Date: Mon, 15 Nov 2010 10:01:02

Author: Paul Nord

Subject: Re: Cloud chamber mystery

Post:


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Urs,

Also consider that the muon may not be the primary particle in the =
cosmic ray. The rare horizontal muon is likely to be from a cosmic ray =
shower.

Paul


On Nov 15, 2010, at 7:18 AM, Robert DeSerio wrote:

> Urs,
>=20
> I would bet on low energy muons. We catch low energy muons stopping =
in
> our muon decay experiment (about 1 per minute in a kilogram or two
> of plastic scintillator). The energy deposition
> rate (stopping power) goes up at low energies,
> but the higher mass would keep the tracks straighter than for =
electrons.
>=20
> Regards,
> Bob
>
>=20
> Robert DeSerio
> Department of Physics
> University of Florida =20
> P.O. Box 118440
> Gainesville, FL 32611-8440 =20
>=20
> Phone: 352 392-1690 (office)
> 352 392-0524 (fax)
> Email: deserio@phys.ufl.edu
> Web: http://www.phys.ufl.edu/~deserio
>=20
>=20
> On 8/27/2010 3:54 PM, Urs Lauterburg wrote:
>>=20
>> Dear Tap-lers worldwide,=20
>>=20
>> I was asked by someone from the Technorama Winterthur (Paul Doherty =
knows the place, the Swiss version of the SF-Exploratorium) about some =
mysterious traces in a cloud chamber they acquired approximately one =
year ago . The chamber seems to be performing very well continuously, =
always during the rather long visitor hours. The person would like to =
give some more detailed descriptions of what type of particle traces can =
be observed. Because we always show our cloud chamber every year in =
modern physics to illustrate the sea of radioactivity we live in, I am =
pretty acquainted with the observed phenomena.=20
>>=20
>> In our case we get the short (ca. 5cm long), fat alphas which have =
the tendency to deposit more energy towards the ends of their paths. =
Then much fainter but still clearly visible we see the straggled and =
bent paths of electrons (betas) and the third kind are the =
characteristically long, thin and really straight traces. In our case =
the later always show about the same thickness. We think that these =
traces are caused by muons.=20
>>=20
>> Now, the person who asked me observes basically the same three kinds =
of traces as well. However, additionally he would occasionally see long, =
thin and straight traces which are much fatter, about as thick as the =
traces from the alpha particles but much longer than these. I posted =
three pictures he sent me from such occurrences here:=20
>>=20
>> https://physicslearning2.colorado.edu/image/thumbnails.php?album=3D12=20=

>>=20
>> I have never seen this effect myself and I could not really come up =
with a plausible explanation. Maybe some of you have seen the phenomena =
and have a plausible answer too. I would certainly be curious to know =
about it.=20
>>=20
>> OK, a cloud chamber can always be viewed as a horizontal, nearly 2 =
dimensional detector because the thickness is much less in size than the =
two horizontal sides. So particles which move parallel the 2 dimensional =
plain would leave the best traces. Still we clearly pick up long, =
straight traces that we link to muons. However, muons produced by cosmic =
rays should hardly be able to travel through the approximately 200km =
path to hit the chamber horizontally after travelling the earth's =
atmosphere from the place they are produced by cosmic rays. Is a cloud =
chamber really not at all sensitive to gammas as it's said? OK, photons =
carry no charge but they can be ionizing right? Are the thick long paths =
maybe caused be slowed down muons which deposit more energy to the =
surrounding right before they die?=20
>>=20
>> Anyway, the long fat traces are a mystery to me. Please help to shed =
some light here.=20
>>=20
>> Best=20
>>=20
>> Urs=20
>>=20
>> Urs Lauterburg=20
>> Physics demonstrator=20
>> Physikalisches Institut=20
>> University of Bern=20
>> Switzerland=20


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Urs,Also consider that the muon may not be the primary particle in the cosmic ray. The rare horizontal muon is likely to be from a cosmic ray shower.PaulOn Nov 15, 2010, at 7:18 AM, Robert DeSerio wrote:

Urs,

I would bet on low energy muons. We catch low energy muons stopping
in
our muon decay experiment (about 1 per minute in a kilogram or two
of plastic scintillator). The energy deposition
rate (stopping power) goes up at low energies,
but the higher mass would keep the tracks straighter than for
electrons.

Regards,
Bob


Robert DeSerio
Department of Physics
University of Florida
P.O. Box 118440
Gainesville, FL 32611-8440

Phone: 352 392-1690 (office)
352 392-0524 (fax)
Email: deserio@phys.ufl.edu
Web: http://www.phys.ufl.edu/~deserio



On 8/27/2010 3:54 PM, Urs Lauterburg wrote:
Dear Tap-lers worldwide,


I was asked by someone from the Technorama Winterthur (Paul
Doherty knows the place, the Swiss version of the
SF-Exploratorium) about some mysterious traces in a cloud chamber
they acquired approximately one year ago . The chamber seems to be
performing very well continuously, always during the rather long
visitor hours. The person would like to give some more detailed
descriptions of what type of particle traces can be observed.
Because we always show our cloud chamber every year in modern
physics to illustrate the sea of radioactivity we live in, I am
pretty acquainted with the observed phenomena.


In our case we get the short (ca. 5cm long), fat alphas which have
the tendency to deposit more energy towards the ends of their
paths. Then much fainter but still clearly visible we see the
straggled and bent paths of electrons (betas) and the third kind
are the characteristically long, thin and really straight traces.
In our case the later always show about the same thickness. We
think that these traces are caused by muons.


Now, the person who asked me observes basically the same three
kinds of traces as well. However, additionally he would
occasionally see long, thin and straight traces which are much
fatter, about as thick as the traces from the alpha particles but
much longer than these. I posted three pictures he sent me from
such occurrences here:


https://physicslearning2.colorado.edu/image/thumbnails.php?album=12


I have never seen this effect myself and I could not really come
up with a plausible explanation. Maybe some of you have seen the
phenomena and have a plausible answer too. I would certainly be
curious to know about it.


OK, a cloud chamber can always be viewed as a horizontal, nearly 2
dimensional detector because the thickness is much less in size
than the two horizontal sides. So particles which move parallel
the 2 dimensional plain would leave the best traces. Still we
clearly pick up long, straight traces that we link to muons.
However, muons produced by cosmic rays should hardly be able to
travel through the approximately 200km path to hit the chamber
horizontally after travelling the earth's atmosphere from the
place they are produced by cosmic rays. Is a cloud chamber really
not at all sensitive to gammas as it's said? OK, photons carry no
charge but they can be ionizing right? Are the thick long paths
maybe caused be slowed down muons which deposit more energy to the
surrounding right before they die?


Anyway, the long fat traces are a mystery to me. Please help to
shed some light here.


Best


Urs


Urs Lauterburg

Physics demonstrator

Physikalisches Institut

University of Bern

Switzerland





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