(some aspects of) cosmogenic nuclide production

1. (some aspects of) cosmogenic nuclide production

2. Z N Chart of the Nuclides http://atom.kaeri.re.kr/

3. Primary Cosmic Rays • 90% protons, ~9% helium nuclei, ~1% electrons and heavier nuclei • Wide spectrum of energies from 10MeV to 1015MeV! • 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.

4. Heliosphere

5. Primary CR Flux

6. 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

7. 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

8. 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)

10. Equivalence of energy and mass • Einstein’s equation: E = mc2 • Binding Energy of nuclear force can be calculated from the difference in nuclide mass

11. Mass – energy units • Standard mass units: kg • Particle physics: amu • Standard Energy: J • Particle Physics: eV & MeV

12. For Example: the alpha particle • Atomic mass of proton (mp): 938.3 MeV • neutron (mn): 939.6 MeV • He-4: 4.0026032 amu = 3728 MeV • Subtract 2 electrons – mass of alpha: 3727 MeV • Find total mass of free nucleons: 2*mn + 2*mp = 3756 MeV • Find the difference in mass of the helium nucleus, and the free nucleons: Δm = 28.03 MeV • Find the binding energy per nucleon: Δm /4 = 7.075 MeV/nucleon

13. Binding energy per nucleon

14. Z N Chart of the Nuclides http://atom.kaeri.re.kr/

15. Secondary Cosmic Rays • Product of spallations • Primarily knock-on and evaporation neutrons • Multiplicity

17. Cosmogenic Nuclide production in the atmosphere: meteoric Two primary modes of production: • Slow neutron capture: 14N(n,p)14C to produce radiocarbon • T1/2 = 5730 years • Atmospheric concentration massively altered by nuclear bomb testing in the 1950s & 1960s • Spallation: 7Be, 10Be, 36Cl and others produced mainly from N, O, and Ar

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

19. Cross sections • Nuclear radius ~ 10-12 cm (1 fm) • Actually … • R ~ a0 A1/3 where a0 ~ 1.35 fm • Hence … ‘geometric’ cross-section of the nucleus: ~ 5.7 x 10-26 A2/3 cm2 ~ 0.057 A2/3 b 1 barn = 10-24 cm2 14N (neutron absorption x-section) … mainly 14N(n,p)14C

20. 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

21. Production! • 10Be: ~5 atoms/g quartz/year • 26Al: ~30 atoms/g quartz/year