Neutron Capture on the s-Process Branching Point

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 A∼170 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 A∼170 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.

Stellar

The ^{36}Ar(n,γ)^{37}Ar (t_{1/2}=35 d) and ^{38}Ar(n,γ)^{39}Ar (269 yr) reactions were studied for the first time with a quasi-Maxwellian (kT∼47 keV) neutron flux for Maxwellian average cross section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ^{37}Ar/^{36}Ar and ^{39}Ar/^{38}Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ^{37}Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ^{36}Ar and ^{38}Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron-capture cross sections of ^{36,38}Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak s process. The new production cross sections have implications also for the use of ^{37}Ar and ^{39}Ar as environmental tracers in the atmosphere and hydrosphere.

The association of time of emergency surgery - day, evening or night - with postoperative 30-day hospital mortality.

It is unclear whether the time of day for emergency surgery is associated with postoperative mortality. We assessed this association in 9319 patients who had emergency surgery as their first surgery at the Jewish General Hospital, Montreal, QC, Canada from April 2010 to March 2015. Of the 7362 (80%) patients with complete data, 168 (2.3%) died within 30 postoperative days. There was no significant association of time of day with postoperative mortality, with adjusted OR (95%CI) of 1.61 (0.96-2.72) for night vs. day, p = 0.07; 1.29 (0.78-2.13) for night vs. evening, p = 0.33; and 1.26 (0.89-1.78) for evening vs. day, p = 0.20. Studies of more patients and more factors, with longer follow-up, should be carried out to exclude important associations of time of emergency surgery with postoperative mortality and morbidity.

Demonstration of a high-intensity neutron source based on a liquid-lithium target for Accelerator based Boron Neutron Capture Therapy.

A free surface liquid-lithium jet target is operating routinely at Soreq Applied Research Accelerator Facility (SARAF), bombarded with a ~1.91 MeV, ~1.2 mA continuous-wave narrow proton beam. The experiments demonstrate the liquid lithium target (LiLiT) capability to constitute an intense source of epithermal neutrons, for Accelerator based Boron Neutron Capture Therapy (BNCT). The target dissipates extremely high ion beam power densities (>3 kW/cm(2), >0.5 MW/cm(3)) for long periods of time, while maintaining stable conditions and localized residual activity. LiLiT generates ~3×10(10) n/s, which is more than one order of magnitude larger than conventional (7)Li(p,n)-based near threshold neutron sources. A shield and moderator assembly for BNCT, with LiLiT irradiated with protons at 1.91 MeV, was designed based on Monte Carlo (MCNP) simulations of BNCT-doses produced in a phantom. According to these simulations it was found that a ~15 mA near threshold proton current will apply the therapeutic doses in ~1h treatment duration. According to our present results, such high current beams can be dissipated in a liquid-lithium target, hence the target design is readily applicable for accelerator-based BNCT.

Note: Proton irradiation at kilowatt-power and neutron production from a free-surface liquid-lithium target.

The free-surface Liquid-Lithium Target, recently developed at Soreq Applied Research Accelerator Facility (SARAF), was successfully used with a 1.9 MeV, 1.2 mA (2.3 kW) continuous-wave proton beam. Neutrons (~2 × 10(10) n/s having a peak energy of ~27 keV) from the (7)Li(p,n)(7)Be reaction were detected with a fission-chamber detector and by gold activation targets positioned in the forward direction. The setup is being used for nuclear astrophysics experiments to study neutron-induced reactions at stellar energies and to demonstrate the feasibility of accelerator-based boron neutron capture therapy.

High-power liquid-lithium jet target for neutron production.

