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Radiation over Atlantic (reprise) October 19, 2008

Posted by dorigo in personal, physics, science, travel.
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Earlier this month I pasted here a graph showing the level of radiation over the Atlantic ocean, recorded by a digital dosimeter I carried with me. I like that device: it is fun to see it becoming alive and counting real cosmic radiation as the plane climbs up the atmosphere (at sea level the thorium contamination inside buildings is the largest source of counts).

On that occasion, I found a strange effect toward the end of my trip over the Atlantic ocean, flying westward. It looked as if there were two dips in the intensity, which I was unable to explain (a list of possible effects was given in the other post). I did the same experiment on my flight back yesterday, with a halved integration time (half-hour intervals instead than one-hour intervals), as suggested by a reader. The results are shown in the graph below, which is collected flying eastward this time:

As you can see, there is a clear dip in the integrated dose (the blue curve) two and a half hours into the flight. Other features of the graph are the remarkable smoothness of both the integrated dose and the maximum recorded flux (the purple line). I am even a bit surprised by the smallness of the fluctuations of the latter: the maximum flux is basically a record of the highest deposited energy, the tail of the distribution of recorded rates. It all goes in the direction of confirming that the measurements are trustworthy.

The location of the dip approximately coincides with the region where the former graph showed one of its two dips, so the new data somehow agrees with the hypothesis that those dips are real variations in the cosmic-ray flux, maybe due to disuniformities in the magnetic field and/or solar wind effects. In other words, while the new data cannot really tell which is the source of the dips, I think they strengthen the hypothesis that the dips are not instrumental artifacts. The instrument in question is, I believe, one of the best devices available in commerce to record personal radiation exposure, and I would indeed be surprised if it failed so clearly.



1. Odysseus - October 19, 2008

Looks like you’ll have to make another trip or two across the Atlantic to confirm this hypothesis. I am willing to believe there is a real local variation, but you really ought to press your employer to pay for a few additional measurements 😉
If your next flight shows a dip at the same position again, it would be worth trying to figure out the cause. Could an irregularity of the magnetic field be stable over a longer time? I’m curios.

2. dorigo - October 19, 2008

I will check this again in a few months indeed… As for the source of the effect, it really is kind of strange that such a big fluctuation should occur. And remember, the blue curve shows a time-integrated measurement. In order for a fall from 0.26 mRem/hr to 0.10 mRem/hr to occur in a 30′ measurement, without the neighboring points being affected in the least, it means that the deficit is wholly contained in that single bin. This means that either:

– the variation is really sharp and it happened by chance that its boundaries coincided with the beginning and end of that 30′ period; in that case, the variation can be as small as a decrease by 60% (0.26 to 0.10). I think such a sharp variation, and the coincidence with the bin boundaries, make it rather unlikely.

– the variation is less sharp, and/or its boundaries are not coincident with the beginning and end of the 30′ period: in that case, the real minimum is much smaller than 0.10. This makes it even more interesting…


3. Fred - October 19, 2008

Hello Tommaso,

My first thought is to look at the instrument you are using and whether it is reliable for your in-flight observations. In 2004, The 11th International Congress of the International Radiation Protection Association featured among others this keynote lecture dealing with APD’s (active personal dosimeters):

The model you have was included among the instruments they used for their study. Some of the conclusions and future needs for APD’s, which they appear to endorse:

– Improvements needed for extremity, low doses, high intensity and neutrons.

– Improvements on effective dose assessment by:
— Choice of detectors and calibration practices
— Simulated workplaces fields calibrations

– Type testing and standard
— Harmonize practices in Europe
— Standards for extremity needed

– APD use for legal Record?

Do any of the above points apply in your case? On your next flight back, might you consider using for a side-by-side comparison an APD offered by a different manufacturer? By the way, your Mini 6100 is no longer available. Don’t let it our of your sight. lol

p.s. Coincidentally, the 12th Congress of the IRPA starts today in Buenos Aires. Their website has detailed papers available from 2004. http://www.irpa.net/

4. Fred - October 19, 2008

Excuse me,

This is the first paper I read from their site titled: “Radiation Exposure on Different Air Routes

5. Daniel de França MTd2 - October 19, 2008

I think the solution it is that your plane flew in a lower altitude. There are several layers of flight to avoid aircraft solution.



