Direct Measurement of the

One of the main neutron sources for the astrophysical s process is the reaction ^{13}C(α,n)^{16}O, taking place in thermally pulsing asymptotic giant branch stars at temperatures around 90 MK. To model the nucleosynthesis during this process the reaction cross section needs to be known in the 150-230 keV energy window (Gamow peak). At these sub-Coulomb energies, cross section direct measurements are severely affected by the low event rate, making us rely on input from indirect methods and extrapolations from higher-energy direct data. This leads to an uncertainty in the cross section at the relevant energies too high to reliably constrain the nuclear physics input to s-process calculations. We present the results from a new deep-underground measurement of ^{13}C(α,n)^{16}O, covering the energy range 230-300 keV, with drastically reduced uncertainties over previous measurements and for the first time providing data directly inside the s-process Gamow peak. Selected stellar models have been computed to estimate the impact of our revised reaction rate. For stars of nearly solar composition, we find sizeable variations of some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular, the two radioactive nuclei ^{60}Fe and ^{205}Pb, as well as ^{152}Gd.

δ13 C values in archaeological 14 C-AMS dated charcoals: assessing mid-Holocene climate fluctuations and human response from a high-resolution isotope record (Arslantepe, Turkey).

RATIONALE: Past climate has always influenced human adaptation to the environment. In order to reconstruct palaeoclimate fluctuations and their role in the evolution of Near Eastern societies during the mid-Holocene, high-resolution Δ13 C records from fossil wood remains at the archaeological site of Arslantepe (eastern Turkey) have been developed. METHODS: After chemical treatment, δ13 C values were measured by sample combustion flow using a FLASH EA-CHNS instrument interfaced with a Delta V isotope ratio mass spectrometer via a CONFLO III. Two replicates per sample were analysed. The measurement precision was evaluated by propagating variations of the δ13 C values of samples and V-PDB standards, whereas the accuracy was checked by a quality control sample. To account for changes in atmospheric CO2 , Δ13 C values were calculated. In addition, 14 C/12 C ratios were measured by means of ann AMS system (3 MV tandem accelerator). RESULTS: Mean Δ13 C curves of deciduous Quercus and Juniperus from archaeological levels between 4700 and 2000 BC (Arslantepe periods VIII-VI D) were produced, where the isotope values were ordered by the available RC ages. Interspecific variations of evergreen vs deciduous plants were postulated for the juniper Δ13 C values being higher than 3‰. The seasonal rainfall amount was recorded by the juniper remains, while the water table levels were obtained from the oak samples. CONCLUSIONS: The local climate experienced times of enhanced/reduced precipitation in concert with regional trends. Anomalies in the air mass circulation from the Mediterranean basin also produced oscillations of rainfall amount. In such a frame the Rapid Climate Change dry events had a consistent signature in the Arslantepe Δ13 C record, thus potentially contributing to social or organisational changes at the site.

First direct measurement of the 17O(p,γ)18F reaction cross section at Gamow energies for classical novae.

Classical novae are important contributors to the abundances of key isotopes, such as the radioactive (18)F, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The (17)O(p,γ)(18)F reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes, but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range E(c.m.)~/= 200-370 keV appropriate to hydrogen burning in classical novae. In addition, the E(c.m.)=183 keV resonance strength, ωγ=1.67±0.12 µeV, has been measured with the highest precision to date. The uncertainty on the (17)O(p,γ)(18)F reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.

Space-time Bayesian analysis of the environmental impact of a dismissing nuclear power plant.

The assessment of the radiological impact of decommissioning activities at a nuclear power plant requires a detailed analysis of the distribution of radionuclides in the environment surrounding it. The present work concerns data of three campaigns carried out during the last twenty years in the plain of the Garigliano river surrounding the Garigliano Nuclear Power Plant (GNPP), which is located in Southern Italy and shut down in 1979. Moreover, some data from surveys held in the eighties, across the Chernobyl accident, have been taken in account. The results for the soil samples, in particular for 137Cs and 236U specific activity, were analyzed for their extension in space and in time. Some of the problems related to the classical analysis of environmental radiological data (non-normal distribution of the values, small number of sample points, multiple comparison and presence of values lesser than the minimum detectable activity) have been overcome with the use of Bayesian methods. The scope of the paper is threefold: (1) to introduce the data of the last campaign held in the Garigliano plain; (2) to insert these data in a larger spatio-temporal frame; (3) to show how the Bayesian approach can be applied to radiological environmental surveys, stressing out its advantages over other approaches, using the data of the campaigns. The results show that radionuclides specific activity in soil is dominated by the natural sources with the contribution of the atmospheric fallout. A detailed study was performed on the 137Cs data to evaluate both their statistical distribution and the trend over the space and the time. It results that (i) no new contribution there was in the last decades, (ii) specific activity values of the area surrounding the GNPP are consistent with those obtained in other farther areas, (iii) the effective depletion half-life factor for 137Cs is much lower than the half-life of the radionuclide.

