Neutrino Fluence after r‐Process Freezeout and Abundances of Te Isotopes in Presolar Diamonds

Abstract

Using the data of Richter, Ott, & Begemann on Te isotopes in diamond grains from a meteorite, we derive bounds on the neutrino fluence and the decay timescale of the neutrino flux relevant for the supernova r-process. Our new bound on the neutrino fluence ℱ after freezeout of the r-process peak at mass number A~130 is more stringent than the previous bound ℱ≾0.045 (in units of 10^(37) ergs cm^(-2)) of Qian et al. and Haxton et al., if the neutrino flux decays on a timescale hat τ≾0.65 s. In particular, it requires that a fluence of ℱ=0.031 be provided by a neutrino flux with hat τ≾0.84 s. Such a fluence may be responsible for the production of the solar r-process abundances at A=124-126. Our results are based on the assumption of Ott that only the stable nuclei implanted into the diamonds are retained, while the radioactive nuclei are lost from the diamonds upon decay after implantation. We consider that the nanodiamonds are condensed in an environment with C/O>1 in the expanding supernova debris or from the exterior H envelope. This environment need not have the ^(13)C/^(12)C ratio of the bulk diamonds, since the Te- and Xe-containing nanodiamond grains are too rare to affect that ratio. The implantation of nuclei would have occurred ~10^4-10^6 s after r-process freezeout. This time interval may be marginally sufficient to permit adequate cooling upon expansion for the formation of diamond grains. The mechanisms of preferential retention/loss of the implanted nuclei are not well understood.