dc.description.abstract |
Recently, equatorial secondary cosmic ray observatory has been established at Equatorial Geophysical Research Laboratory (EGRL),
Tirunelveli, (Geographic Coordinates: 8.71 N, 77.76 E), to study secondary cosmic rays (SCR) produced due to the interaction of primary
cosmic rays with the Earth’s atmosphere. EGRL is a regional center of Indian Institute of Geomagnetism (IIG), located near the equator
in the Southern part of India. Two NaI(Tl) scintillation detectors are installed inside the temperature controlled environment. One detector
is cylindrical in shape of size 7.62 cm 7.62 cm and another one is rectangular cuboid of 10.16 cm 10.16 cm 40.64 cm size. Besides
NaI(Tl) detectors, various other research facilities such as the Geomagnetic observatory, Medium Frequency Radar System, Digital Ionosonde,
All-sky airglow imager, Atmospheric electricity laboratory to measure the near-Earth atmospheric electric fields are also available
at EGRL. With the accessibility of multi- instrument facilities, the objective is set to understand the relationship between SCR and various
atmospheric and ionospheric processes, during space weather and terrestrial events.
For gamma-ray spectroscopy, it is important to test the performance of the NaI(Tl) scintillation detectors and to calibrate the gammaray
spectrum in terms of energy. The present article describes the details of the experimental setup installed near the equator to study
cosmic rays, along with the performance testing and calibration of the detectors under various conditions. A systematic shift in the gain
is observed with varying temperature of the detector system. It is found that the detector’s response to the variations in the temperature is
not just linear or non-linear type, but it depends on the history of the variation, indicating temperature hysteresis effects on NaI detector
and PMT system. This signifies the importance of isothermal environment while studying SCR flux using NaI(Tl) detectors, especially for
the experiments conducted during daytime such as solar eclipses etc |
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