1,721,126 research outputs found
Measurement of the thermal expansion coefficient of an Al-Mg alloy at ultra-low temperatures
No full textWe describe a result coming from an experiment based on an Al-Mg alloy (∼5% Mg) suspended bar hit by an electron beam and operated above and below the temperature of transition from superconducting to normal state of the material. The amplitude of the bar first longitudinal mode of oscillation, excited by the beam interacting with the bulk, and the energy deposited by the beam in the bar are the quantities measured by the experiment. These quantities, inserted in the equations describing the mechanism of the mode excitation and complemented by an independent measurement of the specific heat, allow us to determine the linear expansion coefficient α of the material. We obtain α = [(10.9±0.4)T+(1.3±0.1)T3]×10 -10 K-1 for the normal state of conduction in the temperature interval 0.9 < T < 2 K and α = [(-2.45±0.60)+(- 10.68±1.24)T +(0.13±0.01)T3]×10-9 K-1 for the superconducting state in the interval 0.3 < T< 0.8 K. © 2013 World Scientific Publishing Company
Development and testing of a cryogenic system for radioactive 14CO2 gas separation for nuclear waste monitoring
No full textA prototypal system for the separation of CO2 from air and concentration in small volume containers was developed and tested at ENEA in the frame of two European research projects (MetroRWM and MetroDECOM), funded by the European Metrology Research Programme (EMRP). The aim of the proposed system is to separate and concentrate in an effective way the CO2 content from radioactive air stream in nuclear installations or nuclear waste repositories during normal operation or decommissioning phase, by using a cryogenic process. This system is intended to be used as preparatory stage of the CO2 samples to be analysed by a radioactive gas-in-air monitor using a standardised 14CO2. Connecting the ENEA cryogenic system to the monitor will enable a sample of air to be processed and measured, and its 14CO2 activity concentration calculated, from knowledge of the volume of air sampled by the cryogenic system and the response of the monitor. Our work demonstrates the feasibility of a14C monitoring based on cryogenic method, according to which the components of a gaseous mixture can be separated on the basis of the differences between the phase transition properties of each gas components. The initial design was made considering the readily-available commercial instruments and devices and combining them in an optimum way. System testing showed almost 100% CO2 separation and recovery. © 2018 Elsevier Lt
Future of 99Mo reactor-independent supply
No full textMolybdenum-99 is essential for nuclear medicine, being the parent radionuclide of 99mTc, which is commonly used in single-photon-emission computed tomography scans. Worldwide, the supply of 99Mo has faced considerable disruption twice in recent years: in 2009 triggered by the unexpected simultaneous shutdown of two nuclear research reactors, and in 2020 because of disruption to shipments of 99Mo as a consequence of severe restrictions on flights. This Perspective therefore examines alternative means of 99Mo production, via cyclotrons, electron linear accelerators and fusion neutron sources. The research and development of methods for 99Mo that can be synergic and complementary to reactors in the short-to-medium term and alternative to them in the long term is strategic for addressing potential global events that might produce reduced access to healthcare procedures relying on diagnostic as well as therapeutic radionuclides
99mTc production via 100Mo(n,2n)99Mo reaction using 14 MeV neutrons from a D-T neutron source: Discussion for a scientific case
Full text linkIl 99mTc è un radionuclide ampiamente usato in tutto il mondo per diagnosi di tipo SPECT (Single Photon Emission Computed Tomography) grazie alla sua breve vita media (circa 6 h) e all’emissione di fotoni di bassa energia (140 keV), particolarmente idonei per la strumentazione diagnostica utilizzata. In campo medico, il 99mTc viene principalmente fornito attraverso il suo precursore 99Mo, che ad oggi viene ricavato essenzialmente come prodotto di fissione di target irraggiati in reattori nucleari. Nel 2009 l’Agenzia per l’Energia Nucleare (NEA), a fronte dell’evidenza di un’imminente carenza a livello mondiale di 99mTc, ha costituito un gruppo di lavoro di alto livello sulla sicurezza nella produzione di radioisotopi medici (HLG-MR) allo scopo di studiare tutti i possibili canali di produzione di 99Mo/99mTc nel breve, medio e lungo periodo. Come risultato di questa accurata indagine, il HLG-MR ha rilasciato un rapporto che evidenzia come la carenza di produzione di 99mTc sia principalmente dovuta alla ben consolidata, ma vetusta, catena di produzione, essenzialmente basata su reattori nucleari di vecchia generazione. Il HLG-MR ha anche prodotto una rassegna di differenti tecnologie per la produzione di 99Mo/99mTc, basata rispettivamente su: a) bersagli HEU (Uranio altamente arricchito) e LEU (Uranio a basso arricchimento) nei reattori a fissione; b) attivazione di 98Mo mediante neutroni termici in reattori nucleari; c) produzione diretta da ciclotroni; d) reazioni di fotofissione in 238U; e) foto produzione di 99Mo e f) reazioni indotte da neutroni veloci. Nel presente rapporto tecnico, si descrive l’uso di 99mTc in medicina nucleare focalizzando l’attenzione sulla recente e ben documentata vasta richiesta e critica carenza di tale radionuclide a livello mondiale.
