Tracing Noble Gas Radionuclides in the Environment

Trace analysis of radionuclides is an essential and versatile tool in modern science and technology. Due to their ideal geophysical and geochemical properties, long-lived noble gas radionuclides, in particular, 39Ar (t1/2 = 269 yr), 81Kr (t1/2 = 2.3x10^5 yr) and 85Kr (t1/2 = 10.8 yr), have long been recognized to have a wide range of important applications in Earth sciences. In recent years, significant progress has been made in the development of practical analytical methods, and has led to applications of these isotopes in the hydrosphere (tracing the flow of groundwater and ocean water). In this article, we introduce the applications of these isotopes and review three leading analytical methods: Low-Level Counting (LLC), Accelerator Mass Spectrometry (AMS) and Atom Trap Trace Analysis (ATTA)

A Study of the Residual 39Ar Content in Argon from Underground Sources

The discovery of argon from underground sources with significantly less 39Ar than atmospheric argon was an important step in the development of direct-detection dark matter experiments using argon as the active target. We report on the design and operation of a low background detector with a single phase liquid argon target that was built to study the 39Ar content of the underground argon. Underground argon from the Kinder Morgan CO2 plant in Cortez, Colorado was determined to have less than 0.65% of the 39Ar activity in atmospheric argon.Comment: 21 pages, 10 figure

Influence of nuclear structure on sub-barrier hindrance in Ni+Ni fusion

Fusion-evaporation cross sections for $^{64}$Ni+$^{64}$Ni have been measured down to the 10 nb level. For fusion between two open-shell nuclei, this is the first observation of a maximum in the $S$-factor, which signals a strong sub-barrier hindrance. A comparison with the $^{58}$Ni+$^{58}$Ni, $^{58}$Ni+$^{60}$Ni, and $^{58}$Ni+$^{64}$Ni systems indicates a strong dependence of the energy where the hindrance occurs on the stiffness of the interacting nuclei.Comment: Submitted to Phys. Rev. Lett. 4 pages, 3 figure

Multi-layer coating development for XEUS

Graded depth multi-layer coatings have the potential to optimise the performance of X-ray reflective surfaces for improved energy response. A study of deposition techniques on silicon substrates representative of the XEUS High Performance Pore Optics (HPO) technology has been carried out. Measurements at synchrotron radiation facilities have been used to confirm the excellent performance improvements achievable with Mo/Si and W/Si multilayers. Future activities that will be necessary to implement such coatings in the HPO assembly sequence are highlighted. Further coating developments that may allow an optimisation of the XEUS effective area in light of potential changes to science requirements and telescope configurations are also identified. Finally an initial measurement of effects of radiation damage within the multilayers is reported

Hindrance of Heavy-ion Fusion at Extreme Sub-Barrier Energies in Open-shell Colliding Systems

The excitation function for the fusion-evaporation reaction 64Ni+100Mo has been measured down to a cross-section of ~5 nb. Extensive coupled-channels calculations have been performed, which cannot reproduce the steep fall-off of the excitation function at extreme sub-barrier energies. Thus, this system exhibits a hindrance for fusion, a phenomenon that has been discovered only recently. In the S-factor representation introduced to quantify the hindrance, a maximum is observed at E_s=120.6 MeV, which corresponds to 90% of the reference energy E_s^ref, a value expected from systematics of closed-shell systems. A systematic analysis of Ni-induced fusion reactions leading to compound nuclei with mass A=100-200 is presented in order to explore a possible dependence of the fusion hindrance on nuclear structure.Comment: 10 pages, 9 figures, Submitted to Phys. Rev.

A shorter \u3csup\u3e146\u3c/sup\u3eSm half-life measured and implications for \u3csup\u3e146\u3c/sup\u3eSm-\u3csup\u3e142\u3c/sup\u3eNd chronology in the solar system

The extinct p-process nuclide 146Sm serves as an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its α-decay daughter 142Nd. Based on analyses of 146Sm/147Sm α-activity and atom ratios, we determined the half-life of 146Sm to be 68 ± 7 (1σ) million years, which is shorter than the currently used value of 103 ± 5 million years. This half-life value implies a higher initial 146Sm abundance in the early solar system, (146Sm/144Sm)0 = 0.0094 ± 0.0005 (2σ), than previously estimated. Terrestrial, lunar, and martian planetary silicate mantle differentiation events dated with 146Sm-142Nd converge to a shorter time span and in general to earlier times, due to the combined effect of the new 146Sm half-life and (146Sm/144Sm)0 values

