27 research outputs found

    Determination of the default curve for the unfolding procedure in the measurement of threshold neutron excitation functions

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    In this study, we have improved the technique for measuring the neutron activation cross-section using wide energy neutron beams (NAXSUN). We propose a method for the determination of the default function for the unfolding procedure, which is an important and critical part for extracting reaction cross-sections from this type of measurements. The new method was tested on the measurement of the excitation function from the threshold energy up to 5.6 MeV for the 113In(n,n')113mIn and 115In(n,n')115mIn reactions.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

    Nuclear structure data obtained by the (n

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    The determination of nuclear structure parameters such as gamma transitions, level scheme, nuclear level density and radiative strength functions is one of the most important tasks in low-energy nuclear physics. The two-step gamma cascades method based on detection of gamma coincidences following neutron capture, ie. the (n,2γ) reaction has been proven to give spectroscopic data and data concerning level density and radiative strength function. This method allows for the study of the dynamics of interaction and inter-transition between Fermi-and Bose-states of the nucleus near the neutron binding energy. There is an essential difference between these intranuclear processes from those in classical and high-temperature superfluidity, which is determined by a shape of the investigated nucleus, the nucleon parity in it, existence of nucleons of different types (protons and neutrons) etc. Two-step gamma cascades technique has so far been successfully applied for 45 nuclei in the mass region 28<A<200. Brief description of the method will be included here with examples from the recent researc

    A procedure for the characterization of electron transmission through Frisch grids

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    In Frisch grid ionization chambers special attention must be paid to the operating voltages in order to avoid unwanted collection of electrons on the Frisch grid. Collection of electrons on the grid will lead to a decreased signal to noise ratio and consequently a deteriorated energy resolution. Furthermore, systematic errors in the determination of the angular distribution will be introduced. Theoretical formulas for minimized collection of electrons on the grid were derived by Bunemann et al. in the special case of a Frisch grid consisting of a plane of parallel wires. No such formulas exist for other grid geometries and a careful calibration procedure is needed. We describe here a procedure for characterizing the Frisch grid in terms of its transparency to electrons for a grid consisting of a mesh of crossed wires.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

    Novel approach to imaging by cosmic-ray muons

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    Cosmic-ray muons can be used for imaging of large structures, or high-density objects with high atomic number. The first task can be performed by measurement of muon absorption within very thick material layers, while the second approach is based on muon multiple scattering. However, the muon imaging of small structures with low atomic number and density was not yet solved appropriately. Here we show the first results of cosmic-ray muon imaging of small objects made of elements of low atomic number. This novel approach includes detection of secondary particles produced by muons, which were not used at all in previous muon imaging methods. Thus, the list of elements, as well as the range of dimensions of objects which can be imaged are significantly expanded

    High resolution gamma-ray spectroscopy of fast-neutron induced fission

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    Experiments to perform precision spectroscopy of fast neutron induced fission were carried out during the ν-Ball experimental campaign at the ALTO facility of IJC Laboratory Orsay. Low energy fission of 232Th(n,f), 238U(n,f) and spontaneous fission of 252Cf were studied using this hybrid highresolution spectrometer and calorimeter. New observables such as γ-ray multiplicity distributions correlated with specific fission fragments are presented and discussed. A new method using fast-timing techniques to detect prompt fission neutrons in coincidence with prompt fission γ-rays is described

    High resolution gamma-ray spectroscopy of fast-neutron induced fission

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    International audienceExperiments to perform precision spectroscopy of fast neutron induced fission were carried out during the ν-Ball experimental campaign at the ALTO facility of IJC Laboratory Orsay. Low energy fission of 232Th(n,f), 238U(n,f) and spontaneous fission of 252Cf were studied using this hybrid highresolution spectrometer and calorimeter. New observables such as γ-ray multiplicity distributions correlated with specific fission fragments are presented and discussed. A new method using fast-timing techniques to detect prompt fission neutrons in coincidence with prompt fission γ-rays is described

    Assessment of Radiological Significance of Building Materials and Residues

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    The estimation of the radioactivity levels of materials utilized in construction sectors is crucial in the assessment of possible radiological hazards to human health. In the paper, the results of gamma spectroscopy study of 211 zircon, 425 sand, 781 lime, 348 perlite, 2692 cement, 232 calplex, 968 gypsum, 2741 granite and 21 coal fly ash samples gathered from different countries and imported in Serbia in period 2006-2016 were presented. In order to assess the radiological impact from the investigated samples, the activity concentration index I-RP112 for all samples was ascertained. This research yields insight into the radioactive content in a variety of building materials of different origin. The obtained results were discussed on the basis of relevant national and international legislation and guidance and compared with the corresponding results in the literature

    Determination of the nuclear level densities and radiative strength function for 43 nuclei in the mass interval 28≤A≤200

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    The determination of nuclear level densities and radiative strength functions is one of the most important tasks in low-energy nuclear physics. Accurate experimental values of these parameters are critical for the study of the fundamental properties of nuclear structure. The step-like structure in the dependence of the level densities p on the excitation energy of nuclei Eex is observed in the two-step gamma cascade measurements for nuclei in the 28 ≤ A ≤ 200 mass region. This characteristic structure can be explained only if a co-existence of quasi-particles and phonons, as well as their interaction in a nucleus, are taken into account in the process of gamma-decay. Here we present a new improvement to the Dubna practical model for the determination of nuclear level densities and radiative strength functions. The new practical model guarantees a good description of the available intensities of the two step gamma cascades, comparable to the experimental data accuracy

    The cross-sections for the 187Re(n,p)187W and 185Re(n,3n)183Re reactions in the energy range between 13.08 MeV and 19.50 MeV

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    Using the NAXSUN technique developed at the JRC-Geel, the cross section functions for neutron induced reactions 187Re(n,p)187W and 185Re(n,3n)183Re have been measured in the energy range between 13.08 MeV and 19.5 MeV. These data are the first experimentally obtained values for those nuclear reactions in this neutron energy range. Obtained results have been compared with existing evaluated data from ENDF/B-VII 0, JEFF 3.3, JEFF 3.2, BROND 3.1, JEF - 2.2, JENDL, ROSFO ND-2010. The TALYS 1.9 and EMPIRE 3.2.3 calculations were performed using different available models and calculations using several semi-empirical existing formulas. A comparison between theoretical model calculations and experimental results was made.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

    Multi-quasiparticle sub-nanosecond isomers in 178W

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    We report on the first measurement of the half-lives of K(pi) = 11- and 12+ four-quasiparticle states in the even-even nucleus W-178. The sub-nanosecond half-lives were measured by applying the centroid shift method to data taken with LaBr3 scintillator detectors of the NuBall array at the ALTO facility in Orsay, France. The half-lives of these states only became accessible by the combination of several experimental techniques - scintillator fast timing, isomer spectroscopy with a pulsed beam, and the event-by-event calorimetry information provided by the NuBall array as a whole. The measured half-lives are 476(44)ps and 275(65)ps for the I(pi) = 11- and 12+, respectively. The decay transitions include weakly hindered E1 and E2 branches directly to the ground-state band, bypassing the two-quasiparticle states. This is the first such observation for an E1 transition. The interpretation of the small hindrance hinges on mixing between the ground-state band and the t-band.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard
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