Characterization of the neutron beam at nELBE Beyer, R.; Birgersson, E.; Elekes, Z. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2013, Letnik:
723
Journal Article
Recenzirano
The neutron time-of-flight setup nELBE at the Helmholtz-Zentrum Dresden-Rossendorf uses an intense electron beam impinging on a liquid-lead target to produce neutrons in the energy range from about ...10keV to 10MeV. This neutron source will be used to measure fast-neutron induced reactions with relevance for future nuclear transmutation facilities and nuclear waste management. The spatial profile, the intensity, the energy distribution and the time structure of the nELBE neutron beam have been investigated and the techniques how they were measured are explained in this work.
Cross sections for neutron capture in the range of unresolved resonances and average level distances near the neutron emission threshold are simultaneously predicted for more than 140 spin-0 target ...nuclei with A > 50. Assuming triaxiality in nearly all these nuclei a combined description of both, photon strength and level density, is presented – needing very few fit parameters only.
The M
ajorana
Collaboration is using an array of high-purity Ge detectors to search for neutrinoless double-beta decay in
76
Ge. Searches for neutrinoless double-beta decay are understood to be the ...only viable experimental method for testing the Majorana nature of the neutrino. Observation of this decay would imply violation of lepton number, that neutrinos are Majorana in nature, and provide information on the neutrino mass. The M
ajorana
D
emonstrator
comprises 44.1 kg of p-type point-contact Ge detectors (29.7 kg enriched in
76
Ge) surrounded by a low-background shield system. The experiment achieved a high efficiency of converting raw Ge material to detectors and an unprecedented detector energy resolution of 2.5 keV FWHM at Q
ββ
. The M
ajorana
collaboration began taking physics data in 2016. This paper summarizes key construction aspects of the Demonstrator and shows preliminary results from initial data.
The compact neutron-time-of-flight facility nELBE at the superconducting electron accelerator ELBE of Helmholtz-Zentrum Dresden-Rossendorf has been rebuilt. A new enlarged experimental hall with a ...flight path of up to 10 m is available for neutron time-of-flight experiments in the fast energy range from about 50 keV to 10 MeV. nELBE is intended to deliver nuclear data of fast neutron nuclear interactions e.g. for the transmutation of nuclear waste and improvement of neutron physical simulations of innovative nuclear systems. The experimental programme consists of transmission measurements of neutron total cross sections, elastic and inelastic scattering cross section measurements, and neutron induced fission cross sections. The inelastic scattering to the first few excited states in 56Fe was investigated by measuring the gamma production cross section with an HPGe detector. The neutron induced fission of 242Pu was studied using fast ionisation chambers with large homogeneous actinide deposits.
The photodissociation of the deuteron is a key reaction in Big Bang nucleosynthesis, but is only sparsely measured in the relevant energy range. To determine the cross section of the d(γ,n)p reaction ...we used pulsed bremsstrahlung and measured the time-of-flight of the neutrons. In this article, we describe how the efficiency of the neutron detectors was experimentally determined and how the modification of the neutron spectrum by parts of the experimental setup was simulated and corrected.
Korea has developed a Helium Cooled Ceramic Reflector Test Blanket Module (Ko HCCR TBM) related to the ITER project. Tungsten is considered as a prime candidate for the plasma facing materials in ...fusion reactors, and for the structure material of Ko HCCR TBM. KAERI (Korea Atomic Energy Research Institute) has been evaluating neutron cross sections of tungsten isotopes for neutron energy of up to 150 MeV based on nuclear reaction codes and available measurement data. New experimental data were measured at nELBE of HZDR (Helmholtz-Zentrum Dresden-Rossendorf) for a comparison with the evaluated and existing measurement data. The neutron source nELBE adopts a 40 MeV superconducting electron linac and a liquid Pb target for time-of-flight measurements. The nELBE neutron source uses no moderator and provides fast neutrons. An electron bunch length of 5 ps and a compact target provide a good neutron energy resolution with a relatively short flight length compared to other time-of-flight neutron sources. Transmission data of a natural tungsten sample were measured with a flight path length of 852.1 cm and a repetition rate of 101.56 kHz. The neutron total cross section of natural tungsten was obtained for an energy range of 100 keV to 10 MeV.
Cross section measurements have been performed at the time-of-flight facility GELINA to determine the average capture cross section for
197
Au in the energy region between 3.5 keV and 84 keV. Prompt ...γ-rays, originating from neutron-induced capture events, were detected by two C
6
D
6
liquid scintillators. The sample was placed at about 13m distance from the neutron source. The total energy detection principle in combination with the pulse height weighting technique was applied. The energy dependence of the neutron flux was measured with a double Frisch-gridded ionization chamber based on the
10
B(n,α) reaction. The data have been normalized to the well-isolated and saturated
197
Au resonance at 4.9 eV. Special care was taken to reduce bias effects due to the weighting function, normalization, dead time and background corrections. The total uncertainty due to normalization, neutron flux and weighting function is 1.0%. An additional uncertainty of 0.5% results from the correction for self-shielding and multiple interaction events. Fluctuations due to resonance structures have been studied by complementary measurements at a 30m flight path station. The results reported in this work deviate systematically by more than 5% from the cross section that is recommended as a reference for astrophysical applications. They are about 2% lower compared to an evaluation of the
197
Au(n, γ) cross section, which was based on a least squares fit of experimental data available in the literature prior to this work. The average capture cross section as a function of neutron energy has been parameterized in terms of average resonance parameters. Maxwellian average cross sections at different temperatures have been calculated.
The bremsstrahlung facility at the ELBE accelerator offers the possibility to investigate dipole strength distributions up to the neutron-separation energies with photon up to 16 MeV in energy. The ...facility and various results for nuclides measured during recent years are presented. One example is the study of the N = 80 nuclide 136Ba. The other presented example is the study of the chain of xenon isotopes from N = 70 to N = 80 which aimed to investigate the influence of nuclear deformation an neutron excess on the dipole strength in the pygmy region. An overview of the analysis is given. GEANT4 simulations were performed to determine the non-nuclear background that has to be removed from the measured spectra. This opens up the possibility to take into account also the strength of unresolved transitions. Simulations of gamma-ray cascades were carried out that consider the transitions from states in the quasi-continuum and allow us to estimate their branching ratios. As a result, the photoabsorption cross sections obtained from corrected intensities of groundstate transitions are compared with theoretical predictions and results within the chain of isotopes. With the help of the measured dipole distribution it is possible to describe gamma-ray spectra following neutron capture more precisely.
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