The GBAR (Gravitational Behavior of Antihydrogen at Rest) experiment at CERN requires efficient deceleration of 100 keV antiprotons provided by the new ELENA synchrotron ring to synthesize ...antihydrogen. This is accomplished using electrostatic deceleration optics and a drift tube that is designed to switch from -99 kV to ground when the antiproton bunch is inside – essentially a charged particle “elevator” – producing a 1 keV pulse. We describe the simulation, design, construction and successful testing of the decelerator device at -92 kV on-line with antiprotons from ELENA.
Time projection chambers for the T2K near detectors Abgrall, N.; Andrieu, B.; Baron, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2011, Volume:
637, Issue:
1
Journal Article
Peer reviewed
Open access
The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector ...located 295
km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280
m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator–bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker are used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/NOMAD dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system.
► First large scale time projection chambers with micropattern gas detectors. ► Incorporates new ASIC for electronic readout. ► Includes a pressure equalizing gas system and a photoelectron calibration system. ► Specifications achieved as deduced from neutrino, cosmic, and calibration tests. ► Will play an important role in T2K to measure neutrino oscillations.
For the GBAR (Gravitational Behaviour of Antihydrogen at Rest) experiment at CERN’s Antiproton Decelerator (AD) facility we have constructed a source of slow positrons, which uses a low-energy ...electron linear accelerator (linac). The driver linac produces electrons of 9 MeV kinetic energy that create positrons from bremsstrahlung-induced pair production. Staying below 10 MeV ensures no persistent radioactive activation in the target zone and that the radiation level outside the biological shield is safe for public access. An annealed tungsten-mesh assembly placed directly behind the target acts as a positron moderator. The system produces 5×107 slow positrons per second, a performance demonstrating that a low-energy electron linac is a superior choice over positron-emitting radioactive sources for high positron flux.
Rhizobacteria-induced systemic resistance (ISR) and pathogen-induced systemic acquired resistance (SAR) have a broad, yet partly distinct, range of effectiveness against pathogenic microorganisms. ...Here, we investigated the effectiveness of ISR and SAR in Arabidopsis against the tissue-chewing insects Pieris rapae and Spodoptera exigua. Resistance against insects consists of direct defense, such as the production of toxins and feeding deterrents and indirect defense such as the production of plant volatiles that attract carnivorous enemies of the herbivores. Wind-tunnel experiments revealed that ISR and SAR did not affect herbivore-induced attraction of the parasitic wasp Cotesia rubecula (indirect defense). By contrast, ISR and SAR significantly reduced growth and development of the generalist herbivore S. exigua, although not that of the specialist P. rapae. This enhanced direct defense against S. exigua was associated with potentiated expression of the defense-related genes PDF1.2 and HEL. Expression profiling using a dedicated cDNA microarray revealed four additional, differentially primed genes in microbially induced S. exigua-challenged plants, three of which encode a lipid-transfer protein. Together, these results indicate that microbially induced plants are differentially primed for enhanced insect-responsive gene expression that is associated with increased direct defense against the generalist S. exigua but not against the specialist P. rapae.
Positron accumulation in the GBAR experiment Blumer, P.; Charlton, M.; Chung, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2022, Volume:
1040
Journal Article
Peer reviewed
Open access
We present a description of the GBAR positron (e+) trapping apparatus, which consists of a three stage Buffer Gas Trap (BGT) followed by a High Field Penning Trap (HFT), and discuss its performance. ...The overall goal of the GBAR experiment is to measure the acceleration of the neutral antihydrogen (H¯) atom in the terrestrial gravitational field by neutralising a positive antihydrogen ion (H¯+), which has been cooled to a low temperature, and observing the subsequent H¯ annihilation following free fall. To produce one H¯+ ion, about 1010 positrons, efficiently converted into positronium (Ps), together with about 107 antiprotons (p¯), are required. The positrons, produced from an electron linac-based system, are accumulated first in the BGT whereafter they are stacked in the ultra-high vacuum HFT, where we have been able to trap 1.4(2) × 109 positrons in 1100 s.
The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the free fall acceleration of ultracold neutral anti hydrogen atoms in the terrestrial gravitational ...field. The experiment consists preparing anti hydrogen ions (one antiproton and two positrons) and sympathetically cooling them with B
e
+
ions to less than 10
μ
K. The ultracold ions will then be photo-ionized just above threshold, and the free fall time over a known distance measured. We will describe the project, the accuracy that can be reached by standard techniques, and discuss a possible improvement to reduce the vertical velocity spread.
The CaLIPSO project focuses on the development of an innovative energetic-photon detector. The detector uses a "heavy" organometallic liquid: the TriMethyl Bismuth (TMBi), 82% by weight of Bismuth. ...TMBi efficiently converts through the photo-electric effect photons of energies below 1 MeV. The ionisation signal and light produced in the liquid are both detected. Beyond the measurement of gamma photon energies, this detector will allow locating photon interactions in the detector in three dimensions down to 1 mm 3 and a sub nanosecond timing accuracy. All these desirable properties can be obtained simultaneously with liquid TMBi detector.
DNA duplexes containing unnatural base-pair surrogates are attractive biomolecular nanomaterials with potentially beneficial photophysical or electronic properties. Herein we report the first X-ray ...structure of a duplex containing a phen-pair in the center of the double helix in a zipper like stacking arrangement.
Abstract
Background
Magnetic resonance imaging MRI is a promising tool to evaluate therapeutic efficacy in ileocolonic Crohn’s disease CD.
Aims
We aimed to assess the feasibility of early MRI ...evaluation (week 12 W12) to predict corticosteroid-free remission CFREM at W52 and prevent long-term bowel damage.
Methods
All patients with active CD needing anti-tumour necrosis factor anti-TNF therapy were consecutively enrolled in this multicentre prospective study. MRI was performed before starting therapy, at W12 and W52. CFREM was defined as Crohn’s Disease Activity Index < 150, C-reactive protein < 5 mg/L and faecal calprotectin < 250 µg/g, with no switch of anti-TNF agents, no bowel resection and no therapeutic intensification between W12 and W52.
Results
Among 46 patients, 22 47.8% achieved CFREM at W52. Anti-TNF agents were able to heal almost all CD lesions as soon as W12 p < 0.05. Early transmural response defined as a 25% decrease of either Clermont score (odds ratio OR = 7.7 1.7–34.0, p < 0.001) or Magnetic Resonance Index of Activity (OR = 4.2 1.3–13.3, p = 0.015) was predictive of CFREM at W52. Achieving at least two items on W12-MRI among ulceration healing, disappearance of enlarged lymph nodes or sclerolipomatosis, ΔADC apparent diffusion coefficient > +10% or ΔRCE relative contrast enhancement > −30% was associated with a likelihood of CFREM at W52 of 84.6% vs 37.5% in patients without transmural response p < 0.001. Early transmural response could prevent bowel damage progression over time using Clermont score (hazard ratio = 0.21 0.0–0.9; p = 0.037).
Conclusion
Evaluation of early transmural response by MRI is feasible and is a promising end point to monitor therapeutic efficacy in patients with CD.
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