Neutron cross section according to its neutron cross section and how it reacts to an incident neutron. Nuclides that tend to absorb a neutron and either decay or keep the neutron in its nucleus are neutron absorbers and will have a "capture cross section" for that reaction. Isotopes that fission, are fissionable fuels and have a corresponding "fission cross section". The remaining isotopes will simply scatter the neutron, and have a "scatter cross section". Some isotopes, like uranium-238, have nonzero cross sections of all three. Isotopes which have a large scatter cross section and a low mass are good neutron moderators (see chart
Horizontal gene transfer in evolution transferred. Although this may be rare, this possibility is forcing scrutiny of the validity of phylogenetic trees based on SSU rRNAs. Recent discoveries of "rampant" HGT in microorganisms, and the detection of horizontal movement of even genes for the small subunit of ribosomal RNA, have forced biologists to question the accuracy of at least the early branches in the tree, and even question the validity of trees as useful models of how early evolution occurs. <br> "Sequence comparisons suggest recent horizontal transfer of many genes among diverse species including across the boundaries of phylogenetic "domains". Thus determining the phylogenetic history