A compact liquid-lithium target (LiLiT) was built and tested with a high-power electron gun at the Soreq Nuclear Research Center. The lithium target, to be bombarded by the high-intensity proton beam of the Soreq Applied Research Accelerator Facility (SARAF), will constitute an intense source of neutrons produced by the (7)Li(p,n)(7)Be reaction for nuclear astrophysics research and as a pilot setup for accelerator-based Boron Neutron Capture Therapy. The liquid-lithium jet target acts both as neutron-producing target and beam dump by removing the beam thermal power (>5 kW, >1 MW/cm(3)) with fast transport. The target was designed based on a thermal model, accompanied by a detailed calculation of the (7)Li(p,n) neutron yield, energy distribution, and angular distribution. Liquid lithium is circulated through the target loop at ~200 °C and generates a stable 1.5 mm-thick film flowing at a velocity up to 7 m/s onto a concave supporting wall. Electron beam irradiation demonstrated that the liquid-lithium target can dissipate electron power areal densities of >4 kW/cm(2) and volume power density of ~2 MW/cm(3) at a lithium flow of ~4 m/s while maintaining stable temperature and vacuum conditions. The LiLiT setup is presently in online commissioning stage for high-intensity proton beam irradiation (1.91-2.5 MeV, 1-2 mA) at SARAF.

Sources of anthropogenic lead in sediments from an artificial lake in Brasília-central Brazil.

Pb concentration and Pb isotopic composition are known to represent powerful tools to investigate the history of Pb pollution in water and sediments. In this paper, we present and discuss the results of a detailed study of sediments deposited in the Paranoá Lake, a 44-year-old artificial reservoir in Brasília, central Brazil. Pb concentration and isotopic composition of the sediments were obtained by ID-TIMS, on three different sample fractions: leachate, residue, and bulk sample. The leachate phase has proven to be most efficient to distinguish between anthropogenic and natural Pb inputs. In the Paranoá lake, important sources of contamination were recognized, producing higher Pb concentrations (max. 37.68 ppm) and significant variations in Pb isotopic composition, relative to the regional geogenic background. Contamination of the sediments due to anthropogenic activity produced less radiogenic Pb isotopic compositions (206Pb/207Pb=1.15-1.17), compared with the regional natural composition (206Pb/207Pb=1.19-1.25). 210Pb analyses along one bore hole which sampled the entire sediment section indicated a sedimentation rate of 8.2+/-1.8 mm/year. The combined use of the 210Pb ages and Pb isotopic compositions of these samples revealed three distinct periods in the lake history: (1) the period of the time formation of the lake in 1959 until ca. 1970 was characterized by the deposition of sediments displaying more radiogenic Pb isotopic signature, (2) the time interval from the start of the process of eutrophication at 1970, until 1995, was characterized by the deposition of sediments having less radiogenic average compositions, and (3) from 1995 until the present represents a period of recovery of water quality, after two sewage treatment stations started to operate.

Patient flow in the Post Anesthesia Care Unit: an observational study.

PURPOSE: Anesthesiologists are constantly striving for improvement in health care delivery. We assessed the patient flow in the Post Anesthesia Care Unit (PACU) to determine if patients are being transported out of the PACU when ready. METHODS: A University student recorded the flow of 336 patients who recovered in our Post Anesthesia Care Unit. The corresponding nursing and orderly complements were recorded. If a delay arose between the time the patient was deemed fit for discharge by the PACU nurse and the time the patient was transported from the PACU, the student determined the duration and cause(s) of the delay. RESULTS: The number of patients, nurses, and orderlies increased from three to twelve, three to seven, and one to two respectively throughout the elective working day. Seventy-six per cent of patients studied were delayed in transport from the PACU, with 26% of patients waiting 30 min. The average delay in discharge for patients increased during the day from 0 to 65 +/- 54 min from the time of fit for discharge, as determined by the PACU nurse, until transport. Five causes were identified as contributing to the delay: orderly too busy (41%), awaiting Anesthesia assessment (36%), Post Anesthesia Care Unit nurse too busy (15%), receiving floor not ready (6%), and patient awaiting radiographic interpretation (2%). CONCLUSION: Our study has shown that system errors unnecessarily prolongs the stay of patients in the PACU.

The performance of spinal anesthesia is marginally more difficult in the elderly.

