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The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 24 Nov 2019, 00:21
by Go-Figure
Hello there,
It’s been a while I know.
I’ve been in Japan the first half of November. I stayed in Tokyo but I also spent a day in Fukushima prefecture and as you can imagine I came back with plenty of data to share.
But that’s for the next post, I want to start from…above, namely the low stratosphere, to talk about radiation in flight, at aircraft altitude (11-12 km).

I took four flights, two on the way to Japan (Florence-Munich and then Munich-Tokyo Haneda) and another two on the way back (same itinerary, the other way around).
I will focus in particular on the third one, Tokyo Haneda-Munich, which I took on November 14.

First some context, a few extracts from UNSCEAR’s “Exposures from natural radiation sources” ... s.2679881/

"Galactic cosmic rays incident on the top of the atmosphere consist of a nucleonic component, which in aggregate accounts for 98% of the total, and electrons, which account for the remaining 2%. The nucleonic component is primarily protons (88%) and alpha particles (11%), with the remainder heavier nuclei. These primary cosmic particles have an energy spectrum that extends from 10^8 eV to over 10^20eV.

It is thought that all but the highest energy cosmic rays that reach earth originate within the earth’s own galaxy. The sources and acceleration mechanisms that create cosmic rays are uncertain, but one possibility recently substantiated by measurements from a spacecraft is that the particles are energized by shock waves that expand from supernova.

The fact that protons of such high energy are also observed to be isotropic and not aligned with the plane of the galactic disk suggests that they are probably of extragalactic origin.

The most significant long-term solar effect is the 11-year cycle in solar activity, which generates a corresponding cycle in total cosmic radiation intensity. The periodic variation in solar activity produces a similar variation in the solar wind. The solar wind is a highly ionized plasma with associated magnetic field, and it is the varying strength of this field that modulates the intensity of galactic cosmic radiation. At times of maximum solar activity the field is at its highest and the galactic cosmic radiation intensity is at its lowest.

The magnetic field of the earth partly reduces the intensity of cosmic radiation reaching the top of the atmosphere, the form of the earth’s field being such that only particles of higher energies can penetrate at lower geo-magnetic latitudes. This produces the geomagnetic latitude effect, with minimum intensities and dose rates at the equator and maximum near the geomagnetic poles.

The high-energy particles incident on the atmosphere interact with atoms and molecules in the air and generate a complex set of secondary charged and uncharged particles, including protons, neutrons, pions and lower-Z nuclei. The secondary nucleons in turn generate more nucleons, producing a nucleonic cascade in the atmosphere. Because of their longer mean free path, neutrons dominate the nucleonic component at lower altitudes. As a result of the various interactions, the neutron energy distribution peaks between 50 and 500 MeV; a lower energy peak, around 1 MeV, is produced by nuclear deexcitation (evaporation). Both components are importantin dose assessment.

The pions generated in nuclear interactions are the main source of the other components of the cosmic radiation field in the atmosphere. The neutral pions decay into high-energy photons, which produce high-energy electrons, which in turn produce photons etc., thus producing the electromagnetic, or photon/electron, cascade. Electrons and positrons dominate the charged particle fluence rate at middle altitudes. The charged pions decay into muons, whose long mean free path in the atmosphere makes them the dominant component of the charged-particle flux at ground level. They are also accompanied by a small flux of collision electrons generated along their path.

You can see components of dose rate equivalent from cosmic rays at various altitudes in the picture below, again from UNSCEAR.
01 - Component of Dose Equivalent Rate.png
01 - Component of Dose Equivalent Rate.png (22.12 KiB) Viewed 1302 times
I had with me my Geiger Counter, my Dosimeter and my Gamma Spectrometer so I was well placed to collect a good set of data.

The first thing I noticed was that, in all four flights, both during take off and landing, there was a phase, roughly between 1 and 2 km altitude, where radiation went basically to zero.
02 - DSC03686R.jpg
Best explanation I can found is that at that altitude the effect from terrestrial gammas and Radon+progeny in the atmosphere has faded away, but cosmic rays hasn’t really kicked in properly yet.
From that point on the doserate goes up pretty quickly but unsurprisingly the readings of the dosimeter and the gamma spectrometer diverge just as quickly.
Cosmic rays have such a high energy that most of them goes through the 9cc crystal of my portable spectrometer without interacting with it, therefore the doserate it shows is significantly lower than that from the dosimeter. Once you reach cruising altitude the ratio is almost 1:10.

