1,625 research outputs found
Evaluation of a method for time-of-flight, wavelength and distance calibration for neutron scattering instruments by means of a mini-chopper and standard neutron monitors
Accurate conversion of neutron time-of-flight (TOF) to wavelength, and its
uncertainty, is of fundamental importance to neutron scattering measurements.
Especially in cases where instruments are highly configurable, the
determination of the absolute wavelength after any change must always be
performed. Inspired by the manner with which neutron spectrometers determine
the absolute wavelength, we evaluate for the first time, in the author's
knowledge, a commonly used method for converting TOF to neutron wavelength, the
distance of a monitor from the source of neutrons and we analytically calculate
the uncertainty contributions that limit the precision of the conversion. The
method was evaluated at the V20 test beamline at the Helmholtz Zentrum Berlin
(HZB), emulating the ESS source with a pulse of 2.86 ms length and 14 Hz
repetition rate, by using a mini-chopper operated at 140 Hz, beam monitors
(BMs) and data acquisition infrastructure. The mini-chopper created
well-defined neutron pulses and the BM was placed at two positions, enabling
the average wavelength of each of the pulses created to be determined. The used
experimental setup resulted in absolute wavelength determination at the monitor
positions with a of 1.8% for
\r{A}. With a modest increase of the distance between the
reference monitor positions a of below
0.5% can be achieved. Further improvements are possible by using a thinner
monitor, smaller chopper disc openings and a higher rotational speed chopper.
The method requires only two neutron measurements and doesn't necessitate the
use of crystals or complex fitting, and could constitute a suitable addition to
imaging, diffraction, reflectometers and small angle neutron scattering
instruments, at spallation sources, that do not normally utilise fast choppers
Inter-cultural differences in response to a computer-based anti-bullying intervention
Background and purpose: Many holistic anti-bullying interventions have been attempted, with mixed success, while little work has been done to promote a 'self-help' approach to victimisation. The rise of the ICT curriculum and computer support in schools now allows for approaches that benefit from technology to be implemented. This study evaluates the cross-cultural effects of a computer-based anti-bullying intervention on primary school-aged children's knowledge about bullying and relevant coping strategies.
Programme description: FearNot! is an interactive computer-based virtual learning environment designed for use as an anti-bullying intervention. It includes interactive virtual agents who assume the most common participant roles found in episodes of bullying. FearNot! was used by children over three consecutive weeks to allow its effectiveness to be evaluated in a longitudinal in situ programme.
Sample: Two comparable samples were drawn from the UK and Germany. In the UK, 651 participants (aged 8-11) were recruited from primary schools in Hertfordshire, Coventry and Warwickshire, whereas the 535 German participants (aged 7-10) were sourced from Grundschulen in the Bayern and Hessen regions. Because of lack of parental consent, late joiners and absences/missing responses, data from 908 participants (UK 493; Germany 415) were analysed.
Design and methods: A quasi-experimental, pre/post-tests control group design employed pre-published and bespoke questionnaires to collect data. Descriptive and inferential analyses were conducted.
Results: UK students possessed higher coping strategy knowledge scores than German participants, but German children's scores improved over time and as a result of the FearNot! intervention.
Conclusions: Overall, while not effective at increasing children's coping strategy knowledge in this study, the FearNot! intervention could prove a useful classroom tool to approach the issue of bullying as part of a wider initiative. Cultural differences at baseline and reactions to the intervention are discussed
Simulation of the Response of the Solid State Neutron Detector for the European Spallation Source
The characteristics of the Solid-state Neutron Detector, under development
for neutron-scattering measurements at the European Spallation Source, have
been simulated with a Geant4-based computer code. The code models the
interations of thermal neutrons and ionising radiation in the 6Li-doped
scintillating glass of the detector, the production of scintillation light and
the transport of optical, scintillation photons through the the scintillator,
en route to the photo-cathode of the attached multi-anode photomultiplier.
