ABSTRACT
^{140}Ce(n,γ) is a key reaction for slow neutron-capture (s-process) nucleosynthesis due to being a bottleneck in the reaction flow. For this reason, it was measured with high accuracy (uncertainty ≈5%) at the n_TOF facility, with an unprecedented combination of a high purity sample and low neutron-sensitivity detectors. The measured Maxwellian averaged cross section is up to 40% higher than previously accepted values. Stellar model calculations indicate a reduction around 20% of the s-process contribution to the Galactic cerium abundance and smaller sizeable differences for most of the heavier elements. No variations are found in the nucleosynthesis from massive stars.
ABSTRACT
Neutron capture reaction cross sections on 74 Ge are of importance to determine 74 Ge production during the astrophysical slow neutron capture process. We present new resonance data on 74 Ge( n , γ ) reactions below 70 keV neutron energy. We calculate Maxwellian averaged cross sections, combining our data below 70 keV with evaluated cross sections at higher neutron energies. Our stellar cross sections are in agreement with a previous activation measurement performed at Forschungszentrum Karlsruhe by Marganiec et al., once their data has been re-normalised to account for an update in the reference cross section used in that experiment.
ABSTRACT
The neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable ^{171}Tm (t_{1/2}=1.92 yr) is part of the branching around mass Aâ¼170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of ^{171}Tm at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (n_TOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time-of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384(40) mb, with which the estimation from the n_TOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KADoNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the Aâ¼170 branching, namely, the ^{171}Yb abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation.
ABSTRACT
We report on the measurement of the ^{7}Be(n,p)^{7}Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a ^{7}Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal ^{7}Li(p,n)^{7}Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near-threshold neutron production in the p+^{7}Li reaction is also discussed.
ABSTRACT
The energy-dependent cross section of the ^{7}Be(n,α)^{4}He reaction, of interest for the so-called cosmological lithium problem in big bang nucleosynthesis, has been measured for the first time from 10 meV to 10 keV neutron energy. The challenges posed by the short half-life of ^{7}Be and by the low reaction cross section have been overcome at n_TOF thanks to an unprecedented combination of the extremely high luminosity and good resolution of the neutron beam in the new experimental area (EAR2) of the n_TOF facility at CERN, the availability of a sufficient amount of chemically pure ^{7}Be, and a specifically designed experimental setup. Coincidences between the two alpha particles have been recorded in two Si-^{7}Be-Si arrays placed directly in the neutron beam. The present results are consistent, at thermal neutron energy, with the only previous measurement performed in the 1960s at a nuclear reactor. The energy dependence reported here clearly indicates the inadequacy of the cross section estimates currently used in BBN calculations. Although new measurements at higher neutron energy may still be needed, the n_TOF results hint at a minor role of this reaction in BBN, leaving the long-standing cosmological lithium problem unsolved.
ABSTRACT
OBJECTIVES: The assessment of renal function is essential to follow up the patients with neurogenic bladder. The objective of this study was to determine if renal ultrasonography would both evaluate the morphology of the urinary tract and renal function. METHOD: In a retrospective study, all patients followed for neurogenic bladder were included, regardless of their neurological disease. Renal function was estimated by creatinine clearance (Cl24 h), the reference test in neurological patients, the glomerular filtration rate by the MDRD simplified (MDRDs) and CKD-EPI creatinine formula, and we identified renal abnormalities detected on ultrasonography. RESULTS: One hundred and three patients were included (57 men-36 women), mean age 51±13 years. Fifty-nine patients had multiple sclerosis, 23 spinal cord injury. Depending on the method used (Cl24h, MDRDs, CKD-EPI creatinine) respectively 54, 49 and 39 patients had abnormal renal function; eleven patients had abnormal findings on renal ultrasonography. The sensitivity of ultrasonography as an indirect indicator of renal function depending on the method used (Cl24h, MDRDs, CKD-EPI creatinine) was equal respectively to 14%, 8% and 10%. CONCLUSION: Renal ultrasonography, which is essential to follow up the neurogenic bladder, is not enough sensitive to detect abnormal renal function and should continue to be associated with an evaluation of renal function, which is suitable for neurological patients. LEVEL OF EVIDENCE: 4.
Subject(s)
Kidney/diagnostic imaging , Renal Insufficiency/diagnosis , Urinary Bladder, Neurogenic/complications , Cohort Studies , Creatinine/urine , Female , Glomerular Filtration Rate , Humans , Male , Middle Aged , Predictive Value of Tests , Retrospective Studies , Sensitivity and Specificity , UltrasonographyABSTRACT
The 63Ni(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from kT=5-100 keV with uncertainties around 20%. Stellar model calculations for a 25Mâ star show that the new data have a significant effect on the s-process production of 63Cu, 64Ni, and 64Zn in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.
ABSTRACT
PURPOSE: Lower urinary tract dysfunction is common in multiple sclerosis (MS). The purpose of this study was to prospectively evaluate the impact of intermittent catheterization (IC) on the quality of life of patients affected by MS. METHODS: Between 2007 and 2009, we admitted 23 patients to teach them the technique of IC. Their quality of life was evaluated before and more than 6 months after the beginning of learning the technique, when the urinary situation was stable. Two questionnaires were used: one specific for urinary disorders (QUALIVEEN(®)) and one general (SF-36(®)). RESULTS: Twenty-two patients followed this different way of bladder emptying. More than 6 months (9.3 ± 3 months on average) after first learning to use IC, the impact of urinary disorders explored by Qualiveen(®) had significantly decreased (the overall quality of life; bother with limitation; fears; feelings; Wilcoxon's test, respectively p = 0.004; 0.007; 0.02; 0.02) while the quality of life was not diminished. CONCLUSION: Intermittent catheterization (IC) in association with overall urinary management, among patients affected by MS, is well accepted and reduces the impact of urinary dysfunction on their quality of life.
Subject(s)
Multiple Sclerosis/complications , Quality of Life , Urinary Bladder, Neurogenic/etiology , Urinary Bladder, Neurogenic/therapy , Urinary Catheterization/methods , Adult , Female , Humans , Lower Urinary Tract Symptoms/etiology , Lower Urinary Tract Symptoms/therapy , Male , Middle Aged , Patient Satisfaction , Prospective Studies , Retrospective Studies , Surveys and Questionnaires , Treatment OutcomeABSTRACT
In 2002, an innovative neutron time-of-flight facility started operation at CERN: n_TOF. The main characteristics that make the new facility unique are the high instantaneous neutron flux, high resolution and wide energy range. Combined with state-of-the-art detectors and data acquisition system, these features have allowed to collect high accuracy neutron cross-section data on a variety of isotopes, many of which radioactive, of interest for Nuclear Astrophysics and for applications to advanced reactor technologies. A review of the most important results on capture and fission reactions obtained so far at n_TOF is presented, together with plans for new measurements related to nuclear industry.
Subject(s)
Neutron Capture Therapy/instrumentation , Neutron Capture Therapy/methods , Nuclear Reactors , Equipment Design , Equipment Failure Analysis , Neutrons , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
The151Sm(n,gamma)152Sm cross section has been measured at the spallation neutron facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. The new facility combines excellent resolution in neutron time-of-flight, low repetition rates, and an unsurpassed instantaneous luminosity, resulting in rather favorable signal/background ratios. The 151Sm cross section is of importance for characterizing neutron capture nucleosynthesis in asymptotic giant branch stars. At a thermal energy of kT=30 keV the Maxwellian averaged cross section of this unstable isotope (t(1/2)=93 yr) was determined to be 3100+/-160 mb, significantly larger than theoretical predictions.