We spent most of the flight at 11.5 km altitude, and the corresponding doserate was oscillating between 4 and 4.5µSv/h with peaks nearly double than that coming from fluctuations.
With little less than four hours to go we increased our altitude to 12.2 km and you can see in the diagram below that average doserate increased accordingly to 4.7 - 5 µSv/h, before going back down again as we began the descent to Munich.
03 - PED+ Task2 - Average - Hour - Copia.png
03 - PED+ Task2 - Average - Hour - Copia.png (35.48 KiB) Viewed 1302 times
In the end the accumulated dose recorder by the dosimeter in little more than 11 hours was 44.49 µSv, with a peak dose of 10.60 µSv/h.
04 - DSC03695R.jpg
The peak dose was recorded 800 km from Helsinki at 12.2 km altitude. Of course it had little to do with the location on the ground.
05 - DSC03644R.jpg
This is the diagram if the peak dose of every hour.
06 - PED+ Task2 - Peak - Hour - Copia.png
06 - PED+ Task2 - Peak - Hour - Copia.png (41.25 KiB) Viewed 1302 times
Here’s the itinerary of the flight, photo taken a few minutes before the peak dose was recorded.
07 - DSC03623FR.jpg
During the flight I collected an 8 hours gamma spectrum. It is not really very significant because, as I said, the spectrometer was able to get only a small part of the interactions contributing to the equivalent dose, therefore the average dose it recorded was a mere 0.56 µSv/h.
But a few interesting things can still be took from it.

My PDS G has been converted to GN (meaning it shows a Neutron rate too) as far as the software is concerned, but it doesn’t actually have a neutron detector so it assumes every interaction above a certain energy is a neutron so it’s unable to tell the difference between Neutrons and Cosmic Rays, which makes the reading not really reliable on the ground.
But at such altitude most cosmic rays are actually Neutrons (and Protons) so it gets more interesting.
The reading on the ground is typically 0.15 interactions/second, at 11-12 km altitude it's 100 times higher, 14.4 interactions/second. That’s obviously a big underestimation for the reasons mentioned above, but it’s still interesting to see the difference.
08 - DSC03654.jpg
The spectrum itself is pretty meaningless, a part from the "big" annihilation peak, a clear indication of the presence of plenty of positrons and electrons turning each other into 511 keV photons.
Here it is both in Logarithmic and Linear view. For some reason the Neutron rate showed is 1.4 cps instead of 14.4 and also the total number of counts is less than what you can see on the display above.
09 - 3 - Flight Tokyo Haneda - Munich - ID - 8 Hours - 14-11-19 - LOG.png
10 - 3 - Flight Tokyo Haneda - Munich - ID - 8 Hours - 14-11-19 - LIN.png
One more takeway: this comes from the Munich to Tokyo flight, where, among other things, I compared the readings from spectrometer, the dosimeter and the Geiger Counter.
On the ground the Geiger usually gives you an overestimation of the equivalent dose, because it assumes every count comes from Cs137 and the actual background spectrum has an average energy which is lower than the average energy of Cs137 gamma spectrum.
At 12 km altitude it’s the other way around, so the Geiger reading is a constant underestimation of that from the energy compensated dosimeter.
Since in this flight the altitude was constantly below 11 km the doserate was significantly lower.
11 - DSC07169FR.jpg
Anyway, I have reasons to think even the dose from the dosimeter is an underestimation. The instruments is made to work in terrestrial condition and its energy range is 33keV to 3MeV. At 12 km altitude many interaction are out of this range.

Again from the UNSCEAR, this is the graph of the measured doserate at various altitudes.
12 - UNSCEAR - Dose vs Altitude - Copia.png
12 - UNSCEAR - Dose vs Altitude - Copia.png (17.63 KiB) Viewed 1302 times
Right now we are in the solar minimum phase, as you can see here, where the number of average sunspots for each month is listed
So the doserate is at its maximum, and therefore, looking at the graph, it should be higher than what I measured at 11-12 km altitude, although the graph doesn't say at what exact latitude those measurements were taken, it just says it's more than 50° North.

UNSCEAR concludes: “The results of recent measurements and recentcalculations are broadly consistent. For altitudes of 9-12 km at temperate latitudes, the effective dose rates are in the range 5-8μSv/h, such that for a transatlantic flight from Europe to North America, the route dose would be 30-45 μSv. At equatorial latitudes, the dose rates are lower and in the range of 2-4μSv/h.

There are a number of sources you can use to calculate equivalent dose from commercial flights, I list two of them:

1 – ICARO ... sV4wlZP8eI

This one gives 42 µSv for my flight, which is consistent with my measurement.


This one gives about 70 µSv for my flight.

It’s also worth mentioning this document from the European Commission: ... ts/140.pdf

At page 92 you can see both equivalent and effective dose for selected flights.
According to the table, during a flight from Frankfurt to Tokyo an equivalent dose of roughly 52 µSv and an effective dose of roughly 60 µSv was measured. That was in 2002, which was close to solar maximum, so the same flight will get you an higher dose in 2019.

Anyway, putting all sources together there are significant uncertainties which is often the case talking about radiation. Even the document from the European Commission mentions, in the conclusions, an uncertainty of 25% in the experimentally determined ambient dose equivalent, and we have to live with that.

