Search

The Institute for Nuclear Research and Nuclear Energy at the Bulgarian Academy of Sciences is working on the construction of a cyclotron centre. Оne of the challenges in designing the radiation protection of a cyclotron centre is the preliminary assessment of the expected amounts of radioactive waste that will be generated during the lifetime of the facility. Our aim in this paper is to make an estimation of the expected induced radioactivity in the cyclotron bunker walls after the 20 year operational period of the facility. For this purpose, Monte Carlo simulations with the code FLUKA were performed. The distributions of the specific activity of the generated radionuclides in the concrete walls and of the residual dose rates inside the bunker are obtained. The specific activity of the most important long-lived radionuclides in the concrete walls of the bunker, namely 154Eu, 152Eu, 134Cs, 60Co, 54Mn is estimated. On the basis of these results an optimization of the shielding design is proposed in order to decrease the amount of radioactive waste which will be generated during the facility lifetime.

The nuclear structure of the A=31 and A=47 mirror couples produced by two fusion evaporation reactions has been elaborated, utilizing the Doppler-shift attenuation method. Excited states in 31P and 31S were populated using the 1p and 1n exit channels, respectively, of the reaction 20Ne + 12C, while in 47Cr and 47V couple excited states were populated based on 28Si + 28Si reaction, as products of 2αn and 2αp exit channels. The A=31 mirror couple was studied utilizing Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro with GASP multidetector array and for A=47 one - with the EUROBALL array using XTU Tandem also in Legnaro. In both cases the lifetime measurements in mirror couples at the same experiment open possibilities for investigations of isospin symmetry. Determined B(E1) strengths in the mirror nuclei 31P and 31S allow to extract the isoscalar component, which can reach up to 24% of the isovector one. The B(E1) values can be modeled by the Equation of motion method. In the case of A=47 mirror couple, the quadrupole moments can be described by shell-model calculations.

A study of the tritium content of surface water from three Rila lakes – Moussala lake, Aleko lake and Ice lake, and precipitation at Moussala mount has been performed by means of high precision nuclear and radiochemical methods. The measurements are part of a long-term environmental monitoring program developed and maintained by the Institute for Nuclear Research and Nuclear Energy, Bulgaria Academy of Science. The results for lake water and precipitation samples collected at Moussala part of Rila over the period 2012–2017 were found to range from ˂ 1.20 to 2.77 Bq.L-1 and from 2.14 to 4.12 Bq.L-1 respectively. The content of 3H in all samples is below the recommended level of 100 Bq.L-1. The obtained new results are used to assess the radiation status of the investigated water sources and can be used for evaluation of possible future changes and trends.

The Institute for Nuclear Research and Nuclear Energy at the Bulgarian Academy of Sciences is working on the construction of a cyclotron centre. The facility is on a design level. At this stage of the project, an important task is the radiation shielding assessment of the facility. Nowadays, the Monte Carlo transport codes have become the tool of choice for solving this type of problem. In the current paper, the transport code FLUKA is used for the calculations. It is widely applied for shielding design and analysis of accelerators and their components. The distributions of the radiation fields inside and outside the cyclotron bunker are presented in this paper. Both different irradiation scenarios and bunker configurations are considered in the conducted Monte Carlo simulations. These results will be used as a guidance in site planning.

14-th Scientific Conference of Bulgarian FP of EFSA - Book

International audience; Excited states in the mirror nuclei 31P and 31S were populated in the 1p and 1n exit channels of the reaction 20Ne + 12C, at a beam energy of 33 MeV. The 20Ne beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident γ-rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A=31 mass region. Self-consistent beyond mean field calculations using Equation of Motion method based on a chiral potential and including two- and three-body forces reproduce well the experimental B(E1) strengths, reinforcing our conclusion. Coherent mixing from higher-lying states involving the Giant Isovector Monopole Resonance accounts well for the effect observed. The breaking of the isospin symmetry originates from the violation of the charge symmetry of the two- and three-body parts of the potential, only related to the Coulomb interaction.

The activity concentrations of the naturally occurring radionuclides 238U, 234U and 210Po have been determined for the first time in drinking water from certain sources in Southern Bulgaria using nuclear and radiochemical methods. The results obtained for the water samples vary in the intervals 0.6–678 mBq l−1 for 238U, 1.4–1484 mBq l−1 for 234U

Excited states in the mirror nuclei $^{31}$P and $^{31}$S were populated in the 1p and 1n exit channels of the reaction $^{20}$Ne + $^{12}$C, at a beam energy of 33 MeV. The $^{20}$Ne beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident γ-rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A=31 mass region. Self-consistent beyond mean field calculations using Equation of Motion method based on a chiral potential and including two- and three-body forces reproduce well the experimental B(E1) strengths, reinforcing our conclusion. Coherent mixing from higher-lying states involving the Giant Isovector Monopole Resonance accounts well for the effect observed. The breaking of the isospin symmetry originates from the violation of the charge symmetry of the two- and three-body parts of the potential, only related to the Coulomb interaction.