BACKGROUND AND OBJECTIVES: We sought to determine if spinal anesthesia is more difficult to perform in the elderly. METHODS: All spinal anesthetics administered over 18 months by 18 anesthesiologists were eligible. We excluded anesthetics for hip fractures and cesarean deliveries. We recorded time to completion, number of spinal needles used, and number of approaches. The patients were prospectively divided into three age categories: patients <50 years of age (group 1); 50-70 years of age (group 2); and >70 years of age (group 3). Descriptive statistics and chi-square test were performed. RESULTS: Nine hundred and ninety-nine anesthetics were analyzed. There were 368, 336, and 295 entries in groups 1, 2, and 3, respectively. Although the mean +/- SD (in min) times to accomplish the spinal technique were not significantly different (4.3 +/- 4.1, 4.4 +/- 3.2, and 4.6 +/- 3.4 for groups 1, 2, and 3), there was a statistically greater frequency of more than one spinal needle used and more than one approach needed in the elderly. CONCLUSIONS: We conclude that patient age is a minor independent predictor of increased technical difficulty with spinal anesthesia.

Anesthesiologists and the time interval between cases in cardiac surgery.

STUDY OBJECTIVE: To determine whether an association exists between individual anesthesiologists and nonpatient care time in the operating room (OR). DESIGN: Retrospective chart review. SETTING: Cardiac surgery operating theatre in a University Hospital. PATIENTS: 312 elective coronary artery bypass procedures over 2 years. MEASUREMENTS AND MAIN RESULTS: The time interval between cases, as defined by the time between the first patient out and the second patient in, was compared. Six anesthesiologists, labelled 1 to 6, were involved in the 156 data points analyzed. The mean (+/- SD) time interval between cases, in minutes, for anesthesiologists 1 to 6 were, respectively: 24 +/- 9, 25 +/- 8, 27 +/- 8, 29 +/- 5, 30 +/- 4, 31 +/- 7. The difference among the anesthesiologists' mean time interval between cases was significant (p < 0.01). The mean time interval between cases was significantly different between anesthesiologists 1 and 6 (p < 0.01) and between anesthesiologists 2 and 6 (p < 0.05). CONCLUSION: The impact of a shorter time interval between cases on OR efficiency remains unknown. Further education and investigation of this issue are warranted.

A "zero tolerance for overtime" increases surgical per case costs.

PURPOSE: One technique which some hospitals have used in an attempt to control Operating Room costs is a "zero tolerance for overtime" policy. We used a case cost analysis to determine if this policy was always cost effective. METHOD: A case cost analysis was designed based on a "test case" which would start late in the day. The case would last for three hours of which 1 1/2 hr would be during regular hours, and 1 1/2 hr would incur overtime. Costs were analysed using a "patient pays," "society pays," and "hospital pays" analysis. Costs were based on figures determined from the SMBD-Jewish General Hospital budget, Québec Health Insurance fees, and Government of Canada statistics. RESULTS: Regardless of who pays, in this case scenario it was more cost effective to proceed than to postpone surgery. Costs of proceeding with the surgery in the "patient pays," "society pays," and "hospital pays" models were $1,832.00, $1,227.40, and $1,215.00 respectively. The costs of postponing the surgery in the same three models were $1,937.00, $1,336.80, and $1,436.00. CONCLUSION: A "zero tolerance for overtime" policy may be too rigid to be consistently cost effective.

Videotape feedback in teaching laryngoscopy.

