Astroparticle Physics

136 6 Primary Cosmic Rayswould probably require a coincidence of signals from severalindependent detectors.6.6 ProblemsProblems for Sect. 6.11. What is the reason that primary cosmic-ray nuclei likecarbon, oxygen, and neon are more abundant than theirneighbours in the periodic table of elements (nitrogen,fluorine, sodium)?2. In Sect. 6.1 it is stated that primary cosmic rays consistof protons, α particles, and heavy nuclei. Only 1%of the primary particles are electrons. Does this meanthat the planet Earth will be electrically charged in thecourse of time because of the continuous bombardmentby predominantly positively charged primary cosmicrays? What kind of positive excess charge could havebeen accumulated during the period of existence of ourplanet if this were true?3. The chemical abundance of the sub-iron elements in primarycosmic rays amounts to about 10% of the iron flux.a) Estimate the fragmentation cross section for collisionsof primary iron nuclei with interstellar/intergalacticnuclei.b) What is the chance that a primary iron nucleus willsurvive to sea level?Problems for Sect. 6.21. The Sun converts protons into helium according to thereaction4p → 4 He + 2e + + 2ν e .The solar constant describing the power of the Sun atEarth is P ≈ 1400 W/m 2 . The energy gain per reactioncorresponds to the binding energy of helium (E B ( 4 He) =28.3 MeV). How many solar neutrinos arrive at Earth?2. If solar electron neutrinos oscillate into muon or tau neutrinosthey could in principle be detected via the reactionsν µ + e − → µ − + ν e , ν τ + e − → τ − + ν e .Work out the threshold energy for these reactions to occur.