1,721,142 research outputs found
14 MeV calibration of JET neutron detectors-phase 1: Calibration and characterization of the neutron source
No full textIn view of the planned DT operations at JET, a calibration of the JET neutron monitors at 14 MeV neutron energy is needed using a 14 MeV neutron generator deployed inside the vacuum vessel by the JET remote handling system. The target accuracy of this calibration is 10% as also required by ITER, where a precise neutron yield measurement is important, e.g. for tritium accountancy. To achieve this accuracy, the 14 MeV neutron generator selected as the calibration source has been fully characterised and calibrated prior to the in-vessel calibration of the JET monitors. This paper describes the measurements performed using different types of neutron detectors, spectrometers, calibrated long counters and activation foils which allowed us to obtain the neutron emission rate and the anisotropy of the neutron generator, i.e.The neutron flux and energy spectrum dependence on emission angle, and to derive the absolute emission rate in 4π sr. The use of high resolution diamond spectrometers made it possible to resolve the complex features of the neutron energy spectra resulting from the mixed D/T beam ions reacting with the D/T nuclei present in the neutron generator target. As the neutron generator is not a stable neutron source, several monitoring detectors were attached to it by means of an ad hoc mechanical structure to continuously monitor the neutron emission rate during the in-vessel calibration. These monitoring detectors, two diamond diodes and activation foils, have been calibrated in terms of neutrons/counts within ± 5% total uncertainty. A neutron source routine has been developed, able to produce the neutron spectra resulting from all possible reactions occurring with the D/T ions in the beam impinging on the Ti D/T target. The neutron energy spectra calculated by combining the source routine with a MCNP model of the neutron generator have been validated by the measurements. These numerical tools will be key in analysing the results from the in-vessel calibration and to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the generator neutrons, and taking into account all the calibration circumstances. © 2017 EURATOM
Analysis of the structural properties of polycrystalline silicon germanium films
No full textIn this work, poly SiGe is proposed as a suitable material for surface micromachining applications that require a low thermal budget. The effect of the deposition conditions and layer thickness on the structural and mechanical properties of poly SiGe is analyzed by means of transmission electron microscopy (TEM) and X-ray diffraction spectroscopy (XRD). It is demonstrated that using as-grown poly SiGe (deposited at 625°C), a low tensile stress (+60 MPa) and a negligible stress gradient can be achieved. © 1999 Kuwait University
Photoluminescence and thermoluminescence investigation of europium- and dysprosium-doped dibarium magnesium silicate phosphor
No full textEuropium- and dysprosium-doped barium magnesium silicate powder with different concentrations of dysprosium was synthesized using solid state reactions. The prepared phosphors were characterized using photoluminescence. Prominent green color emissions were obtained under ultraviolet excitation. The thermoluminescence glow curves of the samples were measured after various delay times. With increased delay time, the intensity of the thermoluminescence peak decays, and the position of the thermoluminescence peak shifts to higher temperatures, indicating the considerable retrapping associated with general order kinetics. Refined lattice parameters of monoclinic phosphor were calculated
Activation measurements in support of the 14 MeV neutron calibration of JET neutron monitors
No full textIn preparation for the upcoming deuterium-tritium campaign at the JET tokamak, the ex-vessel fission chamber neutron diagnostics and the neutron activation system will be calibrated in absolute terms at 14 MeV neutron energy, to a required accuracy of less than 10%. Two nominally identical DT neutron generators were chosen as the calibration sources, both of which were fully calibrated and characterized at the UK's National Physical Laboratory. The neutron activation method was adopted as a complementary method for the purpose of determining the absolute value of the neutron yield from the neutron generators and to provide a means of cross check for the active detection methods being employed. The work being presented here shows the derivation of the neutron emission rate from the neutron generators based upon experimental activation foil measurements. © 2017 Elsevier B.V
Tecniche e tecnologie per la progettazione del sistema di monitoraggio di strutture complesse
No full textRecent advances in digital coincidence counting for Radionuclide Metrology