PURPOSE: To evaluate if videotape feedback provides educational insights for students learning laryngoscopy that they would not otherwise perceive. METHODS: Twenty-six medical students were videotaped while performing laryngoscopy for oral intubation. Before and after reviewing their performance on the videotape, they answered a standardized questionnaire assessing the adequacy of positioning, head movement during laryngoscopy, degrees of neck flexion and head extension, time elapsed, and whether the laryngoscope contacted the upper lip or teeth. After the review, they were asked if being videotaped was distracting, whether it provided new instructional insights and, if so, which was most important. RESULTS: Only 4% of students felt that initial head and neck positioning was suboptimal and this increased to 38% after videotape review (P = 0.029). The perceived inadequacy of positioning seemed related to initial overestimation of head extension (34.0 +/- 15 degrees) compared with that seen on videotape (21.5 +/- 13.5 degrees, P = 0.003). The estimated duration of laryngoscopy was underestimated (55 +/- 32 sec vs. 75 +/- 29 sec, P = .024) before videotape review. Although 26.9% (7/26) of students admitted feeling distracted by the video camera, all felt the experience had educational value. CONCLUSION: Videotape feedback changed students' perception of how they performed laryngoscopy. In particular, head extension was overestimated and duration of laryngoscopy underestimated.

Late operating room starts: experience with an education trial.

PURPOSE: This study was undertaken to determine if late starts of first cases in the Operating theatres at the SMBD-Jewish General Hospital remained a problem after identification of the causes of late starts and remedial actions being taken. METHODS: Hospital approval was obtained. A retrospective chart audit analyzed a two week period (10 days with 90 elective surgical cases) in October 1993. The time of entry by the first patient into each Operating Room (OR) was transcribed from the nursing records from each OR. A late start was defined as patient entry into the OR after 0745 hr. This audit revealed 77.8% of patients scheduled' for surgery at 0745 entered the OR late with a cumulative time lost of 1101 min. The reasons for this inefficiency were identified by a follow-up assessment in April 1995 as a result of this audit. Corrective measures included presentation of inpatients for the first case, reorganization of transport personnel schedules to facilitate arrival of patients to the OR, alteration of patient verification procedures prior to entry to the OR, and education of nursing, anaesthesia, and surgical personnel of the scope of the problem of late OR starts. All attending surgeons were notified either by letter or by discussion at departmental rounds. These measures were in effect by July 1995. A second audit, using the same methodology as the first, evaluated a two week period (10 days with 87 elective surgical cases) in October 1995. RESULTS: The second audit showed 65.5% of patients (average of 9 operating rooms daily) scheduled for surgery at 0745 entered the OR late with 601 min lost. The average delay for late starting cases decreased from 15.73 +/- 4.56 to 10.54 +/- 3.92 min (P < 0.05). CONCLUSION: Late OR starts are common and only modest improvements can be achieved without cooperation from anaesthetists and surgeons to arrive on time.

Misleading end-tidal CO2 tensions.

PURPOSE: The aim of this study was to determine if the literature supported the assumption that the values and changes in end-tidal PCO2 (PETCO2) during anaesthesia accurately reflect the values and changes in arterial PCO2 (PaCO2) is tenable. METHODS: The information was obtained by (a) a Medline literature search and the appropriate references quoted in the list generated; (b) appropriate abstracts in recent issues of the annual meeting supplements of Anesth Analg, Anesthesiology, Br J Anaesth and Can J Anaesth. We specifically sought information obtained during major operations, in sick patients, and reports of serial measurements. The information obtained is summarized in graphic form, with a discussion of the mechanisms and clinical implications. RESULTS: (1) Patients with systemic disease, or when placed in the lateral position, or with haemodynamic instability have an increased Pa-PETCO2 gradient. The values during surgery are probably due to marked alterations of ventilation: perfusion relationships. (2) In a number of reports, the gradient varied widely during the procedure. (3) The gradient may be reduced due to an alteration of the configuration of the alveolar plateau. (4) The magnitude and direction of change in PaCO2 and PETCO2 can be disproportionate and in the opposite direction. CONCLUSION: End-tidal PCO2 is often not indicative of PaCO2. Also, changes in PETCO2 do not always accurately indicate the direction and extent of the change in PaCO2.

Changes in PCO2 with acute changes in cardiac index.

