Page 13 - Tlahuizcalli CB-30_Neat

In order to convert the registered counts into time weeks. After that, the operating voltage of the PMT
values, we needed to calibrate it with pulses
separated by a previously known time difference.
A pulse generator was used to produce 2 pulses
separated by a known time interval, that could be
set manually. These pulses were then fed to the TAC
as START and STOP inputs. The amplitudes for
different time separations were registered using the
MCA. Fig. (6) shows the distribution on the
histogram, of the different time intervals measured.
The difference between two consecutive peaks is
1μs.
Figure 6. Pulses separation registered by the MCA.
This data was then used to adjust a curve for the
variation of the bin or channel where a count was
registered, as a function of the time separation of
the pulses. The calibration points, along with the
adjusted linear fit is shown in fig. (7).
Figure 7. Time Calibration of the MCA.
A3. Operation
Once both, the PMT and TAC were correctly
calibrated, the data acquisition phase begun. The
experimental setup was put into operation for 2
Año 10 Núm. 30 septiembre-diciembre 2024
was lowered to 1.95kV to reduce the noise, and it
was put into operation for another week.
The MCA collected the data in the form of a
histogram, indicating the amount of muons or
events per channel or bin. The bins of the histogram
represented the amplitudes of the TAC signal,
which are related to the decay time of the
detected muons through the calibration curve in
fig. (7). The collected data was exported for further
analysis through the USX spectroscopy software, an
accompanying software through which the UCS30
MCA is operated.
B. Measurement of the speed of cosmic ray muons
The second part of the experiment consisted in
measuring the speed of the incoming muons that
are generated in the upper atmosphere from
cosmic rays.
For this purpose, two scintillators were placed on
top of each other, separated by a variable
distance as shown in fig. (8); the upper detector
was fixed, while the lower one could be moved
vertically. This allowed for incoming muons from the
atmosphere to pass first through the upper
scintillator, and then through the second one. This
way, the time difference between the detection of
the muon in each scintillator, is the time the particle
requires to travel the known distance that
separates the detectors. However, the maximum
separation at which we could set the detectors,
was limited by the height of the laboratory where
the experiment was being performed. The roof and
the floor of the laboratory were separated by 3m.
For a particle moving at relativistic speeds like the
muon, this distance will be traveled in a very short
period of time, and the measuring of time intervals
was limited by the resolution of the equipment
(resolution of the TAC).
To avoid these problems, an 8 delay was
applied to the output signal of the lower scintillator
(after being converted into a logic pulse through a
discriminator). Then the time difference between
the upper and lower pulses was large enough to be
measured by the TAC. Nevertheless,
the measured time didn’t correspond to the time
for the muon to go from one detector to the other
anymore, as one of the signals had been delayed.
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