The new experimental setup TANGRA (Tagged Neutrons & Gamma Rays), for the investigation of neutron induced nuclear reactions, e.g. (n,xn’), (n,xn’γ), (n,γ), (n,f), on a number of important isotopes ...for nuclear science and engineering (235,238U, 237Np, 239Pu, 244,245,248Cm) is under construction and being tested at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) in Dubna.
The TANGRA setup consists of: a portable neutron generator ING-27, with a 64-pixel Si charge-particle detector incorporated into its vacuum chamber for registering of α-particles formed in the T(d, n)4He reaction, as a source of 14.1 MeV steady-state neutrons radiation with an intensity of ∼5x107n/s; a combined iron (Fe), borated polyethylene (BPE) and lead (Pb) compact shielding-collimator; a reconfigurable multi-detector (neutron plus gamma ray detecting system); a fast computer with 2 (x16 channels) PCI-E 100 MHz ADC cards for data acquisition and hard disk storage; Linux ROOT data acquisition, visualization and analysis software. The signals from the α-particle detector are used to ‘tag’ the neutrons with the coincident α-particles. Counting the coincidences between the α-particle and the reaction-product detectors in a 20ns time-interval improves the effect/background-ratio by a factor of ∼200 as well as the accuracy in the neutron flux determination, which decreases noticeably the overall experimental data uncertainty.
Although silicon is a promising material for quantum computation, the degeneracy of the conduction band minima (valleys) must be lifted with a splitting sufficient to ensure the formation of ...well-defined and long-lived spin qubits. Here we demonstrate that valley separation can be accurately tuned via electrostatic gate control in a metal-oxide-semiconductor quantum dot, providing splittings spanning 0.3-0.8 meV. The splitting varies linearly with applied electric field, with a ratio in agreement with atomistic tight-binding predictions. We demonstrate single-shot spin read-out and measure the spin relaxation for different valley configurations and dot occupancies, finding one-electron lifetimes exceeding 2 s. Spin relaxation occurs via phonon emission due to spin-orbit coupling between the valley states, a process not previously anticipated for silicon quantum dots. An analytical theory describes the magnetic field dependence of the relaxation rate, including the presence of a dramatic rate enhancement (or hot-spot) when Zeeman and valley splittings coincide.
In this article, we present the nuclear excitation functions of the fast neutron-induced reactions
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Cr(n,p)
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V,
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Cr(n,α)
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Ti,
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Cr(n,2n)
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Cr,
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Fe(n,p)
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Mn,
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Fe(n,α)
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Cr, and
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...Fe(n,2n)
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Fe, because these measurements are critical to estimate the level of the neutron activation for the fusion reactor structural materials. The theoretical computer codes TALYS-1.8 and EMPIRE-3.2.2 have been used for the calculation of the excitation functions. The theoretical calculations consider different nuclear reaction models, level density models and optical model potentials. The calculated excitation function results are compared with the existing experimental data obtained from the IAEA-EXFOR database, as well as with those available in the TENDL-2017 and ENDF/B-VIII.0-evaluated nuclear data libraries. The obtained results show the variation in excitation functions for different level density models. Moreover, we have studied the contribution from different reaction mechanisms in total reaction cross-section which varies with the incident neutron energy. These excitation function results can be useful to estimate the important parameters of nuclear reactors, such as nuclear heating, nuclear transmutation rates, and waste management etc. This kind of information can enhance the basic understanding of the mechanism of the fast neutron-induced nuclear reactions.
