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Influence of solar activity variations on the interplanetary space

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Cosmogenic radionuclides in meteorites 2.1.2 GCR Flux variations GCR measurements are available from the beginning of the 1960s; hereafter I consider only primary protons flux, because their cross section for the production of cosmogenic radionuclides is greater than α particles’ one (Michel and Neumann, 1998) and they constitute almost 90% of the total flux. This and other assumptions will be discussed in chapter 2.2.5. GCR flux J G (particles s -1 sr -1 m -2 MeV -1 ) at 1 AU is referred to the top of terrestrial atmosphere and can be measured by balloons (e.g. Boezio et al., 1999, Seo et al., 1991), satellites or spacecrafts like the Space Shuttle (Alcaraz et al., 2000), Voyager 1(Webber e Yushak, 1983) and 2 or Pioneer 10 (McDonald et al.,1992). Figure 2.3 shows different J G spectra measured in 1965 (Ormes and Webber 1968), 1968 (Hsieh et al., 1971), 1980 (Kroeger, 1986), 1989 (Webber et al., 1991) in different phases of the solar cycle. Note that J G has a maximum for energies of the order of 1 GeV and presents a modulation with the solar cycle, being higher during solar minima and lower during maxima. Above 20 GeV the flux is constant without any modulation. The same figure shows also some comparison of the fitted J G spectra (using Eq. 2.1, see chapter 2.2.2) with the experimental values, and giving values of the modulation parameter M = 390, 600, 820, 1080 MeV, respectively. We can observe a very good agreement between measured and calculated J G (see chapter 2.2.2). 0.001 0.01 0.1 1 10 100 10 100 1000 10000 100000 Energy (MeV) J G ( p r o t o n s m - 2 s - 1 s r - 1 M e V - 1 ) 1965 data 1968 data 1980 data 1989 data MeV 820 MeV 1080 MeV 0 MeV LIS M 390 MeV 600 Figure 2.3. Differential cosmic-ray spectra obtained from Eq. 2.1 for different values of the solar modulation parameter M = 390, 600, 820, 1080 MeV corresponding to the measurements performed with balloons or spacecrafts during 1965, 1968, 1980 and 1989 respectively 13

Anteprima della Tesi di Daniele Cane

Anteprima della tesi: Influence of solar activity variations on the interplanetary space, Pagina 11

Tesi di Dottorato

Dipartimento: DIPARTIMENTO DI FISICA GENERALE

Autore: Daniele Cane Contatta »

Composta da 137 pagine.

 

Questa tesi ha raggiunto 346 click dal 20/03/2004.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.