52 research outputs found
New measurement of the scattering cross section of slow neutrons on liquid parahydrogen from neutron transmission
Liquid hydrogen is a dense Bose fluid whose equilibrium properties are both
calculable from first principles using various theoretical approaches and of
interest for the understanding of a wide range of questions in many body
physics. Unfortunately, the pair correlation function inferred from
neutron scattering measurements of the differential cross section from different measurements reported in the literature are
inconsistent. We have measured the energy dependence of the total cross section
and the scattering cross section for slow neutrons with energies between
0.43~meV and 16.1~meV on liquid hydrogen at 15.6~K (which is dominated by the
parahydrogen component) using neutron transmission measurements on the hydrogen
target of the NPDGamma collaboration at the Spallation Neutron Source at Oak
Ridge National Laboratory. The relationship between the neutron transmission
measurement we perform and the total cross section is unambiguous, and the
energy range accesses length scales where the pair correlation function is
rapidly varying. At 1~meV our measurement is a factor of 3 below the data from
previous work. We present evidence that these previous measurements of the
hydrogen cross section, which assumed that the equilibrium value for the ratio
of orthohydrogen and parahydrogen has been reached in the target liquid, were
in fact contaminated with an extra non-equilibrium component of orthohydrogen.
Liquid parahydrogen is also a widely-used neutron moderator medium, and an
accurate knowledge of its slow neutron cross section is essential for the
design and optimization of intense slow neutron sources. We describe our
measurements and compare them with previous work.Comment: Edited for submission to Physical Review
Measurements of polarized photo-pion production on longitudinally polarized HD and Implications for Convergence of the GDH Integral
We report new measurements of inclusive pion production from frozen-spin HD
for polarized photon beams covering the Delta(1232) resonance. These provide
data simultaneously on both H and D with nearly complete angular distributions
of the spin-difference cross sections entering the Gerasimov-Drell-Hearn (GDH)
sum rule. Recent results from Mainz and Bonn exceed the GDH prediction for the
proton by 22 microbarns, suggesting as yet unmeasured high-energy components.
Our pi0 data reveal a different angular dependence than assumed in Mainz
analyses and integrate to a value that is 18 microbarns lower, suggesting a
more rapid convergence. Our results for deuterium are somewhat lower than
published data, considerably more precise and generally lower than available
calculations.Comment: 4 pages, 4 figures. Submitted for publication in Physical Review
Letter
Enabling ultra-high dose rate electron beams at a clinical linear accelerator for isocentric treatments
BACKGROUND AND PURPOSE
Radiotherapy delivery with ultra-high dose rates (UHDR) has consistently produced normal tissue sparing while maintaining efficacy for tumour control in preclinical studies, known as the FLASH effect. Modified clinical electron linacs have been used for pre-clinical studies at reduced source-surface distance (SSD) and novel intra-operative devices are becoming available. In this context, we modified a clinical linac to deliver 16 MeV UHDR electron beams with an isocentric setup.
MATERIALS AND METHODS
The first Varian TrueBeam (SN 1001) was clinically operative between 2009-2022, it was then decommissioned and converted into a research platform. The 18 MeV electron beam was converted into the experimental 16 MeV UHDR. Modifications were performed by Varian and included a software patch, thinner scattering foil and beam tuning. The dose rate, beam characteristics and reproducibility were measured with electron applicators at SSD = 100 cm.
RESULTS
The dose per pulse at isocenter was up to 1.28 Gy/pulse, corresponding to average and instantaneous dose rates up to 256 Gy/s and 3⋅10 Gy/s, respectively. Beam characteristics were equivalent between 16 MeV UHDR and conventional for field sizes up to 10x10cm and an overall beam reproducibility within ± 2.5% was measured.
