Measurement of gamma spectrogram on a transatlantic flight from Amsterdam to Seattle

Introduction

I recently purchased a portable, energy calibrated, gamma ray detector and spectrometer, Radiacode 103G (RC). The RC is extremly affordable for what it does. The device can be used for many purposes such as identification of isotopes, dose estimation and radiation tracking. The device is equipped with a modern high performance scintillator crystal, GAGG(Ce).

X-ray and gamma ray are the same types of radiation with the difference that the gamma rays come from natural sources e.g. isotopes.

Radiation in an airplane

There are three sources of radiation in an airplane:

1. The earth - dominates on ground
2. Plane - can be mostly neglected
3. Space & sun - dominates on high altitudes

We can write the balance

Total radiation = radiation from ground + radiation from sun or space

Measurement

The measurmed data was captured on an Airbus between Amsterdam and Seattle on the day of 2024-09-07.

Spectrogram

The spectrogram was captured during the whole flight from Amsterdam to Seattle. Every line in the spectrogram is a minute long. The spectrogram shows how the spectrum changes over time.

• y-axis is time
• x-axis is energy expressend in [keV]
• On the x-axis we also have event count but there is no scale

The measured spectrogram looks like this:

Here are some observations

• When the plane takes off and starts to ascend then the radiation from the earth decreases. However, at low altitudes the radiation from space is not increasing much resulting in a ”black zone”, an altitude with less gamma radiation than on the earth or at high altitudes.
• When the plane has ascended to full altitude then the radiation from space is dominating. This radiation has a peak around 50 keV and is similar to what an x-ray machine would produce.
• During the flight there is a jump in the radiation. This is due to either increased space / solar wind or the plane ascended to save fuel.
• When the plane is descending we recognise an gamma ray energy minimum again.
• The full spectrum occupies all energies from 20 keV to 2.8 MeV. However, there are many events that have larger energy that can not be classified. It is normal to have particles in the GeV range at high altitude.
• The gamma spectrum is mainly focused below < 170 keV and this is what we would denote as x-rays
• At 511 keV the electron-positron annihilation line is clearly visible, in other words this is particles and anti-particles colliding.

This is the spectrum for the flight. If you combine all the spectrums in the spectrogram the you obtain the following figure. Here the annihilation peak is much more visible:

Total dose

The total dose received during the flight was 6.9 uSv. This value is highly variable and depends mainly on the radiation from space. According to the web a usual number is 100 uSv so what I measured is significantly lower. I would not like to work on an airplane receiving a dose of 100 uSv potentially many times a week.

The limit for a normal population is considered to be 1.5 mSv per year. This is a conservative limit.

X-ray machine at Zurich airport

While passing through the Zurich airport I?also measured the x-ray spectrum for the luggage scanner. Every line in the sprectogram is a second long. The scale is logarithmic.

The spectrum is covering a wide band up to 3 MeV but most of the energy is focused below < 100 keV as it should be. Energy exceeding 1 MeV is particularly damaging for electronics as it penetrates deep into structures.

Conclusion

The spectrogram for the flight is very interesting - the fact that there is a zone with little gamma energy was new and unexpected to me. This would be the place to live at.

Overall, the dose was smaller than I?expected.

I still have no idea about why the gamma spectrum looks like it does but?I?will dig into the litterature to find out when I have time. If you know then please add a comment to this article.

The RC?is a very versatile device able to capture interesting information for a hobby scientist.