Viene, in particolare, discusso il metodo di generazione del 99mTc per mezzo della reazione
100Mo(n,2n)99Mo. Proprio con riferimento a quest’ultimo canale di produzione, in ENEA è stato recentemente condotto uno studio di fattibilità di produzione del 99Mo, come descritto in dettaglio nel seguito. L’attività di 99Mo, ottenuta irraggiando con neutroni da 14 MeV un bersaglio di Molibdeno naturale presso l’impianto Frascati Neutron Generator (FNG), sito nel Centro Ricerche ENEA di Frascati, è stata accuratamente determinata mediante misure riferibili ai campioni nazionali di attività dell’Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti (INMRI) presso il Centro Ricerche Casaccia dell’ENEA (Santa Maria di Galeria, Roma). I risultati dell’attività specifica di 99Mo ottenuta in ENEA sono stati confrontati con quelli documentati da un gruppo di ricerca giapponese, che ha usato la stessa tecnica, mostrando un ottimo accordo entro le incertezze di misura. L’intero esperimento svolto in ENEA e le stime predittive estrapolate dai risultati sperimentali sono state supportate con simulazioni Monte Carlo effettuate con il codice Fluka. I modelli Monte Carlo sono stati validati attraverso il confronto delle stime di attività prodotte a ENEA-FNG con i corrispettivi valori misurati presso l’ENEA-INMRI, avvalendosi della riferibilità ai campioni primari di attività sviluppati e custoditi nella sezione Radioattività dell’Istituto. Al fine di confrontare in modo quantitativo l’efficienza di produzione del 99Mo attraverso i metodi implementati nelle diverse tipologie di impianti (acceleratori e reattori), è stata introdotta un’adeguata Figura di Merito (FoM) basata sull’attività di 99Mo prodotta dall’impianto e la potenza dello stesso.
Ciò ha consentito di valutare l’efficienza di produzione di 99Mo a FNG, permettendo di estrapolare questo dato all’impianto di nuova concezione di neutroni a 14 MeV quale è la New Sorgentina Fusion Source (NSFS). Infine, ma non meno importante, è stata introdotta una FoM finanziaria, da considerarsi come un parametro di costo delle varie facility prese in esame per la produzione di 99Mo e l’attività prodotta settimanalmente per questo radionuclide.99mTc is a widely used radionuclide for SPECT (Single Photon Emission Computed Tomography) diagnostics thanks to its short half-life (about 6h) and the low-energy gamma ray emission (140 keV) well suited for diagnostic devices. In medicals, 99mTc is mostly provided through its precursor 99Mo. In 2009 the Nuclear Energy Agency (NEA) formed the High-Level Group on Security of Supply of Medical Radioisotopes (HLG-MR), in order to study the supply chain of 99Mo/99mTc in the world for short, medium and long term period. The HLG-MR delivered a report highlighting how the shortage of 99mTc supply was mostly due to the well-established but aged production chain essentially based on old nuclear
reactors. A review of different technologies for producing 99Mo/99mTc was also provided by the HLG-MR based respectively on: a) HEU (highly enriched Uranium) and LEU (low enriched Uranium) targets in fission reactors; b) 98Mo thermal neutron activation in nuclear
reactors; c) direct cyclotron production; d) photo-fission reactions on 238U; e) 99Mo photo-production and f) fast neutron-induced reactions. In this technical report, the use of 99mTc in nuclear medicine is discussed focusing on the recently documented great worldwide demand and shortage of this radionuclide. The specific method for producing 99mTc via 100Mo(n,2n)99Mo reaction is discussed in detail as it was investigated also in ENEA. The
99Mo activity achieved by means of 14 MeV neutron irradiation on natural Molybdenum sample at the Frascati Neutron Generator (FNG) facility, at the Research Centre of ENEA-Frascati, was accurately assessed, by tracing it to the standards provided by the Italian National Institute of Ionizing Radiation Metrology (INMRI), located at the Research Centre of ENEA-Casaccia. The results of 99Mo specific activity obtained at ENEA were then compared with those documented in feasibility studies of a Japanese research group, which used the same technique, showing a good agreement within the uncertainties of measurements. The whole experiment carried out in ENEA was supported by simulations performed with the Fluka Monte Carlo code, whose predictions have been benchmarked against the experimental data collected at ENEA-FNG relying on the traceability to the activity standards developed and maintained at the ENEA-INMRI laboratories, Radioactivity section.
