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Radiation over Atlantic October 8, 2008

Posted by dorigo in personal, physics, science, travel.
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Swamped by last-minute obligations before leaving to Fermilab for an owl shift as a Scientific Coordinator in the CDF control room, I was prevented from contributing to the recent discussions on the Nobel prize in Physics, other than providing the original post below. After an uneventful trip, I find myself jet-lagged this afternoon in my good-old office in the CDF portakamps. Everything looks and feels as always: home.

Anyway, I want to report on a small scientific experiment here. I brought with me in my trip a digital dosimeter, which records exposure to ionizing radiation as a function of time. The device (which I described here) is a nifty little thing I bought some time ago, and still carry around when I work around particle physics experiments. It measures radiation in milliRem, but is actually very sensitive – it can signal doses in increments as small as 100 nanoRems, which I figured out correspond to about a dozen minimum-ionizing particle hits.

So, about the experiment: I set integration times of 3600 seconds, and turned the device on before leaving Munich with LH434, a flight departing to Chicago at 9AM this morning. The plane actually left with a half hour delay, and finally arrived at O’Hare at about noon local time, ten full hours later. Below are the radiation doses recorded by the instrument during the flight.

As you immediately notice, the purple points describe a quickly rising function, which levels off and finally goes back down. The maximum instantaneous levels of radiation recorded by the instrument appear in line with what one would expect: as the plane takes off and gains elevation, the screening effect of our atmosphere is reduced, and the radiation increases. Local effects may have an impact in the distribution, and they thus depend on time, while the plane traveled above Europe, Greenland, Canada, and the north-western US; but they are not observable given the uncertainty in the points -0.1 mRem is the smallest digit provided when rates are measured in the logs.

The blue line instead puzzles me. It is the integrated dose per hour, and it should be a much more accurate description of the radiation field. But it bounces back and forth, after leveling at about 0.25 mRem/h. What are the causes of this funny behavior ? Here is what I can think of:

  • a real fluctuation in the flux of cosmic rays, due to magnetic field effects
  • an erroneous recording of data by the instrument, specifically at 14h and 16h (Munich time)

I instead discard the option that the fluctuations are statistical in nature: 0.01 mRem corresponds, as I noted above, to roughly a thousand hits.

Any other idea ?

PS (mainly for the record): another simple experiment I performed with the dosimeter is discussed here.

Comments

1. Lucian - October 8, 2008

Do you have any idea if that dip-peak structure in the middle corresponds with going over Greenland? Or with another geographical region?

2. Louise - October 8, 2008

Most likely it is cosmic ray flux. The flight from Munich to Chicago reaches a latitude around 57 degrees North. This takes away some of the protection of Earth’s magnetic field. When the US was planning a supersonic transport, environmental effects were a big concern.

Speaking of travel, Dr. Jerome Corsi was detained by immigration authorities just before giving a press conference. The audience was quite puzzled and disappointed. This annoying experience has happened to more and more researchers.

3. Anonymous - October 9, 2008

You would have seen a much bigger effect in the southern hemisphere — see the Wikipedia article on the South Atlantic Anomaly, for example. The Earth’s magnetic field “breaks the symmetry” in cosmic ray flux (for low energy cosmics) depending on where one is on (or above) the Earth’s surface.

4. dorigo - October 9, 2008

Lucian, that is in fact a very good question. It is in principle not hard to find out, by looking at the typical flight path of LH434. One thus learns that the fifth and the seventh hour into the flight happen just past the tip of Greenland and above northern Canada, respectively.

Hi Louise,

I agree that the magnetic field plays a role, but I fail to understand what could possibly change by moving 700 miles west, at about that latitude.

Anon, I will look at that reference, but again, I am unable to figure out whether such a big variation may occur in such a relatively small spatial range.

Cheers,
T.

5. dorigo - October 9, 2008

Hmmm, after reading a quite informative article on terrestrial cosmic ray fluxes, I am inclined to believe that the effect I saw is real. The magnetic field lines in the atmosphere are complex, and they affect cosmic rays of different energy in a highly nontrivial way. Further, there are reported dips in the intensity due to solar activity, and those dips may change abruptly even on the time scale of one or a few hours. Finally, my instrument is sensitive to specific ranges in the energy spectrum, and thus any small effect may be amplified by its response function.

I will of course perform the same experiment when I will travel backwards, a week from now. Of course, the flight path will not be exactly the same (less northern latitudes are reached when flying eastward) but it will be a good cross-check.

Cheers all,
T.

6. Guess Who - October 9, 2008

The magnetic field varies a lot around Greenland’s tip and Newfoundland:

If I could get a buck every time the WordPress spambot eats one of my comments, I might consider doing this full time. Oh well. Let’s see if this one gets through with only a few lines of superfluous fluff. Audentes fortuna juvat, eh?

7. dorigo - October 9, 2008

Hi GW, comment recovered😉

Yes, the effect I saw is probably real. Besides, the instrument is really a precise device, and I would be surprised to see it fail so badly.

More data to come in 9 days!

Cheers,
T.

8. Haelfix - October 9, 2008

It could also be a function of altitude. For instance if you are passing through a turbulence zone, whereby the pilot descends.

Its not clear why it would last for ~2 hours though, or why the effect would be so large. So I’d be tempted to say the Greenland hypothesis is better.

9. Fred - October 9, 2008

Bond, Tommaso Bond,

If the fluctuations are occurring in the vicinity of Greenland, here’s what a conspiracy theorist might suggest: Greenland is a strategic location for multiple coordinated military operations. There could be the slight chance that a measurement of the radiation field has a direct bearing on classified activities. Your instrument maybe sensing the results of jamming techniques frequently deployed by those involved. It seems like you have stumbled upon a good introduction for a spy novel about the new cold-war. Imagine an innocent chess-playing physicist flying back and forth between CERN-LHC and Fermilab suddenly involved in an international episode by simply using a nifty little thing. I hear the theme song already seeping into the background as the perspiration starts trickling down the side of his face. A single drop finally splashes down on the digital dosimeter’s screen, blurring the fall of the blue line.

