Production de tritium dans le thorium par des protons de 135 MeV

We have measured the cross-section of tritium production by bombardement of thorium by 135 MeV protons in the Orsay synchro-cyclotron. The tritium was separated from the targets by heating in a graphite crucible with a high-frequency generator, under hydrogen gas pressure. Tritiated water was synthetised and the tritium was measured with liquid scintillator. A value of 19.5 ± 0.05 mbarns was obtained for the tritium-cross section and ten percent of tritons have energies higher than 35 MeV. This large cross-section is attributed to a double pick-up process.On a mesuré la section efficace de production de tritium après bombardment de thorium par des protons de 135 MeV accélérés au synchro-cyclotron d'Orsay. Le tritium était extrait des cibles par chauffage, dans un creuset de graphite, par courants H. F. sous atmosphère d'hydrogène. L'hydrogène tritié était ensuite transformé en eau tritiée et le tritium mesuré au moyen de scintillateur liquide. La section efficace obtenue est de 19,5 ± 0,5 mbarns et dix pour cent des tritons ont une énergie supérieure à 35 MeV. On attribue cette production à un processus de double pick-up

Phylogenomic Reconstruction of the Neotropical Poison Frogs (Dendrobatidae) and Their Conservation

The evolutionary history of the Dendrobatidae, the charismatic Neotropical poison frog family, remains in flux, even after a half-century of intensive research. Understanding the evolutionary relationships between dendrobatid genera and the larger-order groups within Dendrobatidae is critical for making accurate assessments of all aspects of their biology and evolution. In this study, we provide the first phylogenomic reconstruction of Dendrobatidae with genome-wide nuclear markers known as ultraconserved elements. We performed sequence capture on 61 samples representing 33 species across 13 of the 16 dendrobatid genera, aiming for a broadly representative taxon sample. We compare topologies generated using maximum likelihood and coalescent methods and estimate divergence times using Bayesian methods. We find most of our dendrobatid tree to be consistent with previously published results based on mitochondrial and low-count nuclear data, with notable exceptions regarding the placement of Hyloxalinae and certain genera within Dendrobatinae. We also characterize how the evolutionary history and geographic distributions of the 285 poison frog species impact their conservation status. We hope that our phylogeny will serve as a backbone for future evolutionary studies and that our characterizations of conservation status inform conservation practices while highlighting taxa in need of further study

ESR dating of palaeolithic calcite: Fundamental studies

International audienc

Radioactivité induite par le rayonnement cosmique dans la météorite Granès

International audienceThe activities of 14 radionuclides from the Granes meteorite which fell on 13 November 1964 were measured after chemical separation. The following results, expressed in dpm kg$^{−1}$ at time of fall, were obtained:$^{10}$Be: 23,4 ± 1,4; $^{26}$Al: 37 ± 5; $^{41}$Ca: 4,3 ± 1,9; $^{44}$Ti: 1,8 ± 0,3; $^{45}$Ca: 46 ± 6; $^{46}$Sc: 18,5 ± 1,7; $^{49}$V: 17 ± 4; $^{51}$Cr: 118 ± 36; $^{53}$Mn: 62 ± 8; $^{54}$Mn: 57 ± 7; $^{55}$Fe: 158 ± 17; $^{57}$Co: 11 ± 3; $^{59}$Ni: 10,5 ± 1,5; $^{60}$Co: 6,4 ± 1,5.These results are discussed and compared with those obtained for the Harleton meteorite which is similar in mass and chemical composition. By dividing the radionuclides into three groups according to their half-lives (less than 3 months; between 9 months and 3 years; greater than 40 years) we have established that these two meteorites received essentially identical irradiations during their exposure to cosmic rays.On a mesuré les activités de 14 radionuclides contenus dans la météorite Granès tombée le 13 Novembre 1964; ces radionuclides ont été séparés par traitement chimique. Les résultats suivants exprimés en dpm kg$^{−1}$ à la date de la chute ont été obtenus: $^{10}$Be: 23,4 ± 1,4; $^{26}$Al: 37 ± 5; $^{41}$Ca: 4,3 ± 1,9; $^{44}$Ti: 1,8 ± 0,3; $^{45}$Ca: 46 ± 6; $^{46}$Sc: 18,5 ± 1,7; $^{49}$V: 17 ± 4; $^{51}$Cr: 118 ± 36; $^{53}$Mn: 62 ± 8; $^{54}$Mn: 57 ± 7; $^{55}$Fe: 158 ± 17; $^{57}$Co: 11 ± 3; $^{59}$Ni: 10,5 ± 1,5; $^{60}$Co: 6,4 ± 1,5.Ces résultats sont discutés et comparés avec ceux obtenus pour la météorite Harleton, de niasse et de composition chimique très voisines. Les radionuclides étant répartis en trois groupes suivant leurs périodes—inférieures à 3 mois, 9 mois à 3 ans, supérieures à 40 ans—on constate que les deux météorites ont subi des irradiations sensiblement identiques pendant la durée de leur exposition au rayonnement cosmique

