Tunnel

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ipelupessy
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Tunnel

Post by ipelupessy » 04 Sep 2019, 04:49

Recently on a trip in Switzerland I passed through the Gotthard railway tunnel. On the way back I realized that it may be interesting to take some data with the detector I had with me (this is a small detector+SiPM+ ADC
package based on a 1x1x3 cm CsI(Tl) crystal, it is made by Maxim(.madmax on ebay)).

This is the raw data (left panel: inside tunnel, right panel outside)
monitor.png
Raw counts where ~ 28 cps in the tunnel ~ 9 cps outside (normally, ie at home this detector gives about 15 cps background count)

The dataset is a bit small for very detailed spectra, so at low resolution:
spectrum.png
The nicest thing is the absence of any pulses at higher energies in the Tunnel. Gotthard Base tunnel is covered by more than 1.5 km of rock for most of its profile. So you expect the cosmic rays background to be almost absent. This is quite clear! My question: what is it the detector shows at energies > 2.6 MeV outside the tunnel?? I would naively attribute those events to muons: they loose about 2 MeV cm**2/g, so for CsI (4.5 g/cm**3) this gives an energy deposition rate of 9 MeV/cm. This seems in agreement with the observed energies (detector ADC overflows at about 5.4MeV)..

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Go-Figure
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Re: Tunnel

Post by Go-Figure » 05 Sep 2019, 07:37

Speaking of low background.
I was at the movie theatre tonight. The movie was really bad, so, when I noticed the scintillator was getting very low counts and dose rate I decided to "give meaning" to the evening and recorded a spectrum until the end.
That's the lowest background I encountered so far, 0.02 µSv/h and an average of about 8 CPS. It took 4200 seconds to record the spectrum below (in LOG and Linear view), barely 35K counts.
High energies are almost completely missing.

Not that this is terribly interesting, but still...

Massimo
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Uci Cinema Sala 6 - 4200 Secs - 040919 - LOG.png
Uci Cinema Sala 6 - 4200 Secs - 040919 - LOG.png (83.06 KiB) Viewed 99 times
Uci Cinema Sala 6 - 4200 Secs -  040919 - LIN.png
Uci Cinema Sala 6 - 4200 Secs - 040919 - LIN.png (79.87 KiB) Viewed 99 times

ipelupessy
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Re: Tunnel

Post by ipelupessy » 05 Sep 2019, 15:48

were there many people at the movie? I am always wondering if there is measurably higher gammas from the K40 in a crowd of people....

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Go-Figure
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Re: Tunnel

Post by Go-Figure » 09 Sep 2019, 05:50

ipelupessy wrote:
05 Sep 2019, 15:48
were there many people at the movie? I am always wondering if there is measurably higher gammas from the K40 in a crowd of people....
The room was about half full, and the movie didn't deserve anything better than that.
I wouldn't know if you can actually measure K40 contribution from people in the room even in such a low background.

It was calculated that sleeping close to someone for 8 hours is the equivalent of a 0.05 µSv dose, which would be 0.00625 µSv/h. Additional counts would be mostly concentrated in the K40 zone but I think the increase would be probably far too small to detect with a good level of confidence, with detectors like this at least.

Massimo

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