But I think it’s reasonable to assume the actual equivalent dose of my flight was higher than the one I measured, likely 60 µSv or higher.

That’s it from the low stratosphere.

We go back to the ground for the next one.


Re: The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 24 Nov 2019, 04:41
by pilgrim
Hi Massimo, welcome back!
Thank you for this report, I look forward to reading the next one!

Re: The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 24 Nov 2019, 22:40
by Go-Figure
Thank you Daniel!
I guess everyone is more interested in Fukushima than in an ordinary commercial flight.
I started from here because both defy common beliefs.
The average person expects to to be exposed to much more radiation spending a day in Fukushima prefecture a few km from the Fukushima Daiichi nuclear power plant (including the No-Go Zone) than in an ordinary commercial flight, so it's interesting to make a comparison, which I will do in the next post, likely next week.


Re: The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 24 Nov 2019, 23:47
by cicastol
Welcome back Massimo,
you made a great report, does playing with our toys on airplane generate some sort of suspicion? :-)

Re: The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 25 Nov 2019, 00:22
by Go-Figure
cicastol wrote:
24 Nov 2019, 23:47
Welcome back Massimo,
you made a great report, does playing with our toys on airplane generate some sort of suspicion? :-)
Basically nobody cared about what I was doing.
The only exception was a Lufthansa crewmember on the flight from Tokyo Haneda to Munich who asked me about it. He later told me he's a mechanical engineer (like me) doing that as a temporary job and he was curious to know the results of my measurements in order to compare them with what they are told by the airline.
We talked for a while and other members of the crew stopped by now and then.
They spend much more time than the average person at such altitudes (albeit there are limits that cannot be exceeded) so obviously they are interested in the subject

We later exchanged email addresses and I forwarded him basically the same material I posted here, after which we had a few exchanges commenting the data.

Re: The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 30 Nov 2019, 18:37
by Cosmic
Hi Massimo,

thank you for this very informative and well prepared report!

I wonder if recording shorter spectra, say 5 to 15min, would reveal some differences in the spectra regarding altitude, latitute, day/night?

Re: The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 30 Nov 2019, 21:12
by Taray
Nice report
I have taken my Polimaster and neutronrae on flight before and have registered similar results .
Polimaster about 40 microSv/hr
Neutronrae II about 2 cps
Did not do a spectrum.
Your gamma spectrum is wide spectrum with a 511 annihilation peak.
Correct me if I am wrong here
Cosmic rays like sunlight has a broad spectrum from low to high energies
The low energy ones are absorbed my the plane fuselage and very high energies ones goes right through the detector
What is left is just a mid spectrum without any isotopic peaks unlike on the ground.
I can’t see yr gamma peak values clearly .
Is ur peak on the left corresponds to the 70 to 80 kev background peak seen at sea level ?
Now to extrapolate your results to ground level
I always wanted to detect or capture the solar storm spectrum once it strikes earth
The initial gamma or X-ray spectrums which hits the earth in 8 minutes is missed cos I will not know about it and least prepared.
But the following magnetic plasma consisting of electrons and protons travel to earth in hours to days and exact time of arrival is known.Most of this goes to poles but some make it down to earth depending on magnitude of storm
I usually don’t detect any solar storm radiation with my toys .I am at the equator which has less likelihood of success anyway.
Will one get a big annihilation peak on the ground during a solar storm arrival to earth with gamma spectrometry?

Re: The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 01 Dec 2019, 08:00
by Go-Figure
Hi Taray,
Did you mean 4 µSv/h? 40 µSv/h should be in the region of what astronauts get in the International Space Station at more than 300 km altitude.

As I said above my spectrum is pretty meaningless overall, because a 9cc crystal isn't fit to deal with cosmic rays. The annihilation peak is likely the only significant part.
The low energy peak is located between 87 and 90 keV, but we should probably not read too much into it.

As for the measurability of a difference in the strength of the annihilation peak on the ground during solar storms, it's a good questions but I don't know the answer!
At least not yet.
Cosmic wrote:
30 Nov 2019, 18:37
Hi Massimo,

thank you for this very informative and well prepared report!

I wonder if recording shorter spectra, say 5 to 15min, would reveal some differences in the spectra regarding altitude, latitute, day/night?
A serious spectrum taken with a much bigger crystal would probably reveal some clear difference, one taken with my portable one likely not.
Anyway I was able to measure a clear difference in doserate as we increased and decreased altitude.

Re: The Stratospheric Thread - Radiation at Aircraft Altitude

Posted: 01 Dec 2019, 21:53
by Taray
Maybe 40 cps from memory .
Happened many years ago .
Unfortunately cannot do a Polimaster history recall due to various issues like infra red connectivity and windows incompatibility.