A Figure of Merit (FoM) was then introduced in order to compare the performances of the different methods (accelerator or neutron based) used for 99Mo production. The FoM was obtained by taking into account the 99Mo activity produced and the power of the facility used. This allowed to evaluate the 99Mo efficiency production at FNG and to extrapolate the obtained data to the new infrastructure for generating 14 MeV neutron which is New Sorgentina Fusion Source (NSFS). Last, but not the least, a financial FoM was introduced in order to take into account the cost parameter of each facility considered for 99Mo production respect to the weakly activity produced for this radionuclide
Quantification of the validity of simulations based on Geant4 and FLUKA for photo-nuclear interactions in the high energy range
No full textPhoto-nuclear interactions are relevant in many research fields of both fundamental and applied physics and, for this reason, accurate Monte Carlo simulations of photo-nuclear interactions can provide a valuable and indispensable support in a wide range of applications (i.e from the optimisation of photo-neutron source target to the dosimetric estimation in high energy accelerator, etc). Unfortunately, few experimental photo-nuclear data are available above 100 MeV, so that, in the high energy range (from hundreds of MeV up to GeV scale), the code predictions are based on physical models. The aim of this work is to compare the predictions of relevant observables involving photon-nuclear interaction modelling, obtained with GEANT4 and FLUKA, to experimental data (if available), in order to assess the code estimation reliability, over a wide energy range. In particular, the comparison of the estimated photo-neutron yields and energy spectra with the experimental results of the n@BTF experiment (carried out at the Beam Test Facility of DaΦne collider, in Frascati, Italy) is here reported and discussed. Moreover, the preliminary results of the comparison of the cross sections used in the codes with the"evaluated' data recommended by the IAEA are also presented for some selected cases (W, Pb, Zn). © The Authors, published by EDP Sciences, 2017
A new 3He-free thermal neutrons detector concept based on the GEM technology
No full textA thermal neutron detector based on the Gas Electron Multiplier technology is presented. It is configured to let a neutron beam interact with a series of borated glass layers placed in sequence along the neutron path inside the device. The detector has been tested on beam both at the ISIS (UK) spallation neutron source and at the TRIGA reactor of ENEA, at the Casaccia Research Center, near Rome in Italy. For a complete characterization and description of the physical mechanism underlying the detector operation, several Monte Carlo simulations were performed using both Fluka and Geant4 code. These simulations are intended to help in seeking the optimal geometrical set-up and material thickness (converter layer, gas gap, sheet substrate) to improve the final detector design in terms of achieving the best detector efficiency possible. © 2013 Elsevier B.V
3He-free triple GEM thermal neutron detector
No full textA novel type of thermal neutron detector based on the gas electron multiplier (GEM) technology is presented in the framework of the research and development activity on the 3He replacement for neutron detection. The device relies on a series of boron-coated alumina sheets placed perpendicularly to the incident neutron beam direction. The detector, named side-on GEM (S-GEM), was tested on beam at the High Flux Isotope Reactor at the Oak Ridge National Laboratory (US) to assess its performance in terms of beam position resolution, efficiency and signal-to-background (S/B) ratio as compared to a 10 bar 3He tube for sub-thermal neutrons. Using 3 mm wide PADs, a sub-millimeter position resolution was obtained. The achieved efficiency is about 30% with a quite good S/B ratio. The obtained results demonstrate the effectiveness of the proposed detector configuration to achieve a good spatial resolution and, in the perspective, a higher thermal neutron efficiency, comparable to 3He tubes typically used for diagnostic in nuclear reactors. The main issues to be addressed to reach the goal, mostly related to boron coating procedures and characterization, are also pointed out. © Copyright EPLA, 2014
Genomic analysis of three cheese-borne pseudomonas lactis with biofilm and spoilage-associated behavior
