Archive for March, 2011

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Uncle Helium Gets Married

Physicists observe antihelium-4 nucleus, the heaviest antinucleus yet

[S]cientists with the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory have observed another state of antimatter for the first time: the antimatter helium-4 nucleus, which is the heaviest antinucleus observed so far.

Not Letting the Facts Get in the Way

A case of never letting the source spoil a good story

Of course, this is a problem that generalises well beyond science. Over and again, you read comment pieces that purport to be responding to an earlier piece, but distort the earlier arguments, or miss out the most important ones: they count on it being inconvenient for you to check. There’s also an interesting difference between different media: most bloggers have no institutional credibility, so they must build it by linking transparently and allowing you to double-check their work easily.

But more than anything, because linking to sources is such an easy thing to do and the motivations for avoiding links are so dubious, I’ve detected myself using a new rule of thumb: if you don’t link to primary sources, I just don’t trust you.

If I Did It

Several weeks ago we had an office discussion that eventually got around to xkcd and the fascination with ball pits, to pranks involving filling up a cubicle with balls or packing peanuts. The problem with such pranks, it was observed, is that balls are expensive and balls or peanuts take up the same volume ahead of time — storage is an issue. But balloons … they don’t suffer from this problem. You could fill a colleague’s office with balloons.


“That would be cool,” that colleague was heard to utter.


To me, such a statement is an invitation. It would be rude to not fill that person’s office with balloons, should such an opportunity arise, and I fear that someone might do it. So it got me thinking. How would one go about doing such a thing? (Not that I would do such a dastardly thing — I wouldn’t want to expose myself to a wrongful breath suit)

First thing would be to obtain a pump. Double-action, so it fills on both the up- and down-stroke.

When filling the balloons, I would use a balloon clip to speed things up (tying is such a pain) and would find that twisting the neck is important, otherwise the air would tend to quickly leak out.

Then, I would start filling the office. Maybe during lunch hour, or at odd times during the day (and staying late to ensure my real work was done). Get an idea of how many balloons I and any co-conspirators could fill. The progress after one day might look something like this

After four days, it might look something like this


I’ll bet with some help I could use up 200 12″ balloons and 122 (50+72) 17″ balloons, along with a few balloon-animal style balloons (which would be close to useless, since they take up so little volume). With that many, I’d probably notice that there is significant balloon-stink. And I would find the non-stick agent they use (probably cornstarch) to be really annoying after a while.

To be especially devious I might even fill some of the balloons with confetti, so that popping them all would become more of a challenge. I might be tempted to also fill some with helium, but they wouldn’t survive the weekend, so I wouldn’t bother. I’d probably find that about 10% of the balloons would be lost to defect and breakage, and would be amused by the occasional “boom” coming from the office. I’ll bet it would remind me of the episode of the Simpsons where Homer becomes the Beer Baron (Homer vs. the 18th Amendment), and his stills kept blowing up.

If I were to do such a thing.

Because People Could Die

Back when I was teaching in the Navy’s nuclear propulsion program, I saw that there was an foundational attitude towards operational systems: these are the rules — obey them. It is not up to you to decide that it’s OK to not follow them. And the unspoken undercurrent to that is because if you don’t, people could die. This applied to the reactor systems, because they were designed to work a certain way and had safeguards that assumed you were operating it according to procedure. The attitude was also present, as far as I could tell, to general shipboard operations. Most of my students were going to serve aboard submarines, and the potential for disaster is magnified by orders of magnitude when you are in a closed container some depth below the surface, and a loss of propulsion or breathable air could spell your doom. (Not that duty aboard a surface ship means tolerance for corner-cutting, either). That’s why they continually drill — practice your responses to emergency situations and do it right, because if you don’t, people could die. Commanding officers are used to orders being carried out, rather than getting “that’s not in my job description.” And you know what? The navy has a pretty good track record for a task that’s just a little dangerous. (As a side note, I can only imagine the frustration of the navy folk atop my org chart, dealing with a staff that is >90% civilian and who generally lack this ingrained response to following orders and rules without question*, and among whom are several people who do decide that a rule is silly and therefore will not be followed)

This attitude goes beyond the military. It’s why we have safety rules and building codes, and people who work within professions that have them, you will generally find a serious attitude toward such protocols. The people with experience do not relish putting their health or life at risk at the behest of someone looking for a shortcut. And usually a shortcut is a temptation for those who wish to save time and/or money, and for whom it means putting someone else at risk.

