make some of that material radioactive, and the force of the explosion will blow all this material up into the air as well, massively increasing the amount of radioactive stuff up in the air.
So far so good. Now for the ‘fall’ part of the word fallout. All that stuff in the air is going to gradually settle back down to earth. An air explosion will typically blow its remaining ‘stuff’ way up into the upper atmosphere, and it will spread perhaps all around the world and gradually settle, more or less evenly, over a huge portion of the earth’s surface. This is actually a good thing – there is unlikely to be any massive concentration of radioactive fallout in any one place as a result.
But the ground and near ground bursts are very different. Some of the material will be hurled up into the upper atmosphere, and will slowly fall down over the weeks and months that follow, all around the world, the same as air burst type fallout. But some of it will only go up a relatively small distance and will fall back to earth more quickly (usually within 24 hours), and more intensely. Depending on things like wind and rain, this material is likely to come back down to earth in the area downwind of the explosion, and perhaps spread out over 50 – 300 miles.
A ground burst not only creates a massively greater amount of radioactive fallout, but it deposits it more quickly and in a more concentrated pattern. This is all bad.
Fallout particles range in size from less than 0.1 microns in diameter up to many microns in diameter. They are dangerous because wherever they land, they are emitting whatever type of radiation it is they will emit. They can potentially be breathed in to your lungs, and – for example – if you then have an alpha radiation emitter in your lungs, it doesn’t matter that the alpha particles only travel an inch or two and are stopped even by a sheet of paper, because wherever it is they stop, and whatever damage they then do, it will be inside you and to part of you.
Not only can you breathe fallout particles in, you can ingest them from the water you drink, and the food you eat. Plus, the vegetables and animals you in turn eat or take milk from are doing the same things, and so your food may not only have surface contamination, but may have internal contamination too. You can reasonably wash fallout off the outside of some food, but you can’t get rid of it once it has become a part of the thing, itself.
How Long is Fallout Dangerous For?
There’s no exact answer to this, any more than there’s an answer to the question ‘How high is up?’. The danger life of fallout depends on several things – the level of radiation being emitted, and the half-life of the radioactive materials in the fallout. Fall-out has a veritable soup of different radioactive substances in it, all with different properties.
The ‘half-life’ of something is the time it takes to reduce in activity by 50%. Half-lives can range in duration from the tiniest fraction of a second at one extreme, to thousands of years at the other extreme.
To give an example of how half-lives work, let’s say there is a product with a 10 day half-life. If it is emitting 1024 units of radiation a second at the start of the measuring period, then in 10 days it will be emitting half that rate, 512 units/second. Now for the trick. In another ten days time, it doesn’t use up the other half, and drop to zero. Instead, it uses up half of what remains, so it loses half of the 512 units, and at the end of the 20 days, it will be emitting 256 units of radiation/second.
In another 10 days (30 days total), it will be down to 128 units of activity per second. At the 40 day point it is down to 64 units, at 50 days it is 32 units, and at 60 days – two months – it is now down to 16 units.
So the rate of reduction of radioactivity slows down. The first 10 days saw a drop from 1024 units of radiation a second down to 512 units/second. But the ten days from 60 days to 70 days sees a reduction from 16 down to 8 units – not really much of a change at all. Furthermore, it sort of never ever gets all the way to zero. When it is down to 1 unit, the next half-life period takes it to 0.5 units, then to 0.25, and so on down and down but never quite reaching zero.
If the acceptable level of radiation is, say, 10 units/second, then at the 70 day point, when it is down to 8 units a second, it has become relatively ‘safe’, and at the 80 day point and only 4 units a second, it is even safer still, and at 100 days (1 unit/second) you sort of forget about it entirely.
The good news is that many of the most radioactive substances have relatively short half-lives – their half-lives are short because they are so radioactive. So while you read about radioactive contaminated materials with half-lives of thousands of years, it is usually the case that these very long-lived substances only emit low levels of radiation.
Defending Against Radiation and Fallout From a Nuclear Explosion
Your best defense against the initial release of radiation is to choose your location carefully, so you’re not within range of any likely targets. If you’re a ‘glass half full’ kinda guy, the ‘good news’ is that if you are within range of the initial radiation release from a nuclear explosion, that is probably the least of your worries. You’ll probably be toasted to death from the heat, or crushed by the blast, long before the radiation kills you.
The bigger risk is the fallout from the blast. Again, you should choose your location as wisely as you can. As long as you can keep at least 20 miles from all air-burst targets, you’re probably going to be okay from air burst effects. Unfortunately, the ground bursts are much more troublesome, because who is to really know which direction for sure will be downwind on the day? You don’t want to be within several hundred miles of targets that are likely to receive ground bursts.
What types of targets will qualify for ground bursts? Only specialized targets, because for general effect and damage, air bursts are much more effective. But things like missile silos will definitely get ground bursts, and depending on their nature, other ‘hardened targets’ may also get ground bursts.
