Trip Radiation Notes: GMC500+, GMC600+, RadiaCode 110

[Jeff]

@ullix, Magnus Linner,
Eager to hear your comments.
BTW, using flightradar24 as a gold member, so far, does NOT provide downloadable GPS altitude - only viewable in play mode. I am very disappointed. I have an on-going discussion with flightradar24 to get downloaded GPS altitude data.

Now, the reason for this post.
Recently took two US domestic flights; Austin, Tx (AUS)<-> San Francisco, CA (SFO). The graphics below are for the return flight. Note, the gmc500+ is in the overhead bin (not disturbed during flight); gmc600+ is in the seatback pocket in front of me. I occasionally took gmc600+ out to look at the sensor display. The rc110 was in my hand on on my knee for most of the trip. Laptop on the other knee looking at rc110 data, etc...

1st graphic (sfo_aus_gmc_20251007.png), gmc500+ (bottom blue line) and gmc600+ (top blue line).
(1) I expect the pancake tube design in gmc600+ to have a directional sensitivity. Mostly this sensor is in the seatback pocket in front of me. In this case I assume the most sensitive direction pointing to the front of the plane (defined by me as vertical orientation). On two occasions I put the sensor on my tray table pointing to the bottom of the plane. Within seconds I see counts increase. Then to check/verify directional sensitivity, while on the tray, I change the sensor orientation to vertical and verify the counts return as before. I did not expect the change of ~300 cpm depending on the sensor orientation.

(2) As expected, I note the gmc600+ responds faster to altitude changes than the gmc500+.

2nd graphic (sfo_aus_rc110_20251007.png), added RadiaCode 110 data; same time frame (mostly).
Data from the rc110 is the "Event log" csv download. Then I used python/pandas to extract the cpm/date_time data. The graphic shows all raw cpm data, including the alarm extra data collections; I have not had an opportunity to explore the big rc110 spikes, but I expect they are from the extra data collection when the rc110 crosses alarm thresholds.

(3) As expected the rc110 response is faster then the Geiger tubes. But note, I do not think the rc110 real-time stamp is well synchronized well with the flight data - off by a few minutes or more.

(4) Intriguing to me. In the graphic, notice the rc110 data dip on take-off. I watched the values drop from about 350 cpm to <100 cpm. I estimate the plane was ~50 feet off the ground BEFORE the dip started; the slowly the counts increased with altitude, as expected. I saw the same rc110 cpm profile for take-off and landing at both AUS and SFO. For the data dip/minimum, my initial thinking is the plane is leaving the terrestrial radiation influences, and the atmospheric influences are not yet dominating.

(5) Not had an opportunity to make sense of rc110 flight spectral data.

Thank you.
\Jeff

[ullix]

Really too bad you can't download the GPS data!

Interpretation of the data is a bit demanding. The low blue curve is the GMC500? Quite a textbook result with near constant CPM. Which makes the Altitude jump about halfway to Texas all the more surprising. Can you look in retrospec at weathermaps ? Any obvious transition from low to high pressure systems? GPS would really be helpful!

The black spikes are from RC110? Very odd. No idea, where they come from.

Wild guess, the GMC600 increased levels during "horizontal" might result from Potassium in the airplane furniture. K-40 gives many betas, and the GMC600 is more sensitive to them. Perhaps you should keep the GMC600 in a case with 5mm plastic to keep out the betas?

I believe the GMC-600 will NOT be directionally sensitive, as long as the radiation is Gamma-only. The difference of Gamma from behind vs. Gamma from the front is minuscule. However, if there were any betas, than there would clearly be directional sensitivity!

[Jeff]

Yes the black spikes are rc110 data.
Based on csv event log review, the spikes are real, but I need to adjust how I graph the data...

There are times when the rc110 shortens the measurement interval reporting; seemingly around crossing alarm thresholds. Sometimes the measurement interval is < 1 second or two, thus for high count rates the reported CPM can be high. Much of my data is ~1:36 minute intervals. Not sure yet what my graphing software need to do.

I am not sure if I need to use the RadiaCode count rate error assigned to each reported value. I will let you know what I come up with...

[Simone]

I'd have thought a gmc600 laid flat w/ the pancake surface parallel w/ the fuselage would register more gamma hits from space (that manage to get through the fuselage and the few tens of thousands of feet of atmosphere above the plane) than when on its side, given the much larger surface area. Thoughts?

