Japan-Australia Cooperative Observation of North-South Asymmetry in Intensity Variation of High Energy Cosmic Rays(r1012/!V)

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Japan-Australia cooperative observation between Shinshu University and University of Tasmania commenced in December 1991 to measure the north-south (N-S) asymmetry in the intensity variation of high energy cosmic rays (d1012/!V). In the project an emphasis is particularly laid on the measurement of the N-S asymmetric sidereal anisotropy to reveal three-dimensional nature of anisotropies of galactic origin. This is the first bi-hemisphere comparative underground observation, and was motivated on the basis of recent data obtained by multi-directional telescopes at Matsushiro (220 m.w.e. depth underground) of Shinshu University and at Sakashita (80 m.w.e. depth underground) of Nagoya University. The data show that at rigidities ～400 GV to ～1 TV, the observed diurnal amplitudes appear to increase as the detector's latitude of viewing moves southward, suggesting its N-S asymmetric nature of the sidereal time variation. The evidence is, however, limited only in the northern hemisphere, and has no positive confirmation yet in the southern hemisphere. To get further information about the N-S asymmetric anisotropy, Japanese group proposed the bi-hemisphere comparative observation with similar equipments and at similar rigidities. Two cosmic ray groups of Shinshu University and University of Tasmania, Australia agreed with each other, both financially supported, to push a joint project and open a pair underground stations; one at Matsushiro (in operation since 1984), Japan and the other at Liapootah (newly constructed) in Tasmania, Australia. The Liapootah underground station (42°20'S, 146°28'E) is situated in a central part of Tasmania Island, and has such characteristics as; located at almost conjugate position to Matsushiro (36°32' N, 138°01' E), at almost comparable underground depth (approximately 154 m.w.e.) to Matsushiro (220 m.w.e. depth), and with almost similar rigidities of primaries (～500 GV-1 TV). The muon telescope used at Liapootah is quite similar to that at Matsushiro; of plastic scintillators viewed with double photomultipliers and of multi-directional. Nearly equal counting-rates of muons are obtained at two stations ; ～2・ 10t /hr for the vertical telescope, and 5-7・103/hr for the inclined telescope (towards north-, south-, east- and west-direction). In the present paper, we describe the underground site and the muon telescope at Liapootah in some details, with a comparsion of those at Matsushiro. All the electronics system including data sending are controlled by means of the micro-computer system via public telephone lines from both universities at Hobart and Matsumoto.
信州大学理学部の論文
1993-02-26

Japan-Australia Cooperative Observation of North-South Asymmetry in Intensity Variation of High Energy Cosmic Rays(r1012/!V)

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