What would a muon (cosmic ray) peak look like?

[Magnus7]

Terrestial muons are not very frequent.
"Approximately one muon hits every square centimeter of the Earth every minute at sea level"
[US Department of Energy https://www.energy.gov/science/doe-explainsmuons]

My approximation of the projected area for a normal CsI scintillator is 10 cm^2
So around 10 hits per minute for an ordinary CSI scint.
It would be great to see a comparison of measurements inside an airplane at 10000 meters.
From diagrams I think it is like a couple of hundred times more muons at 10000 meters.

[Bob-O-Rama]

With the GS-PRO-V5 and the 2x2" Scionix probe in 4" of lead all around I get this:



Or



The big hump on the right I am interpreting as Muons, you can see a little potassium hump just left if it. The total activity for the whole spectrum is around 0.9 cps, so if you carve off the right hump, that is maybe 10 / minute which sort of makes sense, and given they are not generally stopped, the I am imagining the curve is energy deposited by the trail cutting across portions of the detector. Also callibration is probabaly off so ignore the energy scale, but the K-40 hump is a guidepost.

Now don't ask me why the low energy side is different, according to the file names, they both were taken with the same inner copper + tin inner shield, so "should" be the same, but one of them I see a lot of Pb XRF, so I suspect I had removed the inner shield - as that was a test for trace Am-241 peak I was seeing, and suspected I had contaminated the shield.



This above one was with different shield materials and used a lot of iron, you see a lot of lower energy stuff, but essentially identical amplitude of that 1800-ish KeV peak as the others. I also suspect the lead itself acts as a muon "antenna" in that the muons interacting with the shield crap up the low end with Compton stuff. When I use the Tin - Copper graded shield, a lot of that gets blocked.

[ColoRad-o]

Magnus and Bob,
Thanks for your notes!

My understanding at present is that muons (produced at the top of the atmosphere) are prodigiously more energetic than gamma rays and have a range of energies (GeV up to hundreds of TeV), average about 6 GeV. You can see in background count rates with a Geiger-Muller counter the seasonal variation in the muon flux--in the summer the top of the atmosphere is further from the surface due to thermal expansion, and fewer muons reach the surface. (That they make it at ALL, given their finite lifetime, is a relativistic effect: time dilation or length contraction depending on your preference.)

In NaI they lose energy at a rate of 4.785 MeV per cm. Naturally depending on the angle of incidence on the scintillator there is a range of traversal distances. I wrote a quickish Fortran program (thanks chatGPT!) to do a Monte Carlo calculation. The figure shows the AVERAGE path lengths traversed (I *should* have computed the distribution too) and the inset shows the energy loss of the muon in MeV for this range of path lengths.

This predicts energy losses of from 10-25 MeV in NaI:Tl. I'm not sure how to reconcile all the data shown above.