Astroparticle Physics

16 Glossary 323Transmutation of a neutrino flavour into another by vacuum or matteroscillations.Neutrino flavour oscillation in vacuum which can occur if neutrinoshave mass and if the weak eigenstates are superpositions ofdifferent mass eigenstates.neutrino oscillationsneutrino vacuum oscillationn; a baryon with electric charge zero. A neutron is a fermion with neutronan internal structure consisting of two down quarks and one upquark, which are bound together by gluons. Neutrons constitutethe neutral component of atomic nuclei. Different isotopes of thesame chemical element differ from each other only by a differentnumber of neutrons in the nucleus.Neutron decay process into a proton, an electron, and an electronantineutrino.Nuclear decay by emission of a neutron.Star of extremely high density consisting predominantly of neutrons.Neutron stars are remnants of supernova explosions wherethe gravitational pressure in the remnant star is so large that theelectrons and protons are merged to neutrons and neutrinos (e − +p → n + ν e ). Neutron stars have a diameter of typically 20 km.If the gravitational pressure surmounts the degeneracy pressure ofneutrons, the neutron star will collapse to a black hole.For an external observer the black hole has only three properties:mass, electric charge, and angular momentum. If two black holesagree in these properties they are indistinguishable.Star with a sudden increase in luminosity (≈ 10 6 fold). The starexplosion is not as violent as in supernova explosions. A nova canalso occur several times on the same star.The energy, which is required to desintegrate an atomic nucleusinto its constituents; ≈ 8MeV/nucleon.Fission of a nucleus in two fragments of approximately equal size.In most cases fission leads to asymmetric fragments. It can occurspontaneously or be induced by nuclear reactions.Fusion of light elements to heavier elements. In a fusion reactorprotons are combined to produce helium via deuterium. Our Sun isa fusion reactor.neutron decayneutron evaporationneutron star‘no hair’ theoremnovanuclear binding energynuclear fissionnuclear fusion