Production of Na²²and H³in a thick silicate target and its application to meteorites

Abstract

A number of glass plates chosen from a stack of thick target having the gross chemical composition of stone meteorites, and exposed to 3 Gev protons, were analyzed for Na22 and H3. Na22 was measured by the non‐destructive γ‐γ coincidence counting, and H3 was measured in gas phase after chemical processing. Complete distributions of these nuclides in the thick target assembly were mapped. Effective cross sections for H3 and Na22 production were calculated on the oxygen and the silicon target basis, respectively. The cross sections show significant buildup factors along the depth followed by an exponential decrease. The distribution of H3, in both the radical as well as the lateral directions, is comparatively steeper. The results are compared with similar published studies on iron targets. The data are used to calculate H3 and Na22 production rates in spherical chondrites exposed to cosmic radiation, assuming that only primary nucleons of energy greater that 1.2 Gev are effective in the nuclide production, and that these can be represented by an average energy of 3 Gev. The calculated production rates of H3 (450–670 atom min−1 kg−1) and Na22 (80–110 atom min−1 kg−1) are comparable to the observed range of concentrations of these nuclides in stone meteorites.

Interaction of solar and galactic cosmic-ray particles with the Moon

“…In previous models for the production of nuclides by galactic cosmic rays, there have been two main approaches. One is to use thicktarget bombardments [Honda, 1962;Shedlow sky and Rayudu, 1964;Van Ginneken and Turkevich, 1970] to simulate the natural conditions well enough to calculate nuclide production either directly or through the use of nuclear systematics and multiple-group diffusion theory [Kohman and Bender, 1967;Trivedi and Goel, 1969]. These approaches have the advantage of a fairly close relation between the laboratory experiment and the natural event.…”

Cosmogenic radionuclides in the Allende and Murchison carbonaceous chondrites

“…One of the problems besetting the interpretation of cosmogenic nuclide data is the lack of knowledge of how nuclide productions within a meteorite vary with depth. Cyclotron bombardments have resulted in data [Honda, 1962;Shedlovsky and Rayudu, 1964;Rayudu, 1968;Trivedi and Goel, 1969] and calculations [Arnold eta/., 1961; Kohman and Bender, 1967] describing the depth dependences of several nuclides produced by monoenergetic proton beams in (especially) iron targets. It is not entirely satisfactory to apply these data to such a complex target system as a stone meteorite bombarded by a cosmic-ray flux that js itself definitely not monoenergetic and that generates within the meteorite a considerable low-energy secondary-particle flux, of which neutrons comprise a large fraction.…”

Nuclide production rates in stone meteorites and lunar samples by galactic cosmic radiation

“…The irradiation geometry can be assumed to be that of a semi-infinite slab. However, the assumption that the primary alphas and the heavy nuclei can be replaced by equivalent number of protons [Arnold et al, 1961;Goel, 1962;Ko.hman and Bender, 1969;Trivedi and Goel, 1969] is not valid because of the absence of backside irradiation. Reedy and Arnold [1972] have suggested that a primary alpha particle may be replaced by 2.8 nucleons.…”