Neutron capture cross sections: from theory to experiments and back

The method for an experimental determination of the stellar enhancement factor for the cross section of the $^{151}$Sm$(n,\gamma)$ reaction process is proposed. This study offered the pretext for an excursus on the interconnections between capture and dissociation reactions and the interplay between theory and experiments in the determination of neutron capture cross sections.Comment: Proceedings of the International Conference on Nuclear Data for Science and Technology, Santa FE, NM - September 200

Re-evaluation of the ¹⁶O(n, γ)¹⁷O cross section at astrophysical energies and its role as a neutron poison in the s-process

The doubly magic nucleus ¹⁶O has a small neutron-capture cross section of just a few tens of microbarns in the astrophysical energy region. Despite this, ¹⁶O plays an important role as a neutron poison in the astrophysical slow neutron capture (s) process due to its high abundance. We present in this paper a re-evaluation of the available experimental data for ¹⁶O(n, γ)¹⁷O and derive a new recommendation for the Maxwellian-averaged cross sections between kT = 5 and 100 keV. Our new recommendations are lower up to kT = 60 keV compared to the previously recommended values but up to 14% higher at kT = 100 keV. We explore the impact of this different energy dependence on the weak s-process during core helium burning (kT = 26 keV) and shell carbon burning (kT = 90 keV) in massive stars where ¹⁶O is the most abundant isotope

Exploring the resident gut microbiota of stranded odontocetes: high similarities between two dolphin species Tursiops truncatus and Stenella coeruleoalba

AbstractThe evaluation of symbiotic microbial communities occurring in the intestinal tract of animals has received great interest in recent years. However, little is known about gut microbial communities in cetaceans, despite their relevance in the ecology of marine communities. Here, we report an investigation using 16S rRNA gene amplicon sequencing of the resident gut microbiota of the two cetacean species Stenella coeruleoalba and Tursiops truncatus by sampling intestinal mucosa from specimens retrieved stranded along the Tyrrhenian coast of Tuscany (Italy). We found an abundance of members from Clostridiaceae and Fusobacteriaceae, which in total accounted for more than 50% of reads, in agreement with gut microbiota composition of other carnivorous mammals. Probably due to the limited number of samples available, sex, preservation status and also species, did not correlate with overall differences in the microbiota. Indeed, a high similarity of the taxonomic (family-level) composition between the gut microbiota of the two species was found. However, Pedobacter spp. was found abundant in amplicon sequencing libraries from S. coeruleoalba, while clostridia were more abundant from T. truncatus samples. Our results shed some light on the gut microbiota composition of two dolphin (S. coeruleoalba and T. truncatus) species, with specimens collected in the wild. Studies with a larger number of individuals are now needed to confirm these first results and evaluate the interspecific differences in relation to sex and age

Composition of supralittoral sediments bacterial communities in a Mediterranean island

Marine coasts represent highly dynamic ecosystems, with sandy beaches being one of the most heterogeneous. Despite the key importance of sandy beaches as transition ecosystems between sea and land, very few studies on the microbiological composition of beach sediments have been performed. To provide a first description of microbial composition of supralittoral sediments, we investigated the composition of bacterial communities of three sandy beaches, at Favignana Island, Italy, using metagenetic approaches (Terminal-Restriction Fragment Length Polymorphism, sequencing of 16S rRNA genes by Illumina-Solexa technology, functional genes detection, and quantitative Real-Time PCR). Results showed that the investigated beaches are harboring a rich bacterial diversity, mainly composed by members of classes Alphaproteobacteria, Gammaproteobacteria, Flavobacteria and Actinobacteria. The metagenetic analysis showed profiles of decreasing beta diversity and increasing richness, as well as a differentiation of communities, along the sea-to-land axis. In particular, members of Firmicutes and Proteobacteria displayed contrasting profiles of relative abundance (to decrease and to increase, respectively) along the sea-to-land axis of the beach. Finally, a search for the presence of genes related to the nitrogen and carbon biogeochemical cycle (nifH, nosZ, pmoA/amoA) detected the presence of ammonia monoxygenase sequences (amoA) only, suggesting the presence of bacterial ammonia oxidation to some extent, probably due to members of Nitrospira, but with the lack of nitrogen fixation and denitrification

Pulse shape analysis of signals from BaF2 and CeF3 scintillators for neutron capture experiments

The scope of this work is to study the characteristics of BaF2 and CeF3 signals using fast digitizers, which allow the sampling of the signal at very high frequencies and the application of the fitting method for analysis of the recorded pulses. By this procedure particle identification and the reconstruction of pile-up events can be improved, while maintaining the energy and time-of-flight resolution as compared to traditional methods. The reliability of the technique and problems connected with data acquisition are discussed with respect to accurate measurements of neutron capture cross-sections

Exploring the Gut Microbiome Alteration of the European Hare (Lepus europaeus) after Short-Term Diet Modifications

This study aimed to characterise the gut microbiome composition of European hares (Lepus europaeus) and its potential changes after a short-term diet modification. The high sensitivity of European hare to habitat changes makes this species a good model to analyse possible alterations in gut microbiome after the introduction of additional nourishment into the diet. In total, 20 pairs were chosen for the experiments; 10 pairs formed the control group and were fed with standard fodder. The other 10 pairs represented the experimental group, whose diet was integrated with apples and carrots. The DNA from fresh faecal pellets collected after 4 days from the start of the experiment was extracted and the V3-V4 hypervariable regions were amplified and sequenced using the Illumina MiSeq® platform. The obtained amplicon sequence variants were classified into 735 bacterial genera belonging to 285 families and 36 phyla. The control and the experimental groups appeared to have a homogenous dispersion for the two taxonomic levels analysed with the most abundant phyla represented by Bacteroidetes and Firmicutes. No difference between control and experimental samples was detected, suggesting that the short-term variation in food availability did not alter the hares’ gut microbiome. Further research is needed to estimate significant time threshold

NEAR: A New Station to Study Neutron-Induced Reactions of Astrophysical Interest at CERN-n_TOF

We present NEAR, a new experimental area at the CERN-n_TOF facility and a possible setup for cross section measurements of interest to nuclear astrophysics. This was recently realized with the aim of performing spectral-averaged neutron-capture cross section measurements by means of the activation technique. The recently commissioned NEAR station at n_TOF is now ready for the physics program, which includes a preliminary benchmark of the proposed idea. Based on the results obtained by dedicated Monte Carlo simulations and calculation, a suitable filtering of the neutron beam is expected to enable measurements of Maxwellian Averaged Cross Section (MACS) at different temperatures. To validate the feasibility of these studies we plan to start the measurement campaign by irradiating several isotopes whose MACS at different temperatures have recently been or are planned to be determined with high accuracy at n_TOF, as a function of energy in the two time-of-flight measurement stations. For instance, the physical cases of 88Sr(n,γ ), 89Y(n,γ ), 94Zr(n,γ ) and 64Ni(n,γ ) are discussed. As the neutron capture on 89Y produces a pure β -decay emitter, we plan to test the possibility to perform activation measurements on such class of isotopes as well. The expected results of these measurements would open the way to challenging measurements of MACS by the activation technique at n_TOF, for rare and/or exotic isotopes of interest for nuclear astrophysic