Posts Tagged ‘NUKEMAP’


Hiroshima and Nagasaki at 70

Friday, August 21st, 2015

This month marked the 70th anniversary of the atomic bombings of Hiroshima and Nagasaki, and the cessation of hostilities in World War II. Anniversaries are interesting times to test the cultural waters, to see how events get remembered and talked about. I was exceptionally busy this summer, doing my part to try to participate in the discourse about these events. In case you missed them and wished you had not, here are a few of my appearances:

I also published a second blog post with the New Yorker on the often-overlooked second use of the atomic bomb: “Nagasaki: The Last Bomb.” I am proud of it as a piece of writing, as I was really trying to pull off something deliberate and subtle with it, and feel that I somewhat accomplished that.

New Yorker - Nagasaki - The Last Bomb

On this latter piece, I would also like to say that very little of what I wrote would come as a surprise to historians, though the particular arrangement of Nagasaki-as-JANCFU (that is, with an emphasis on the less-than-textbook aspects of the operation, as a herald of the later chaotic possibilities of the nuclear age) is usually under-emphasized. We tend to lump Hiroshima and Nagasaki together when we talking about the atomic bombings during World War II, and I think they should probably be separated out a bit in terms of how we regard them. The first use of the bomb, at Hiroshima, was in many ways a very straightforward affair, both in terms of the strategic and ethical considerations, and the tactical operation. Whether one agrees with the strategic and ethical considerations is a separate matter, of course, but a lot of thought went into Hiroshima as a target, and into the first use of the bomb. Nagasaki, by contrast, was less straightforward on all counts — less thought-out, less justified, and was very nearly a tactical blunder. For me, it reflects on the very real dangers that can occur when human judgment gets mixed with the extremely high stakes that come with weapons as powerful as these. Any bomber crew can have a mishap of a mission, but when that mission is nuclear-armed, the potential consequences multiply.

The one notable exception to the “very little would come as a surprise to historians” bit in this piece is that Nagasaki was never put on the “reserved” list. For whatever reason, the idea that both Hiroshima and Nagasaki were “reserved” from conventional bombing is very commonly repeated, but it is just not true. The final “reserved” list contained only Kyoto, Hiroshima, Kokura, and Niigata. Aside from the fact that no documentation exists of Nagasaki being put on the list (whereas we do have such documentation for the others), we also have the documentation actively rescinding the “reserved” status for Hiroshima, Kokura, and Niigata, so that they could become formal atomic targets.1

Detail from a damage map of Nagasaki, produced by the United States Strategic Bombing Survey, 1946. I have the original of this in my possession. I find this particular piece of the map quite valuable to examine up close — one gets a sense of the nature of the area around "Ground Zero" very acutely when examining it. There were war plants to the north and south of the detonation point, but mostly the labeled structures are explicitly, painfully civilian (schools, hospitals, prisons). Click to enlarge.

Detail from a damage map of Nagasaki, produced by the United States Strategic Bombing Survey, 1946. I have the original of this in my possession. I find this particular piece of the map quite valuable to examine up close — one gets a sense of the nature of the area around “Ground Zero” very acutely when examining it. There were war plants to the north and south of the detonation point, but mostly the labeled structures are explicitly, painfully civilian (schools, hospitals, prisons). Click to enlarge. Here is a not-great photo of the whole map, to compare it with, and here is a detail of the legend. At some point, when finances allow, I will get this framed for my office, but it is quite large and not a cheap endeavor.

John Coster-Mullen’s book provided a lot of documents and details about the bombing run. One thing I appreciate about John is his dedication to documentation, even though his views on the meaning of the history are not always the same as mine. I thoroughly believe that rational people can look at the same facts and come up with different narratives and interpretations — the trick, of course, is to make sure you are at least getting the facts right.2

It would be interesting at some point for someone to do a scholarly analysis of the popular discourse surrounding each decade of anniversaries since the bombs were dropped. 1955 was a fairly raw time, right after McCarthyism had peaked and the hydrogen bomb had been developed. 1965 marked an outpouring of new books and revelations from those involved in the bomb project, enabled by new declassifications (allowed, in part, because of the fostering of a civilian nuclear industry) and the fact that some of the major participants (like Groves) were still alive. I have no distinct impressions of 1975 being a major anniversary year, but 1985 resulted in a lot of hand-wringing about the relationship between the birth of the nuclear age and the nuclear fears of the 1980s. 1995, of course, was the first post-Cold War anniversary and one of the “hottest” years of controversy, catalyzing around the Smithsonian’s Enola Gay exhibit controversy and the “culture wars” of the mid-Clinton administration. We are still dealing with the hyper-polarization of the narratives of the atomic bombings that became really prominent in the mid-1990s — where there were only two options available, an orthodox/reactionary view or a critical/revisionist view. The 2005 anniversary did not make a large impression on me at the time, and seemed muted in comparison with 1995 (perhaps a good thing), except for the fact that some very noteworthy scholarship made its appearance to coincide with it.

A small sampling of some of the international press coverage of the NUKEMAP around the Hiroshima anniversary.

A small sampling of some of the international press coverage of the NUKEMAP around the Hiroshima anniversary.

And what of 2015? There were, of course, many stories about the bombings. Nagasaki got a better representation in the discourse than usual, in no small part because Susan Southard’s Nagasaki: Life After Nuclear War received heavy promotion. (I have not read it yet.) The general discussion seemed less polarized than they have been, though I did see a fair share of hand-wringing and defending editorials pop up on my Google Alerts feed. I have speculated that I think anniversaries from this point forward will be somewhat more interesting and reflective than those in the recent past, in part because of the declining influence of American World War II veterans, who were such a strong force in the more recent ones. My (perhaps overly idealistic) hope is that our narratives of the bombings can settle into something more historically informed, more quietly reflective, and less keyed to contemporary politics than in the past.