No full textThe radioactivity measurement techniques developed within the EURAMET EMRP 'MetroFission' Joint Research Project, were aimed at performing on-site activity measurements at the primary standard level (4πβ-γ coincidence counting) for a wide range of radionuclides utilizing recent advances in high-speed digital sampling and digital signal processing. The state-of-the-art technology employed within this project provides up to 14-bit digitizer systems operating with sampling rates in the order of 108 to 109 samples-per-second, incorporating on-board FPGA devices, which greatly enhances the application of digital signal processing for the implementation of digital coincidence counting. These devices when coupled to suitable analysis software, demonstrate a significant improvement in the provision of primary standards of radioactivity. This manuscript provides a description of the systems employed, along with recommendations regarding optimization of the digital sampling of signals from photo-multiplier tubes and pre-amplifiers and compare the benefits of 'off-line' versus 'on-line' 4πβ-γ digital coincidence counting systems. © 2013 IEEE
14 MeV calibration of JET neutron detectors - Phase 2: In-vessel calibration
No full textA new DT campaign (DTE2) is planned at JET in 2020 to minimize the risks of ITER operations. In view of DT operations, a calibration of the JET neutron monitors at 14 MeV neutron energy has been performed using a well calibrated 14 MeV neutron generator (NG) deployed, together with its power supply and control unit, inside the vacuum vessel by the JET remote handling system. The NG was equipped with two calibrated diamond detectors, which continuously monitored its neutron emission rate during the calibration, and activation foils which provided the time integrated yield. Cables embedded in the remote handling boom were used to power the neutron generator, the active detectors and pre-amplifier, and to transport the detectors' signal. The monitoring activation foils were retrieved at the end of each day for decay γ-ray counting, and replaced by fresh ones. About 76 hours of irradiation, in 9 days, were needed with the neutron generator in 73 different poloidal and toroidal positions in order to calibrate the two neutron yield measuring systems available at JET, the 235U fission chambers (KN1) and the inner activation system (KN2). The NG neutron emission rates provided by the monitoring detectors were in agreement within 3%. Neutronics calculations have been performed using MCNP code and a detailed model of JET to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the NG neutrons, and taking into account the anisotropy of the neutron generator and all the calibration circumstances. These calculations have made use of a very detailed and validated geometrical description of the neutron generator and of the modified MNCP neutron source subroutine producing neutron energy-angle distribution for the neutrons emitted by the NG. The KN1 calibration factor for a DT plasma has been determined with ±4.2% experimental uncertainty. Corrections due to NG and remote handling effects and the plasma volume effect have been calculated by simulation modelling. The related additional uncertainties are difficult to estimate, however the results of the previous calibration in 2013 have demonstrated that such uncertainties due to modelling are globally ±3%. It has been found that the difference between KN1 response to DD neutrons and that to DT neutrons is within the uncertainties in the derived responses. KN2 has been calibrated using the 93Nb(n,2n)92mNb and 27Al(n,a)24Na activation reactions (energy thresholds 10 MeV and 5 MeV, respectively). The total uncertainty on the calibration factors is ±6% for 93Nb(n,2n)92mNb and ±8% 27Al(n,a)24Na (1σ). The calibration factors of the two independent systems KN1 and KN2 will be validated during DT operations. The experience gained and the lessons learnt are presented and discussed in particular with regard to the 14 MeV neutron calibrations in ITER. © 2018 EURATOM
EXAFS - A NEW APPROACH TO THE STRUCTURE OF MICELLAR AGGREGATES
No full textA helical model was previously proposed for sodium (NaDC) and rubidium (RbDC) deoxycholate micellar aggregates in
aqueous solutions. SAXS, NMR, ESR, and CD meehurements verified the helical model. Here we report an EXAFS study
by the spherical wave formalism on the coordination of the Rb' ions in the crystal, macromolecular fiber, and micellar aqueous
solution of RbDC together with measurements carried out on rubidium oxalate (crystal and aqueous solution). The results
show that the Rb" ions of the micellar aggregates have the same (or very similar) peculiar coordination as that inside the
helices of the crystal and macromolecular fiber. Moreover, their coordination remarkably differs from that observed in the
aqueous solutions of rubidium oxalate, where the situation would be similar to that of a classical micelle. Thus, the helical
model is unquestionably confirmed
Identification of hrp genes, encoding harpin, in Pseudomonas avellanae (Psallidas) Janse et al.
No full textPreliminary investigation of hrpZ gene presence in Pseudomonas avellanae and in a bacterium inducing HR on tobacco.
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