18 research outputs found

    Pushing the high count rate limits of scintillation detectors for challenging neutron-capture experiments

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    One of the critical aspects for the accurate determination of neutron capture cross sections when combining time-of-flight and total energy detector techniques is the characterization and control of systematic uncertainties associated to the measuring devices. In this work we explore the most conspicuous effects associated to harsh count rate conditions: dead-time and pile-up effects. Both effects, when not properly treated, can lead to large systematic uncertainties and bias in the determination of neutron cross sections. In the majority of neutron capture measurements carried out at the CERN n\_TOF facility, the detectors of choice are the C6_{6}D6_{6} liquid-based either in form of large-volume cells or recently commissioned sTED detector array, consisting of much smaller-volume modules. To account for the aforementioned effects, we introduce a Monte Carlo model for these detectors mimicking harsh count rate conditions similar to those happening at the CERN n\_TOF 20~m fligth path vertical measuring station. The model parameters are extracted by comparison with the experimental data taken at the same facility during 2022 experimental campaign. We propose a novel methodology to consider both, dead-time and pile-up effects simultaneously for these fast detectors and check the applicability to experimental data from 197^{197}Au(nn,ő≥\gamma), including the saturated 4.9~eV resonance which is an important component of normalization for neutron cross section measurements

    Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF

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    This article presents a few selected developments and future ideas related to the measurement of (n,ő≥) data of astrophysical interest at CERN n_TOF. The MC-aided analysis methodology for the use of low-efficiency radiation detectors in time-of-flight neutron-capture measurements is discussed, with particular emphasis on the systematic accuracy. Several recent instrumental advances are also presented, such as the development of total-energy detectors with ő≥-ray imaging capability for background suppression, and the development of an array of small-volume organic scintillators aimed at exploiting the high instantaneous neutron-flux of EAR2. Finally, astrophysics prospects related to the intermediate i neutron-capture process of nucleosynthesis are discussed in the context of the new NEAR activation area

    Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF

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    This article presents a few selected developments and future ideas related to the measurement of (n,ő≥) data of astrophysical interest at CERN n_TOF. The MC-aided analysis methodology for the use of low-efficiency radiation detectors in time-of-flight neutron-capture measurements is discussed, with particular emphasis on the systematic accuracy. Several recent instrumental advances are also presented, such as the development of total-energy detectors with ő≥-ray imaging capability for background suppression, and the development of an array of small-volume organic scintillators aimed at exploiting the high instantaneous neutron-flux of EAR2. Finally, astrophysics prospects related to the intermediate i neutron-capture process of nucleosynthesis are discussed in the context of the new NEAR activation area

    Polyclonal Outbreak of Vancomycin-resistant Enterococcus faecium in a Pediatric Oncology Department

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    We present a polyclonal outbreak of vancomycin-resistant enterococci (VRE) colonization in a pediatric oncology department and the role of a bundle of actions. After the occurrence of VRE bloodstream infections in 2 patients, an active surveillance of VRE colonization was started. Enhanced infection control measures and closure of the department to new admissions for the first 3 months were implemented. Among 32 patients screened for VRE, 21 were found colonized. Daily prevalence of VRE colonization among hospitalized patients ranged from 40% to 75%, but no new VRE infections occurred. Monthly incidence of VRE colonization decreased from 2.5 to 0.6 cases per 100 occupied bed-days at the end of this outbreak by the implementation of the above-mentioned measures. All VRE isolates tested were Enterococcus faecium carrying VanA gene. Pulsed field gel electrophoresis showed a polyclonal outbreak. A case-control study did not show any particular risk factors for colonization. High use of glycopeptide was noted before study outbreak that was drastically decreased during the study but only temporarily. Control of VRE in pediatric oncology departments with high colonization rates is challenging and requires a multifaceted strategy. Polyclonal spread of VRE found in this study suggests a possible effect of prior antimicrobial overuse and the critical need for antimicrobial stewardship especially in the era of multidrug-resistant bacteria

    On the accuracy of cross-section measurements of neutron-induced reactions using the activation technique with natural targets: The case of Ge at E<math altimg="si5.svg" display="inline" id="d1e1043"><mrow><msub><mrow/><mrow><mi mathvariant="normal">n</mi></mrow></msub><mo linebreak="goodbreak" linebreakstyle="after">=</mo><mn>17</mn><mo>.</mo><mn>9</mn></mrow></math> MeV

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    International audienceSeveral cross-section measurements of neutron-induced reactions on Ge found in literature, are performed utilizing natGe targets. The production of the same residual nucleus as the measured one might occur as a result of the unavoidable presence of neighboring isotopes in the same target, acting as a contamination. Corrections must be made based on theoretical calculations and models in order to resolve this problem. The accuracy and limits of a methodology for these ‚Äútheoretical corrections‚ÄĚ are investigated in this work using isotopically enriched targets, which can produce very accurate results without the need for such corrections. Experimental cross-section measurements have been made for the 76Ge(n,2n)75Ge, 72Ge(n,őĪ)69mZn and 72Ge(n,p)72Ga reactions, via the activation technique, with the 27Al(n,őĪ)24Na reaction used as reference, employing both a natGe and isotopically enriched Ge targets. The 3H(d,n)4He (D‚ÄďT) reaction was used for producing the quasi-monoenergetic neutron beam in the 5.5 MV Tandem Accelerator Laboratory of the National Centre for Scientific Research ‚ÄúDemokritos‚ÄĚ in Athens, Greece, at an incident deuteron beam energy of 2.9 MeV. Using HPGe detectors, ő≥-ray spectroscopy was applied to determine the induced ő≥-ray activity of the residual nuclei. ‚ÄĘCross section measurements with natural Ge targets need to be corrected for contaminations from neighboring isotopes‚ÄĘA methodology is proposed for the correction of the contribution from parasitic channels‚ÄĘThe accuracy and limits of the methodology are investigated with two sets of measurements‚ÄĘEnriched and natural Ge targets were employed for cross-section measurements via the activation techniqu

