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.
Diffusion processes in solids are characterized by complex mechanisms occurring at the atomistic level. The relevant theoretical concepts are sufficiently developed in the case of the diffusion of ...point defects. At the same time, the diffusion of objects such as clusters of vacancies or nanometer-size cavities in the crystal lattice is described only in terms of continuous-medium approximation. This paper attempts to link the existing theory of diffusion of bubbles in a crystalline matrix with the atomistic description of the process on the basis of the molecular dynamics method. For simplicity, the diffusion of cavities in a two-dimensional Lennard-Jones lattice is considered. A controlled molecular dynamics method is proposed to speed up the direct computation of the diffusion rate of bubbles. Based on the results of simulation, a practical interpretation is given to a parameter of the continuum theory such as the rate of surface self-diffusion. The applicability range of the continuum theory is demonstrated, and principles for the refinement of the theory in the case of minimum-size bubbles are formulated.
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.
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.
Mechanistic models of nuclear fuels require development of multi-scale models that provides the necessary microscopic parameters that are usually cannot be determined experimentally. In this work we ...present the results of atomistic calculations of the surface diffusivity for nanometer bubbles in gamma-uranium that is used as a parameter in the rate-theory approach describing bubble diffusion. The unexpected features of surface diffusion are revealed and the accuracy of the rate-theory approach is estimated.
The cross sections for the reactions
165
Ho(γ, n)
164
Ho,
165
Ho(γ, 3n)
162m
Ho,
165
Ho(γ, 4n)
161
Ho,
165
Ho(γ, 5n)
160m1
Ho,
165
Ho(γ, 5n)
160
Ho, and
165
Ho(γ, 6n)
159
Ho were experimentally ...determined in the energy range from 50 to 110 MeV. Also, calculations were performed using the Geant4 code and the Talys program to determine the cross section of reactions in holmium samples. Calculation results are compared with the obtained experimental results. The dependence of the isomeric ratio
160m1
Ho/
160
Ho on the electron energy has been measured.
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.
•Uranium spallation target was irradiated by up to 4AGeV deuteron beams.•Neutron production was investigated through (n,γ), (n,f), and (n,2n) reactions in natU.•Reaction rates were also calculated ...employing the MCNPX 2.7.0 code.•Agreement between experiment and simulation of neutron-induced reactions was found.Overestimation in simulation of production of charged particles is discussed.
A renewed interest in experimental research on Accelerator-Driven Systems (ADS) has been initiated by the global attempt to produce energy from thorium as a safe(r), clean(er) and (more) proliferation-resistant alternative to the uranium-fuelled thermal nuclear reactors. The ADS research has been actively pursued at the Joint Institute for Nuclear Research (JINR), Dubna, since decades. Most recently, the emission of fast neutrons was experimentally investigated at the massive (m=512kg) natural uranium spallation target QUINTA. The target has been irradiated with the relativistic deuteron beams of energy from 0.5AGeV up to 4AGeV at the JINR Nuclotron accelerator in numerous experiments since 2011. Neutron production inside the target was studied through the gamma-ray spectrometry measurement of natural uranium activation detectors. Experimental reaction rates for (n,γ), (n,f) and (n,2n) reactions in uranium have provided valuable information about the neutron distribution over a wide range of energies up to some GeV. The experimental data were compared to the predictions of Monte Carlo simulations using the MCNPX 2.7.0 code. The results are presented and potential sources of partial disagreement are discussed later in this work.
The natural uranium assembly, QUINTA, was irradiated with 6GeV deuterons. The 232Th samples were placed at the central axis of the setup QUINTA. The spectra of gamma rays emitted by the activated ...232Th samples have been analysed and more than one hundred nuclei produced have been identified. For each of those products, reaction rates have been determined. The ratio of the weight of produced 233U to 232Th is presented. Experimental results were compared with the results of Monte Carlo simulations by FLUKA code.
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