Factors which affect the optical-photon transport, such as surface finish,
pixelation of the glass sheet, provision of a front reflector and optical
coupling media are compared. Predictions of the detector response are compared
with measurements made with neutron and gamma-ray sources, a collimated alpha
source and finely collimated beams of 2.5 MeV protons and deuterons.Comment: Preprint 22 pages, 12 figures, published in NIM
Vanadium based neutron beam monitor
A prototype quasiparasitic thermal neutron beam monitor based on isotropic neutron scattering from a thin natural vanadium foil and standard 3He proportional counters is conceptualized, designed, simulated, calibrated, and commissioned. The European Spallation Source designed to deliver the highest integrated neutron flux originating from a pulsed source is currently under construction in Lund, Sweden. The effort to investigate a vanadium based neutron beam monitor was triggered by a list of requirements for beam monitors permanently placed in the ESS neutron beams in order to provide reliable monitoring at complex beamlines low attenuation, linear response over a wide range of neutron fluxes, near to constant efficiency for neutron wavelengths in a range of 0.6 10 , calibration stability and the possibility to place the system in vacuum are all desirable characteristics. The scattering based prototype, employing a natural vanadium foil andstandard 3He proportional counters, was investigated at the V17 and V20 neutron beamlines of the Helmholtz Zentrum in Berlin, Germany, in several different geometrical configurations of the 3He proportional counters around the foil. Response linearity is successfully demonstrated for foil thicknesses ranging from 0.04 mm to 3.15 mm. Attenuation lower than 1 for thermal neutrons is demonstrated for the 0.04 mm and 0.125 mm foils. The geometries used for the experiment were simulated allowing for absolute flux calibration and establishing the possible range of efficiencies for various designs of the prototype. The operational flux limits for the beam monitor prototype were established as a dependency of the background radiation and prototype geometry. The herein demonstrated prototype monitors can be employed for neutron intensities ranging from 103 1010 n s
A Very Intense Neutrino Super Beam Experiment for Leptonic CP Violation Discovery based on the European Spallation Source Linac: A Snowmass 2013 White Paper
Very intense neutrino beams and large neutrino detectors will be needed in
order to enable the discovery of CP violation in the leptonic sector. We
propose to use the proton linac of the European Spallation Source currently
under construction in Lund, Sweden to deliver, in parallel with the spallation
neutron production, a very intense, cost effective and high performance
neutrino beam. The baseline program for the European Spallation Source linac is
that it will be fully operational at 5 MW average power by 2022, producing 2
GeV 2.86 ms long proton pulses at a rate of 14 Hz. Our proposal is to upgrade
the linac to 10 MW average power and 28 Hz, producing 14 pulses/s for neutron
production and 14 pulses/s for neutrino production. Furthermore, because of the
high current required in the pulsed neutrino horn, the length of the pulses
used for neutrino production needs to be compressed to a few s with the
aid of an accumulator ring. A long baseline experiment using this Super Beam
and a megaton underground Water Cherenkov detector located in existing mines
300-600 km from Lund will make it possible to discover leptonic CP violation at
5 significance level in up to 50% of the leptonic Dirac CP-violating
phase range. This experiment could also determine the neutrino mass hierarchy
at a significance level of more than 3 if this issue will not already
have been settled by other experiments by then. The mass hierarchy performance
could be increased by combining the neutrino beam results with those obtained
from atmospheric neutrinos detected by the same large volume detector. This
detector will also be used to measure the proton lifetime, detect cosmological
neutrinos and neutrinos from supernova explosions. Results on the sensitivity
to leptonic CP violation and the neutrino mass hierarchy are presented.Comment: 28 page
Psychopolitics: Peter Sedgwick’s legacy for mental health movements
