Independence of fragment charge distributions of the size of heavy multifragmenting sources

International audienceCharged product multiplicities and Z distributions were measured for single multifragmenting sources produced in collisions between Full-size image (<1 K) and Full-size image (<1 K) at the same available energy per nucleon. Z distributions are found identical for both reactions while fragment multiplicities scale as the charge of the total systems. A complete dynamical simulation, in which multifragmentation originates in the spinodal decomposition of a finite piece of nuclear matter resulting from an incomplete fusion of projectile and target, well accounts for this experimental observation

Investigating the Shallow to Mid-Depth (>100–300 °C) Continental Crust Evolution with (U-Th)/He Thermochronology: A Review

International audienceQuantifying geological processes has greatly benefited from the development and use of thermochronometric methods over the last fifty years. Among them is the (U-Th)/He dating method, which is based on the production and retention, within a crystal structure, of radiogenic 4He atoms associated with the alpha decay of U, Th and Sm nuclei. While apatite has been the main target of (U-Th)/He studies focusing on exhumation and burial processes in the upper levels of the continental crust (~50–120 °C), the development of (U-Th)/He methods for typical phases of igneous and metamorphic rocks (e.g., zircon and titanite) or mafic and ultramafic rocks (e.g., magnetite) over the last two decades has opened up a myriad of geological applications at higher temperatures (>100–300 °C). Thanks to the understanding of the role of radiation damage in He diffusion and retention for U-Th-poor and rich mineral phases, the application of (U-Th)/He thermochronometry to exhumation processes and continental evolution through deep time is now mainstream. This contribution reviews the (U-Th)/He thermochronometer principle and the influence of radiation damage in modifying the diffusion behavior. It presents applications of (U-Th)/He dating to problems in tectonic and surface processes at shallow to middle crustal depths (>100–300 °C). New and promising applications using a combination of methods will stimulate a research avenue in the future

Effects of valve replacement for aortic stenosis on mitral regurgitation.

We aimed to prospectively and quantitatively assess the effects of aortic valve replacement (AVR) for aortic stenosis (AS) on mitral regurgitation (MR) and to examine the determinants of the changes in MR. Fifty-two patients with AS scheduled for AVR were included if holosystolic MR not being considered for replacement or repair was detected. MR was quantified using the proximal isovelocity surface area method before and 8 +/- 4 days after surgery. Mitral valvular deformation parameters did not change significantly, but the mitral effective regurgitant orifice (ERO) and regurgitant volume decreased from 11 +/- 6 mm(2) to 8 +/- 6 mm(2) and from 20 +/- 10 ml to 11 +/- 9 ml, respectively (both p <0.0001). Using multiple linear regression analysis, preoperative severity of MR, mitral leaflet coaptation height, and end-diastolic volume decrease were independently associated with postoperative reduction in MR, whereas changes in mitral valve morphology after surgery were not. MR etiology did not predict the reduction in MR. In conclusion, the decrease in MR observed in most patients after AVR is associated with the magnitude of acute left ventricular reverse remodeling. As the reduction in left ventricular systolic pressure contributes to the decrease in regurgitant volume, the preoperative quantitative assessment of MR should best be performed by measurement of the ERO

Technical note: Analytical protocols and performance for apatite and zircon (U-Th) ∕ He analysis on quadrupole and magnetic sector mass spectrometer systems between 2007 and 2020

International audienceApatite and zircon (U-Th) / He thermochronological data are obtained through a combination of crystal selection, He content measurement by crystal heating with analysis using noble gas mass spectrometry, and measurement of U, Th, and Sm contents by crystal dissolution as well as solution analysis using inductively coupled plasma mass spectrometry (ICP-MS). This contribution documents the methods for helium thermochronology used at the GEOPS laboratory, Paris-Saclay University, between 2007 and the present that allow apatite and zircon (U-Th) / He data to be obtained with precision. More specifically, we show that the He content can be determined with precision (at 5 %) and accuracy using a calibration of the He sensitivity based on the Durango apatite, and its use also appears crucial to check for He and U-Th-Sm analytical problems. The Durango apatite used as a standard is therefore a suitable mineral to perform precise He calibration and yields (U-Th) / He ages of 31.1 ± 1.4 Ma with an analytical error of less than 5 % (1σ). The (U-Th) / He ages for the Fish Canyon Tuff zircon standard yield a dispersion of about 9 % (1σ) with a mean age of 27.0 ± 2.6 Ma, which is comparable to other laboratories. For the long-term quality control of the (U-Th) / He data, attention is paid to evaluating the drift of He sensitivity and blanks through time as well as that of (U-Th) / He ages and Th / U ratios (with Sm / Th when possible), all relying on the use of Durango apatite and Fish Canyon Tuff zircon as standards

Astrophysical rate of the 11^{11}C+p reaction with Coulomb break-up of a 12^{12}N radioactive beam

International audienc

Astrophysical rate of the 11^{11}C+p reaction with Coulomb break-up of a 12^{12}N radioactive beam

International audienc