Cosmogenic radioisotopes in the Dhajala chondrite: implications to variations of cosmic ray fluxes in the interplanetary space

Abstract

Activities of a suite of radioisotopes ranging in half-life from 5.6 days ( 52Mn) to 3.7 m.y. ( 53Mn) have been measured in the Dhajala chondrite. The results show that all the radioactivities are close to the expected levels except 54Mn and 22Na. Their activities are higher than those based on the interplanetary fluxes at 1 A.U. near the ecliptic, expected immediately before the fall of Dhajala, corresponding to the time of solar minimum. Furthermore, activity ratios of 54Mn/ 53Mn and 22Na/ 26Al are higher by 30–50% than expected. The departure from the expected values is discussed in terms of spatial variations of cosmic rays based on the computed orbital parameters of the meteoroid. If the galactic cosmic ray fluxes in the equatorial region (±15°) are assumed to be the same as in the ecliptic plane then these results suggest higher fluxes by 33 ± 7% at heliographic latitudes 15–40°S, during solar minimum.