Iulian Pojar Vintila, Sorin Ujeniuc, Irina Catianis
et al.
This paper focuses on the natural and anthropogenic radioactivity of sediment samples from key spots located in the Lower Danube area and the Danube Delta region. The idea of the study is to confirm that gamma spectrometry is an efficient method for geological sample characterization in terms of isotopic ratios and also for evaluating the impact of nuclear activi- ties, namely testing artificial contamination. This is a preliminary study meant to analyze the relevance of a database for reference sediments from the Danube River built via gamma ray spectrometry.
By studying the total fusion and breakup cross-sections in the interaction of the neutron-halo $^{11}{\rm Be}$ projectile on the lead target $^{208}$Pb, it is shown that, even for the neutron-halo projectile, the breakup channel remains the most dominant reaction channel at sub-barrier energies, following a characteristic behavior that was also previously verified for the case of the proton-halo projectile $^8{\rm B}$. This feature is found to emanate from the enhancement of the breakup cross-section, due to the continuum-continuum couplings coming exclusively from its Coulomb component. We further speculate that the enhancement of the Coulomb breakup cross-section at sub-barrier incident energies by the continuum-continuum couplings could be associated with the projectile breaking up on the outgoing trajectory, provided these couplings can be proven to delay the breakup process.
Thorium, in this case, 232Th has a higher thermal neutron capture cross-section than 238U, which means that more fertile isotopes can be transmuted and could lead to higher fissile isotope 233U. In addition, 233U has a good performance in the thermal spectrum. Theoretically, a nuclear reactor using thorium fuel can also last longer than one using uranium fuel. The use of TRISO duplex fuel is predicted to produce better neutronic behavior in a pebble bed reactor. This work aims to study the kinetic parameters of a pebble bed reactor with TRISO duplex fuel. The configuration of the TRISO duplex fuel pebble consists of an inner region filled with UO2 TRISO particles and an outer region filled with ThO2 TRISO particles surrounded by a graphite matrix of fuel pebble. Three configurations with volume fraction of UO2-ThO2 were considered in this study: 80-20 %, 75-25 %, and 70-30 %. The HTR-10 reactor was chosen as a reactor model because its geometry and material specifications are known. A series of calculations were conducted using the Monte Carlo transport code MCNP6 and ENDF/B-VII.1 nuclear data library. The calculation results were then analyzed to investigate the effect of UO2 and ThO2 compositions in TRISO duplex fuel on the kinetic parameters of the pebble bed reactor with various TRISO packing fractions of 1-50 %. It can be concluded that the utilization of TRISO duplex fuel in a pebble bed reactor could significantly affect the core multiplication factor and kinetic parameters caused by an increase in Th content. On the other hand, the TRISO packing fraction is taking part in neutron moderation since a lower packing fraction means higher moderation for fueled pebble.
This work aims to measure the scattered radiation energy spectrum and radiation dose at different positions during radiological diagnosis through the Monte Carlo simulation and experiment. The results show that the average energy of the scattered radiation energy spectrum increases with the increase of the tube voltage and decreases with the increase of the scattering angle, but it changes very little with the measuring distance. It is not unified for the scattered radiation distribution in the space around the water phantom at the same tube voltage, and the exposure to scattered radiation is greater on the side closer to the water phantom or the X-ray tube. This indicates that the radiation exposure is not unified for medical staff in the scattered radiation field. The scattering energy spectrum and dose distribution are helpful to evaluate the scattered radiation exposure and enhance the self-protection awareness of medical staff in practice.
As predicted by theory and confirmed by measurements, one, two or three neutrons are emitted frequently in ultraperipheral collisions (UPCs) of heavy relativistic nuclei, in particular, $^{208}$Pb. The exchange of low-energy Weizsäcker--Williams photons dominates in such interactions. This leads to the excitation and decay of Giant Dipole Resonances (GDR) in colliding nuclei below the proton emission threshold. Less is known about the electromagnetic dissociation of $^{208}$Pb induced by energetic photons leading to violent fragmentation of $^{208}$Pb. The UPCs of lead nuclei at the LHC were modelled with Relativistic ELectromagnetic Dissociation (RELDIS) model to evaluate the contribution of photonuclear reactions in the domain of quasideuteron absorption and at higher photon energies. It was demonstrated that due to the presence of a single heavy residue in the final state mostly accompanied by free protons and neutrons, the cross sections of the production of specific elements can be well approximated by the proton emission cross sections, which can be measured in the ALICE experiment at the LHC.
