1995 Fiscal Year Final Research Report Summary
Total flux of Cosmic Rays around knee region using Tibet Air Shower Array
| Project/Area Number |
06640374
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
素粒子・核・宇宙線
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| Research Institution | Utsunomiya University |
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Principal Investigator |
HOTTA Naoki Utsunomiya Univ., Faculty of Education, Assistant, 教育学部, 助手 (60157039)
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| Co-Investigator(Kenkyū-buntansha) |
OHTA Itaru Utsunomiya Univ., Faculty of Education, Professor, 教育学部, 教授 (30008023)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Cosmic ray / Flux of primary cosmic-rays / Air shower / Knee region |
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| Research Abstract |
We analyzed the experimental data obtained with Tibet array and obtained the energy spectrum of the primary cosmic rays in the energy range between 3*10^<14>and2*10^<16>eV.
The overall primary energy spectrum obtained does not resemble a single power law and shows a gradual steepening of the slope at energies around E_b=10^<15.25>eV.The spectrum can be expressed as
J(E_o)=1.5*10^<-20>(E_o/10^<14.75>eV)^<-2.60<plus-minus>0.04>(m^<-2>sec^<-1>sr^<-1>eV^<-1>)atE_o<10^<14.75>eVand=1.2*10^<-23>(E_o/10^<15.85>eV)^<-3.00<plus-minus>0.05>(m^<-2>sec^<-1>sr^<-1>eV^<-1>)atE_o>10^<15.85>eV,while this changes gradually between 10^<14.75>and 10^<15.85>eV and takes the value J(E_o)=6.7*10^<-22>(m^<-2>sec^<-1>sr^<-1>eV^<-1>)atE_o=10^<15.25>eV
Our spectrum to be smoothly connected to the direct measurements by Grigorov et al.(1971) and JACEE Collaboration (Burnett et al.1993) at the lower energy region. The flux values around 10^<15> eV are higher than the Akeno data (Nagano et al.1984), while those at energies around 10^<16> are about 10 % lower than theirs. The bending of the spectrum is not as abrupt as the Akeno and its energy (E_b) is also lower than theirs. Their lower flux at energies around 10^<15> could be attributed to very low detection effciencies of air showers at the Akeno altitude.
Our spectrum obtained around the knee is almost independent of the primary mass composition and will be rated as most standard.
The gradual steepening of the spectrum at lower energy may be in favor of shock acceleration at SNRs which suggests a considerable change in the relative abundance of the various cosmic ray nuclei as the energy increases, but its confirmation requires more direct information about the primary mass composition at energies around the knee.
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