For my part, I was impressed by the number of people online who were interested in re-creating Hiroshima on their hometowns. The featuring of NUKEMAP on the Washington Post’s Wonkblog drove an incredible amount of traffic to the site. It was one of those stories that could be essentially lifted and re-written to fit a wide variety of different cities or countries, and there were variations of the “What would happen if Hiroshima happened here?” written in dozens of languages over the days leading up to and beyond the anniversary. The result is that NUKEMAP’s traffic had an all-time high spike over 300,000 people on August 6. The traffic is a typical long-tail distribution, so in the week of August 5-12, there were well over 1 million pageviews for the NUKEMAP. There have been other spikes in the past, but none quite as big as this one.

Locations where the Little Boy bomb was "dropped," August 5-12, 2015. These are unweighted (each dot represents an indeterminate number of detonations). Here is a heatmap (capped at 1,000 detonations — the actual cap is 28,116 — to make it easier to see the broader spread) showing where repeat detonations occurred. Here is a version where I have thrown out all locations where fewer than 10 detonations took place, and scaled their size and color by repetition. Total detonations is 266,483.

Locations where the Little Boy bomb was “dropped,” August 5-12, 2015. These are unweighted (each dot represents an indeterminate number of detonations). Here is a heatmap (capped at 1,000 detonations — the actual cap is 28,116 — to make it easier to see the broader spread) showing where repeat detonations occurred. Here is a version where I have thrown out all locations where fewer than 10 detonations took place, and scaled their size and color by repetition. Total detonations is 266,483.

Where do people nuke, when they recreate Hiroshima? Well, all over the world, not surprisingly, though the biggest single draws are New York (which is a NUKEMAP default if it cannot figure out where you probably live) and Hiroshima itself (re-creating the actual bombing). I’ve exported the log data for people using the Little Boy bomb setting (15 kiloton airbursts) for the week of August 5-12, and the maps are shown and linked to above. Obviously it correlates very heavily with both population and Internet access, but still, it is interesting.

Lastly, a week after the anniversary, what more reflection is there to be had? A new poll came out in late July of a thousand Americans, asking them what they thought about the bombings. Overall, 46% of those polled thought that the dropping of the bombs on Japan was the “right decision” to do, while 29% thought it was the “wrong decision,” and 26% said they were “not sure.” Which one can interpret in a number of ways. The feelings appear to correlate directly with age — the older you are, the more likely you think it was “right,” and the younger, with “wrong.” It also correlates with a few other factors, notably political affiliation (Republicans strongly in favor, Democrats and Independents not so much), race/ethnicity, and income. I suspect all of these variables (age, political affiliation, race/ethnicity, and income) to be pretty highly correlated in general. Separately, the gender gap is pretty extreme — men defend the bombings by a very large margin compared to women.

The head of the Nagasaki mushroom cloud — like a monstrous brain.

The head of the Nagasaki mushroom cloud — like a monstrous brain. Source: National Archives/

None of this is extremely surprising, I don’t think. But I was taken aback by another question in the same poll, a strictly factual one: “Which country was the first country to build a nuclear weapon?” Only 57% of the total polled correctly identified the United States, and it gets very depressing when one looks at how this breaks down by age. Less than half of Americans under the age of 45 could correctly identify that their country was the first country to develop nuclear weapons. I don’t really mind if a lot of people can’t identify when the first weapons were used (another question in the poll); exact years can be hard for people, especially on the spot, and the differences between the options given were not so vast that they represent much, in my view. But 23% were “not sure” who made the first bomb, 15% thought it was the USSR, and 3% thought it was China! (Almost nobody, alas, thought it was France.) This is not a minor factual error — it is a fundamental lack of knowledge about the historical composition of the world. It reflects, I suspect, the waning attention given to nuclear issues in the post-Cold War.

One last reflection: How do I, a historian of these matters, find myself thinking about Hiroshima and Nagasaki these days? Increasingly I find myself uninterested in the question of whether they were “justified” or not, which contain so much predictable posturing, the same old arguments, with very few new facts or analyses. I think the bombings were a very muddy affair from an ethical, strategic, and historical perspective, and I don’t think they fit into any simplistic view of them. I’ve come to feel my position on these could be described as an “inverse moderate,” where a moderate seeks to make everyone feel comfortable, but my goal is to make everyone feel uncomfortable. If you think this history supports some easy, straightforward interpretation, you are probably throwing out a lot of the data and filling it in with what you’d like to believe. It is complex history; it does not boil down easily.

  1. See Potsdam cable WAR 37683, July 24, 1945, copy in the Harrison-Bundy files, Roll 10, Target 10, Folder 64, “Interim Committee — Potsdam Cables.” []
  2. And, of course, I am not so naive to believe that “getting the facts right” is a simple or straightforward process. Indeed, contextualization of documents is a large part of understanding what the “facts” often are, and that requires narrative and interpretation, and so we end up in a somewhat circular epistemological loop. But there is a difference between people outright getting them wrong and people who are at least trying to get them right. I have been frustrated to see the number of people who still claim that the US warned the Japanese before the atomic bombings, a myth perpetuated in no small part due to shoddy citation by archivists at the Truman Library on their website. []

The trouble with airbursts

Friday, December 6th, 2013

Both the Little Boy and Fat Man atomic bombs were detonated high in the air above their target cities. That they did this was no accident — specialized circuitry, some invented just for the atomic bombs, was used so that the bombs could detect their height off of the ground and detonate at just the right moment. Little Boy detonated 1,968±50 feet above Hiroshima, Fat Man detonated 1,650±10 feet above Nagasaki. At least as early as the May 1945 Target Committee meeting at Los Alamos, “the criteria for determining height” of detonation had been agreed upon: the goal was to maximize the 5 psi (pounds-per-square-inch) overpressure blast radius of the bombs, with a knowledge that this was going to be a tricky thing since they weren’t really sure how explosively large the bombs would be, and a bomb either too big or too large would reduce the total range of the 5 psi radius. At the time, they estimated Little Boy would be between 5 and 15 kilotons, Fat Man between 0.7 and 5 kilotons — obviously this was pre-“Trinity,” which showed the Fat Man model could go at least up to 18-20 kilotons.