J. E. Perez Velasquez, O. L. Caballero, N. G. Kelkar
One of the prominent decay modes of heavy nuclei which are produced in astrophysical environments at temperatures of the order of $10^9$ K is the $α$ ($^4$He) decay. Thermally enhanced $α$ decay rates are evaluated within the standard scheme of a tunneling decay where the $α$ particle tunnels through the potential barrier formed by its interaction with the daughter nucleus. Following the observation that there exist several excited levels with the possibility of an $α$ decay when the daughter nucleus is at a shell closure, we focus in particular on decays producing daughter nuclei with the neutron number, N = 126. Within a statistical approach we find that the half-lives, $t_{1/2}(T)$, for temperatures ranging from $T$ = 0 to 2.4 GK can decrease by 1 - 2 orders of magnitude with the exception of the decay of $^{212}$Po which decays to the doubly magic daughter $^{208}$Pb, where $t_{1/2}(T)$ decreases by 5 orders of magnitude. The effect of these thermally enhanced $α$ decays on the $r$-process nucleosynthesis can be significant in view of the mass build up at the waiting point nuclei with closed neutron shells.
To assess the characteristics of 13N decay, a monitoring method of the primary loop leakage rate based on the ?-? coincidence method was proposed. In this work, sampling and measurement devices were designed, in which NaI (Tl) crystals were used as coincidence detectors. The Geant4 simulation method was used to study the relationship between the efficiency e and capacity V change of different devices, and the eV value under the corresponding capacity was obtained. According to the value of eV, the optimal sampling and measurement device was determined, and then the detection efficiency of the device was calibrated experimentally. Taking the 600 000 kW reactor of Qinshan Phase II as the research object, the lower limit of detection was discussed. When the sampling point was located in the fume hood of the control rod drive mechanism, the theoretical lower limit of the coincidence method was 0.756 Lh-1.
Special high-protein foods suitable for diabetics must be treated to ensure the complete absence of microorganisms and bacteria. It is also important to achieve that this treatment does not change the nutritional value of the product. Among the new decontamination technologies, low-energy electron-beam treatment has proven to be an effective technique for inactivating bacteria with minimal impact on food quality. The paper aims to analyze the influence of low-energy electron-beam irradiation on the microbiological properties and nutritional value of high-protein foods.
Jelena Stankovic-Petrovic, Zeljka Knezevic, Nikola Krzanovic
et al.
Passive solid state dosimeters, such as thermoluminescence dosimeters, provide integrated measurement of the total dose and are widely used in environmental monitoring programs. The objective of this paper is to provide a comprehensive review on the use of thermoluminescent dosimetry methods for monitoring radiation dose in the environment. The article presents the part of the research results of the project PREPAREDNESS (EMPIR 2016 call for Metrology for Environment joint research project) with a particular objective to harmonize procedures used by dosimetry services, relevant authorities and Institutes across the Europe. To achieve this, different monitoring routines that are based on passive environ mental dosimetry methods are investigated. Differences in performing specific steps such as preheating, reading, annealing, minimizing fading, and others, are analyzed. The investigation was performed by means of qualitative literature review that showed the lack of information about specific steps. The conclusion of this work is that thermoluminescent dosimetry measurement system has to be type-tested even though the testing procedure is complicated. In addition to this, control dosimeters should be introduced, International Organization for Standardization protocols should be followed during calibration, and finally, parameters influencing the measurement uncertainty have to be identified and well understood in order to pro duce ac cu rate dose measurement results.
We present systematic large-scale shell-model calculations for Rn isotopes with $A=$ 207 to 216. For the $^{207-212}$Rn isotopes, we perform calculations with KHH7B interaction, while for $^{213-216}$Rn isotopes with KHPE and KHH7B interactions. The calculated energies and electromagnetic properties are compared with the available experimental data and predicted where experimental data are not available. We also suggest spins and parities of several unconfirmed states available from the recent experimental data. Comprehensive study of several isomeric states from the calculated shell-model configurations and half-lives is also reported.
Slavko Dimovic, Boris Vakanjac, Ivana Jelic
et al.
The aim of the study was to evaluate the potential risks of radiation near abandoned uranium mines, tailing dumps, or uranium deposits on Mountain Stara Planina, Serbia. For risk assessment several parameters were determined: radium equivalent activity, Raeq, external hazard index, Hex, gamma radiation absorbed dose rate, D, annual effective dose on background outdoor gamma exposure, AEDoutdoor, and excess lifetime cancer risk, ELCR. Obtained results showed that all the samples, except one, have the Raeq value up to two times higher than the reference limit. The Raeq of the sample from the Mezdreja mine tailings was increased by almost eight times. The value of Hex followed the same pattern as Raeq. All the investigated localities have increased D values, while all the samples have shown the moderately low AEDoutdoor, except Mezdreja mine tailings that have 5.5-2.8 times higher dose relative to the world's average. ELCR at the Mezdreja mine tailings is 4.58 times higher than the world's average of 1.45?10?3. In the context of human activity in the area of Stara Planina such as different kinds of tourism, livestock breeding, dairy products, and herbal manufacturing, etc. there is a need for detailed analysis in order to evaluate potential human exposure and health impacts.