Full text linkPsychrotrophic pseudomonads cause spoilage of cold fresh cheeses and their shelf-life reduction. Three cheese-borne Pseudomonas sp., ITEM 17295, ITEM 17298, and ITEM 17299 strains, previously isolated from mozzarella cheese, revealed distinctive spoilage traits based on molecular determinants requiring further investigations. Genomic indexes (ANI, isDDH), MLST-based phylogeny of four housekeeping genes (16S rRNA, gyrB, rpoB and rpoD) and genome-based phylogeny reclassified them as Pseudomonas lactis. Each strain showed distinctive phenotypic traits at 15 and 30◦C: ITEM 17298 was the highest biofilm producer at both temperatures, whilst ITEM 17295 and ITEM 17299 showed the strongest proteolytic activity at 30◦C. A wider pattern of pigments was found for ITEM 17298, while ITEM 17295 colonies were not pigmented. Although the high genomic similarity, some relevant molecular differences supported this phenotypic diversity: ITEM 17295, producing low biofilm amount, missed the pel operon involved in EPS synthesis and the biofilm-related Toxin-Antitoxin systems (mqsR/mqsA, chpB/chpS); pvdS, required for the pyoverdine synthesis, was a truncated gene in ITEM 17295, harboring, instead, a second aprA involved in milk proteolysis. This work provided new insight into the food spoiler microbiota by identifying these mozzarella cheese spoilers as P. lactis; molecular targets to be exploited in the development of novel preservative strategies were also revealed
Carteolol, a non-conventional partial agonist of β1-adrenoceptors, relaxes phenylephrine-constricted rat aorta through antagonism at α1-adrenoceptors
No full textThis in vitro study was designed to investigate whether carteolol, a non-conventional partial agonists of β1-adrenoceptors, relaxes phenylephrine-constricted rat aorta through activation of the low-affinity state of β1-adrenoceptors or antagonist effect at α1-adrenoceptors. Carteolol-induced complete concentration-dependent relaxation of phenylephrine-contracted aorta (pD2 = 3.65 ± 0.04), this effect not being modified by endothelium removal and not antagonised by NO-synthase inhibitor NG-nitro-l-arginine methyl ester (100 μM) or cyclo-oxygenase inhibitor indomethacin (10 μM). The effect of carteolol was unaffected by the non-selective β-adrenoceptor antagonist propranolol (1 μM), or the β2-adrenoceptor selective antagonist (±)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol (ICI 118,551, 1 μM). Increasing concentrations of carteolol produced a parallel rightward shift of the concentration-response curves for phenylephrine-induced contraction, exhibiting a pKB of 4.28 ± 0.07. Carteolol affinity for α1-adrenoceptors was evaluated by means of competition experiments carried out in BHK-21 cell membranes expressing rat recombinant α1D-adrenoceptor, the α1-adrenoceptor subtype mainly present in rat aorta. Carteolol competed monophasically with [3H]prazosin, exhibiting a pKi value (3.39 ± 0.31) similar to its pD2 and not very far from its pKB. In conclusion, this study indicates that carteolol relaxes phenylephrine-contracted aorta through its α1-adrenoceptor antagonist properties, excluding the possibility that the relaxant effect is due to the activation of β-adrenoceptors, particularly of the low-affinity state of β1-adrenoceptors, by the drug. © 2008 Elsevier B.V. All rights reserved
A salicylate-functionalized PET packaging to counteract blue discoloration on mozzarella cheese under cold storage
No full textIn this work we tested a new technological solution to extend the shelf-life of Mozzarella cheese using a salicylate-functionalized PET packaging. To this aim, we inoculated ready-to-sell Mozzarella cheeses with Pseudomonas lactis ITEM 17298 strain, responsible for blue discoloration; mozzarella cheeses packed in treated or untreated trays were stored at 4 °C and monitored up to blue discoloration occurred. Results from microbiological analyses showed inhibitory effect against the pigmenting strain up to 8 days of cold storage in Mozzarella cheese packed in treated trays compared to the control samples. Likewise, CIELab values of b* and hue did not differ from those found on the uninoculated Mozzarella cheeses, delaying the appearance of bluish spots by approximately 2 days. Furthermore, the use of treated trays unpaired the formation of the biofilm by significantly reducing the amount deposited inside the treated trays compared to the control ones. For the first time, therefore, the use of an antimicrobial packaging with high technology readiness level has delayed the blue mozzarella occurrence specially contaminated samples. Further trials will have to be undertaken to optimize the salicylate concentration released in the tray in order to abate the risk of this fresh dairy product withdrawal from the market
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