10. Lucian - October 9, 2008

Hi Tommaso,

I think there are a bunch of effects overlapping.
1) Most important the magnetic field of the earth which has quite high gradients and variations in the Greenland -northern Canada region.
Because what you are measuring is solar cosmic radiation (not cosmic) then also important factors are:
2) The depth of the atmosphere to the plane in each point with respect to the position of the Sun
3) possible magnetic funnels , arcs or structures where the solar radiation is trapped into by the earth magnetic field.

Now if all this 3 things are kind of working together … you might get the graphic that you got.
On the way back it would be interesting if you could set the integration to 15-20 minutes …. that way there would be more points and if there is some structure might be better visible.

11. dorigo - October 9, 2008

Haelfix, yes, I did not observe any large altitude variations – I would have certainly noticed significant ones. To halve the radiation exposure, the plane should go down by at least 2000-3000 meters (although that figure is entirely not trivial to compute, since the recorded flux depends on the energy spectrum and the particle species involved, which in turn depends on altitude in a complicated way).

Fred, your plot is imaginative and fun. I will watch my shoulders when I fly back, for an agent trying to kill me to prevent me from confirming the effect…

Lucian, I am not sure I understand why you say that I am measuring solar radiation. I deny that. The counter measures x-rays, which are either prompt products of electromagnetic showers, or secondary effects due to compton scattering inside the detector volume.
In any case I concur, the effect may be explained by magnetic effects. I will take 30 minute points when I fly back. Less is not a good idea, since the digital output is only in hundredths of milliRems. In 30 minutes, at sea level the reading bounces between 0.00 and 0.01 with no meaningful structure.

Cheers,
T:

12. Lucian - October 9, 2008

Hi Tommaso,

By solar radiation I wanted to imply that most of the cosmic ray flux seen by your detector is induced by solar wind. I might be wrong though… I couldn’t find a source that says how much of the CRs at low energy are of solar origin.

L.

13. dorigo - October 10, 2008

Oh, I see. Sorry for misunderstanding. I honestly do not know… It is the combination of my ignorance on the response function of the counter and my ignorance of the fluxes.

Cheers,
T.

14. chimpanzee - October 10, 2008

I saw a program on the Science Channel, which described a European researcher who claims correlation between solar gamma ray (?) & Earth weather patterns. (In the audience, a British researcher who is part of the status-quo theory, scoffed at it). The gamma rays were correlated with cloud formation. The controversial issue of Global Warming, pits A vs B. B is convinced that human-based CO2 emissions are correlated with GW (there IS an upward trend), whereas A claims that GW is created by more powerful phenomenon (solar cycle, et al). A geologist friend of mine considers B (along with Lumo, & others) as crackpots. He points out, that an Ice Age is preceeded by a “thermal pulse”.

Back to your experiment. Those European researchers are claiming sun-sourced gamma rays (at your elevation) is causing cloud formation. Maybe, there are additional radiation phenomenon going on. Who knows, maybe you’ve stumbled onto something by accident (most of the big discoveries in Science are serendipitous).

Is that instrument research grade? I checked back, & the cost of the replacement unit for your unit, is ~$600 (USD). I have a Texas Instruments CBL (Calculator Based Laboratory) which is used in conjunction with TI graphing calculators, mainly targeting High-School students. It can take a wide variety of probes (temp, light, acceleration, etc). ~$300 pricepint. Data seems to be terribly noisy! Maybe your graph in question is the result of noisy measurement? (noisy transducers)

15. chimpanzee - October 10, 2008

Correction to above:

apparently not gamma rays, but cosmic rays are theorized to correlate with cloud formation. See here

“Several studies of GCR [ Galactic Cosmic Rays ] and cloud cover variations have found positive correlation at latitudes greater than 50° and negative correlation at lower latitudes.[24] However, not all scientists accept this correlation as statistically significant, and some that do attribute it to other solar variability (e.g. UV or total irradiance variations) rather than directly to GCR changes.[25][26] Difficulties in interpreting such correlations include the fact that many aspects of solar variability change at similar times, and some climate systems have delayed responses.”

16. Alejandro Rivero - October 10, 2008

Can you collect input on the elevation of the plane? It could be it has moved up or down in order to avoid some storm. Is it noticeable?

17. dorigo - October 10, 2008

Hi Alejandro,

no, I do not think the plane moved up and down enough to make a difference. To explain the drops, the plane would have had to really change the altitude by a lot. I did not notice any variation of altitude.

I will be more careful on my fly back.

Cheers,
T.

18. Ross - October 10, 2008

It’s clear to me that excessive radiation has fried the brains of the digital dosimeter and this has produced the strange results you are getting, Tommaso. Either that or it has fried yours and you are not reading it properly.

However, I also like Fred’s theory of an international conspiracy in which an ‘innocent physicist’ has accidentally stumbled on an international conspiracy. It reminds me of a best-selling novel I read a few years ago, featuring a psychopathic Pope and a murder at CERN. As I recall (my memory could be disfunctional) the Pope murdered a physicist who had accidentally stumbled on his dastardly plan. It was the silliest thing I have ever read but it makes me wonder if anyone has ever been murdered at CERN or come close to it.

19. dorigo - October 11, 2008

Ross, the unit may be malfunctioning, sure. I would not say it is “clear” though, because 1) it is a rather well-built device and it has worked properly until now. Besides, 2) the rad levels are ridiculously low, the thing can measure much, much stronger fields without being damaged.

Cheers,
T.

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