CONCLUSIONS
We report on the first technical conversion of a Varian TrueBeam to produce 16 MeV UHDR electron beams. This research platform will allow isocenter experiments and deliveries with conventional setups up to field sizes of 10x10 cm within a hospital environment, reducing the gap between preclinical and clinical electron FLASH investigations
First Observation of -odd Asymmetry in Polarized Neutron Capture on Hydrogen
We report the first observation of the parity-violating 2.2 MeV gamma-ray
asymmetry in neutron-proton capture using polarized cold
neutrons incident on a liquid parahydrogen target at the Spallation Neutron
Source at Oak Ridge National Laboratory. isolates the , \mbox{} component of the weak
nucleon-nucleon interaction, which is dominated by pion exchange and can be
directly related to a single coupling constant in either the DDH meson exchange
model or pionless EFT. We measured , which implies a DDH weak coupling of
and a pionless
EFT constant of MeV. We describe the experiment, data
analysis, systematic uncertainties, and the implications of the result.Comment: 6 pages, 5 figure
Emergence of new Salmonella Enteritidis phage types in Europe? Surveillance of infections in returning travellers
BACKGROUND: Among human Salmonella Enteritidis infections, phage type 4 has been the dominant phage type in most countries in Western Europe during the last years. This is reflected in Salmonella infections among Swedish travellers returning from abroad. However, there are differences in phage type distribution between the countries, and this has also changed over time. METHODS: We used data from the Swedish infectious disease register and the national reference laboratory to describe phage type distribution of Salmonella Enteritidis infections in Swedish travellers from 1997 to 2002, and have compared this with national studies conducted in the countries visited. RESULTS: Infections among Swedish travellers correlate well with national studies conducted in the countries visited. In 2001 a change in phage type distribution in S. Enteritidis infections among Swedish travellers returning from some countries in southern Europe was observed, and a previously rare phage type (PT 14b) became one of the most commonly diagnosed that year, continuing into 2002 and 2003. CONCLUSIONS: Surveillance of infections among returning travellers can be helpful in detecting emerging infections and outbreaks in tourist destinations. The information needs to be communicated rapidly to all affected countries in order to expedite the implementation of appropriate investigations and preventive measures
Brief review on systematic hypothermia for the protection of central nervous system during aortic arch surgery: a double-sword tool?
Antegrade selective cerebral perfusion in conjunction with hypothermia attenuate postoperative neurological injury, which in turn still remains the main cause of mortality and morbidity following aortic arch surgery. Hypothermic circulatory arrest however could be a useful tool during arch surgery, surgery for chronic thromboembolic disease, air on the arterial line during CPB, during cavotomy for extraction of renal cell carcinoma with level IV extension, or when dealing with difficult trauma to the SVC or IVC. Cerebral protective effects with hypothermic procedures including inhibition of neuron excitation, and discharge of excitable amino acids, and thereby, prevention of an increase in intercellular calcium ions, hyperoxidation of lipids in cell membranes, and free radical production
Loneliness Levels of Students with Special Needs in Inclusive Classrooms
This study examines whether the self-concepts, social skills, problem behaviors, and loneliness levels of students with special educational needs (SEN) in inclusive elementary classrooms differ from those of students without special educational needs (non-SEN). This study also aimed to identify the roles of self-concept, social skills, and problem behaviors in predicting the loneliness levels of SEN students. The study group comprised 272 students (4th and 5th graders) attending inclusive elementary classrooms. A total of 140 were SEN and 132 were non-SEN students. The Social Skills and the Problem Behaviors Scales of the Social Skills Rating System-Teacher Form (SSRS-TF), the Children's Loneliness Scale (CLS), and the Piers-Harris Children's Self-Concept Scale (PHCSCS) were used as data collection tools. The findings showed that the self-concepts, social skills, problem behaviors, and loneliness levels of the SEN students were significantly different than those of the non-SEN students. It was also found that self-concept and social skills were significant predictors of the loneliness levels of SEN students. The findings were discussed regarding the related literature and the inclusive practices in Turkey
Loneliness Levels of Students with Special Needs in Inclusive Classrooms
This study examines whether the self-concepts, social skills, problem behaviors, and loneliness levels of students with special educational needs (SEN) in inclusive elementary classrooms differ from those of students without special educational needs (non-SEN). This study also aimed to identify the roles of self-concept, social skills, and problem behaviors in predicting the loneliness levels of SEN students. The study group comprised 272 students (4th and 5th graders) attending inclusive elementary classrooms. A total of 140 were SEN and 132 were non-SEN students. The Social Skills and the Problem Behaviors Scales of the Social Skills Rating System-Teacher Form (SSRS-TF), the Children's Loneliness Scale (CLS), and the Piers-Harris Children's Self-Concept Scale (PHCSCS) were used as data collection tools. The findings showed that the self-concepts, social skills, problem behaviors, and loneliness levels of the SEN students were significantly different than those of the non-SEN students. It was also found that self-concept and social skills were significant predictors of the loneliness levels of SEN students. The findings were discussed regarding the related literature and the inclusive practices in Turkey
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