126Xe from 126Te as a Test of the Standard Solar Model

Details 126Xe from 126Te as a Test of the Standard Solar Model 126Xe from 126Te as a Test of the Standard Solar Model

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27q.202b&link_type=abstract

Meteoritics, vol. 27, no. 3, volume 27, page 202

Physics

Scientific paper

The standard solar model predicts that the sun's photon luminosity increases monotonically, and that the ^8B neutrino flux increases exponentially with a doubling time of ~0.85 Ga. A test of this prediction has been proposed by Haxton (1990). He argues that tellurium ores will accumulate excess ^126Xe from the reactions: nu + ^126Te --> ^126I + beta^- (2.15 MeV Threshold) (1) ^126I --> beta^- + nu bar + ^126Xe (branching ratio 0.46) (2) Only the high-energy neutrino from ^8B decay can cause the first reaction. Since there are Te ores known to be very ancient (~2 Ga), one can in principle measure the ^8B neutrino flux integrated over the Xe closure age of the ore. In an experiment designed to measure the betabeta-decay lifetimes of ^128Te and ^130Te, we have completed mass spectrometric analysis of the Xe isotopes from three different native Te samples from Colorado (Bernatowicz et al. 1992). After subtraction of the trapped component (and a small contribution from actinide fission), we observe excesses in ^128Xe and ^130Xe due to betabeta-decay of ^128Te and ^130Te, and excesses in ^129Xe and ^13lXe from neutron capture on these Te isotopes. Although no excesses are observed for ^124Xe, small (~10^4 atom/g) excesses of ^126Xe are present. The ^126Xe excess is correlated with ^130Xe, and therefore is probably due to a nuclear transmutation of Te. However, this excess is at least 50 times the amount expected from the neutrino-induced reaction. It is also too large to be explained by nuclear processes such as those induced by neutrons and alpha particles. The most plausible explanation for the excess ^126Xe is that it is generated in the interactions of cosmic-ray muons and their secondaries through the reactions mu+- + ^126Te mu+- + ^126I + pi (3) and p + ^126Te --> ^126I + n (4) followed by reaction (2). Since the muon flux does not attenuate rapidly with depth, its contribution exceeds that of the neutrino-induced reaction up to a depth of ~2.8 km. w.e. (0.4 km of rock ~1 km.w.e) and is probably the dominant source of ^126Xe in our samples, which were collected from depths of no more than a few hundred meters. In order to carry out the test of the standard solar model suggested by Haxton, the candidate Te ore should be retrieved from a depth of at least 4.4 km.w.e., where the muon contribution to ^126Xe drops to 10% of the solar neutrino contribution. References. Haxton W. (1990) Phys. Rev. Lett. 65, 809. Bernatowicz T., Brannon J., Brazzle R., Cowsik R., Hohenberg C. and Podosek F. (1992) in preparation

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