    Compton imaging for enhanced sensitivity (n,ő≥) cross section TOF experiments: Status and prospects

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    Radiative neutron-capture cross sections are of pivotal importance in many fields such as nucle-osynthesis studies or innovative reactor technologies. A large number of isotopes have been measured with high accuracy, but there are still a large number of relevant isotopes whose cross sections could not be experimentally determined yet, at least with sufficient accuracy and completeness, owing to limitations in detection techniques, sample production methods or in the facilities themselves. In the context of the HYMNS (High-sensitivitY Measurements of key stellar Nucleo-Synthesis reactions) project over the last six years we have developed a novel detection technique aimed at background suppression in radiative neutron-capture time-of-flight measurements. This new technique utilizes a complex detection set-up based on position-sensitive radiation-detectors deployed in a Compton-camera array configuration. The latter enables to implement gamma-ray imaging techniques, which help to disentangle true capture events arising from the sample under study and contaminant background events from the surroundings. A summary on the main developments is given in this contribution together with an update on recent experiments at CERN n_TOF and an outlook on future steps

    Measurement of the Gd-160(n, gamma) cross section at n_TOF and its medical implications

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    Neutron-capture reactions on gadolinium isotopes play an important role in several fields of physics, in particular in nuclear Astrophysics for the understanding of the nucleosynthesis of heavy elements (beyond iron) in stars via the s- and r-processes [1] and in nuclear technology. Another important application of gadolinium is linked to the production of terbium, that offers a set of clinically interesting isotopes for theranostics, characterized by complementary physical decay characteristics. In particular, the low -energy beta(-) emitter terbium-161 is very similar to lutetium-177 in terms of half-life (6.89 d), beta(-) - energy and chemical properties. Being a significant emitter of conversion/Auger electrons, greater therapeutic effect can therefore be expected in comparison to Lu-177 [2, 3]. For this reason, in the last decade, the study of the neutron capture reaction Gd-160(n,,gamma)(161) Gd and the subsequent beta(-) - decay in terbium-161 is getting particular attention. As the nuclear data on the Gd-160 neutron capture reaction are quite scarce and inconsistent, a new measurement of the capture cross section of Gd-160 at the CERN neutron Time -Of-Flight facilty was performed in order to provide high resolution, high -accuracy data on this important reaction, in the energy range from thermal to hundreds of keV. In this contribution, the preliminary results of the n_TOF measurement are presented

    The neutron time-of-flight facility n_TOF at CERN Recent facility upgrades and detector developments

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    International audienceBased on an idea by Carlo Rubbia, the n_TOF facility at CERN has been operating for over 20 years. It is a neutron spallation source, driven by the 20 GeV/c proton beam from the CERN PS accelerator. Neutrons in a very wide energy range (from GeV, down to sub-eV kinetic energy) are generated by a massive Lead spallation target feeding two experimental areas. EAR1, horizonal with respect to the proton beam direction is set at 185 meters from the spallation target. EAR2, on the vertical line from the spallation source, is placed at 20 m. Neutron energies for experiments are selected by the time-of-flight technique (hence the name n_TOF), while the long flight paths ensure a very good energy resolution. Over one hundred experiments have been performed by the n_TOF Collaboration at CERN, with applications ranging from nuclear astrophysics (synthesis of the heavy elements in stars, big bang nucleosynthesis, nuclear cosmo-chronology), to advanced nuclear technologies (nuclear data for applications, nuclear safety), as well as for basic nuclear science (reaction mechanisms, structure and decay of highly excited compound states). During the planned shutdown of the CERN accelerator complex between 2019 and 2021, the facility went through a substantial upgrade with a new target-moderator assembly, refurbishing of the neutron beam lines and experimental areas. An additional measuring and irradiation station (the NEAR Station) has been envisaged and its capabilities for performing material test studies and new physics opportunities are presently explored. An overview of the facility and of the activities performed at CERN is presented in this contribution, with a particular emphasis on the most relevant experiments for nuclear astrophysics

    Status report of the n_TOF facility after the 2nd CERN long shutdown period

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    Abstract During the second long shutdown period of the CERN accelerator complex (LS2, 2019-2021), several upgrade activities took place at the n_TOF facility. The most important have been the replacement of the spallation target with a next generation nitrogen-cooled lead target. Additionally, a new experimental area, at a very short distance from the target assembly (the NEAR Station) was established. In this paper, the core commissioning actions of the new installations are described. The improvement in the n_TOF infrastructure was accompanied by several detector development projects. All these upgrade actions are discussed, focusing mostly on the future perspectives of the n_TOF facility. Furthermore, some indicative current and future measurements are briefly reported

    Overview of the dissemination of n_TOF experimental data and resonance parameters

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    The n_TOF neutron time-of-flight facility at CERN is used for nuclear data measurements. The n_TOF Collaboration works closely with the Nuclear Reaction Data Centres (NRDC) network to disseminate the experimental data through the international EXFOR library. In addition, the Collaboration helps integrate the results in the evaluated library projects. The present contribution describes the dissemination status of n_TOF results, their impact on evaluated libraries and ongoing efforts to provide n_TOF resonance parameters in ENDF-6 format for further use by evaluation projects
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