I was reminded of this when I read Millions saved in Japan by good engineering and government building codes. (The link title is a play on a tweet by Dave Ewing, who proclaimed that it was a headline you would not see.) And though some of the numbers are out of date (it was posted on the 12th, and the death toll is significantly larger), the idea is still valid. The Japanese have recognized the continual danger of earthquake and tsunami and instituted building codes to minimize the destruction, despite the fact that it costs more to do that. While such efforts did not (and probably cannot) result in no damage or loss of life, the devastation was far less than has occurred with weaker earthquakes elsewhere.

The difference is that Japan has made a commitment to earthquake-safe buildings, and had the money to carry out that commitment. Haiti lacked the money to implement strict construction standards and a government capable of compelling compliance. Builders and government regulators in the United States have the power and the resources to ensure Japanese standards of construction apply here, but my sense from living in California for 3 years is that we may lack the commitment needed to do this.

I think Josh is right about the US lacking the commitment — it’s just not how we do things here. We moan and wail about how damnably expensive regulation is, and how we should be free from government intrusion (curiously, I have yet to see any small-government proponents claim that the nuclear power industry is over-regulated). The question of how much money a regulation will cost is always asked, but the question of how many lives will be lost or saved does not seem to get the same attention. We bemoan the loss of life and note the monetary costs when a bridge or dam fails, but the money to inspect, repair and modify them isn’t always spent. There is a push to let businesses regulate themselves, to let “the market” take care if such things, except that “the market” doesn’t punish transgressors until after the fact, if at all. Action is taken, or not taken, for money, not because people could die. Prevention is usually invisible, which was the point behind the tweet, and too often we reward politicians for bold responses, not bold prevention.

* “without question” is not the same as “without grumbling.” Generally speaking (or Admirally speaking, since this is the navy) you grumble but do the task, and sailors are excellent grumblers.

I’ll Take Perspective for $200, Alex

Deaths per TWH by energy source

What is the worst kind of power plant disaster? Hint: It’s not nuclear.

The disaster in Tokyo is horrific, and we aren’t trying to say it isn’t a terrible situation. The question we’re trying to answer rationally here is whether nuclear power plant accidents cause more damage than other kinds of power plants. We’ve put together a list of five of the worst power plant disasters in recent history, measured by death toll, monetary damage, and regions affected. The lesson? The issue isn’t so much the kind of energy you use, but how you design the power plants that contain it.

It’s Not All Stick Figures

xkcd Radiation Dose Chart

The Deepening Time Sink

Awesome new physics blogs

Which reminds me that my blogroll disappeared at some point in my layout reshuffling, and I should do something about that someday…

Misplaced Angst

Your iPod is polluting China and L.A.—and Wyoming might be next

You may have been aware too that in manufacturing your electronic marvel, the Shenzhen plant emitted roughly 25 pounds of the greenhouse gas carbon dioxide. It’s even possible that you were aware of the 9-10 pounds of CO2 emitted in transporting the device to you from China.

Oh my GOD! 35 POUNDS of CO2 in getting my iPod delivered to me. That’s horrible!

Um, no, not really.

Bbbbut, 35 POUNDS!

Let’s look at that. Of 35 pounds (16 kg), about 9.5 lbs (a little over 4 kg) is Carbon. Two gallons of gasoline contain 11 pounds of Carbon. It sounds like a lot, but realize that driving 10,000 miles a year in a car that gets 25 mpg you dump 4 tons of CO2 into the atmosphere. Context matters.

Further, the blurb about China burning coal to generate the electricity to do the manufacturing needs to put in context as well. In the United States, the average person uses FOUR TIMES as much electricity as the average person in China. Add to that the China has been aggressively pursuing green energy — they already lead the US in wind energy generation, and are pushing forward in solar while we drag our feet. The US is not “greener than thou” and shifting the blame for pollution/CO2 distracts from the need to get our own house in order.