I was on the road quite a lot the last month, so I apologize about the radio silence for the past couple of weeks. But I’m happy to report to you that I managed to recently update the NUKEMAP’s effects code in a way I’ve been meaning to for a long while: you can now set arbitrary heights for detonations. I thought I would explain a little bit about how that works, and why that matters, in today’s post.

The 1962 edition of Glasstone and Dolan's The Effects of Nuclear Weapons and the Lovelace Foundation's "Nuclear Bomb Effects Computer."

The 1962 edition of Glasstone’s The Effects of Nuclear Weapons and the Lovelace Foundation’s “Nuclear Bomb Effects Computer.”

Why did it take me so long to add a burst height feature? (A feature that, to both me and many others alike, was obviously lacking.) Much of the NUKEMAP’s code is based on the calculations that went into making the famous Lovelace Foundation “Nuclear Bomb Effects Computer,” which itself were based on equations in Samuel Glasstone’s classic The Effects of Nuclear Weapons. This circular slide rule has some wonderful retro charm, and is a useful way of boiling down a lot of nuclear effects data into a simple analog “computer.” However, like most nuclear effects calculations, it wasn’t really designed with the kind of visualization that the NUKEMAP had in mind. For something like the NUKEMAP, one wants to be able to plug in a yield and a “desired” overpressure (such as 5 psi), and get a measurement of the ground range of the effect as a result. But this isn’t how the Lovelace Computer works. Instead, you put in your kilotonnage and the distance you want to know the overpressure at, and in return you get a maximum overpressure in the form of pounds-per-square-inch. In other words, instead of asking, “what’s the distance for 5 psi for a 15 kiloton surface burst?,” you are only allowed to ask, “if I was 2 miles from a 15 kiloton surface burst, what would the overpressure be?”

For surface bursts and a few low height (400 feet and under) airbursts, the Lovelace Foundation did, in a separate report, provide equations of the sort useful for the NUKEMAP, and the NUKEMAP’s code was originally based on these. But they didn’t allow for anything fancy with regards to arbitrary-height airbursts. They let one look for pressure information at “optimal” airburst heights, but did not let one actually set a specific airburst height. For awhile I thought this might just have been a strange oversight, but the more I dug into the issue, I realized this was probably because the physics of airbursts is hard.

Grim geometry: calculating the ground range of the 500 rem radiation exposure radius for a Hiroshima-sized nuclear weapon set off at the height of the Hiroshima bomb. Most objects roughly to scale.

Grim geometry: calculating the ground range of the 500 rem radiation exposure radius for a Hiroshima-sized nuclear weapon set off at the height of the Hiroshima bomb. Most objects roughly to scale.

There are three immediate effects of nuclear weapons that the NUKEMAP models: thermal radiation (heat), ionizing radiation (radioactivity), and overpressure (blast). Thermal and ionizing radiation pretty much travels in a straight line, so if you know the slant-line distance for a given effect, it’s no problem figuring out the ground distance at an arbitrary height through a simple application of the Pythagorean theorem, as shown above. The report the Lovelace Computer was based on allowed for the calculation of slant-line airburst distances for both of these, so that was a snap to implement. Somewhat interestingly, the ranges of the “interesting” thermal radiation categories (e.g. burns and burning) are so large that except with very high airbursts one often finds almost no difference between ground ranges computed using slant versus straight-line distances. Ionizing radiation, however, is relatively short in its effects, and so the height of the burst really does matter in practical terms for how much radiation the ground receives. This has a relevance to Hiroshima and Nagasaki that I will return to.

But this isn’t how the physics of blast pressure works. The reason is somewhat subtle but important for understanding nuclear weapons targeting decisions. The pressure wave that emerges from the nuclear fireball does not stop when it hits the ground. Rather, it reflectsbounces upward again — like so:

Reflection of the shockwave of a 20 kiloton nuclear explosion exploded at 1,770 foot altitude. Via Wikipedia.

Reflection of the shockwave of a 20 kiloton nuclear explosion exploded at 1,770 foot altitude. Via Wikipedia.

You don’t have to take my word for it (or Wikipedia’s, for that matter) — you can actually see the reflection of the shockwave in some nuclear testing photography, like this photograph of Shot Grable, the “atomic cannon” test from 1953:

Shot Grable, Operation Upshot-Knothole — a 15 kiloton nuclear artillery shell detonated at an altitude of 524 feet.

Shot Grable, Operation Upshot-Knothole — a 15 kiloton nuclear artillery shell detonated at an altitude of 524 feet, with the reflection of the blast wave clearly visible under the fireball.

The initial blast wave is the “incident” or “primary” blast wave. The bounded wave in the “reflected” wave. When they touch, as shown in the Wikipedia diagram, they combine — which dramatically increases the overpressure at that location. So, referring the Wikipedia diagram again, by the time the primary shockwave was at the final radius of the diagram, it would have lost a considerable amount of energy. But when it merges with the reflected shockwave, it forms a single, vertical shock front known as the “Mach stem.” In the diagram above, that has an overpressure of 15 psi — enough to destroy pretty significant buildings. If the shockwave did not work in this fashion, the primary shockwave would itself be considerably less than 15 psi at that point.

So the overall point here is that blast reflection can dramatically increase the blast pressure of the bomb at the point where it occurs. But the location at this point varies depending on the height of the bomb detonation — so you can use the choice of bomb detonation altitude to maximize certain pressures in particular. So this is what the Target Committee was talking about in May 1945: they wanted to maximize the radius of the 5 psi overpressure range, and they recognized that this involved finding the correct detonation height and knowing the correct yield of the bomb. They knew about the reflection property and in fact referred to the Mach stem explicitly in their discussion. Why 5 psi? Because that is the overpressure used to destroy “soft” targets like the relatively flimsy houses used by Japanese civilians, which they had already realized would be much easier to destroy than German-style houses.

