The abundance of radioactive nuclei under different physical environments around the solar system

• Published in: Advances in space research Vol. 27; no. 4; pp. 743 - 748
• Main Authors: Streitmatter, R.E., Stephens, S.A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.2001
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/S0273-1177(01)00115-6

Differential equations describing the propagation of cosmic-ray nuclei from 7Be to 56Fe in a homogeneous interstellar medium (ISM) were solved simultaneously in the time domain, so as to determine the escape path length using the observed B/C ratio as a constraint. The spectra of nuclei thus obtained were then used to obtain the 10Be/ 9Be ratio as a function of energy. From a comparison with the data, we determined the mean density of n H in the confinement volume of cosmic rays to be 0.2 atom/cc and the corresponding escape life time of 30 My. The effect of the solar system being in a “local bubble” of low density was examined. It was found that if cosmic-ray nuclei have spent considerable amount of time in the local bubble, the mean value of n H in the Galaxy needs to be raised to account for the observation. The ratio of 26Al/ 27Al and 36Cl/Cl are more sensitive to the propagation in the local hole and our study showed that in order that the data are consistent with each other, the diffusion co-efficient in the local bubble should be > 10 29cm 2/s. This clearly demonstrates the need to include in the diffusion models the variation of diffusion co-efficient with gas density. We then examined the effect of the local hole on the abundance ratio of 14C/ 13C and bring out the need to measure 14C to further constrain the diffusion co-efficient in the local hole.