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Raj Bhavan, India

Gupta S.K.,Tata Institute of Fundamental Research | Gupta S.K.,Cosmic Ray Laboratory
Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011 | Year: 2011

Here, we summarize the papers involving studies of cosmic rays with extensive air showers below 1016eV that were presented during the 32nd International Cosmic Ray Conference (August 11-18, 2011) in Beijing. A total of 55 papers including oral and poster were submitted. However, 47 papers were actually presented in the conference and only these are discussed. For better organization, we have divided the 47 papers into four broad areas namely, the composition studies, anisotropy studies, other related phenomena, techniques and measurements. A total of 12 papers reported studies of the composition of cosmic rays that included several new results. Many exciting results on the anisotropy of multi-TeV cosmic rays were reported possibly for the first time through nine papers. There were ten papers on various other phenomena that included hadronic properties, search for anti-protons and γ-rays, moon shadow studues etc. A total of 16 papers discussed advances made in various techniques and measurements. The breadth and depth of topics covered in most of the papers was very impressive and the future of the field appears to be really exciting. Source

Bhaskar A.,Indian Institute of Geomagnetism | Vichare G.,Indian Institute of Geomagnetism | Arunbabu K.P.,Cosmic Ray Laboratory | Raghav A.,University of Mumbai
Astrophysics and Space Science | Year: 2016

The relationship of Forbush decreases (FDs) observed in Moscow neutron monitor with the interplanetary magnetic field (B) and solar wind speed (Vsw) is investigated in detail for the FDs associated with Interplanetary Coronal Mass Ejections (ICMEs) during 2001–2004. The classical two-step FD events are selected, and characteristics of the first step (mainly associated with shock), as well as of complete decrease (main phase) and recovery phase, are studied here. It is observed that the onset of FD occurs generally after zero to a few hours of shock arrival, indicating in the post-shock region that mainly sheath and ICME act as important drivers of FD. A good correlation is observed between the amplitude of B and associated FD magnitude observed in the neutron count rate of the main phase. The duration of the main phase observed in the neutron count rate also shows good correlation with B. This might indicate that stronger interplanetary disturbances have a large dimension of magnetic field structure which causes longer fall time of FD main phase when they transit across the Earth. It is observed that Vsw and neutron count rate time profiles show considerable similarity with each other during complete FD, especially during the recovery phase of FD. Linear relationship is observed between time duration/e-folding time of FD recovery phase and Vsw. These observations indicate that the FDs are influenced by the inhibited diffusion of cosmic rays due to the enhanced convection associated with the interplanetary disturbances. We infer that the inhibited cross-field diffusion of the cosmic rays due to enhanced B is mainly responsible for the main phase of FD whereas the expansion of ICME contributes in the early recovery phase and the gradual variation of Vsw beyond ICME boundaries contributes to the long duration of FD recovery through reduced convection–diffusion. © 2016, Springer Science+Business Media Dordrecht. Source

Gupta S.K.,Tata Institute of Fundamental Research | Gupta S.K.,Cosmic Ray Laboratory
EPJ Web of Conferences | Year: 2013

The GRAPES-3 is a dense extensive air shower array operating with ~400 scintillator detectors and a 560 m2 large tracking muon detector (Eμ > 1 GeV), at Ooty in India. The muon detector has been used to observe acceleration of muons during thunderstorm conditions. The muon multiplicity distribution of the EAS is used to probe the composition of primary cosmic rays below 1 PeV, with an overlap with direct measurements. More recently we have explored the possibility of using the angular distribution of >1 GeV muons to identify the best from among several low- and high-energy hadronic interaction models. We have major expansion plans to enhance the sensitivity of the GRAPES-3 experiment in all of the areas listed above. © Owned by the authors, published by EDP Sciences, 2013. Source

Shukla R.A.,Tata Institute of Fundamental Research | Achanta V.G.,Tata Institute of Fundamental Research | Dugad S.R.,Tata Institute of Fundamental Research | Freeman J.,Fermi National Accelerator Laboratory | And 11 more authors.
Review of Scientific Instruments | Year: 2016

Silicon Photo-Multipliers (SiPMs) are increasingly becoming popular for discrete photon counting applications due to the wealth of advantages they offer over conventional photo-detectors such as photo-multiplier tubes and hybrid photo-diodes. SiPMs are used in variety of applications ranging from high energy physics and nuclear physics experiments to medical diagnostics. The gain of a SiPM is directly proportional to the difference between applied and breakdown voltage of the device. However, the breakdown voltage depends critically on the ambient temperature and has a large temperature co-efficient in the range of 40-60 mV/°C resulting in a typical gain variation of 3%-5%/°C [Dinu et al., in IEEE Nuclear Science Symposium, Medical Imaging Conference and 17th Room Temperature Semiconductor Detector Workshop (IEEE, 2010), p. 215]. We plan to use the SiPM as a replacement for PMT in the cosmic ray experiment (GRAPES-3) at Ooty [Gupta et al., Nucl. Instrum. Methods Phys. Res., Sect. A 540, 311 (2005)]. There the SiPMs will be operated in an outdoor environment subjected to temperature variation of about 15 °C over a day. A gain variation of more than 50% was observed for such large variations in the temperature. To stabilize the gain of the SiPM under such operating conditions, a low-cost, multi-channel programmable power supply (0-90 V) was designed that simultaneously provides the bias voltage to 16 SiPMs. The programmable power supply (PPS) was designed to automatically adjust the operating voltage for each channel with a built-in closed loop temperature feedback mechanism. The PPS provides bias voltage with a precision of 6 mV and measures the load current with a precision of 1 nA. Using this PPS, a gain stability of 0.5% for SiPM (Hamamatsu, S10931-050P) has been demonstrated over a wide temperature range of 15 °C. The design methodology of the PPS system, its validation, and the results of the tests carried out on the SiPM is presented in this article. The proposed design also has the capability of gain stabilization of devices with non-linear thermal response. © 2016 AIP Publishing LLC. Source

Nayak P.K.,Tata Institute of Fundamental Research | Nayak P.K.,Cosmic Ray Laboratory | Gupta S.K.,Tata Institute of Fundamental Research | Gupta S.K.,Cosmic Ray Laboratory | And 6 more authors.
Astroparticle Physics | Year: 2016

A number of groups have reported significant reduction in the flux of low energy (0.1-3 MeV) γ-rays in observations carried out during the past total solar eclipses. However, the contribution of the radon induced radioactivity to the overall γ-ray background can become substantial, especially during episodes of rain. Depending upon the pattern of the rainfall radon induced γ-ray background may vary significantly on time scales of ∼10 min, making the interpretation of the data in terms of an extraterrestrial effect such as a total solar eclipse rather difficult. A reliable estimate of the low energy terrestrial γ-ray (TGR) background is necessary before attempting to measure the possible contribution of any extraterrestrial phenomenon. The knowledge of the precise energies and branching ratios of radon and other radio-isotope induced γ-rays was exploited to accurately reproduce the TGR background, even in the presence of a large and variable contribution from radon induced radioactivity from fresh rain water. The measurement of the TGR background has paved the way for studying the variation of the soft γ-ray flux during the long duration total solar eclipse that occurred on 22 July 2009 in the middle of the Monsoon season in India. © 2015 Elsevier B.V. Allrightsreserved. Source

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