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When an incident photon from the scintillator hits the scintillator needs to be large enough so that the
the photocathode, an electron is emitted via the muons can be stopped, otherwise, most of muons
photoelectric effect. Because of the electric will have enough energy to just pass through the
potential difference, the electron is accelerated scintillator. This has to be considered for anyone
towards the first dynode. This causes secondary trying to reproduce this technique.
electrons to be produced, which are accelerated
towards the next dynode, where more electrons With this methodology, the detector (scintilla-
are emitted and accelerated again: an electron tor+PMT) will generate 2 separate signals: The first
cascade is created. This cascade is collected at signal will be produced when the muon trapped in
the anode to give a current which can be the detector loses energy, while the second one
amplified and analyzed. The overall amplification will be produced when the residual electron
factor of a PMT depends on the number of interacts with the scintillator, indicating the decay
dynodes and of the potential difference applied. of the muon. The time interval between the two
Since photomultipliers are extremely signals, represents the time between the arrival of
photosensitive, one must be careful not to expose the muon, and its decay, that is, the decay time.
them to ambient light when operating. Otherwise Measuring this time for a large enough number of
one would be getting signals corresponding to muons, allowed to obtain a distribution of decay
ambient light and not to the radiation on the times. After that, a curve fit was carried out for the
scintillator (Melissinos, 2003). distribution based on Equation (6), where the mean
lifetime was the parameter to be obtained
Given that the muon is a charged particle, it can based on the experimental data.
be detected using a scintillator. Even more, given
that during its decay, an electron is produced, we A1. Experimental setup
can also determine when a muon has decayed
inside a scintillator, as the electron produced will A 30cm large cylindrical plastic scintillator was used
also generate a scintillation some time later. for this part of the experiment. Notice that despite
Cosmic muons are relativistic particles, and being this large, there were still a portion of muons
previous works determined their speed to be close with enough energy to not be stopped inside the
to that of the speed of light. Thus, if one hopes to material, however, we achieved a large enough
measure this speed, detectors with a fast response count of muons with this scintillator. It is also worth
time like scintillators, could be a good choice. In noticing that, if we assume that the radiation of
the experiment described in this report, scintillation muons arriving to the detector is isotropic, then the
detection is used as a basis to measure the mean muons arriving vertically will be the ones with more
lifetime , and velocity , of muons produced in probability to be stopped, since they will have to
the upper atmosphere. get through more material that the ones that pass
obliquely.
II. Methodology
A photomultiplier connected to a H.V. power
A. Measurement of the muon’s mean lifetime supply was coupled in one of the circular faces of
the scintillator. It can be seen in fig. (1) that the
When muons arrive from the atmosphere at speeds scintillator was covered with reflecting foil in order
close to the speed of light, they are subject to to prevent most of the photons from escaping
relativistic effects like time dilation. Therefore, if one through the face where the PMT was placed. The
tries to measure the muons lifetime while in motion, output signal was visualized using an oscilloscope
more than one detector would be needed, in order and then analyzed using NIM logic electronics (see
to keep track of its motion. Appendix A).
To avoid these complications, we aimed at The entire circuit layout employed to measure the
capturing low energy incoming muons inside the time difference between the arrival of the muon
scintillator. Once they have been stopped, and its decay is shown in fig. (2). The signal coming
relativistic effects are avoided. After a certain time, from the PMT is first introduced to a Fan-in/Fan- out
the trapped muon will decay, emitting an electron module that allowed us to get multiple identical
in the process. In order for this approach to work, signals to be used with different purposes. One the
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Tlahuizcalli ISSN: 2448-7260 Año 10 Núm. 30 septiembre-diciembre 2024