For the NUKEMAP, this reflection made the modeling difficult. There are lots of models out there for calculating overpressure based on altitude, but they all do it similar to the Lovelace Foundation’s “Computer”: they tell you the maximum overpressure at a pre-specified point from ground zero. They don’t let you ask, “where would the 5 psi radius be for a blast of 15 kilotons and a height of 1,968 feet?” Which was inconvenient for me. The data is out there, though — just not in computational form. Graphs of pressure ranges plotted on axes of ground range and burst height are quite common in the nuclear literature, where they are sometimes known as “knee curves” because of the characteristic “bulge” in ground range produced by the aforementioned Mach reflection, the spot where the pressure range dramatically enlarges. Glasstone and Dolan’s 1977 Effects of Nuclear Weapons contains three of these graphs for pressure ranges between 10,000 and 1 psi. Here is the “low-pressure” graph showing the characteristic “knees”:

Glasstone and Dolan Fig 3-73c - Peak overpressures

Reading these is fairly straightforward once you understand what they show. If you want to maximize the 2 psi pressure range, find the point at which the “2 psi” curve is as far to the right as possible. Then look at the vertical axis to find what the corresponding height of burst is. Or, if you want to know what the pressure will be on the ground at a given distance from a bomb detonated at a given burst height, simply figure out which pressure regions that point is between on the graph. The graphs are always given for 1 kiloton bursts, but scaling from these to arbitrary detonations (with the caveat that very high and very low yields can sometimes be a little different) is pretty straightforward according to the scaling laws given in the text.

I searched high and low for a computational solution to the airburst question, without much luck. I had attempted to do polynomial curve fits on the graphs above, and just found them to be too irregular — the equations I was able to produce made huge errors, and splitting them up into sub-curves produced a mathematical mess. The only other computational solution I found was someone else who had done curve fits and also come up with equations that produced relatively large errors. I wasn’t happy with this. I discussed my frustrations with a few people (let me do a shout out to Edward Geist, currently a Stanton Fellow at the Rand Corporation, who has been doing his own modeling work regarding Soviet nuclear effects handbooks, and to Alex Montgomery at Reed College, both of whom were extremely helpful as people to talk to about this), and gradually came to the conclusion that there probably wasn’t an obvious analytical solution to this problem. So I did the next-best thing, which was to take samples of all of the curve values (less tedious than it sounds because of a little script I whipped up for the job) and just set up some tables of data that could then be sifted through very quickly by the computer. In other words, the way the NUKEMAP’s code works is pretty much the Javascript equivalent to consulting the graphs in Glasstone and Dolan’s book — it treats it as a simple interpolation problem between known values. Which turns out to give results which are no worse than those involved with using the book itself:

The NUKEMAP's overpressure data, graphed using R. Point samples are represented by circles, lines connect given pressure ranges. Color corresponds (logarithmically) with pressure ranges from 1 to 10,000 psi.

The NUKEMAP’s overpressure data, graphed using R. Point samples are represented by circles, lines connect given pressure ranges. Color corresponds (logarithmically) with pressure ranges from 1 to 10,000 psi. Unknown points on the graph are interpolated between known values.

The end result is that now the NUKEMAP can do arbitrary-burst height airbursts. In fact, the NUKEMAP pressure model goes all the way up to 10,000 psi — a pressure zone equivalent to being 4 miles under the ocean. Yow.

With this data in hand, and the NUKEMAP model, let’s go back to the Hiroshima and Nagasaki question. They knew about the Mach reflection, they knew about the height of the burst. It’s not clear that their assumptions for how this would work would line up exactly with those in Glasstone and Dolan, since those were modified according to actual empirical experience with airbursts in the kiloton range, something that they did not have on hand in 1945, even if they intuited much of the physics behind it. What can we say about their knowledge, and their choices, with regards to what they actually did with selecting the blast heights?

The Hiroshima yield has been calculated as about 15 kilotons, and the Nagasaki yield was about 21 kilotons. According to the Glasstone and Dolan model, to optimize the 5 psi pressure range for each, you’d want a burst height of ~2,500 feet for Little Boy and ~2,800 feet for Fat Man. Those are significantly higher altitudes than the actual detonation heights of 1,968 and 1,650 feet. The Target Committee meeting shows that they were assuming that 2,400 feet was the correct height for a 15 kiloton bomb — which is about right. Which means either than the detonating circuitry fired late (not impossible though I haven’t seen it mentioned), or they changed their blast range criteria (for a 15 kiloton bomb, 1,940 feet maximizes the 9 psi radius rather than the 5 psi radius), or that they were being very conservative about the yields (a 1,960 feet burst height corresponds with maximizing the 5 psi radius of a 7 kiloton burst, whereas 1,700 feet corresponds to a 5 kiloton burst). My guess is that the latter was what was going on — they were being very conservative about the yield.

The net result is that at both Hiroshima and Nagasaki, you had lower burst heights than were optimal. The effect on the ground is that while the 5 psi blast radius didn’t go quite as far out as it might have ideally, the range of radiation effects and radiation around Ground Zero was significantly increased, and the maximum overpressures around Ground Zero were substantially higher. Overall, it is interesting to see that they were apparently, even after Trinity, still being pretty un-optimistic regarding the explosive yields of the bombs, calibrating their burst heights to half or even one quarter of what the actual blasts were. For a “soft” targets, like Hiroshima and Nagasaki, this doesn’t matter too much, as long as the fireball is above the altitude which produces local fallout, but for a “hard” target, where the goal is to put a lot of pressure in one spot, this would be a serious miscalculation.

Meditations | Visions

What the NUKEMAP taught me about fallout

Friday, August 2nd, 2013

One of the most technically difficult aspects of the new NUKEMAP was the fallout generation code. I know that in practice it looks like just a bunch of not-too-complicated ellipses, but finding a fallout code that would provide what I considered to be necessary flexibility proved to be a very long search indeed. I had started working on it sometime in 2012, got frustrated, returned to it periodically, got frustrated again, and finally found the model I eventually used — Carl Miller’s Simplified Fallout Scaling System — only a few months ago.