Donghoon Kim, Lucas Albright, Brittney Saenz
et al.
A novel polar angular quadrature set called the Kim-Jevremovic polar angular quadrature set is derived for the method of characteristics. It is based on neutron anisotropic scattering cross-sections in the Evaluated Nuclear Data File. This new set is implemented within the state-of-the-art neutron transport code AGENT and tested in comparison to MCNP6 as well as to other known quadrature sets for the UO2 unit cells, the well-known C5G7 benchmark, unreflected cylinders of uranyl-fluoride solutions in heavy water, and the University of Utah 100 kWth TRIGA MARK-I reactor core. These comparisons show that the newly proposed polar angular quadrature set provides better agreements than other quadrature sets for the lower order of anisotropic scattering expansions. This paper presents a complete derivation of the Kim-Jevremovic polar angular quadrature set and the analysis for the mentioned bench-mark examples.
We employ the non-perturbative time-dependent basis function (tBF) approach to study the scattering of the deuteron on $^{208}$Pb below the Coulomb barrier. We obtain the bound and discretized scattering states of the projectile, which form the basis representation of the tBF approach, by diagonalizing a realistic Hamiltonian in a large harmonic oscillator basis. We find that the higher-order inelastic scattering effects are noticeable for sub barrier scatterings with the tBF method. We have successfully reproduced experimental sub Coulomb barrier elastic cross section ratios with the tBF approach by considering only the electric dipole ($\mathit{E1}$) component of the Coulomb interaction between the projectile and the target during scatterings. We find that the correction of the polarization potential to the Rutherford trajectory is dominant in reproducing the data at very low bombarding energies, whereas the role of internal transitions of the deuteron projectile induced by the $\mathit{E1}$ interaction during the scattering becomes increasingly significant at higher bombarding energies.
Using the model of hexagonal clusters we express the surface, curvature and Gauss curvature coefficients of the nuclear binding energy in terms of its bulk coefficient. Using the derived values of these coefficients and a single fitting parameter we are able to reasonably well describe the experimental binding energies of nuclei with more than 100 nucleons. To improve the description of lighter nuclei we introduce the same correction for all the coefficients. In this way we determine the apparent values of the surface, curvature and Gauss curvature coefficients which may be used for infinite nuclear matter equation of state. This simple model allows us to fix the temperature dependence of all these coefficients, if the temperature dependence for the bulk term is known. The found estimates for critical temperature are well consistent both with experimental and with theoretical findings.
What can we learn about the density dependence of nuclear symmetry energy $E_{\rm{sym}}(ρ)$ from precise measurements of the radius ($R_{\rm{1.4}}$) and/or tidal polarizability ($Λ_{1.4}$) of canonical neutron stars (NSs) with a mass of 1.4 M$_\odot$? With the $E_{\rm{sym}}(ρ)$ parameterized using three parameters $L$, $K_{\rm{sym}}$, and $J_{\rm{sym}}$ which have the asymptotic meaning of being respectively the slope, curvature, and skewness of symmetry energy at saturation density, we found that, while both the $R_{\rm{1.4}}$ and $Λ_{1.4}$ depend strongly on the slope $L$, the $K_{\rm{sym}}$ and $J_{\rm{sym}}$ parameters characterizing the high-density behavior of $E_{\rm{sym}}(ρ)$ also play appreciable roles. Thus, there is not a simple relation between the $Λ_{\rm{1.4}}$/$R_{\rm{1.4}}$ and $L$ alone. Precise measurements of just the $Λ_{\rm{1.4}}$ and $R_{\rm{1.4}}$ can not completely determine the $E_{\rm{sym}}(ρ)$ but limit combinations of its parameters. In particular, stringent constraints approximately independent of the $J_{\rm{sym}}$ on the $L$-$K_{\rm{sym}}$ correlations can be obtained. However, infinite combinations of the larger (smaller) $L$ and smaller (larger) $K_{\rm{sym}}$ can lead to the same $Λ_{\rm{1.4}}$ and $R_{\rm{1.4}}$. Additional observables including those from terrestrial nuclear experiments are thus necessary to break this degeneracy in order to completely determine the density dependence of nuclear symmetry energy $E_{\rm{sym}}(ρ)$.