Isotopic evidences for microbiologically mediated and direct C input to soil compounds from three different leaf litters during their decomposition.

We show the potentiality of coupling together different compound-specific isotopic analyses in a laboratory experiment, where (13)C-depleted leaf litter was incubated on a (13)C-enriched soil. The aim of our study was to identify the soil compounds where the C derived from three different litter species is retained. Three (13)C-depleted leaf litter (Liquidambar styraciflua L., Cercis canadensis L. and Pinus taeda L., delta(13)C(vsPDB) approximately -43 per thousand), differing in their degradability, were incubated on a C4 soil (delta(13)C(vsPDB) approximately -18 per thousand) under laboratory-controlled conditions for 8 months. At harvest, compound-specific isotope analyses were performed on different classes of soil compounds [i.e. phospholipids fatty acids (PLFAs), n-alkanes and soil pyrolysis products]. Linoleic acid (PLFA 18:2omega6,9) was found to be very depleted in (13)C (delta(13)C(vsPDB) approximately from -38 to -42 per thousand) compared to all other PLFAs (delta(13)C(vsPDB) approximately from -14 to -35 per thousand). Because of this, fungi were identified as the first among microbes to use the litter as source of C. Among n-alkanes, long-chain (C27-C31) n-alkanes were the only to have a depleted delta(13)C. This is an indication that not all of the C derived from litter in the soil was transformed by microbes. The depletion in (13)C was also found in different classes of pyrolysis products, suggesting that the litter-derived C is incorporated in less or more chemically stable compounds, even only after 8 months decomposition.

AMS assessment of U-contamination of structural materials of the Garigliano NPP under decommissioning.

The assessment of the radiological impact of decommissioning activities at a Nuclear Power Plant requires a detailed mapping of the distribution of radionuclides both in the environment surrounding the NPP and in its structural material. The detection of long-lived actinide isotopes and possibly the identification of their origin is particularly interesting and valuable if ultrasensitive measurement of the relative abundance of U isotopes is performed via Accelerator Mass Spectrometry (AMS). In this paper we present an investigation carried out on the structural materials of the Garigliano NPP aiming to determine the abundance of 235,236,238U in the various compartments of the plant buildings under decommissioning. Since the expected values both for isotopic ratios and total U concentrations range over different orders of magnitude, we have developed a novel methodology for the measurement of 234,235U/238U isotopic ratios in low U concentration samples. This allowed a systematic investigation of the distribution of all U isotopes in concrete and metal matrices of the NPP. The behavior of 235,236U/238U isotopic ratios in the different compartments of the NPP is discussed. The correlation of these ratios with 60Co and 137Cs specific activities is also studied to show a different behavior for concrete and metal samples. These data represent a very valuable information to direct the decommissioning procedures under course.

Optimized sample preparation for isotopic analyses of CO2 in air: systematic study of precision and accuracy dependence on driving variables during CO2 purification process.

A systematic analysis of efficiency, reproducibility and accuracy of cryogenic purification of CO(2) from air samples for isotopic analyses is presented. The technical characteristics of the cryogenic line are given in detail. To study the cryogenic process, three different operating parameters are considered: flow rate of the gas entering the line, pressure of the gas in the line, and CO(2)-trap shape. Experimental results demonstrate that efficiency, reproducibility and accuracy strongly depend on the CO(2)trap shape. Moreover, a dependence of reproducibility and accuracy on the flow rate of the gas is found, but not on its pressure. High precision (< or =0.02 per thousand for delta(13)C and < or =0.05 per thousand for delta(18)O) and good accuracy (<0.09 per thousand for delta(13)C and <0.14 per thousand for delta(18)O) is achieved after applying the N(2)O correction.

Uranium beam characterization at CIRCE for background and contamination determinations.

The Accelerator Mass Spectrometry (AMS) is the most sensitive technique, compared either to the Inductively Coupled Plasma (ICP-MS) or Thermal Ionization (TI-MS) mass spectrometer, for the actinide (e.g. (236)U, (x)Pu isotopes) measurements. They are present in environmental samples at the ultra trace level since atmospheric tests of Nuclear Weapons (NWs) performed in the past, deliberate dumping of nuclear waste, nuclear fuel reprocessing, on a large scale, and operation of Nuclear Power Plants (NPPs), on a small scale, have led to the release of a wide range of radioactive nuclides in the environment. At the Center for Isotopic Research on Cultural and Environmental heritage (CIRCE) in Caserta, Italy, an upgraded actinide AMS system, based on a 3-MV pelletron tandem accelerator, has been developed and routinely operated. At CIRCE a charge state distribution as a function of terminal voltage, the beam emittance, measured in the 20° actinides dedicated beam line, as well as the energy and position validation of the U ions were performed in order to determine the best measurement conditions. A (236)U/(238)U isotopic ratio background level of about 5×10(-12) or 3×10(-13), depending on the Time of Flight-Energy (TOF-E) configurations, as well as the spatial distribution of the (235)U, (238)U interferences ions and a (236)U contamination mass of about 0.5 fg have been determined.