The sorts of contours the Miller model produces.

The sorts of contours the Miller scaling model produces.

The fallout model used is what is known as a “scaling” model. This is in contrast with what Miller terms a “mathematical” model, which is a much more complicated beast. A scaling model lets you input only a few simple parameters (e.g. warhead yield, fission fraction, and wind speed) and the output are the kinds of idealized contours seen in the NUKEMAP. This model, obviously, doesn’t quite look like the complexities of real life, but as a rough indication of the type of radioactive contamination expected, and over what kind of area, it has its uses. The mathematical model is the sort that requires much more complicated wind parameters (such as the various wind speeds and sheers at different altitudes) and tries to do something that looks more “realistic.”

The mathematical models are harder to get ahold of (the government has a few of them, but they don’t release them to non-government types like me) and require more computational power (so instead of running in less than a second, they require several minutes even on a modern machine). If I had one, I would probably try to implement it, but I don’t totally regret using the scaling model. In terms of communicating both the general technical point about fallout, and in the fact that this is an idealized model, it does very well. I would prefer people to look at a model and have no illusions that it is, indeed, just a model, as opposed to some kind of simulation whose slickness might engender false confidence.

Fallout from a total nuclear exchange, in watercolors. From the Saturday Evening Post, March 23, 1963.

Fallout from a total nuclear exchange, in watercolors. From the Saturday Evening Post, March 23, 1963. Click to zoom.

Working on the fallout model, though, made me realize how little I really understood about nuclear fallout. I mean, my general understanding was still right, but I had a few subtle-but-important revelations that changed the way I thought about nuclear exchanges in general.

The most important one is that fallout is primary a product of surface bursts. That is, the chief determinant as to whether there is local fallout or not is whether the nuclear fireball touches the ground. Airbursts where the fireball doesn’t touch the ground don’t really produce fallout worth talking about — even if they are very large.

I read this in numerous fallout models and effects books and thought, can this be right? What’s the ground got to do with it? A whole lot, apparently. The nuclear fireball is full of highly-radioactive fission products. For airbursts, the cloud goes pretty much straight up and those particles are light enough and hot enough that they pretty much just hang out at the top of the cloud. By the time they start to cool and drag enough to “fall out” of the cloud, they have diffused themselves in the atmosphere and also decayed quite a bit.1 So they are basically not an issue for people on the ground — you end up with exposures in the tenths or hundreds of rads, which isn’t exactly nothing but is pretty low. This is more or less what they found at Hiroshima and Nagasaki — there were a few places where fallout had deposited, but it was extremely limited and very low radiation, as you’d expect with those two airbursts.

I thought this might be simplifying things a bit, so I looked up the fallout patterns for airbursts. And you know what? It seems to be correct. The radiation pattern you get from a “nominal” fission airburst looks more or less like this:

The on-side dose rate contours for the Buster-Jangle "Easy" shot (31 kilotons), in rads per hour. Notice that barely any radiation goes further than 1,100 yards from ground zero, and that even that is very low level (2 rads/hr).

The on-side dose rate contours for the Buster-Jangle “Easy” shot (31 kilotons), in rads per hour. Notice that barely any radiation goes further than 1,100 yards from ground zero, and that even that is very low level (2 rads/hr). Source.

That’s not zero radiation, but as you can see it is very, very local, and relatively limited. The radiation deposited is about the same range as the acute effects of the bomb itself, as opposed to something that affects people miles downwind.2

What about very large nuclear weapons? The only obvious US test that fit the bill here was Redwing Cherokee, from 1956. This was the first thermonuclear airdrop by the USA, and it had a total yield of 3.8 megatons — nothing to sniff at, and a fairly high percentage of it (at least 50%) from fission. But, sure enough, appears to have been basically no fallout pattern as a result. A survey meter some 100 miles from ground-zero picked up a two-hour peak of .25 millirems per hour some 10 hours later — which is really nothing to worry about. The final report on the test series concluded that Cherokee produced “no fallout of military significance” (all the more impressive given how “dirty” many of the other tests in that series were). Again, not truly zero radiation, but pretty close to it, and all the more impressive given the megatonnage involved.3

Redwing Cherokee: big boom, but almost no fallout.

Redwing Cherokee: quite a big boom, but almost no fallout.

The case of the surface burst is really quite different. When the fireball touches the ground, it ends up mixing the fission products with dirt and debris. (Or, in the case of testing in the Marshall Islands, coral.) The dirt and debris breaks into fine chunks, but it is heavy. These heavier particles fall out of the cloud very quickly, starting at about an hour after detonation and then continuing for the next 96 hours or so. And as they fall out, they are both attached to the nasty fission products and have other induced radioactivity as well. This is the fallout we’re used to from the big H-bomb tests in the Pacific (multi-megaton surface bursts on coral atolls was the worst possible combination possible for fallout) and even the smaller surface bursts in Nevada.

The other thing the new model helped me appreciate more is exactly how much the fission fraction matters. The fission fraction is the amount of the total yield that is derived from fission, as opposed to fusion. Fission is the only reaction that produces  highly-radioactive byproducts. Fusion reactions produce neutrons, which are a definite short-term threat, but not so much a long-term concern. Obviously all “atomic” or fission bombs have a fission fraction of 100%, but for thermonuclear weapons it can vary quite a bit. I’ve talked about this in a recent post, so I won’t go into detail here, but just emphasize that it was unintuitive to me that the 50 Mt Tsar Bomba, had it been a surface burst, would have had much less fallout than the 15 Mt Castle Bravo shot, because the latter had some 67% of its energy derived from fission while the former had only 3%. Playing with the NUKEMAP makes this fairly clear:

Fallout comparisons

The darkest orange here corresponds to 1,000 rads/hr (a deadly dose); the slightly darker orange is 100 rads/hr (an unsafe dose); the next lighter orange is 10 rads/hr (ill-advised), the lightest yellow is 1 rad/hr (not such a big deal). So the 50 Mt Tsar Bomba is entirely within the “unsafe” range, as compared to the large “deadly” areas of the other two. Background location chosen only for scale!

