175 research outputs found
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
Effects of graft pretensioning in anterior cruciate ligament reconstruction
Purpose Graft pretensioning is used in anterior cruciate ligament (ACL) reconstruction to prevent secondary slackening. Its effects on collagen fibrillar ultrastructure are not known. In this study, we hypothesized that graft pretensioning in ACL reconstruction creates ultrastructural changes detectable in scanning electron microscopy (SEM). Methods A prospective comparative study was carried out on 38 ACL reconstructions using a 4-strand semitendinosus graft. Samples were harvested intra-operatively before and after pretensioning for 30 s, 2 or 5 min. The images produced in SEM were analyzed using an original semi-quantitative «CIP» score taking into account collagen cohesion, integrity, and parallelism. Intra- and inter-tester reliability for the CIP score were tested. Results The CIP scores decreased by 3.5 (1.6) points after pretensioning (P < 0.05). Significant differences were found in the 5, 2 min and 30 s subgroups for the global CIP score. Relative decrease (Delta CIP) was significantly higher in the 2 and 5 min subgroups after pretensioning in comparison with the 30 s subgroups. Intra- and inter-tester reliability for the CIP score were 0.85 and 0.92 (P < 0.05). Conclusion Pretensioning ACL grafts resulted in alteration of the collagen fibrillar ultrastructure, detectable using SEM. These results confirm the existence of collagen ultrastructural changes after pretensioning that may be related to its duration. Level of evidence Prospective comparative study, Level II
Stellar ArAr reactions and their effect on light neutron-rich nuclide synthesis
The ArAr ( = 35 d) and
ArAr (269 y) reactions were studied for the first time
with a quasi-Maxwellian ( keV) neutron flux for Maxwellian Average
Cross Section (MACS) measurements at stellar energies. Gas samples were
irradiated at the high-intensity Soreq applied research accelerator
facility-liquid-lithium target neutron source and the Ar/Ar and
Ar/Ar ratios in the activated samples were determined by
accelerator mass spectrometry at the ATLAS facility (Argonne National
Laboratory). The Ar activity was also measured by low-level counting at
the University of Bern. Experimental MACS of Ar and Ar, corrected
to the standard 30 keV thermal energy, are 1.9(3) mb and 1.3(2) mb,
respectively, differing from the theoretical and evaluated values published to
date by up to an order of magnitude. The neutron capture cross sections of
Ar are relevant to the stellar nucleosynthesis of light neutron-rich
nuclides; the two experimental values are shown to affect the calculated mass
fraction of nuclides in the region A=36-48 during the weak -process. The new
production cross sections have implications also for the use of Ar and
Ar as environmental tracers in the atmosphere and hydrosphere.Comment: 18 pages + Supp. Mat. (13 pages) Accepted for publication in Phys.
Rev. Let
Influence of nuclear structure on sub-barrier hindrance in Ni+Ni fusion
Fusion-evaporation cross sections for Ni+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 -factor, which signals a strong
sub-barrier hindrance. A comparison with the Ni+Ni,
Ni+Ni, and Ni+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
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.
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
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
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