538 research outputs found
Characterisation of the Temperature-dependent Dark Rate of Hamamatsu R7081-100 10" Photomultiplier Tubes
Dark noise is a dominant background in photomultiplier tubes (PMTs), which
are commonly used in liquid-filled particle detectors for single-photon
detection to see the results of particle interactions. A major contribution to
dark noise is thermionic emission from the photocathode.
The dark noise of Hamamatsu R7081-100 PMTs is characterised in a temperature
and purity controlled water tank, with the thermionic emission contribution
isolated. The results suggest that the intrinsic dark rate of PMTs does not
depend on the medium, but does follow Richardson's law of thermionic emission.
There are external contributions to the overall observed PMT count rate
identified, but the intrinsic PMT dark rate in water matches that measured in
air.Comment: 11 pages, 7 figures, 2 tables, prepared for submission to J. Instru
The sensory features of a food cue influence its ability to act as an incentive stimulus and evoke dopamine release in the nucleus accumbens core
The sensory properties of a reward-paired cue (a Conditioned Stimulus; CS) may impact the motivational value attributed to the cue, and in turn influence the form of the conditioned response (CR) that develops. A cue with multiple sensory qualities, such as a moving lever-CS, may activate numerous neural pathways that process auditory and visual information, resulting in CRs that vary both within and between individuals. For example, CRs include approach to the lever-CS itself (rats that “sign-track;” ST), approach to the location of reward delivery (rats that “goal-track;” GT), or an “intermediate” combination of these behaviors. We found that the multimodal sensory features of the lever-CS were important to the development and expression of sign-tracking. When the lever-CS was covered, and thus could only be heard moving, STs continued to approach the lever location, but also started to approach the food cup during the CS period. While still predictive of reward, the auditory component of the lever-CS was a much weaker conditioned reinforcer than the visible lever-CS. This plasticity in behavioral responding observed in STs closely resembled behaviors normally seen in rats classified as “intermediates.” Furthermore, the ability of both the lever-CS and reward-delivery to evoke dopamine release in the nucleus accumbens was also altered by covering the lever – dopamine signaling in STs resembled neurotransmission observed in rats that normally only GT. These data suggest that while the visible lever-CS was attractive, wanted, and had incentive value for STs, when presented in isolation the auditory component of the cue was simply predictive of reward, lacking incentive salience. Therefore, the specific sensory features of cues may differentially contribute to responding and ensure behavioral flexibility
Gas Gains Over 10 and Optimisation using Fe X-rays in Low Pressure SF with a Novel Multi-Mesh ThGEM for Directional Dark Matter Searches
The Negative Ion Drift (NID) gas SF has favourable properties for track
reconstruction in directional Dark Matter (DM) searches utilising low pressure
gaseous Time Projection Chambers (TPCs). However, the electronegative nature of
the gas means that it is more difficult to achieve significant gas gains with
regular Thick Gaseous Electron Multipliers (ThGEMs). Typically, the maximum
attainable gas gain in SF and other Negative Ion (NI) gas mixtures,
previously achieved with an Fe X-ray source or electron beam, is on the
order of ; whereas electron drift gases like CF and similar mixtures
are readily capable of reaching gas gains on the order of or greater. In
this paper, a novel two stage Multi-Mesh ThGEM (MMThGEM) structure is
presented. The MMThGEM was used to amplify charge liberated by an Fe
X-ray source in 40 Torr of SF. By expanding on previously demonstrated
results, the device was pushed to its sparking limit and stable gas gains up to
50000 were observed. The device was further optimised by varying the
field strengths of both the collection and transfer regions in isolation.
