Nothing Lasts Forever: Environmental Discourses on the Collapse of Past Societies

The study of the collapse of past societies raises many questions for the theory and practice of archaeology. Interest in collapse extends as well into the natural sciences and environmental and sustainability policy. Despite a range of approaches to collapse, the predominant paradigm is environmental collapse, which I argue obscures recognition of the dynamic role of social processes that lie at the heart of human communities. These environmental discourses, together with confusion over terminology and the concepts of collapse, have created widespread aporia about collapse and resulted in the creation of mixed messages about complex historical and social processes

Measurement of the cross section of the Li-8(d,alpha)He-6 reaction of possible relevance to big bang nucleosynthesis

We report measurements of the cross section of the Li-8(d, alpha) He-6 reaction in the energy range E-c.m. =2.3-3.5 MeV using a Li-8-radioactive beam on a CD2 foil. The astrophysical S factor and reaction rate were calculated from the measured cross section. The He-6 nuclei produced in the reaction were detected in solidstate detector telescopes. This reaction might have affected the primordial abundance of Li-6 in big bang nucleosynthesis, since He-6 beta decays to Li-6. However, several big bang nucleosynthesis network calculations were found to be insensitive to this reaction, suggesting that the Li-8(d, alpha) He-6 reaction does not affect Li-6 primordial production

Total reaction and neutron-removal cross sections of (30-60)A MeV He and Li isotopes on Pb

Total reaction cross sections sigma(R) of (30-60)A MeV He-4,He-6,He-8 and Li-6,Li-7,Li-8,Li-9,Li-11 on Ph, and 2n-removal cross sections sigma-(2n) of He-6,He-8 and Li-11 on Pb, were measured by injecting magnetically separated, focused, monoenergetic, secondary beams of those projectiles into a telescope containing Pb targets separated by thin Si detectors. All these sigma(R)s (except He-4), and sigma-(2n) for He-6 and Li-11, are underpredicted by microscopic model calculations which include only nuclear forces. Better agreement is achieved by including electromagnetic dissociation in the model, for those projectiles for which either the electric dipole response functions or the dominant photodissociation cross sections were known. The cross sections sigma-(4n) for He-8, sigma-(xn) for Li-7,Li-8,Li-9, and (sigma-(3n)+ sigma-(4n)) for Li-11 were found to be less than or equal to 0.7 b. All sigma(R)s were measured to better than 5% accuracy, showing that the method is usable for other target elements sandwiched into a Si telescope

Total reaction and neutron-removal cross sections of (30-60)A MeV Be isotopes on Si and Pb

Total reaction cross sections sigma (R) of all particle-stable Be isotopes on Si, and several of their neutron-removal cross sections sigma (-xn), were measured near (30-60)A MeV by injecting magnetically separated, focused, monoenergetic secondary beams of these projectiles into a telescope containing nine Si transmission detectors. Similar measurements were made for Be10-12 on Pb, by placing Pb targets between the Si detectors of another telescope. A Glauber analysis of the Be+Si sigma (R) data, including only nuclear forces, yields rms radii for the Be isotopes in general agreement with those found by other workers. Similar calculations underpredict the CTR data for Be+Pb, showing the importance of electromagnetic dissociation. A simple microscopic theory reproduces the n-removal cross sections for Be-11 and Be-14 on Si, but overpredicts n removal for Be-11 on Ph. For Be-12 incident upon both Si and Pb targets, sigma (-2n) significantly exceeds sigma (-n), as is expected since 1n removal leaves the weakly bound halo nucleus Be-11. A similar effect for Be-10 on Si is attributed to the weak binding of the last neutron of Be-9; however, for Be-10+Pb, sigma (-n) slightly exceeds sigma (-2n)