Post-discharge recurrences of new-onset atrial fibrillation following cardiac surgery: impact of low-dose amiodarone and beta-blocker prophylaxis.

BACKGROUND: Atrial fibrillation (AF) is the most frequent complication following cardiac surgery. It occurs mostly between the second and fourth postoperative days and often recurs within 30 days after surgery. While postoperative AF has been well analyzed, post-discharge recurrences of AF have not been clearly described even if they are reported as a frequent cause of re-hospitalization. METHODS: We followed up 185 patients for 10 +/- 5 months with the aim of characterizing the post-discharge recurrences of AF. All patients had recently undergone cardiac surgery complicated by AF and were in sinus rhythm at the time of admission to our Center. We also compared the efficacy of the main prophylactic regimens adopted in the referral Centers (amiodarone, beta-blockers, amiodarone plus beta-blockers) during the first postoperative month. RESULTS: In the first postoperative month AF recurred after discharge in 60 patients. The event rate was not different in patients treated with amiodarone and controls (47 vs 50%, p = NS), while it was significantly lower in patients taking beta-blockers either alone or associated with amiodarone (10 and 9% respectively, p = 0.002). At the end of follow up (10 +/- 5 months), AF persisted in 3 out of 176 study patients (1.7%). CONCLUSIONS: In patients undergoing cardiac surgery, post-discharge recurrences of AF are frequent during the first postoperative month and have a clinical relevance. Beta-blockers (not amiodarone) seem to be an effective prophylactic measure. The phenomenon tends to vanish in the long term, and a chronic prophylaxis is not justified.

Characterization of post-discharge atrial fibrillation following open-heart surgery in uncomplicated patients referred to an early rehabilitation program.

BACKGROUND: Atrial fibrillation (AF) is frequently observed after open-heart surgery, following discharge from the cardiac surgery clinic. Compared to those usually reported in the early postoperative period, this arrhythmia is delayed in onset and is often a cause of re-hospitalization. Post-discharge AF has never been characterized in the literature. METHODS: We retrospectively analyzed post-discharge AF occurring within 30 days of coronary artery bypass graft or of valvular procedures in 376 patients referred to an early postoperative rehabilitation program. To investigate the probability of the persistence of post-discharge AF, we prospectively examined 232 patients who had undergone valvular procedures. RESULTS: An arrhythmia was recognized in 61/376 patients (16%), resulted in worsening of the NYHA functional class in 27 (44%) and in life-threatening hemodynamic effects requiring urgent cardioversion in 5 (8%). Events were predicted by the occurrence of postoperative AF (6-fold higher risk), left ventricular hypertrophy, an enlarged left atrium and valvular pathology (3-fold) and by the lack of beta-blocker protection (5-fold). AF persisted in 20/232 (9% of the study population, 18% of patients who had post-discharge AF) and had a relevant impact on the patient's clinical status. Predictors of events were older age, an enlarged left atrium and a lower left ventricular ejection fraction. CONCLUSIONS: Post-discharge AF following open-heart surgery is frequent in patients undergoing valvular procedures and often persists over time. The clinical impact of the arrhythmia is relevant, it might cause re-hospitalizations in many circumstances and, consequently, may have an impact on hospital resources. Events are much less frequent in patients taking beta-blockers than in those who do not, and they can be predicted by simple variables observed in the early stages after surgery.

Transfer of 137Cs and 60Co from irrigation water to a soil-tomato plant system.

An experiment has been performed at the nuclear power plant of Garigliano (Caserta, Italy), aiming at the measurement of transfer factors of 137Cs and 60Co radionuclides from the irrigation water to a soil-plant system, with particular attention to the influence on such transfers of the irrigation technique (ground or aerial). Tomato plants were irrigated weekly with water contaminated with 137Cs and 60Co (about 375 Bq/m2 week), using both irrigation techniques. After 13 weeks, fruits, leaves, stems, roots and soil were sampled, and radionuclide concentrations were measured by high-resolution gamma spectroscopy. It was found that the activity allocated to the plant organs is significantly dependent upon the irrigation technique, amounting to 2.1% and 1.6% of the activity given in the cultivation for aerial treatment and 0.4% and 0.3% for the ground treatment, for 137Cs and 60Co respectively. The activity absorbed by plants is allocated mainly in leaves (> 55%), while less then 10% is stored in the fruits, for both irrigation techniques. Transfer factors (soil-plant and irrigation water-plant) of tomato plants and of weeds have been determined for 137Cs and 60Co, as well as for natural 40K in the soil.