This paper re-considers the relevance of Peter Sedgwick's Psychopolitics (1982) for a politics of mental health. Psychopolitics offered an indictment of ‘anti-psychiatry’ the failure of which, Sedgwick argued, lay in its deconstruction of the category of ‘mental illness’, a gesture that resulted in a politics of nihilism. ‘The radical who is only a radical nihilist’, Sedgwick observed, ‘is for all practical purposes the most adamant of conservatives’. Sedgwick argued, rather, that the concept of ‘mental illness’ could be a truly critical concept if it was deployed ‘to make demands upon the health service facilities of the society in which we live’. The paper contextualizes Psychopolitics within the ‘crisis tendencies’ of its time, surveying the shifting welfare landscape of the subsequent 25 years alongside Sedgwick's continuing relevance. It considers the dilemma that the discourse of ‘mental illness’ – Sedgwick's critical concept – has fallen out of favour with radical mental health movements yet remains paradigmatic within psychiatry itself. Finally, the paper endorses a contemporary perspective that, while necessarily updating Psychopolitics, remains nonetheless ‘Sedgwickian’
Light-yield response of liquid scintillators using 2–6 MeV tagged neutrons
Knowledge of the neutron light-yield response is crucial to the understanding of scintillator-based neutron detectors. In this work, neutrons from 2–6MeV have been used to study the scintillation light-yield response of the liquid scintillators NE 213A, EJ 305, EJ 331 and EJ 321P using event-by-event waveform digitization. Energy calibration was performed using a GEANT4 model to locate the edge positions of the Compton distributions produced by gamma-ray sources. The simulated light yield for neutrons from a PuBe source was compared to measured recoil proton distributions, where neutron energy was selected by time-of-flight. This resulted in an energy-dependent Birks parameterization to characterize the non-linear response to the lower energy neutrons. The NE 213A and EJ 305 results agree very well with existing data and are reproduced nicely by the simulation. New results for EJ 331 and EJ 321P, where the simulation also reproduces the data well, are presented
Response of a Li-glass/multi-anode photomultiplier detector to collimated thermal-neutron beams
The response of a position-sensitive Li-glass scintillator detector being
developed for thermal-neutron detection with 6 mm position resolution has been
investigated using collimated beams of thermal neutrons. The detector was moved
perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and
vertical steps. Scintillation was detected in an 8 X 8 pixel multi-anode
photomultiplier tube on an event-by-event basis. In general, several pixels
registered large signals at each neutron-beam location. The number of pixels
registering signal above a set threshold was investigated, with the
maximization of the single-hit efficiency over the largest possible area of the
detector as the primary goal. At a threshold of ~50% of the mean of the
full-deposition peak, ~80% of the events were registered in a single pixel,
resulting in an effective position resolution of ~5 mm in X and Y. Lower
thresholds generally resulted in events demonstrating higher pixel
multiplicities, but these events could also be localized with ~5 mm position
resolution.Comment: 23 pages, 8 figure
Time- and energy-resolved effects in the boron-10 based Multi-Grid and helium-3 based thermal neutron detectors
The boron-10 based Multi-Grid detector is being developed as an alternative
to helium-3 based neutron detectors. At the European Spallation Source, the
detector will be used for time-of-flight neutron spectroscopy at cold to
thermal neutron energies. The objective of this work is to investigate fine
time- and energy-resolved effects of the Multi-Grid detector, down to a few
eV, while comparing it to the performance of a typical helium-3 tube.
Furthermore, it is to characterize differences between the detector
technologies in terms of internal scattering, as well as the time
reconstruction of ~ s short neutron pulses. The data were taken at the
Helmholtz Zentrum Berlin, where the Multi-Grid detector and a helium-3 tube
were installed at the ESS test beamline, V20. Using a Fermi-chopper, the
neutron beam of the reactor was chopped into a few tens of s wide pulses
before reaching the detector, located a few tens of cm downstream. The data of
the measurements show an agreement between the derived and calculated neutron
detection efficiency curve. The data also provide fine details on the effect of
internal scattering, and how it can be reduced. For the first time, the chopper
resolution was comparable to the timing resolution of the Multi-Grid detector.
This allowed a detailed study of time- and energy resolved effects, as well as
a comparison with a typical helium-3 tube.Comment: 37 pages, 21 figure
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