Here is some information about flight procedures over the atlantic:


Maybe you should check your flight number.

6. Neil B. - October 19, 2008

If it happened on one given flight, I might suggest it was from the Moon occulting a notable cosmic ray source (if that could hold up – it depends on the map of intensity from the sky and I don’t know much about that.) But repetition of the effect puzzles me, I don’t have any immediate ideas.

However, it is true that the Earth’s magnetic field is getting lumpy, isn’ it, as we muddle towards a blatant magnetic pole reversal in centuries or even decades. That could have an impact of course on charged particles (many people think cosmic rays are mostly high energy gamma rays, but most are protons.)

Also, why isn’t more written about the the Earth’s ever more mottled field as it slides towards pole reversal? (That would have major effects on life, electronics, and communications here!) Ever since that Nova show a few years ago about the issue, it seems to have gone off the radar… Did the show exaggerate? Who knows the score, about this geomagnetic issue of great importance?

7. Daniel de França MTd2 - October 20, 2008

I posted something here, twice, but it doesn’t showed up. Why?

I found your comment in my spam filter (only one tho). It is now restored, see above. – T.

8. forrest noble - October 20, 2008


Think that is great science, recording and graphing this variation, I think it is exiting. It’s a new hypothesis begging for investigation. I agree with your general theory above that this variation is probably “due to disuniformities in the magnetic field and/or solar wind effects. I would word it by paraphrasing your statement above, asserting that “these variations might be explained by disuniformities in the Earth’s magnetic field as it somewhat alters the path of charged solar-wind particles, primarily protons, electrons and alpha particles (the solar wind traveling at a million miles per hour).”

My preliminary guess is that this is a dominant variation that would change primarily in periods when sun spots (solar storms) are very active or it also might be used someday to detect subtle changes in the Earth’s magnetic field. Maybe an important find in that instrumentation that functions more efficiently or less costly in an atmosphere of reduced cosmic radiation, could be preferentially used in these geographic locations, maybe even geo-stationary satellites.

I also agree with Odysseus above, both his thread and humor — a worthy experiment which might inspire your employer to finance further investigations, I say ;), maybe even destined for publication, possibly no joke.

your friend forrest

9. dorigo - October 20, 2008

Hi Fred,

thank you very much for the paper you provided a link to. Very informative. I also had a look at the slides – I am surprised to see how many models there are: when I bought the MINI 6100, I did a search in the internet but could not find many choices.

Daniel, on a second thought (I had discarded the possibility) it is a quite meaningful suggestion, because the radiation rate is highly non-linear as a function of altitude, since my detector is mostly sensitive to gammas and x-rays. What I mean is that even a decrease of the altitude by 20% might have caused a halving of the rate. I found out that during a shorter flight from Munich to Venice last Saturday the rate was just twice higher than that on the ground, and the flight was at a height of 5000m.

I originally discarded the possibility based on my perception of the height on the Munich-US flight, but if the height varied, say, from 11,000 to 9,000 meters and back, I would probably not notice it.

Hi Forrest,

Daniel persuaded me that the most probable cause is a variation of flight altitude. Other options are not excluded, but they now look less plausible.

Cheers all,

10. Alejandro Rivero - October 20, 2008

I tend to agree on the “variation of flight altitude” answer. Furthermore, it is verifiable by using a GPS next time. The G is for Global, not for Ground.

11. Lucian - October 21, 2008

Hi Tommaso,

Nice that you did the traveling back experiment as well.
One small suggestion regarding the plots though: it would be easier to compare them if for the second one you would plot on the x-axis 24-x instead of x. That will give you more or less an approximation of the meridian on x.

The way plots are right now one has to flip one of them and then compare them.

12. dorigo - October 21, 2008

I know, but the dips are in the same region but the one in the second plot does not match perfectly either of the two in the first one. In any case, if these were connected with longitude, we would not be able to say much from overlying the plots because there is some uncertainty in he x-axis (time of start of flights), plus a sizable difference in route while flying eastward or westward.

That is why I decided to just plot the second set of data as is.

13. X-Ray Galore - with sticky tape! « Blog of too many things - October 23, 2008

[…] Galore – with sticky tape! Since Tomaso likes to play around with his personal dosimeter on airplanes, I’d like to propose him a new 50 keV X-Ray […]

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