David Argento (some aspects of) cosmogenic nuclide production

David Argento Chart of the Nuclides Z N

David Argento Primary Cosmic Rays 90% protons, ~9% helium nuclei, ~1% electrons and heavier nuclei Wide spectrum of energies from 10MeV to MeV! Origins: extra solar! –Most are from supernovae, being accelerated on the shockwave –The ultra-energetic CRs come from extra-galactic sources, possibly accelerated by galactic magnetic fields.

David Argento Heliosphere

David Argento Primary CR Flux

David Argento Interactions Ionization – cosmic rays strike/scatter electrons attached to atoms, creating ion-electron pairs Scattering – strikes nucleus, but glancing, and does not overcome the Coulomb Barrier Transmitted energy often re-emitted as X-rays and gamma rays Spallation – strikes nucleus, overcomes the Coulomb Barrier, causes nuclear fragmentation

David Argento Spallation Nuclear fragmentation Protons & neutrons ejected by (i) knock- on, (ii) ‘evaporation’ from excited nucleus Pions ejected if E > 140 MeV Breakup results in a new atom, with a different number and configuration of nucleons

David Argento The chronology of a spallation event Nucleus is struck by an energetic particle Some or no nucleons ejected immediately from kinetic energy transfer (knock-on) Nucleus briefly remains in an excited state Nucleus ejects more nucleons to reduce energy and find more stable configuration (evaporation)

David Argento

Equivalence of energy and mass Einstein’s equation: E = mc 2 Binding Energy of nuclear force can be calculated from the difference in nuclide mass

David Argento Mass – energy units Standard mass units: kg Particle physics: amu Standard Energy: J Particle Physics: eV & MeV

David Argento For Example: the alpha particle Atomic mass of proton (m p ): MeV neutron (m n ): MeV He-4: amu = 3728 MeV Subtract 2 electrons – mass of alpha: 3727 MeV Find total mass of free nucleons: 2*m n + 2*m p = 3756 MeV Find the difference in mass of the helium nucleus, and the free nucleons: Δ m = MeV Find the binding energy per nucleon: Δm /4 = MeV/nucleon

David Argento Binding energy per nucleon

David Argento Chart of the Nuclides Z N

David Argento Secondary Cosmic Rays Product of spallations Primarily knock-on and evaporation neutrons Multiplicity

David Argento

Cosmogenic Nuclide production in the atmosphere: meteoric Two primary modes of production: –Slow neutron capture: 14 N(n,p) 14 C to produce radiocarbon T 1/2 = 5730 years Atmospheric concentration massively altered by nuclear bomb testing in the 1950s & 1960s –Spallation: 7 Be, 10 Be, 36 Cl and others produced mainly from N, O, and Ar

David Argento Cosmogenic Nuclide production in the lithosphere: in-situ Four primary modes of nuclide production –Spallation: 3 He, 7 Be, 10 Be, 14 C, 21 Ne, 26 Al, 32 Si, 36 Cl, 38 Ar, 41 Ca, 53 Mn, 93 Zr, 129 I, others –Slow neutron capture: 36 Cl, 41 Ca –Fast Muons: All of the above ( 10 Be, 26 Al, 36 Cl have been experimentally calibrated) –Slow Muon capture: All of the above ( 10 Be, 26 Al, 36 Cl have been experimentally calibrated)

David Argento Cross sections Nuclear radius ~ cm (1 fm) Actually … R ~ a 0 A 1/3 where a 0 ~ 1.35 fm Hence … ‘geometric’ cross-section of the nucleus: ~ 5.7 x A 2/3 cm 2 ~ A 2/3 b 1 barn = cm 2 14 N (neutron absorption x-section) … mainly 14 N(n,p) 14 C

David Argento What does all this get us? Primary Cosmic Rays Interact with upper atmosphere: –Ionization, scattering, and spallation Secondary cosmic Rays formed, and cascade through atmosphere Small portion of original flux makes it to the surface of the earth In-Situ spallation gives us

David Argento Production! 10 Be: ~ 5 atoms/g quartz/year 26 Al: ~ 30 atoms/g quartz/year