The Stratospheric Thread - Radiation at Aircraft Altitude
Posted: 24 Nov 2019, 00:21
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”
https://forum.wordreference.com/threads ... 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.
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.
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.
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.
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.
This is the diagram if the peak dose of every hour.
Here’s the itinerary of the flight, photo taken a few minutes before the peak dose was recorded.
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.
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.
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.
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.
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
https://www.sws.bom.gov.au/Solar/1/6
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
https://icaro.world/?fbclid=IwAR0QKoN59 ... sV4wlZP8eI
This one gives 42 µSv for my flight, which is consistent with my measurement.
2 - FEDERAL AVIATION ADMINISTRATION OFFICE OF AEROSPACE MEDICINE CIVIL AEROSPACE MEDICAL INSTITUTE
http://jag.cami.jccbi.gov/cariprofile.asp
This one gives about 70 µSv for my flight.
It’s also worth mentioning this document from the European Commission:
[broken link removed - Steven]
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.
Massimo
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”
https://forum.wordreference.com/threads ... 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 (22.12 KiB) Viewed 11344 times
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.
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 (35.48 KiB) Viewed 11344 times
- 06 - PED+ Task2 - Peak - Hour - Copia.png (41.25 KiB) Viewed 11344 times
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.
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.
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.
Again from the UNSCEAR, this is the graph of the measured doserate at various altitudes.
- 12 - UNSCEAR - Dose vs Altitude - Copia.png (17.63 KiB) Viewed 11344 times
https://www.sws.bom.gov.au/Solar/1/6
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
https://icaro.world/?fbclid=IwAR0QKoN59 ... sV4wlZP8eI
This one gives 42 µSv for my flight, which is consistent with my measurement.
2 - FEDERAL AVIATION ADMINISTRATION OFFICE OF AEROSPACE MEDICINE CIVIL AEROSPACE MEDICAL INSTITUTE
http://jag.cami.jccbi.gov/cariprofile.asp
This one gives about 70 µSv for my flight.
It’s also worth mentioning this document from the European Commission:
[broken link removed - Steven]
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.
Massimo