Following this optimisation procedure, the device was able to produce a maximum
stable gas gain of 90000. These results demonstrate an order of magnitude
improvement in gain with the NID gas over previously reported values and
ultimately benefits the sensitivity of a NITPC to low energy recoils in the
context of a directional DM search
Structure of the protective nematode protease complex H-gal-GP and its conservation across roundworm parasites
Roundworm parasite infections are a major cause of human and livestock disease worldwide and a threat to global food security. Disease control currently relies on anthelmintic drugs to which roundworms are becoming increasingly resistant. An alternative approach is control by vaccination and ‘hidden antigens’, components of the worm gut not encountered by the infected host, have been exploited to produce Barbervax, the first commercial vaccine for a gut dwelling nematode of any host. Here we present the structure of H-gal-GP, a hidden antigen from Haemonchus contortus, the Barber’s Pole worm, and a major component of Barbervax. We demonstrate its novel architecture, subunit composition and topology, flexibility and heterogeneity using cryo-electron microscopy, mass spectrometry, and modelling. Importantly, we demonstrate that complexes with the same architecture are present in other Strongylid roundworm parasites including human hookworm. This suggests a common ancestry and the potential for development of a unified hidden antigen vaccine
PocketWATCH: design and operation of a multi-use test bed for water Cherenkov detector components in pure and gadolinium loaded water
The PocketWATCH facility is a unique multi-purpose test bed designed to replicate the conditions of large water Cherenkov detectors. Housed at the University of Sheffield, the facility consists of a light-tight 2000 L ultrapure water tank with purification and temperature control systems. Water temperature, resistivity, and UV attenuation in the tank are monitored and shown to be stable over time. The system is also shown to be compatible with a solution of 0.2% gadolinium sulfate, allowing further utility in testing equipment bound for the next generation neutrino and nucleon decay water Cherenkov particle detectors. The relevant water quality parameters are shown to be stable whilst running in Gd-mode, thereby providing a suitable test bed for hardware development in a realistic, ex situ environment
Lowering the energy threshold in COSINE-100 dark matter searches
COSINE-100 is a dark matter detection experiment that uses NaI(Tl) crystal
detectors operating at the Yangyang underground laboratory in Korea since
September 2016. Its main goal is to test the annual modulation observed by the
DAMA/LIBRA experiment with the same target medium. Recently DAMA/LIBRA has
released data with an energy threshold lowered to 1 keV, and the persistent
annual modulation behavior is still observed at 9.5. By lowering the
energy threshold for electron recoils to 1 keV, COSINE-100 annual modulation
results can be compared to those of DAMA/LIBRA in a model-independent way.
Additionally, the event selection methods provide an access to a few to sub-GeV
dark matter particles using constant rate studies. In this article, we discuss
the COSINE-100 event selection algorithm, its validation, and efficiencies near
the threshold
PocketWATCH: Design and operation of a multi-use test bed for water Cherenkov detector components in pure and gadolinium loaded water
The PocketWATCH facility is a unique multi-purpose test bed designed to replicate the conditions of large water Cherenkov detectors. Housed at the University of Sheffield, the facility consists of a light-tight 2000L ultrapure water tank with purification and temperature control systems. Water temperature, resistivity, and UV attenuation in the tank are monitored and shown to be stable over time. The system is also shown to be compatible with a solution of 0.2% gadolinium sulfate, allowing further utility in testing equipment bound for the next generation neutrino and nucleon decay water Cherenkov particle detectors. The relevant water quality parameters are shown to be stable whilst running in Gd-mode, thereby providing a suitable test bed for hardware development in a realistic, ex situ environment
Demonstration of radon removal from SF6 using molecular sieves
The gas SF6 has become of interest as a negative ion drift gas for use in directional
dark matter searches. However, as for other targets in such searches, it is important that radon
contamination can be removed as this provides a source of unwanted background events. In this
work we demonstrate for the first time filtration of radon from SF6 gas by using a molecular
sieve. Four types of sieves from Sigma-Aldrich were investigated, namely 3Å, 4Å, 5Å and 13X.
A manufactured radon source was used for the tests. This was attached to a closed loop system in
which gas was flowed through the filters and a specially adapted Durridge RAD7 radon detector.
In these measurements, it was found that only the 5Å type was able to significantly reduce the
radon concentration without absorbing the SF6 gas. The sieve was able to reduce the initial radon
concentration of 3875 ± 13 Bqm−3
in SF6 gas by 87% when cooled with dry ice. The ability of
the cooled 5Å molecular sieve filter to significantly reduce radon concentration from SF6 provides
a promising foundation for the construction of a radon filtration setup for future ultra-sensitive SF6
gas rare-event physics experiments
Microsurgical third ventriculocisternostomy as an alternative to ETV: report of two cases
OBJECTIVE: To describe a microsurgical alternative to endoscopic third ventriculocisternostomy. METHODS: Two children with shunt-dependent hydrocephalus and multiple shunt revisions were considered candidates for third ventriculocisternostomy (TVS). Because of slit ventricles, an endoscopic approach was not possible and, therefore, both patients received a microsurgical TVS by a supraorbital approach. RESULTS: In both cases, microsurgical TVS was successful and the patients became shunt free. CONCLUSION: Microsurgical TVS by a supraorbital craniotomy is a viable alternative to endoscopic TVS in selected cases
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