During the last 15 years at JINR, Dubna a large number of experiments have been done to investigate the neutron field generated in big spallation targets. The Energy plus Transmutation project has ...two set-ups: big U/Pb 1 and Quinta 2,3. These set-ups are irradiated by high energy deuteron and proton beams. The project continues with the next generation "quasi infinite target", a cylinder of 21 tons of depleted uranium packed in a steel cage (the experiments have not been done yet) 4. Such a target has simple requirements: all generated neutrons deliver more than 90% of their energy in the target volume and the leakage ranges between 5 and 10% of the generated neutrons. There is a significant number of experimental results and simulations with different transport codes MCNPX, FLUKA, GEANT 4 for big U/Pb target and Quinta set ups. The comparison of simulations with reaction rate measurements shows very good agreement with an error range of 10-20%. These results provided the basis for additional simulations for similar set-ups. In the big U/Pb set-up the lead target is replaced by natU and the polyethylene (PE) cage is replaced by natPb. Similar calculations are done with the Quinta set-up. The natPb shield is replaced with polyethylene (PE). The integral number of neutron induced reactions, neutron production and leakage are calculated and compared.
We discuss recent experiments performed with an upgraded version of the main magnetic focus ion source (MaMFIS) at the Joint Institute for Nuclear Research in Dubna. The device operates in the range ...of electron beam energies extended up to 40 keV. The achieved electron current densities are of the order of 10 kA cm−2. This assessment is consistent both with the very short ionization time and with the utmost ionization degree of the produced highly charged ions. Due to its high efficiency, the MaMFIS technology is especially promising for ionization of short-lived radionuclides and heavy elements. A new scheme for charge breeding is proposed.
A comparative study about the energy efficiency of proton and light ion beams used for energy production in accelerator driven systems (ADS) is performed. The energy gain G, defined as the ratio of ...the energy produced to the energy spent to accelerate the beam is used as measure for the energy efficiency. The energy released in the target is obtained through simulation with the code Geant4, and the spent energy is calculated by scaling from the data about the accelerator efficiency for a reference particle. An optimal proton energy of 1.5 GeV is revealed, when the beam is accelerated in a linac. The advantage of light ion beams, especially 7Li at energies below 0.5 AGeV, which allows a reduction of the accelerator length, is substantiated.
A study about the target design and the choice of the converter meant to maximize the efficiency of the energy ADS irradiated with light ion beams (7Li) with energies in the range 0.25–0.5 AGeV is presented. The influence of the fuel composition, of the geometry of the target, of the coolant and the converter materials are investigated. The most significant influence on the energy released has the material used for the converter. Cylindrical converters from various materials, from very light (Li, Be) to very heavy (W, Pb, U) are analyzed. The influence of the dimensions of the converter on the energy released in the target is studied and the conditions which maximize the energetic efficiency and ensure a high level of burning of the actinides are determined. Solid fuel with different compositions (metal, oxide, carbide) and liquid fuel (molten salt) are considered.
The advantage of a target with beryllium converter for both proton and lithium beams is underlined. The use of a Be converter with length 100–120 cm makes a beam of 7Li with the energy 0.25AGeV (in solid fuel) and 0.275 AGeV (in liquid fuel) equivalent from the point of view of the net power produced with a beam of 1.5 GeV proton, and allow the building of an accelerator 2.2–2.6 times shorter.
A comparison between the evolution of the fuel composition during irradiation and its influence on the period of operation without refueling for target with LBE and Be converters is realized. The Be converter allows also to achieve a higher level of burning of the actinides and consequently a larger period between refueling.
•Light ion beams present a higher energy efficiency in ADS than proton beam.•Light ion beams with energy below 0.5 AGeV allow to build a shorter accelerator.•Variation in the target geometry does not change the shape of the neutron spectrum.•A Be converter increase 5–6 times the energy produced with light ion beams at low energy.
A method for analyzing the atomic composition of pollutants in marine sediments using a spectrometer based on a filament RF discharge is proposed. The carbon content in the sediment samples of the ...Mediterranean Sea region (Croatia) is at a level of 1%. Measurement accuracy is ±0.15%.
Fast neutron detectors with silicon photomultiplier readouts Akbarov, R.A.; Ahmadov, G.S.; Ahmadov, F.I. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2019, Letnik:
936
Journal Article
Recenzirano
This work summarizes a fast neutron detection performance of two different silicon photomultipliers from two manufacturers. The first SiPM (MAPD-3NK) from Zecotek Photonics consists of deeply buried ...cells with the active area 3.7×3.7 mm2. The second one (MPPC-S12572-010P) from Hamamatsu, however, consists of surface cell structure which the active area is 3×3 mm2. Both SiPMs have the same pixel density of 10000 mm−2. Both SiPMs coupled to Stilbene (5∗5∗5 mm3) and p-terphenyl (5∗5∗5 mm3) plastic scintillators were evaluated for detection ability of fast neutrons using a PuBe neutron source. Charge comparison and zero crossing neutron/gamma discrimination techniques were performed for these detectors and the results were compared. The obtained results prove a good fast neutron detection performance of the SiPMs which makes it possible to use these types of neutron detectors in fast neutron detection applications.