I'd love to have (and afford) a reliable neutron detector as, compared to gamma/xrays/cosmic rays, they create the most biological damage (especially at altitude). I wonder if pilots/crew (who are "soft classified" as "radiation workers") have dosimeters which also measure neutron or dosimeters at all. Or do they just track the flight hours per year.

I could chatgpt all this but hate to rely on ai too much.

Be interested to hear your thoughts and counters if I'm off the mark.

Simone

[ullix]

The pancake detector is like a bell: a hard bowl on one side, and a very thin window "glass" on the other. The hard side is almost unpenetratable for betas, while they can pass through the window much easier than through the glass of glass tube. For gammas, however, both hard and thin side are almost invisible! This is true even for X-rays!

If you have no plastic case for the 600, then a regular Paper magazine, hold on the window side, would do.

Laying the counter on its small side would reduce the cross section for cosmic rays, I agree.

Neutrons? Hmmm, such detectors exist at acceptable size?

[Simone]

not sure i understand what you mean by "hard and thin side are almost invisible" to gamma/xrays.
maybe i dont understand how pancakes are contructed and operate. ill research this.
(i do know that in the US they are pretty thick and sodden with maple syrup whilst where i grew up they're more like French crepe with a little lemon and a dusting of sugar)

oh sure, there are a few; practicality, purchase price, and maintenace/calibration costs, aside...

[Bob]

LOL! The LND 7314 is the Pancake GM tube used in the GMC 600+ and the RadEye B20.
The window is a thin film of Mica which allows Alpha,Beta and of course ganmma to be detected.
Bob

[ullix]

;-) - I don't mind either variant of your pancakes!

@Bob posted the spec sheet of the LND7314 - and if the naming is unexpected, they themselves call it "Pancake mica window alpha-beta-gamma detector".

LND says that the "Window" is made of Mica, and its "AREAL DENSITY" is "1.5 - 2.0 MG/CM²". Assuming a density of Mica of 3 g/cm³, we arrive at a thickness of roughly 10µm (micrometer)!

LND does not give a thickness of the bell-part of the detector. Let's assume it is iron (density 7.9 g/cm³), and has 1 mm (=1000 µm) thickness. Its areal density is then 790 mg/cm².

Now you need to know the Gamma absorption, for which I refer you to the pic and the links therein. With than one can calculate how much makes it through:

Material   Gamma-Energy        Mass/Area      Penetration
Iron        10 keV            0.79   g/cm²    5*10E-57 %
Iron         2 MeV            0.79   g/cm²    97 %      
Mica        10 keV            0.002  g/cm²    71 %      
Mica         2 MeV            0.002  g/cm²    99.99 %       

One perhaps surprising note: it does NOT depend on the atomic number Z; it is all captured in Mass/Area!

So, for iron and 10 keV gammas, you have no chance of seeing any radiation coming through. For 2 MeV gammas you get a reduction of 3%. Technically it is possible to demonstrate, but it takes quite some effort. See e.g. my "Going Banana" article, where I demonstrated that you can measure the famous K-40 radiation in banans with a plain glass-tube Geiger counter!

For a Mica window both energies pass through.

Therfore my saying "hard and thin side are almost invisible" to gamma/xrays.

Inside an airplane cabine I do not expect any X-rays from outside being visible. All the body parts of the plane will hold them. But I wouldn't rule out that some high-energy gammas from outside create X-rays inside.

[Simone]

thank you both for the explanation. not sure I understand it all, but I'll try :)

(what do you think about the neutron detectors? probably not much of a use-case at sea level outside off ISM applications. it's interesting how alpha beta and gamma are measured in terms of CPM whilst neutrons are measured using n/cm^2/s. this makes a lot more sense to me because it factors in surface area.)

[Bob]

they’re kind of pricey I actually know the guy that’s selling this on eBay. He reconditions instruments so you can rest assured if you buy something from him and there’s an issue he will make it right.
Bob

https://ebay.us/m/6l1BS3

[ullix]

I really have neither experience nor any good knowledge on neutron counters. I believe you need to moderate neutrons to get to "slow" neutrons, which you can then detect via nuclear reactions, which do send out gammas?

[Bob]

Yeah, the only thing I remember about neutrons was when I worked at the nuclear power plant they always had a neutron detector in reactor containment, and it would be occasionally make a beeping sound as it detected free neutrons and during our training, they said if it started beeping very fast you would need exit the containment stuucture.
Bob

[Jeff]

Just a cleaned up graphic from my post, 2025-10-10. I decided to just plot rc-110 data as the epoch log records the values - no averaging or data manipulation.