Just in case world events have you a little down. Here is 30 minutes of “Scenes from a hat”

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Let’s Overreact Some More

There are calls to shut down US reactors owing to earthquake concerns, despite the Japan situation being caused by a tsunami (which resulted from an earthquake).

Global earthquake activity since 1973 and nuclear power plant locations

This map shows a heatmap of 175,000 4.5+ magnitude earthquakes since 1973 based on data from the USGS (United States Geological Survey). And worldwide locations of nuclear power stations using information from the IAEA (International Atomic Energy Agency)

Amazing display revealing where the major fault lines are, along with the realization that there have been more than 175,000 earthquakes above this magnitude (and many more weaker than this) in the last (almost) 40 years and how few reactors are actually near earthquake activity.

Those Procrastinating Radionuclides

In all the discussion of nuclear power, there’s one bit that hasn’t been discussed in any of the summaries, which may be a good thing because I’m not confident that the general science media would get it right: How can you control the fission reaction in a reactor?

First, a bit of terminology. A critical reactor is one in which each fission result in one neutron, on average, inducing another fission. Which makes the fission rate from this chain reaction constant. So all those times you’ve seen on a TV show or in a movie, where a character shrieks, “OH my GOD! The reactor has gone CRITICAL!” it’s really no big deal. The population of neutrons from fission is constant over some period of time. If you are supercritical this population is increasing, and subcritical means it is decreasing. And the rate of fissioning is proportional to the neutron population.

The neutrons that come from fission (called “prompt neutrons,” for reasons which should become clear shortly) have a lot of energy — an MeV or so, typically, so they are called “fast,” — and they bounce around, scattering off nuclei and losing energy in those collisions. Most of the collisions are with the material that’s there for the express purpose of slowing the neutrons down — the moderator — and if the neutron gets down to thermal energies (“slow” or “thermal” neutrons) before it leaks out of the reactor or gets captured by some nucleus, it can be absorbed by the uranium and induce another fission. And this happens really quickly. A matter of a few tens of microseconds. It’s convenient to look at this in discrete steps, even though the reactions are continuous: each set of fissions releases neutrons which slow down or are lost, and these then induce more fissions. That constitutes a generation with some characteristic lifetime. If the lifetime were that of prompt neutrons alone there’s no way you could ever control a nuclear reactor. Because when a reactor is supercritical, the effect compounds: more than one neutron survives to cause a fission, which means more fissions, which gives you even more neutrons, and so on, ad infinitum. And if your time constant for doing this compounding is 25 microseconds, that’s of order 40,00 generations in just one second. Even if you had just a 0.01% increase in population per generation, you’d increase the population (and power) by a factor of 50 in just one second. There are no systems that could react fast enough to stay within reasonable limits.

But that’s not the whole picture. Not all neutrons come directly from the fission process. Some neutrons appear as the result of beta decays. Beta minus decay occurs in nuclei that have an overabundance of neutrons, and as you look at nuclei that are far from stability (that is, it takes several decays before you would end up with a stable nucleus) there is a tendency for the decays to release more energy and happen quicker.

In beta minus decay, a neutron changes into a proton and a positron and neutrino are emitted from the nucleus. This “reshuffles” the nucleus and the energy states it has; in a lot of cases, the daughter nucleus is not in the ground state, so a gamma is also emitted as it de-excites. For some nuclei far from stability, there is so much energy left over that the nucleus can emit a neutron instead of a gamma. But before this neutron can appear, we have to wait for the beta decay to happen, and that delay is on a time scale best measured in seconds. These are called “delayed neutrons,” and they comprise a little less than 1% of the neutrons from fissions in a critical reactor. But because they take so relatively long to appear, the effective generation time is much greater. Which means only a handful of neutron generations will occur in the time it would take for the system to respond — the reactor is actually subcritical from just the prompt neutrons, and any neutron population increase is relying on decays that won’t occur for around a second.

This works as long as the reactor is subcritical on prompt neutrons. If the reactor went “prompt critical” there would be a spike in power before the system could respond; this is what happened at Chernobyl, because safeguards were intentionally disabled and procedures violated in order to run a test. In a bomb the design is to be highly prompt supercritical using fast neutrons; you aren’t thermalizing neutrons or relying on delayed neutrons for anything. One of many ways a bomb is different from a reactor.

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