The real relevance of all of this for understanding nuclear war is fairly important. Weapons that are designed to flatten cities, perhaps surprisingly, don’t really pose as much of a long-term fallout hazard. The reason for this is that the ideal burst height for such a weapon is usually set to maximize the 10 psi pressure radius, and that is always fairly high above the ground. (The maximum radius for a pressure wave is somewhat unintuitive because it relies on how the wave will be reflected on the ground. So it doesn’t produce a straightforward curve.) Bad for the people in the cities themselves, to be sure, but not such a problem for those downwind.

But weapons that are designed to destroy command bunkers, or missiles in silos, are the worst for the surrounding civilian populations. This is because such weapons are designed to penetrate the ground, and the fireballs necessarily come into contact with the dirt and debris. As a result, they kick up the worst sort of fallout that can stretch many hundreds of miles downwind.

So it’s sort of a damned-if-you-do, damned-if-you-don’t sort of situation when it comes to nuclear targeting. If you try to do the humane thing by only targeting counterforce targets, you end up producing the worst sort of long-range, long-term radioactive hazard. The only way to avoid that is to target cities — which isn’t exactly humane either. (And, of course, the idealized terrorist nuclear weapon manages to combine the worst aspects of both: targeting civilians and kicking up a lot of fallout, for lack of a better delivery vehicle.)

A rather wonderful 1970s fallout exposure diagram. Source.

A rather wonderful 1970s fallout exposure diagram. Source.

And it is worth noting: fallout mitigation is one of those areas were Civil Defense is worth paying attention to. You can’t avoid all contamination by staying in a fallout shelter for a few days, but you can avoid the worst, most acute aspects of it. This is what the Department of Homeland Security has been trying to convince people of, regarding a possible terrorist nuclear weapon. They estimate that hundreds of thousands of lives could be saved in such an event, if people understood fallout better and acted upon it. But the level of actual compliance with such recommendations (stay put, don’t flee immediately) seems like it would be rather low to me.

In some sense, this made me feel even worse about fallout than I had before. Prior to playing around with the details, I’d assumed that fallout was just a regular result of such weapons. But now I see it more as underscoring the damnable irony of the bomb: that all of the choices it offers up to you are bad ones.

  1. Blasts low enough to form a stem do suck up some dirt into the cloud, but it happens later in the detonation when the fission products have cooled and condensed a bit, and so doesn’t matter as much. []
  2. Underwater surface bursts, like Crossroads Baker, have their own characteristics, because the water seems to cause the fallout to come down almost immediately. So the distances are not too different from the airburst pattern here — that is, very local — but the contours are much, much more radioactive. []
  3. Why didn’t they test more of these big bombs as airdrops, then? Because their priority was on the experimentation and instrumentation, not the fallout. Airbursts were more logistically tricky, in other words, and were harder to get data from. Chew on that one a bit… []

The bomb and its makers

Tuesday, July 30th, 2013

In part of the “make this blog actually work again” campaign, I’ve changed some things on the backend which required me to change the blog url from to Fortunately, even if you don’t update your bookmarks, the old links should all still work automatically. It seems to be working a lot better at the moment — in the sense that I can once again edit the blog — so that’s something!

In all of the new NUKEMAP fuss, and the fact that my blog kept crashing, I didn’t get a chance to mention that I had two multimedia essays up on the website of The Bulletin of the Atomic Scientists. I’m pretty happy with both of these, both visually and in terms of the text.

The first was published a few weeks ago, and was related to my much earlier post relating to the badge photographs at Los Alamos. The faces that made the Bomb has so far proved to be the one thing I’ve done that people end up bringing up in casual conversation without realizing I wrote it. (The scenario is, I meet someone new, I mention I work on the history of nuclear weapons, they ask me if I’ve seen this thing on the Internet about the badge photographs, I answer that I in fact wrote it, a slight awkwardness follows.)


Some of the badge photographs are the ones that anyone on here would be familiar with — Oppenheimer, Groves, Fuchs, etc. But I enjoyed picking out a few more obscure characters. One of my favorites of these is Charlotte Serber, wife of the physicist and Oppenheimer student Robert Serber. Here’s my micro-essay:

Charlotte Serber was one of the many wives of the scientists who came to Los Alamos during the war. She was also one of the many wives who had their own substantial jobs while at the lab. While her husband, Robert Serber, worked on the design of the first nuclear weapons, Charlotte was the one in charge of running the technical library. While “librarian” might not at first glance seem vital to the war project, consider J. Robert Oppenheimer’s postwar letter to Serber, thanking her that “no single hour of delay has been attributed by any man in the laboratory to a malfunctioning, either in the Library or in the classified files. To this must be added the fact of the surprising success in controlling and accounting for the mass of classified information, where a single serious slip might not only have caused us the profoundest embarrassment but might have jeopardized the successful completion of our job.” Serber fell under unjustified suspicion of being a Communist in the immediate postwar, and, according to her FBI file, her phones were tapped. Who had singled her out as a possible Communist, because of her left-wing parents? Someone she thought of as a close personal friend: J. Robert Oppenheimer.

Charlotte was also the only woman Division Leader at Los Alamos, as the director of the library. She was also the only Division Leader barred from attending the Trinity test — on account of a lack of “facilities” for women there. She considered this a gross injustice.

What I like about Charlotte is not only that she highlights that many of the “Los Alamos wives” actually did work that was crucial to the project (and there were scientists amongst the “wives” as well, such as Elizabeth R. Graves, who I also profiled), and that the work of a librarian can be pretty vital (imagine if they didn’t have good organization of their reports, files, and classified information). But I also find Charlotte’s story amazing because of the betrayal: Oppenheimer the friend, Oppenheimer the snitch.