PURPOSE: A direct relationship between cardiac index (CI) and end-tidal PCO2 (PETCO2) shortly after decreased CI was reported, but arterial PCO2 was not measured. Our purpose was to supply the missing information on the immediate effects of alterations in CI on PaCO2, PETCO2 and thus on Pa-PETCO2. METHODS: We measured CI, Pa and PETCO2 and calculated the difference in 20 patients scheduled for elective heart surgery just before and immediately after the sternotomy. The measurements were made using standard methods: thermodilution for CI, infra-red and blood gas analysis for PET and PaCO2 respectively. The results were analyzed by linear regression. RESULTS: Very significant, direct and immediate changes in PET and PaCO2 with changes in CI were noted. The ratios were 3.8 and 4.2 mmHg L-1 respectively. The calculated values of r were 0.75 (P < 0.001) for PETCO2 and 0.64 (P < 0.005) for PaCO2. The magnitude of individual change in PCO2 varied considerably such that the alterations in Pa-PETCO2 were also variable, without any correlation with the direction or magnitude of change in CI. CONCLUSION: Our results explain the reported wide variations in Pa-PETCO2 that accompany perturbations of cardiac output. Our observations pertain to the unsteady state only. The results suggest that PETCO2 can be used to estimate changes in CI with a reasonable degree of confidence.

Acute ventilatory complications during laparoscopic upper abdominal surgery.

PURPOSE: This article examines and summarizes the published reports dealing with subcutaneous emphysema, pneumothorax and carbon dioxide (CO2) embolism during laparoscopic upper abdominal surgery. The purpose is to describe the expected clinical picture, the differential diagnosis and the management of these complications. SOURCE: The information was obtained from a Medline literature search and the annual meeting supplements of Anesthesiology, Anesth Analg, Br J Anaesth and Can J Anaesth. PRINCIPAL FINDINGS: An abrupt increase in PETCO2 is the first sign of subcutaneous emphysema and of pneumothorax. Desaturation and increased airway pressure occur with pneumothorax, but not with subcutaneous emphysema alone. Desaturation and increased airway pressure also occur with bronchial intubation. The preliminary diagnosis is made by verifying the position of the tube, examination of the patient for swelling and crepitus and auscultation for air entry. Chest radiography and paracentesis confirm the diagnosis of pneumothorax, which frequently occurs with subcutaneous emphysema but is rarely of the tension type. Pulmonary embolism due to CO2 during LUAS has not been reported, but the available data suggest that small, haemodynamically inconsequential CO2 embolism occurs without change in PETCO2. Massive embolism is possible and will markedly decrease PETCO2, arterial O2 saturation (SpO2) and blood pressure. CONCLUSION: The immediate recognition of the three complications requires continuous monitoring of PETCO2, arterial saturation, airway pressure, and an index of pulmonary compliance.

A retrospective comparison of spinal and general anesthesia for vaginal hysterectomy: a time analysis.

The authors sought to compare time efficiency of spinal versus general anesthesia. The charts of 106 consecutive patients who had undergone a vaginal hysterectomy were analyzed. This analysis divided the patients into three groups: Group 1, spinal anesthesia; Group 2, general anesthesia; Group 3, spinal anesthesia with subsequent general anesthesia. The perioperative time course was divided into six intervals from entry into the operating room to discharge from the postanesthesia care unit (PACU). Total time was calculated by adding the six intervals. There were 85 patients in Group 1, 17 patients in Group 2, and 4 patients in Group 3. The mean times for surgical readiness once the anesthesiologist was present for Group 1, Group 2, and Group 3 were 21.4 +/- 7.3, 21.4 +/- 6.0, and 25.0 +/- 5.8 min, respectively. The total time for the three groups was 278.3 +/- 72.0, 245.9 +/- 23.1, and 295.0 +/- 101.2 min, respectively (P < 0.01 Group 1 vs Group 2). The difference in total time between Groups 1 and 2 was accounted for mainly by the stay in the PACU. This study concludes that there is no difference in the efficiency of operating room time use between spinal and general anesthesia.