[Errors in digestive surgery. A case of tension pneumothorax during laparoscopic cholecystectomy]. / Errori in chirurgia digestiva. Un caso di pneumotorace sotto tensione durante colecistectomia laparoscopica.

A case of tension pneumothorax caused by an accidental diaphragm injury during laparoscopic cholecystectomy is presented. This complication occurred during one of the first laparoscopic cholecystectomies caused by the crochet abandoned for few seconds, into the peritoneal cavity. Therefore laparoscopy was performed and diaphragm injury repaired.

The first use of (236)U in the general environment and near a shutdown nuclear power plant.

We present a first effort to investigate (236)U in the environment near a shutdown nuclear power plant far away from highly contaminated sites, by using accelerator mass spectrometry. The detection limit of about 1pg (236)U allowed us to identify a minimal increase of the (236)U/(238)U isotopic ratio correlated to a peak of (137)Cs in river sediments downstream of the nuclear power plant, and to detect anthropogenic (236)U also upstream, where it is probably not related to the power plant but to global fallout. The (236)U content shoved variations of the (236)U/(238)U isotopic ratio in relation to the chemical-physical characteristics of the sediments. This demonstrates the potential of (236)U as an environmental tracer, and as an indicator for releases from nuclear facilities.

Stellar and primordial nucleosynthesis of 7Be: measurement of 3He(alpha,gamma)7Be.

The 3He(alpha,gamma)7Be reaction presently represents the largest nuclear uncertainty in the predicted solar neutrino flux and has important implications on the big bang nucleosynthesis, i.e., the production of primordial 7Li. We present here the results of an experiment using the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the 7Be ejectiles. In addition, off-beam activation and coincidence gamma-ray measurements were performed at selected energies. At energies above 1 MeV a large discrepancy compared to previous results is observed both in the absolute value and in the energy dependence of the cross section. Based on the available data and models, a robust estimate of the cross section at the astrophysical relevant energies is proposed.

An isotopic method for testing the influence of leaf litter quality on carbon fluxes during decomposition.

During microbial breakdown of leaf litter a fraction of the C lost by the litter is not released to the atmosphere as CO(2) but remains in the soil as microbial byproducts. The amount of this fraction and the factors influencing its size are not yet clearly known. We performed a laboratory experiment to quantify the flow of C from decaying litter into the soil, by means of stable C isotopes, and tested its dependence on litter chemical properties. Three sets of (13)C-depleted leaf litter (Liquidambar styraciflua L., Cercis canadensis L. and Pinus taeda L.) were incubated in the laboratory in jars containing (13)C-enriched soil (i.e. formed C4 vegetation). Four jars containing soil only were used as a control. Litter chemical properties were measured using thermogravimetry (Tg) and pyrolysis-gas chromatography/mass spectrometry-combustion interface-isotope ratio mass spectrometry (Py-GC/MS-C-IRMS). The respiration rates and the delta(13)C of the respired CO(2) were measured at regular intervals. After 8 months of incubation, soils incubated with both L. styraciflua and C. canadensis showed a significant change in delta(13)C (delta(13)C(final) = -20.2 +/- 0.4 per thousand and -19.5 +/- 0.5 per thousand, respectively) with respect to the initial value (delta(13)C(initial) = -17.7 +/- 0.3 per thousand); the same did not hold for soil incubated with P. taeda (delta(13)C(final:)-18.1 +/- 0.5 per thousand). The percentages of litter-derived C in soil over the total C loss were not statistically different from one litter species to another. This suggests that there is no dependence of the percentage of C input into the soil (over the total C loss) on litter quality and that the fractional loss of leaf litter C is dependent only on the microbial assimilation efficiency. The percentage of litter-derived C in soil was estimated to be 13 +/- 3% of total C loss.

Activation measurement of the 3He(alpha,gamma)7Be cross section at low energy.

The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted by solar models and in the 7Li abundance obtained in big-bang nucleosynthesis calculations. The present work reports on a new precision experiment using the activation technique at energies directly relevant to big-bang nucleosynthesis. Previously such low energies had been reached experimentally only by the prompt-gamma technique and with inferior precision. Using a windowless gas target, high beam intensity, and low background gamma-counting facilities, the 3He(alpha,gamma)7Be cross section has been determined at 127, 148, and 169 keV center-of-mass energy with a total uncertainty of 4%. The sources of systematic uncertainty are discussed in detail. The present data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the 3He(alpha,gamma)7Be astrophysical S factor to solar energies.