I should note that Oppenheimer’s labeling of Charlotte was probably not meant to be malicious — he was going over lists of people who might have Communist backgrounds when talking to the Manhattan Project security officers. He rattled off a number of names, and even said he thought most of them probably weren’t themselves Communists. This, of course, meant that they got flagged as possible Communists for the rest of their lives. Oppenheimer’s attempt to look loyal to the security system, even his attempts to be benign about it, were terrible failures in the long run, both for him and for his poor friends. Albert Einstein put it well: “The trouble with Oppenheimer is that he loves a woman who doesn’t love him—the United States government.”

Kenneth Bainbridge

The other one I want to highlight on here is that of Kenneth T. Bainbridge. Bainbridge was Harvard physicist and was in charge of organizing Project Trinity, the first test of the atomic bomb in July 1945. It was a big job — bigger, I think, than most people realize. You don’t just throw an atomic bomb on top of a tower in the desert and set it off. It had a pretty large staff, required a ton of theoretical and practical work, and, in the end, was an experiment that, ideally, destroyed itself in the process. Here was my Bainbridge blurb:

During the Manhattan Project, Harvard physicist Kenneth Bainbridge was in charge of setting up the Trinity test—afterward he became known as the person who famously said: “Now we are all sons of bitches.” Years later he wrote a letter to J. Robert Oppenheimer explaining his choice of words: “I was saying in effect that we had all worked hard to complete a weapon which would shorten the war but posterity would not consider that phase of it and would judge the effort as the creation of an unspeakable weapon by unfeeling people. I was also saying that the weapon was terrible and those who contributed to its development must share in any condemnation of it. Those who object to the language certainly could not have lived at Trinity for any length of time.” Oppenheimer’s reply to Bainbridge’s sentiments was simple: “We do not have to explain them to anyone.

I’ve had that Bainbridge/Oppenheimer exchange in my files for a long time, but never really had a great opportunity to put it into print. To flesh out the context a little more, it came out in the wake of Lansing Lamont’s popular book, Day of Trinity (1965). Bainbridge was one of the sources Lamont had talked to, and he gave him the “sons of bitches” quote. Oppenheimer’s full reply to Bainbridge took some digs at the book:

“When Lamont’s book on Trinity came, I first showed it to Kitty; and a moment later I heard her in the most unseemly laughter. She had found the preposterous piece about the ‘obscure lines from a sonnet of Baudelaire.’ But despite this, and all else that was wrong with it, the book was worth something to me because it recalled your words. I had not remembered them, but I did and do recall them. We do not have to explain them to anyone.”

The “obscure lines” was some kind of code supposedly sent by Oppenheimer to Kitty to say that the test worked. In Bainbridge’s files at the Harvard Archives there is quite a lot of material on the Lamont book from other Manhattan Project participants — most of them found a lot of fault with it on a factual basis, but admired its writing and presentation.

Bainbridge makes for a good segue into my other BAS multimedia essay, “The beginning of the Bomb,” which is about the Trinity test and which came out just before the 68th anniversary, which was two weeks ago. It also was somewhat of a reprise of themes I’d first played with on the blog, namely my post on “Trinity’s Cloud.” I’ve been struck that while Trinity was so extensively documented, the same few pictures of it and its explosion are re-used again and again. Basically, if it isn’t one of the “blobs of fire” pictures, or the Jack Aeby early-stage fireball/cloud photograph (the one used on the cover of The Making of the Atomic Bomb), then it doesn’t seem to exist. Among other things related to Trinity, I got to include two of my favorite alternative Trinity photographs.

Trinity long exposure

The first is this ghostly apparition above. What a strange, occult thing the atomic bomb looks like in this view. While most photographs of the bomb are concerned about capturing it at a precise fraction of a second — a nice precursor to the famous Rapatronic photographs of the 1950s — this one does something quite different, and quite unusual. This is a long exposure photograph of several seconds of the explosion. The caption indicates (assuming I am interpreting it correctly) that it is an exposure of several seconds before the explosion and then two seconds after the beginning of the detonation. Which would explain why there are so many pre-blast details available to see.

The result is what you see here: a phantom whose resemblance to the “classic” Trinity explosion pictures is more evocative than definite. And if you view it at full size, you can just make out features of the desert floor: the cables that held up the tower, for example. (Along with some strange, blobby artifacts associated with dark room work.) I somewhat wish this was the image of “the atomic bomb” that we all had in our minds — dark, ghastly, tremendous. Instead of seeing just a moment after the atomic age began, we instead see in a single image the transition between one age and the next.

Trinity mushroom cloud

Most of the photographs of Trinity are of its first few seconds. But this one is not. It may be the only good photograph I have seen of the late-stage Trinity mushroom cloud. It is striking, is it not? A tall, dark column of smoke, lightly mushroomed at the top, with a larger cloud layer above it. “Ominous” is the word I keep coming back to, especially once you know that the cloud in question was highly radioactive.

One of the things I found while researching the behavior of mushroom clouds for the NUKEMAP3D was that while the mushroom cloud is an ubiquitous symbol of the bomb, it is specifically the early-stage mushroom cloud whose photograph gets shown repeatedly. Almost all nuclear detonation photographs are of the first 30 second or so of the explosion, when the mushroom cloud is still quite small, and usually quite bright and mushroomy. The late-stage cloud — about 4-10 minutes, depending on the yield of the bomb — is a much larger, darker, and unpleasant thing.

Why did we so quickly move from thinking of the atomic bomb as a burst of fire into a cloud of smoke? The obvious answer would be Hiroshima and Nagasaki, where we lacked the instrumentation to see the fireball, and only could see the cloud. But I’m still struck that our visions of these things are still so constrained to a few examples, a few moments in time, out of so many other possibilities, each with their own quite different visual associations.

News and Notes | Visions

The NUKEMAPs are here

Thursday, July 25th, 2013

I’m super excited to announce that last Thursday, at an event hosted by the Center for Nonproliferation Studies at the Monterey Institute for International Study, I officially launched NUKEMAP2 and NUKEMAP3D. I gave a little talk, which I managed to record, but I haven’t had the time (more details below on why!) to get that up on YouTube yet. Soon, though.