Extra-terrestrial 53^{53}Mn in Antarctic ice

International audienceThe reasons why $^{53}$Mn (a cosmogenic radionuclide with a half-life of 3.7 × 10$^6$ y) appears as one of the best indicators of the presence of interplanetary dust are summarized. This paper reports the detection of $^{53}$Mn in pre-1952 snow samples collected on the Eastern Antarctic Plateau in the vicinity of Plateau Station. The measurements were carried out by neutron activation and X-ray spectrometry on three samples weighing a few hundred kg and covering each the time interval 1935–1950. The specific activity of $^{53}$Mn was found to be (0.82 ± 0.17) disint.min$^{−1}$/10$^3$ tons of snow, corresponding to a deposition rate at Plateau Station of (2.2 ± 0.5) × 10$^{−5}$ disint. min$^{-1}$ m$^{-2}$ y$^{-1}$. The mean global deposition rate would be three times higher if $^{53}$Mn were assumed to behave in the same way as stratospheric $^{90}$Sr. By comparing this figure with existing data on the meteorite flux reaching the earth and with the galactic and solar production rates of $^{53}$Mn, it is concluded that the bulk of the $^{53}$Mn found at Plateau Station is associated with interplanetary dust in which it had been produced by the action of solar protons on iron. The deposition rate of extra-terrestrial dust-borne iron must be between 1.3 × 10$^{-5}$ and 1.3 × 10$^{-4}$ g m$^{-3}$ y$^{-1}$ at Plateau Station. These results support jointly with other studies the concept of an interplanetary zodiacal cloud of dust with a chemical composition and density not essentially different from chondritic meteorites, with a relatively ‘flat’ grain size distribution and a mass influx to the earth of the order of 10$^5$ tons/y

Descriptive osteology and patterns of limb loss of the European limbless skink Ophiomorus punctatissimus

The limbless skink Ophiomorus punctatissimus is a cryptozoic species found in the Peloponnese region of Greece and on the Greek island Kythira. To provide the first thorough description of the cranial and postcranial osteology of this species, both disarticulated specimens and X‐ray computed tomographies of wet‐preserved specimens were examined in detail. Resulting from this, an anatomical atlas of this species is provided. Two separate considerations, an evolutionary and an ecomorphological one, are made based on the observed adaptations related to limb loss in this skink. The structure of the girdles shows a particular pattern of reduction: whereas the pelvic girdle is mostly vestigial, the pectoral girdle is instead well developed, with all the elements typical of limbed lizards except for the actual limbs. This led us to hypothesize an asynchronous pattern of limb reduction during the evolution of this species, in which the hindlimbs regressed earlier than the forelimbs. Furthermore, considerations based on overall body morphology, osteology and the structure of the inner ear led to the recognition of this species as a burrowing ecomorph. In contrast to the morphology normally displayed in this ecomorph, O. punctatissimus is characterized by the retention of autotomic vertebrae in its tail. This is consistent with the habitats in which it lives, where active burrowing would be difficult because of the hard, rocky terrain. Instead, this skink hides among rocks on the surface and is, therefore, subject to greater predation risk