Neutron capture measurement at the n TOF facility of the 204Tl and 205Tl s-process branching points

Neutron capture cross sections are one of the fundamental nuclear data in the study of the s (slow) process of nucleosynthesis. More interestingly, the competition between the capture and the decay rates in some unstable nuclei determines the local isotopic abundance pattern. Since decay rates are often sensible to temperature and electron density, the study of the nuclear properties of these nuclei can provide valuable constraints to the physical magnitudes of the nucleosynthesis stellar environment. Here we report on the capture cross section measurement of two thallium isotopes, 204Tl and 205Tl performed by the time-of-flight technique at the n TOF facility at CERN. At some particular stellar s-process environments, the decay of both nuclei is strongly enhanced, and determines decisively the abundance of two s-only isotopes of lead, 204Pb and 205Pb. The latter, as a long-lived radioactive nucleus, has potential use as a chronometer of the last s-process events that contributed to final solar isotopic abundances

Transverse momentum spectra of charged particles in proton-proton collisions at s=900\sqrt{s} = 900 GeV with ALICE at the LHC

The inclusive charged particle transverse momentum distribution is measured in proton-proton collisions at $\sqrt{s} = 900$ GeV at the LHC using the ALICE detector. The measurement is performed in the central pseudorapidity region $(|\eta|<0.8)$ over the transverse momentum range $0.15<p_{\rm T}<10$ GeV/$c$. The correlation between transverse momentum and particle multiplicity is also studied. Results are presented for inelastic (INEL) and non-single-diffractive (NSD) events. The average transverse momentum for $|\eta|<0.8$ is $\left<p_{\rm T}\right>_{\rm INEL}=0.483\pm0.001$ (stat.) $\pm0.007$ (syst.) GeV/$c$ and \left_{\rm NSD}=0.489\pm0.001 (stat.) $\pm0.007$ (syst.) GeV/$c$, respectively. The data exhibit a slightly larger $\left<p_{\rm T}\right>$ than measurements in wider pseudorapidity intervals. The results are compared to simulations with the Monte Carlo event generators PYTHIA and PHOJET.Comment: 20 pages, 8 figures, 2 tables, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/390

80Se(n,γ) cross-section measurement at CERN n TOF

Radiative neutron capture cross section measurements are of fundamental importance for the study of the slow neutron capture (s-) process of nucleosynthesis. This mechanism is responsible for the formation of most elements heavier than iron in the Universe. Particularly relevant are branching nuclei along the s-process path, which are sensitive to the physical conditions of the stellar environment. One such example is the branching at 79Se (3.27 × 105 y), which shows a thermally dependent ß-decay rate. However, an astrophysically consistent interpretation requires also the knowledge of the closest neighbour isotopes involved. In particular, the 80Se(n,?) cross section directly affects the stellar yield of the "cold"branch leading to the formation of the s-only 82Kr. Experimentally, there exists only one previous measurement on 80Se using the time of flight (TOF) technique. However, the latter suffers from some limitations that are described in this presentation. These drawbacks have been significantly improved in a recent measurement at CERN n TOF. This contribution presents a summary of the latter measurement and the status of the data analysis

Geophysical investigation in the Flumendosa River delta, Sardinia (Italy) — Seismic reflection imaging

A geophysical investigation that included seismic-reflection surveying and time-domain electromagnetics (EM) was carried out in the Flumendosa River Delta plain in southeastern Sardinia, Italy. The objective was to improve knowledge of geologic and hydrogeologic controls on a highly productive aquifer hosted in thick Quaternary deposits and known to be affected by an extensive saltwater intrusion. The seismic reflection survey, whose results are reported here, aimed to image the Paleozoic bedrock topography and to obtain detailed structural and stratigraphic information on the sequence of largely fluvial sediments extending from the surface down to bedrock. The survey consisted of two inline profiles, nearly parallel to the coastline and 1 km inland. The sources (0.25 kg of explosives buried at 2 m depth) and receivers (50-Hz vertical geophones) produced a twelvefold data set with common midpoints every 2.5 m. Detailed integrated velocity analysis (constant velocity gathers, constant velocity stacks, and semblance plots) and frequency-wavenumber- domain dip moveout (DMO) proved to be the most important processing steps in producing the two stacked sections. Both sections were characterized by distinct seismic units bounded by quasi-continuous reflectors. The lowermost reflection, imaged on section 1 at two-way traveltimes between 310 ms (~300 m) and 580 ms (~530 m) and on section 2 between 200 ms (~190 m) and 65 ms (~52 m), was interpreted to be Paleozoic bedrock. A maximum depth twice as deep as expected was the primary and somewhat surprising result. Imaging of oblique progradational facies - another major finding - proved the existence of undocumented marine Pleistocene sediments that could help in revising the area’s geology