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.

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.

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.

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.

Body esteem in Israeli university students.

Body-esteem is an important dimension in the general concept of body-image. The Body Esteem Scale (BES) was developed and tested in the USA. We tested young men and women in Israel all of whom were university students after their army service. Our results show that Israeli men score lower (feel more negative) on the virility reflecting subscale while Israeli women score higher (feel more positive) in the weight concern subscale--compared to their American counterparts. We discuss the possible explanations of this difference, focusing mainly on the impact of army discharge and the move to the academic field.

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.

Light intensity and area of illumination provided by various laryngoscope blades.

Several brands of laryngoscopes and commonly used blades are evaluated for differences in direct light intensity and area of illumination. The purpose of this study was to determine which laryngoscope/blade combination provided the best lighting conditions for tracheal intubation. The direct light intensity was assessed by directing various laryngoscope/blade combinations towards a multifunction exposure meter (Flash Meter III, Minolta Corp.). Light intensity expressed in Lux was calculated using the formula: lux = 2.5 x 2 exposure index. The area of illumination provided by the laryngoscopes was assessed by taking photographs when the laryngoscope blade tips were touching a wall. The widest diameter of bright illumination in the photograph was measured in centimeters (cm). The direct light intensity ranged from 0.4-5.5 x 10(3)lux. The field of illumination ranged from 3.2 to 8.8 cm. When fitted on regular size handles, blades with incandescent bulbs provided more intense light than blades using fibreoptic light sources (P = 0.0078). For blades using incandescent light, the use of a short handle laryngoscope resulted in a decrease in light intensity (P = 0.0117). The results of this study suggest that blades using incandescent light provide greater light intensity than blades using fibreoptics.

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.

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.

Spinal anaesthesia for patients with previous lower limb amputations.

Phantom limb pain has been reported as a transient phenomenon in patients with lower limb amputations during subsequent spinal anaesthesia. In order to determine its incidence and to define any predisposing factors we prospectively studied 23 spinal anaesthetics in 17 patients with previous lower limb amputation. Only one patient developed clinically significant phantom limb pain and we were unable to define any predisposing factors. Given the low incidence of recurrent phantom limb with spinal anaesthesia, its transient nature, and the fact that it can be treated if it occurs, we conclude that spinal anaesthesia is not contraindicated in patients with previous lower limb amputation.

Patient-controlled analgesia (PCA) using fentanyl in a parturient with a platelet function abnormality.

A term parturient with documented platelet dysfunction presented to the case room for induction of labour. Since this bleeding abnormality contraindicated the use of lumbar epidural analgesia (LEA), we elected to use an iv fentanyl patient-controlled analgesia (PCA) technique for pain relief during labour. The patient received a 50 micrograms fentanyl loading dose after which 20 micrograms boluses of fentanyl were self-administered every three minutes as required. The patient received a total of 400 micrograms of fentanyl over the 3 1/2 hr of active labour. Mother and neonate tolerated the fentanyl without sequelae. If facilities to monitor the neonate and mother are present, this method of analgesia is useful in those patients where LEA is contraindicated.

Postdural puncture headache: a randomized prospective comparison of the 24 gauge Sprotte and the 27 gauge Quincke needles in young patients.

This study was designed to compare the frequency of postdural puncture headaches (PDPH) using the 24 gauge Sprotte and the 27 gauge Quincke spinal needles in a population of patients less than 45 yr of age undergoing spinal anaesthesia for non-obstetrical surgery. Patients were randomly assigned to receive spinal anaesthesia with either the 24 gauge Sprotte spinal needle (n = 46) or the 27 gauge Quincke spinal needle (n = 47). Patients were interviewed on either postoperative day one or two and on postoperative day three. A PDPH was defined as a headache involving the occipital or frontal areas that is made worse when assuming either the sitting or standing position. Ninety-three patients were included in the analysis of data. The overall incidence of PDPH was 14% (13 of 93), and no difference was found between the Sprotte (15.2%) and Quincke (12.8%) needles. The distribution of the PDPHs by severity was not different between the two groups. None of the 13 patients with PDPHs required on epidural blood patch for relief of symptoms. Both the Sprotte needle and the Quincke needles were judged as easy to use and both required the same number of attempts in order to locate cerebrospinal fluid (first attempt successful: 73.9% versus 66%). Neither patient satisfaction nor the acceptability of spinal anaesthesia for a future procedure was adversely affected by the occurrence of a PDPH. The results of this study suggest that the risk of PDPH after spinal anaesthesia in young patients is similar using either the 24 gauge Sprotte or the 27 gauge Quincke spinal needle.

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.