The fast and thermal neutron attenuation properties through polymer composites based on high density polyethylene (HDPE) reinforced by micro-sized and nano-sized Cadmium Oxide (CdO) particles with ...weight fractions of 10% and 40% have been investigated. This study was carried out to present a new composite material based on HDPE filled with CdO in the form of micro and nano particles to be used as a promising neutron radiation shielding material. The composites were fabricated by compression molding technique and characterized by a scanning electron microscope (SEM). The composites were subjected to fast neutrons generated from 238Pu–Be neutron source with activity 12 × 109 Bq and detected by a Stilbene scintillator. The fast neutron shielding properties were determined in terms of the fast neutron transmission fractions of the composites. The neutron activation method was applied by using Indium foils and Indium foils covered with Cadmium as a detector to study the properties of the thermal and epithermal neutron fluxes of the composites upon exposure to neutron flux generated from 241Am–Be neutron source. It is clear from this study that the transmitted fractions for fast neutron in case of nano CdO/HDPE composites are less than the case of micro CdO/HDPE composites, however, the capture of thermal neutrons inside the micro CdO/HDPE composites is more probable than that in nano CdO/HDPE composites at the same weight fraction. Tensile mechanical testing has been conducted and showed that particle addition percentage and size have significant effect on the mechanical properties of composites. Nano CdO/HDPE composites showed more superior mechanical properties compared to micro CdO/HPDE composites at the same particle addition level.
•Fast and thermal neutron attenuation properties through polymer composites.•High density polyethylene (HDPE) reinforced by micro-sized and nano-sized Cadmium Oxide (CdO).•Nano CdO particles will enhance the shielding properties of the HDPE against fast neutrons.•Capture of thermal neutrons inside the micro CdO/HDPE composites is more probable than that in nano CdO/HDPE composites.•Particle addition percentage and size have significant effect on the mechanical properties of composites.
Low cost scintillation detectors as compared with HPGe detectors are considered to be one of most important radiation detection tools. Therefore, these detectors can be manufactured in different ...shapes and work at room temperature without any cooling systems, which added an extra advantage to it. This work presents a study of a cubic detector with a rectangular cavity in different experimental setup geometries, using standard point-like gamma-ray sources, where the efficiency of the detector in these geometries was the target to be studied. According to this aim, the data from the experimental measurements was used to determine the detector efficiency. An analytical calculation of the detector efficiency was done by using a new mathematical expression, this mathematical expression depends on the efficiency transfer technique and effective solid angle calculations. To support the mathematical model, the source-to-detector arrangement was simulated by Geant4 Monte Carlo code. All the compared efficiency results were found to be promising and trusted based on the calculated deviation percentages.
•Calibration of cubic with rectangular NaI (Tl) detectors using a non-axial radioactive point-like gamma-sources.•New analytical approach and Geant4 simulation were used to calculate the full-energy peak efficiency.•Simulation of photons was modeled mathematically.•The analytical equations and complex integrations were used over the radioactive point sources placed non-axially.•Remarkable agreement between measured, calculated, Geant4 efficiencies were achieved.
Gas-puff fast Z-pinches are of considerable interest as a neutron source that can be operated in a repeatable mode and which may lead to a magneto-inertial fusion energy source. In our experiments on ...the 1-MA pulsed power generator Zebra a krypton gas shell was imploded to compress a central deuterium gas column. An external axial magnetic field <inline-formula> <tex-math notation="LaTeX">B_{z} = 0.5-3.0 \text {kG} </tex-math></inline-formula> was used to stabilize the pinch against magneto Rayleigh-Taylor instabilities. A consistent neutron yield of <inline-formula> <tex-math notation="LaTeX">(0.83 \pm 0.19) \times 10^{10} </tex-math></inline-formula> was measured with a silver activation detector with <inline-formula> <tex-math notation="LaTeX">B_{z}\ge 0.5 \text {kG} </tex-math></inline-formula>. The neutron emission isotropy was assessed with three neutron time of flight (nTOF) detectors.
The work is devoted to measuring the angular distribution of 4.43-MeV γ-rays produced in inelastic scattering of 14.1-MeV neutrons by
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C nuclei. A portable ING-27 neutron generator (designed and ...fabricated at VNIIA, Moscow) with a built-in 64-pixel silicon α-detector was used as a source of tagged neutrons. The γ-rays of characteristic nuclear radiation from
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C were detected with a spectrometric system that consisted of 22 γ-detectors based on NaI(Tl) crystals arranged around the carbon target. The measured angular distribution of 4.43-MeV γ-rays is analyzed and compared with the results of other published experimental works.
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