Cosmic radiation

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pietkuip
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Cosmic radiation

Post by pietkuip » 07 Jun 2015, 03:33

I would sometimes see or hear giant pulses, way off the scale. I had kind of assumed that these were artifacts from the PMT or something. But now I know: they are atmospheric muons, with typical energies of 4 GeV. I looked at them with the coincidence setup that Tom Andersson described yesterday. I just reduced the multiplier voltages with a few hundreds of volt. Even this produced coincidences at the top of the scale.

I compared two orientations: with the plastic scintillator above the NaI detector and with both detectors next to each other. The vertical setup gives the same number of coincidences in two hours as the horizontal one in a 24-hour period. So that is a clear result.

I have also looked at the signal from one detector. Sometimes it happens that the muon is stopped inside. This results in two peaks: one from the muon, the other one from the electron or positron produced in the decay, separated by about the muon lifetime of 2.2 microseconds. In the picture, the separation is about 0.8 microseconds. I used the plastic scintillator for that because it is faster. The signal cable is terminated with 50 Ohm at the BNC T of the scope input.

I watched this for a while, and I saw three of these doublets. Getting statistics is a bit boring, so I think I will have a class do this: each student needs to make at least one observation, and then we determine the median value, which should be close to the halflife.
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Muon.jpeg
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Pieter Kuiper, Växjö (Sweden)
Course lab: 3 mCi neutron source; five 3" NaI(Tl) detectors, CdZnTe detector (Amptek); lead bricks, two GDM 20

pietkuip
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Re: Cosmic radiation

Post by pietkuip » 11 Jun 2015, 07:56

I noticed that the oscilloscope can act as a webserver, so I put it online. Have a look: http://ife-labb-89.lnu.se/getImage.html.

There the scope is set to trigger when there is a second pulse within 9 microseconds of an earlier one. It is just a 2" scintillator, so muon decays are not more than a few per hour. Also there is sometimes what looks like electrical interference.
Pieter Kuiper, Växjö (Sweden)
Course lab: 3 mCi neutron source; five 3" NaI(Tl) detectors, CdZnTe detector (Amptek); lead bricks, two GDM 20

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Steven Sesselmann
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Re: Cosmic radiation

Post by Steven Sesselmann » 11 Jun 2015, 10:22

That's very cool...

I have been trying to repeat this with my 3" NaI(Tl) detector, but have not been lucky enough to see a doublet yet.

Must see if my scope can be set to trigger for doublets only. What scale are you looking at, is it 20 mV divisions on the Y axis and 1 µs on the X axis?

pietkuip
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Re: Cosmic radiation

Post by pietkuip » 11 Jun 2015, 16:42

Yes, 1 microsecond per division on the time axis, that catches the time scale of muon decay. I have seen doublets with an NaI scintillator, but those pulses are wider, so those are more likely to overlap.

The vertical axis depends of course on PMT voltage etcetera. The energies are about a thousand times larger than those of gammas due to radioactivity. Single events should occur at a rate of 10 per minute or something of that order. Doublets are much rarer.

A student will be using the plastic scintillator for other stuff today. I will try to connect an NaI scintillator.

PS: Right now triggering on the second pulse is not working, because of noise from the high-voltage supply (not a GammaSpectacular).
Pieter Kuiper, Växjö (Sweden)
Course lab: 3 mCi neutron source; five 3" NaI(Tl) detectors, CdZnTe detector (Amptek); lead bricks, two GDM 20

pietkuip
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Re: Cosmic radiation

Post by pietkuip » 13 Jun 2015, 00:47

I connected the NaI detector to high voltage from the GammaSpectacular Pro and now it works :)
Here is an image. First a pulse when the muon moves through the detector, four microseconds later the decay:
NaI_muon2.png
NaI_muon2.png (33.48 KiB) Viewed 5278 times
The NaI scintillator is clearly too slow to detect decays that occur within half a microsecond or so.
Pieter Kuiper, Växjö (Sweden)
Course lab: 3 mCi neutron source; five 3" NaI(Tl) detectors, CdZnTe detector (Amptek); lead bricks, two GDM 20

pietkuip
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Re: Cosmic radiation

Post by pietkuip » 14 Jun 2015, 08:12

muonerna.png
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Now both the NaI and the plastic scintillator are connected to the oscilloscope on http://ife-labb-89.lnu.se/getImage.html.
The NaI is on top. The image above shows first a muon passing through the NaI detector, then almost immediately entering the plastic detector. It came to a stop and decayed 1.2 microsecond later inside the plastic. Some gamma radiation from that decay is then detected by the NaI scintillator.

I am going to make an online course lab out of this.
Pieter Kuiper, Växjö (Sweden)
Course lab: 3 mCi neutron source; five 3" NaI(Tl) detectors, CdZnTe detector (Amptek); lead bricks, two GDM 20

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Steven Sesselmann
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Re: Cosmic radiation

Post by Steven Sesselmann » 14 Jun 2015, 08:54

Thanks for posting the NaI comparison. I tried to capture the same on my 3" here, but so far no luck. My OWON oscilloscope does not have the function to capture a second pulse automatically, I have to capture one by one and reset the scope each time a big pulse occurs.

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Steven Sesselmann
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Re: Cosmic radiation

Post by Steven Sesselmann » 15 Jun 2015, 22:55

Pieter,

Well it took me a while, but when I get my teeth into a problem I don't easily give up ;)

I wonder if your lead bricks are increasing the odds of catching muons, because I had to wait a heck of a long time to catch one.

Anyway there it is, an Australian muon, every bit as pretty as the Swedish ones.
muon.jpg
Muon
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lodovico
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Re: Cosmic radiation

Post by lodovico » 18 Jun 2015, 00:06

Very interesting.
I have some experience in catching cosmic rays with classic set up of geiger tubes working in coincidence (see the attached report ) but I have never tried with scintillators. The stopping power of geiger tubes is neraly 100% for muons I do not know how it could be for scintillator crystals.
Lodovico
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pietkuip
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Re: Cosmic radiation

Post by pietkuip » 18 Jun 2015, 00:41

Good work! That would be a nice way to use our Geiger tubes. Thanks for the detailed description.

Just to avoid possible confusion, I would say that detection efficiency is close to 100 %, also for scintillators. The stopping power, however, is small as most muons pass right through anything, which is also clear from your measurements. I believe that less than 1 % of the muons gets stopped inside our plastic scintillator.
Pieter Kuiper, Växjö (Sweden)
Course lab: 3 mCi neutron source; five 3" NaI(Tl) detectors, CdZnTe detector (Amptek); lead bricks, two GDM 20

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