Cosmic Ray Laboratory

MAIN OBJECTIVES
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The origin, acceleration and propagation of UHE (>1014 eV) particles in the galaxy and beyond.
“Knee” in energy spectrum of UHE particles and their nuclear composition.
Production and/or acceleration of highest energy (~1020 eV) particles in cosmic rays.
Astronomy of UHE gamma-rays from neutron stars and other compact object.
Sun the closest astrophysical source and accelerator of energetic particles and its effects on the Earth.

FEW INTERESTING RESULTS
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Recently, we have got some very interesting results from GRAPES-3 experiment on primary cosmic ray composition and solar flares and we are able to establish excellent world-class quality instrumental for studying later mentioned aspects resulting their publication on various primary journals of National and International status. The composition of primary cosmic rays has been measured from 1014 to 1015 eV using the muon multiplicity distribution with very high precision. The sensitivity of the present experiment can be gauged from the fact that changes in atmospheric pressure even of about 1 millibar can be taken into account, since it significantly affects the rate of the detected cosmic ray showers. From these studies, a consistent picture of the hadronic interaction model and the nuclear composition of primary cosmic rays have emerged. We have also been able to map the composition over the `knee' region. A significantly striking outcome was observed that the iron and other heavier nuclei start to become dominant component of primary cosmic rays beyond 1015 eV. In another occasion, the GRAPES experiment provide new information on the Forbush decrease by a massive solar flare (occurred on 28 October 2003), which was able to knocked out the power supply in several northern countries and destroyed many communication satellites. It was only possible by the use of the tracking feature of our muon detectors that provide clear evidence for time evolution, during the onset phase of the Forbush decrease. For the first time, we are able to measure the rigidity dependence of the magnitude of the Forbush decrease with geomagnetic cutoff rigidity, that to, from a single instrument. All these were possible by the use of our in-house developed high quality plastic scintillators (first time in the country) and processing of the nanosecond signals from scintillators by the use of in-house developed ultra-fast Amplifiers, Discriminators and Time to Digital Converters (TDCs). Due to non-availability of indigenous manufacturers of such equipment within the country, imported equipment can be of very high cost about Rs 5000-10000 per channel, whereas in-house products are only within 10 % of the imported cost, without compromising on performance.