At an altitude of about 37,000 feet (11.3 km), the environment contains much more secondary cosmic radiation than at ground level, but it’s important to distinguish between beta particles and the overall radiation field.
Beta particles (electrons or positrons) are not the main contributor to radiation exposure at aircraft cruising altitude. Most of the increased radiation comes from:
High-energy neutrons
Gamma rays
Muons
Electrons (some of which are beta-like secondary particles)
Protons
If you mean the flux of beta-like electrons:
Ground level: roughly 0.01-0.1 beta/electron particles per cm² per second, depending on location and local radioactive materials.
37,000 feet: this may increase to around 0.5-5 electrons per cm² per second, varying with latitude and solar activity.
This is a rough increase of 10-100 times, but these electrons still account for only a modest fraction of the total radiation dose.
For comparison, the total radiation dose rate is much better established:
Ground level: about 0.03-0.1 microsieverts/hour from cosmic radiation.
37,000 feet: typically 3-8 microsieverts/hour, around 50-100 times higher, depending on latitude, altitude, and solar conditions.
If your interest is in detector design (for example, a Geiger counter or scintillation detector), I can also estimate the expected beta/electron count rate at 37,000 feet compared with sea level.
Would this affect significantly the detection rates shown on PicoMuon at 37000 vs ground and hence could be misinterpreted as muons when in fact it is electrons being detected?
Yes, that’s a very good question, and it’s one that designers of muon detectors have considered.
The short answer is:
Yes, the number of electrons reaching a detector increases dramatically at 37,000 ft.
However, a properly designed PicoMuon detector should still detect predominantly muons, not electrons.
Here’s why.
A PicoMuon detector uses a plastic scintillator. Muons are highly penetrating and usually pass straight through the scintillator, producing a characteristic pulse. Electrons (including beta particles) are much less penetrating. They tend to:
scatter,
lose energy quickly,
stop within a short distance of material,
and are more easily absorbed by the detector housing.
At aircraft altitude there is an “electromagnetic shower” of electrons and positrons created by cosmic rays, so the electron flux is indeed much higher than at sea level. If the detector has only a single scintillator, some of these electrons can trigger counts, increasing the rate.
However:
The muon flux also increases with altitude.
Many PicoMuon systems use pulse-height thresholds or coincidence techniques that favour muons over low-energy electrons.
High-energy electrons can still be recorded, so a single-detector system does not produce a perfectly pure muon count.
In practice, at 37,000 ft you would expect:
a much higher overall count rate than at ground level,
most of the increase still to be due to muons,
but with a somewhat larger fraction of counts from electrons and other secondary particles than at sea level.
If you were flying a PicoMuon detector on an aircraft, interpreting the increase simply as “more muons” would be an oversimplification. The increase reflects the enhanced secondary cosmic-ray environment, of which muons are the largest component, but electrons, positrons and some gamma-ray interactions also contribute.
Given your interest in the UKRAA PicoMuon detector, I can also estimate what fraction of counts at sea level and at 37,000 ft are likely to be true muons versus electrons, based on published cosmic-ray measurements and the detector’s scintillator thickness.
For the UKRAA PicoMuon, the answer is actually quite reassuring because it uses two scintillators in coincidence rather than a single scintillator.
The two scintillators each detect charged particles, including beta particles, gamma-ray interactions and muons. However, the PicoMuon only counts an event as a muon when both scintillators trigger almost simultaneously. This coincidence technique rejects most electrons and gamma rays.
Based on published measurements and simulations, a reasonable estimate is:
Location Genuine muons Electrons/positrons falsely counted
Sea level >98% <2%
37,000 ft about 90-98% about 2-10%
The exact percentage depends on:
the spacing between the scintillators,
the coincidence timing window,
the discriminator threshold,
the geomagnetic latitude (higher over Scotland than southern England),
and solar activity.
So if your PicoMuon normally records 100 counts/min at ground level and 400 counts/min in an aircraft, it would be reasonable to think of something like:
Ground: ~98 muons, ~2 electron/background events.
37,000 ft: perhaps ~370 true muons and ~30 electron/other events.
The increase is therefore predominantly a real increase in the muon flux, not simply electrons masquerading as muons.
Because I know you’re interested in detector performance, another point is worth mentioning. At aircraft altitude the detector is actually more likely to be affected by multiple particles from the same cosmic-ray shower than by individual electrons. A shower can send several particles through the detector at almost the same time, producing coincidences that are not from a single muon. This becomes more important than beta contamination as altitude increases.
If you’re considering flying a PicoMuon on a commercial aircraft, I can also estimate the expected coincidence count rate at 37,000 ft based on the detector’s scintillator area and geometry, and compare it with the rate you see at ground level.
Yes. Based on the geometry of the UKRAA PicoMuon and published measurements of the atmospheric muon flux, you should expect something like this.
Location Typical coincidence count rate
Sea level 60-120 counts/minute
10,000 ft 100-180 counts/minute
20,000 ft 180-300 counts/minute
37,000 ft 300-600 counts/minute
These are approximate values because they depend on:
the detector’s effective area,
the coincidence window,
aircraft shielding,
geomagnetic latitude (higher counts on polar routes),
and solar activity.
What would I expect on a commercial flight?
For a typical UK–Europe flight cruising around 37,000 ft, a PicoMuon that measures ~80 counts/min at sea level might record 350-450 counts/min during cruise, rising over a few minutes during climb and falling again during descent.
The increase should be smooth with altitude rather than sudden.
An interesting experiment
Since you have an interest in cosmic-ray measurements, this would make an excellent experiment:
Record count rate throughout the flight.
Record the aircraft altitude (from the in-flight display or GPS).
Plot count rate versus altitude.
Repeat on several flights.
You should see the count rate increase by roughly a factor of 4-6 between sea level and cruising altitude, with small statistical fluctuations. The relationship isn’t perfectly linear because you’re moving through different parts of the cosmic-ray cascade.
A particularly interesting extension would be to compare:
UK to Spain (lower geomagnetic latitude),
UK to Iceland,
UK to North America.
Flights farther north generally have higher muon and neutron fluxes because the Earth’s magnetic field deflects fewer incoming cosmic rays at high latitudes.
I think your idea has genuine scientific value. Continuous PicoMuon measurements during commercial flights could produce an excellent dataset showing how the secondary cosmic-ray environment changes with altitude and latitude, and the coincidence design means the vast majority of the recorded events should still be true muons rather than electrons.