Marija Radmilovic-Radjenovic, Petar Belicev, Branislav Radjenovic
Electron field emission limiting the accelerating gradient in superconducting cavities remains the dominant setback in cavity production. The need to understand and control the field emission has become increasingly important because of the prospect of using high-gradient structures in linear colliders. Since building an accelerator structure is a complicated and costly process, elimination of unnecessary steps has priority. In this paper an analysis of the influence of the enhanced field emission in superconducting radio frequency cavity together with modal field calculations by using COMSOL finite elements package has been presented. The obtained results reveal that the electric field required for the field emission is generated in the cavity irises. The imperfection of the cavity surface leading to very high fields is modelled by a simple cone. The estimated value of the enhancement factor for the cone tip of around 4 is in a good agreement with the data found in the literature. In addition, from the slopes and the intercepts of the Fowler-Nordheim plots, a dependence of the enhancement factor and the effective area on the work function has been estimated.
An algorithm for the Monte Carlo simulation of electron multiple elastic scattering based on the framework of SuperMC (Super Monte Carlo simulation program for nuclear and radiation process) is presented. This paper describes efficient and accurate methods by which the multiple scattering angular deflections are sampled. The Goudsmit-Saunderson theory of multiple scattering has been used for sampling angular deflections. Differential cross-sections of electrons and positrons by neutral atoms have been calculated by using Dirac partial wave program ELSEPA. The Legendre coefficients are accurately computed by using the Gauss-Legendre integration method. Finally, a novel hybrid method for sampling angular distribution has been developed. The model uses efficient rejection sampling method for low energy electrons (<500 keV) and larger path lengths (>500 mean free paths). For small path lengths, a simple, efficient and accurate analytical distribution function has been proposed. The later uses adjustable parameters determined from the fitting of Goudsmith-Saunderson angular distribution. A discussion of the sampling efficiency and accuracy of this newly developed algorithm is given. The efficiency of rejection sampling algorithm is at least 50 % for electron kinetic energies less than 500 keV and longer path lengths (>500 mean free paths). Monte Carlo Simulation results are then compared with measured angular distributions of Ross et al. The comparison shows that our results are in good agreement with experimental measurements.
The spatial and urban planning is one of the key instruments for the planned formation and development of locations for nuclear facilities, especially in terms of meeting the strict spatial conditionality, as well as in terms of the formation of protection zones in their surroundings. This paper systemizes the international criteria and requirements for the locations of nuclear facilities and analyses the spatial distribution of nuclear facilities in the surrounding countries of the Republic of Serbia. The research was conducted on the example of the location of the Vinca Institute of Nuclear Sciences, within which the fulfilment of spatial requirements, treatment of the location in the existing spatial and urban plans and relationship between other functions in the surrounding area were analysed. The paper proves the starting hypothesis that the general requirements related to both the spatial development of nuclear facilities locations and the protection from radiation have not been met in the Vinca location and its surroundings. It was determined that the spatial and urban plans encompassing the area of Vinca do not contain sufficiently specific planning solutions and that, as such, they do not provide a sufficient planning basis for meeting the necessary requirements and obligations regarding the protection from radiation. The paper also gives recommendations for further spatial development and protection of the Vinca location and its surroundings. The research condcted in this paper indicates the importance and priority of further research so that the necessary planning solutions for further development of the complex in Vinca and for the formation of protection zones could be defined through creating a new planning documentation. In addition, the paper particularly highlights the need for conducting a research to identify a location for permanent disposal of radioactive waste. It also indicates the necessity of considering the aspects of environmental protection and protection from radiation in the national and international context.
The studies, from several independent methods, consistently show that $π^-/π^+$ ratio in the $^{132}$Sn+$^{124}$Sn reaction at 300 MeV/nucleon, which is being carried out at Radioactive Isotope Beam Facility (RIBF) in Japan, just probes the symmetry energy around saturation density.
The goal of nuclear structure theory is to build a comprehensive microscopic framework in which properties of nuclei and extended nuclear matter, and nuclear reactions and decays can all be consistently described. Due to novel theoretical concepts, breakthroughs in the experimentation with rare isotopes, increased exchange of ideas across different research areas, and the progress in computer technologies and numerical algorithms, nuclear theorists have been quite successful in solving various bits and pieces of the nuclear many-body puzzle and the prospects are exciting. This article contains a brief, personal perspective on the status of the field.