The photon self-absorption effect of uranium on the full-energy peak (FEP) efficiency calibration of high purity germanium (HPGe) detector was studied as a function of energy using an activated ...uranium sample has a thickness of 1 mm. The absolute efficiencies of the detector were obtained with the use of gamma standard sources and gamma rays of radionuclides created by irradiating the uranium sample with secondary neutrons. The measurements were carried out with the use of a Planar HPGe detector. MCNP simulation code was used to verify the experimental results. The comparison of the empirical results with the simulation results showed a good agreement. To interpret the efficiencies, the reaction rates were calculated using two methods: (1) - the use of the efficiency curve from the standard sources combined with the self-absorption correction of the uranium material and (2) - the use of the efficiency curve obtained from gamma rays in the sample.
•The effect of self -absorption of photons inside the uranium sample on the efficiency of HPGE detector was studied theoretically and experimentally. The calculated results were compared with the obtained experimental data.•The absolute efficiency curve, which treated the photon self-absorption correction was obtained from gamma rays of the radionuclides formed in the sample.•We developed a new method for the quantitative calculation of reaction products and used in this study.
The influence of the target size on the particle yield and doses is analyzed in order to clarify the concern about a possible increased radiation hazard in a target with higher dimensions. The ...analysis of the doses demonstrates that such concern is not justified. On the contrary, a bigger target is more advantageous from the point of view of the shielding needs, because the number of particles leaving the target and their energy decreases when the dimensions of the target increase. A faster method to calculate the shielding is proposed. The method implies a simulation in the real geometry but with the unshielded target. The dose at a given position in the presence of the shielding is calculated from the neutron spectrum registered without shielding and a parameterization of the attenuation curves in concrete. A comparison between the doses obtained with the targets “Quinta” and “Buran” in the experimental hall of the Laboratory of Nuclear Problems (LNP) is presented and the needed shielding for the experiments planned at LNP and at the Laboratory of High Energy Physics (LHEP) is analyzed.
A massive lead spallation target was irradiated with 660 MeV protons to generate a secondary neutron field. The field was studied via measurement of the residual nuclei generation in the lead ...activation samples located inside the target. Experimental results were compared with the Monte Carlo simulations using Geant4 and MCNPX 2.7.0 codes. The comparison shows a general agreement between experiment and simulation and thus serves as a validation of the utilized codes, high-energy nuclear models (ICLXX_HP, BIC_HP, BERT_HP, and INCL4.2) and nuclear data libraries (ENDF/B-VII.1), which can be used for the development of the subcritical accelerator-driven systems in the future.
A number of neutronics of JNIR big uranium target are simulated towards the planning of experimental investigations aimed to the transmutation of radioactive waste. Integral data of the neutron yield ...and energy spectra are given for several homogeneous spallation targets which are planned to be used as insertions in uranium blanket. Combined spallation targets are also of interest, because it can help to obtain an optimal neutron energy spectrum for effective burning of long-lived fission products and minor-actinides. For this purpose, uranium-beryllium dual insertion was also considered and described in this work.
The activation experiment was performed using the accelerated beam of Phasotron accelerator at the Joint Institute for Nuclear Research (JINR). The natural uranium spallation target QUINTA was ...irradiated with protons with energy 660 MeV. Monte Carlo simulations of neutron production were performed using the Geant4 code. The number of leakage neutrons from the sections of the uranium target surrounded by the lead shielding and the number of leakage neutrons from lead were determined. The total number of fissions in the setup QUINTA was determined. Experimental values of reaction rates for the produced nuclei in the 127I sample were obtained and several values of reaction rates were compared with the results of simulations. Experimentally determined fluence of neutrons in energy interval 10–175 MeV using the (n,xn) reactions in the 127I(NaI) sample was compared with the results of simulations. Possibility of transmutation of the long-lived radionuclide 129I in the QUINTA setup was estimated.
•Natural uranium assembly was irradiated with 660 MeV protons.•Fluence of fast neutrons was measured using 127I(n,xn) reactions.•Monte Carlo simulations provided the information about the number of total fissions in the assembly and number of leakage neutrons from the assembly and from the lead shielding.
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