Low-energy galactic cosmic ray carbon, nitrogen, and oxygen isotopic composition

Journal Article · Sun Mar 01 04:00:00 EST 1981 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/158747· OSTI ID:6197873

Guzik, T G

The elemental and isotopic composition of galactic cosmic ray carbon, nitrogen, and oxygen has been measured in the energy interval 45--211 MeV per nucleon, during 1975--1978, using the University of Chicago cosmic ray instruments on the IMP 7 and IMP 8 spacecraft in interplanetary space. Calibration of an identical instrument with C, N, and O beams at the Bevatron accelerator of the Lawrence Berkeley Laboratory has shown that the instrument's resolution for C, N, O isotopes is 0.4--0.7 amu. The IMP 7 measurements give elemental ratios N/O = 0.25 +- 0.02 and C/O = 1.06 +- 0.03, which agree with previous results from IMP 8. The isotopic ratios are /sup 13/C/(/sup 13/C+/sup 12/C) = 0.04--0.10, /sup 15/N/(/sup 15/N+/sup 14/N) = 0.47 +- 0.06, and /sup 18/O/(/sup 18/O+/sup 17/O+/sup 16/O)< or =0.03. Propagation calculations, using a steady state model of interstellar cosmic ray transport and including the effects of solar modulation, were used to determine the source abundances implied by the C, N, O measurements. The measured /sup 13/C/C and /sup 18/O/O ratios are compatible with the absence of /sup 13/C and /sup 18/O at the source, and the source C/O ratio is approx.1.5 times the solar system value. The most critical factors remaining in the determination of the nitrogen source abundance are the proton-induced partial cross sections for the production of /sup 14/N and /sup 15/N from /sup 16/O spallation. For cross sections based upon semiempirical formulae the source abundance of N inferred from the /sup 15/N/N measurement leads to a N/O ratio at Earth which is below the experimental value. On the other hand, for N cross sections based upon measurements of the /sup 10/B and /sup 11/B cross sections in /sup 12/C spallation, a single value of the source N/O ratio predicts both elemental and isotopic ratios in agreement with this experiment. Thus, at the cosmic ray source /sup 14/N/O = 0.07 +- 0.03 with no /sup 15/N required.

• Research Organization: Enrico Fermi Institute, University of Chicago
• OSTI ID: 6197873
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 244:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics &amp; Cosmology-- Cosmic Radiation
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ACCELERATORS
BEVATRON
CALIBRATION
CARBON
CHEMICAL COMPOSITION
CNO CYCLE
COSMIC NUCLEI
COSMIC RADIATION
COSMIC RAY DETECTION
COSMIC RAY PROPAGATION
CROSS SECTIONS
CYCLIC ACCELERATORS
DETECTION
ELEMENTS
GALAXIES
INTERPLANETARY SPACE
IONIZING RADIATIONS
ISOTOPE RATIO
ISOTOPES
MILKY WAY
NITROGEN
NONMETALS
NUCLEI
OXYGEN
RADIATION DETECTION
RADIATIONS
SOLAR SYSTEM
SPACE
STAR BURNING
SYNCHROTRONS
TELESCOPE COUNTERS