Discovery of underground argon with low level of radioactive 39Ar and possible applications to WIMP dark matter detectors

We report on the first measurement of 39Ar in argon from underground natural gas reservoirs. The gas stored in the US National Helium Reserve was found to contain a low level of 39Ar. The ratio of 39Ar to stable argon was found to be <=4x10-17 (84% C.L.), less than 5% the value in atmospheric argon (39Ar/Ar=8x10-16). The total quantity of argon currently stored in the National Helium Reserve is estimated at 1000 tons. 39Ar represents one of the most important backgrounds in argon detectors for WIMP dark matter searches. The findings reported demonstrate the possibility of constructing large multi-ton argon detectors with low radioactivity suitable for WIMP dark matter searches.Comment: 6 pages, 2 figures, 2 table

Cultic resilience and inter-city engagement at the dawn of urban history: protohistoric Mesopotamia and the ‘city seals’, 3200-2750 BC

Within the context of early urbanism, elite groups developed the world’s earliest writing in Mesopotamia, 3200-2750 BC, comprising administrative documents in the form of inscribed clay tablets. How did these proto-literate urban communities engage with each other and what strategies did they employ to address major challenges to their survival? The ‘city seal’ evidence survives as seal impressions on clay bureaucratic artefacts, both inscribed tablets and impressed sealings. These impressions feature signs representing the names of Mesopotamian cities, many of them identifiable with known sites. The documents stand at the threshold of history, as the earliest evidence for inter-city engagement. Using an innovative methodology and interpretive framework of cultic resilience, we integrate archaeometric, iconographic, and functional analyses of the earliest stages of writing and sealing, to argue that the city seal evidence provides unique insights into inter-city cooperation by Mesopotamian cities during a critical episode of early urban development

Study of the fusion reaction \u3csup\u3e12\u3c/sup\u3eC + \u3csup\u3e12\u3c/sup\u3eC at low beam energy

In this article we discuss two aspects related to the 12C + 12C fusion reaction at low energies for carbon burning in supermassive stars. First we present plausible arguments for the notion that the observed resonance structures at the lowest measured energies arise from the relatively large spacing and narrow width of 24Mg compound levels at the corresponding excitation energy region. We thus point out that the Incoming Wave Boundary Condition is inappropriate for calculating the fusion cross section under these situations. Secondly, we report on a particle-γ coincidence technique that has been used for the first time to measure the fusion cross section in the system 12C + 12C at low beam energies. Based on these results, it should be possible to measure this important fusion cross section down to the 10 pb level within a reasonable length of time

Second-line paclitaxel in non-small cell lung cancer initially treated with cisplatin: a study by the European Lung Cancer Working Party

In the context of a phase III trial comparing in advanced non-small cell lung cancer (NSCLC) sequential to conventional administration of cisplatin-based chemotherapy and paclitaxel, we evaluated the activity of paclitaxel as second-line chemotherapy and investigated any relation of its efficacy with the type of failure after cisplatin. Patients received three courses of induction GIP (gemcitabine, ifosfamide, cisplatin). Non-progressing patients were randomised between three further courses of GIP or three courses of paclitaxel. Second-line paclitaxel was given to patients with primary failure (PF) to GIP and to those progressing after randomisation to further GIP (secondary failure or SF). One hundred sixty patients received second-line paclitaxel. Response rates were 7.7% for PF and 11.6% for SF (P=0.42). Median survival times (calculated from paclitaxel start) were 4.1 and 7.1 months for PF and SF (P=0.002). In multivariate analysis, three variables were independently associated with better survival: SF (hazard ratio (HR)=1.55, 95% confidence interval (CI) 1.08–2.22; P=0.02), normal haemoglobin level (HR=1.56, 95% CI 1.08–2.26; P=0.02) and minimal weight loss (HR=1.79, 95% CI 1.26–2.55; P=0.001). Paclitaxel in NSCLC patients, whether given for primary or for SF after cisplatin-based chemotherapy, demonstrates activity similar to other drugs considered active as second-line therapy