There’s another factor at play, too. Fratricide and general errors, failures and mistake. Not all missiles that are sent in our direction are guaranteed to explode exactly on their designated targets, and at the heights programmed into their warheads. Some may explode high, others low, and some might go way off target. Not only are ICBMs a little-tested technology, but routes over the North Pole are difficult to navigate, and with the very high re-entry speeds, even a slight second of delay can mean a missile is way off course or too high or too low. Add to that possible distortions caused by anti-missile events, and also what is termed ‘fratricide’ – the result of one missile’s detonation impacting on other missiles close to it, and a high intensity exchange of warheads could well end up with explosions going off hundreds of miles from where they were planned.
So the further away you are from anywhere that might receive any type of attack, the better you’ll be.
Now, for the fallout protection. If you end up getting a bucket load of high intensity fall-out dumped on you, and survive the initial experience, then you’re just plain completely out of luck for the next some decades, possibly even hundreds of years. Your only strategy will be to shelter until the fallout has all settled, and then to evacuate to a safer area, probably tens or even hundreds of miles away.
If you however get only a mild level of fallout, you’d be well advised to stay inside and to filter your air supply until the fall-out has done its thing and settled.
Your initial forays outside (ie to sample the area for radioactivity levels) should involve you wearing protective clothing (ideally exposing no skin at all), a breathing mask and goggles, and a decontamination process outside your dwelling prior to re-entering it, so you don’t bring in any radioactive material upon your return.
Opinions differ as to how long to expect radiation levels in fallout to subside – perhaps because different types of nuclear weapons, and different scenarios for their use, result in different mixes of radioactive materials, with different levels of radiation being emitted and different half-lives.. It seems that using three to five weeks as a prudent period to allow for levels to appreciably drop might be appropriate, and so you should factor the ability to survive, entirely inside, for at least twice that period of time, so as to be reasonably well prepared for such situations.
You should also be measuring radioactivity levels yourself, and keeping a record of them so you can try to see what the trend lines suggest (although this is difficult because there are a mix of different materials with differing half-lives, so there is no simple curve that you can plot and extrapolate).
Note also that radiation will probably not be evenly distributed everywhere on your property. You’ll want to survey the property, and to map out ‘hot spots’ and safe zones, and to then keep away from the hot spots (and/or take steps to mitigate the dangers they pose) while concentrating your ongoing activities in the safer areas.
Beyond that point, practical considerations also intrude. If it is winter, and there’s no need to be outside, then of course you can play it safer and stay inside more. But if it is summer and there is work to be done outside, you need to decide what to do, and maybe rotate outside assignments between different people in your community, spreading the exposure more widely.
A Different Scenario – A Nuclear Power Plant Problem
The good thing about a bomb is that it does its work all in a fraction of a second, and after that fraction of a second, it is done and finished. Sure, you might have to live with the consequences for a long time, but at least the initial event that created the problem has ceased.
But a nuclear power plant problem can be an ongoing issue, that releases nuclear material not just for a split second, but for hours or even days or weeks. You may have ongoing releases of new material for an extended time.
Perhaps the best (worst?) example of such a scenario occurred in Japan in March 2011 at the Fukushima Daichii power plant in Japan. An earthquake caused the working reactors at the multi-reactor site to shut down, and emergency diesel power generators started up to keep the cooling pumps circulating water through the power plant cores. The subsequent tsunami flooded the generator rooms, causing the generators to fail, and without power, the cooling pumps stopped, allowing temperatures in the reactor cores to go dangerously high, with three reactors melting down.
The problems started on 11 March, and significant releases of nuclear materials continued for two weeks or longer (depending on where you draw the line on ‘significant’ releases), and material was still being released a month after the event started. Here’s a great timeline.
It is probable that less radioactive material, in total, was released at Fukishima than at Chernobyl, but it occurred more recently, over a longer time line, and in full real-time view of the world’s news programs, making it a higher-profile event.
Furthermore, the Chernobyl disaster was relatively short-lived (pretty much all over and done with in less than a day), and we in the west only got wind of it (almost literally so) some time after the problem had been controlled, so there was less opportunity for angst and anguish.
There are a lot of variables at play with a nuclear power plant release of radioactive material. It could involve any or all types of radiation, and it might be released into the upper atmosphere or instead have a short ride up and a fast ride down again, pooling in concentrated area. Have a look at this map of contamination levels that were still in place in 1996, ten years after the event, to get a visual feeling for how strange the pattern of radiation concentration can be.
Try and locate up wind of nuclear power plants, and the further away you can be from them, the less risk you’ll run (although note the distribution pattern from Chernobyl where there was a relatively safe zone in the middle distance, with more dangerous areas both closer to the power plant, as you’d expect, but also further away, too).