A Soviet weapon from the Cuban Missile Crisis, centered on Washington, DC, with fallout and casualties shown.

A Soviet weapon from the Cuban Missile Crisis, centered on Washington, DC, with fallout and casualties shown.

NUKEMAP2 is an upgraded version of the original NUKEMAP, with completely re-written effects simulations codes that allow one a huge amount of flexibility in the nuclear detonation one is trying to model. It also allows fallout mapping and casualty counts, among other things. I wanted to make it so that the NUKEMAP went well beyond any other nuclear mapping tools on the web — I wanted it to be a tool that both the layman and the wonk could use, a tool that rewarded exploration, and a tool that, despite the limitations of a 2D visualization, could work to deeply impress people with the power of a nuclear explosion.

The codes that underly the model are all taken from Cold War effects models. At some point, once it has been better documented than it is now, I’ll probably release the effects library I’ve written under an open license. I don’t think there’s anything quite like it out there at the moment available for the general public. For the curious, there are more details about the models and their sources here.

The mushroom cloud from a 20 kiloton detonation, centered on downtown DC, as viewed from one of my common stomping grounds, the Library of Congress.

The mushroom cloud from a 20 kiloton detonation, centered on downtown DC, as viewed from one of my common stomping grounds, the Library of Congress.

NUKEMAP3D uses Google Earth to allow “3D” renderings of mushroom clouds and the nuclear fireball. Now, for the first time, you can visualize what a mushroom cloud from a given yield might look like on any city in the world, viewed from any vantage-point you can imagine. I feel like it is safe to say that there has never been a nuclear visualization tool of quite this nature before.

I got the idea for NUKEMAP3D while looking into a story for the Atlantic on a rare photo of the Hiroshima mushroom cloud. One of the issues I was asked about was how long after the detonation the photograph was taken — the label on the back of the photograph said 30 minutes, but there was some doubt. In the process of looking into this, I started to dig around the literature on mushroom cloud formation and the height of the Hiroshima cloud at various time intervals. I realized that I had no sense for what “20,000 feet” meant in terms of a cloud, so I used Google Earth to model a simple 20,000 foot column above the modern-day city of Hiroshima.

I was stunned at the size of it, when viewed from that perspective — it was so much larger than it even looked in photographs, because the distance that such photographs were taken from makes it very hard to get a sense of scale. I realized that modeling these clouds in a 3D environment might really do something that a 2D model could not. It seems to switch on the part of the brain that judges sizes and areas in a way that a completely flat, top-down overlay does not. The fact that I was surprised and shocked by this, despite the fact that I look at pictures of mushroom clouds probably every day (hey, it’s my job!), indicated to me that this could be a really potent educational tool.

That same 20 kiloton cloud, as viewed from airplane height.

That same 20 kiloton cloud, as viewed from airplane height.

I’m also especially proud of the animated mode, which, if I’m allowed to say, was a huge pain in the neck to program. Even getting a somewhat “realistic”-looking cloud model was a nontrivial thing in Google Earth, because its modeling capabilities are somewhat limited, and because it isn’t really designed to let you manipulate models in a detailed way. It lets you scale model sizes along the three axes, it allows you to rotate them, and it allows you to change their position in 3D space. So I had to come up with ways of manipulating these models in realtime so that they would approximate a semi-realistic view of a nuclear explosion, given these limitations.

It’s obviously not quite as impressive as an actual nuclear explosion (but what is?), and my inability to use light as a real property (as you could in a “real” 3D modeling program) diminishes things a bit (that is, I can’t make it blinding, and I can’t make it cast shadows), but as a first go-around I think it is still a pretty good Google Earth hack. And presumably Google Earth, or similar tools, will only get better and more powerful in the future.

Screen captures of the animation for a 20 kt detonation over DC. These screenshots were taken in 10 second intervals, but are accelerated 100X here. The full animation takes about five minutes to run, which is roughly how the cloud would grow in real life.

Screen captures of the animation for a 20 kt detonation over DC. These screenshots were taken in 10 second intervals, but are accelerated 100X here. The full animation takes about five minutes to run, which is roughly how the cloud would grow in real life.

If you’ve been following my Twitter feed, you also probably have picked up that this has been a little bit of a saga. I tried to launch it on last Thursday night, but the population database wasn’t really working very well. The reason is that it is very, very large — underneath it is a population density map of the entire planet, in a 1km by 1km grid, and that means it is about 75 million records (thank goodness for the oceans!). Optimizing the queries helped a bit, and splitting the database up helped a bit. I then moved the whole database to another server altogether, just to make sure it wasn’t dragging down the rest of the server. But on Monday,just when the stories about NUKEMAP started to go up, my hosting company decided it was too much traffic and that I had, despite “unlimited bandwidth” promises, violated the Terms of Service by having a popular website (at that point it was doing nothing but serving up vanilla HTML, Javascript, and CSS files, so it wasn’t really a processing or database problem). Sigh. So I frantically worked to move everything to a different server, learned a lot about systems administration in the process, and then had the domain name issue a redirect from the old hosting company. And all of that ended up taking a few days to finalize (the domain name bit was frustratingly slow, due to settings chosen by the old hosting company).

But anyway. All’s well that ends well, right? Despite the technical problems, since moving the site to the new server, there have been over 1.2 million new “detonations” with the new NUKEMAPs, which is pretty high for one week of sporadic operation! 62% of them are with NUKEMAP3D, which is higher than I’d expected, given the computer requirements required to run the Google Earth plugin. The new server works well most of the time, so that’s a good thing, though there are probably some tweaks that still need to be done for it to happily run the blog and the NUKEMAPs. There is, though I don’t want to make it too intrusive or seem too irritating, a link now on the NUKEMAP for anyone who wanted to chip in to the server fund. Completely optional, and not expected, but if you did want to chip in, I can promise you a very friendly thank-you note at the very least.

Now that this is up and “done” for now, I’m hoping to get back to a regular blogging schedule. Until then, try out the new NUKEMAPs!