Excited states in mirror nuclei 31S and 31P were populated in the 1n and 1p exit channels, respectively, of the reaction 20Ne + 12C. The beam of 20Ne, with an energy of 33 MeV, was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident pairs and Doppler-shift attenuation lifetime measurements in 31S and 31P were performed using the multidetector array GASP in conjunction with the EUCLIDES charged particle detector. A comparison of the determined B(E1) strengths of the analog mirror 7/2- → 5/2+ transitions indicates the presence of a violation of isospin symmetry.

The development and the optimisation of negative hydrogen/deuterium ion sources goes hand in hand with modelling. In this paper a brief introduction on the physics and types of different sources, and on the Kinetic and Fluid theories for plasma description is made. Examples of some recent models are considered whereas the main emphasis is on the model behind the concept and design of a matrix source of negative hydrogen ions. At the Institute for Nuclear Research and Nuclear Energy of the Bulgarian Academy of Sciences a new cyclotron center is under construction which opens new opportunities for research. One of them is the development of plasma sources for additional proton beam acceleration. We have applied the modelling technique implemented in the aforementioned model of the matrix source to a microwave plasma source exemplifying a plasma filled array of cavities made of a dielectric material with high permittivity. Preliminary results for the distribution of the plasma parameters and the component of the electric field in the plasma are obtained.

The paper is in the scope of studies on the rf driving of a matrix source of negative hydrogen ions: a matrix of small radius discharges with planar-coil inductive driving and single aperture extraction from each discharge. The results from a three-dimensional model, in which plasma description is coupled to electrodynamics, confirm former conclusion that a single coil driving of the whole matrix by a zigzag coil with an omega-shaped conductor on the bottom of each discharge tube ensures efficient rf power deposition to the plasma. The latter is due to similarities with the rf driving of a single discharge by a single planar coil, shown by the obtained induced current and spatial distribution of the plasma parameters. Distinctions associated with the coil configuration as a single coil for the whole matrix are also discussed.

$In\sb{1-{\rm x}}Ga\sb{\rm x}As\sb{\rm y}P\sb{1-{\rm y}}$ epilayers lattice matched to InP and $In\sb{1-{\rm x}}Ga\sb{\rm x}As\sb{\rm y}P\sb{1-{\rm y}}/InP$ Multiple Quantum Wells (MQWs) grown by Chemical-Beam Epitaxy (CBE) are being studied systematically using the Photovoltaic (PV) effect. At first, the Schottky barriers on the interfaces (metal-semiconductor, metal-insulator-semiconductor) are determined as an important factor for the electrical and optical properties of the samples. Samples with identical Schottky contact deposition but with an insulating layer on the front surface, have shown much smaller leakage current and yield enhanced barrier heights. The photovoltaic signal in the temperature interval 4-300K has maximum amplitude at about 150-180K for the MQW samples and at about 190K for the epilayer. An applied electric field changes the integrated intensity and spectrally shifts the allowed and forbidden transitions observed in bias dependent PV spectra of various InGaAsP/InP MQWs. The combined effect of two external factors, the thermal ionization and the electric field on the shape and magnitude of the 11H exciton peak, are discussed in terms of exciton binding energy and field ionization. The optically induced changes and energy shifting of the 11H/ exciton peak are observed, when excitation dependent double beam experiments are conducted on the $In\sb{0.72}Ga\sb{0.28}As\sb{0.68}P\sb{0.32}/InP$ MQWs. The photomodulation of the internal fields through carrier transport results in observing effective nonlinearities at milliwatt power levels. The experimentally measured transition energies for the MQWs show good agreement with the envelope wave function calculations. The observed Schottky barrier heights and band gap energies are consistent with the interpolation scheme estimations. (Abstract shortened by UMI.)

Photovoltaic Spectroscopy is used to study lattice matched Au/InGaAsP/InP multiple quantum wells at 4.2 < T < 300 K. Four quantum transitions are clearly identified in the spectra and their temperature shift mapped. The Au/InGaAsP Schottky barrier is found to be nearly temperature independent at φB ≃ 0.68 eV, and the binding energy of the 11H associated exciton estimated at Eb ≃ 11 meV. The 11H exciton displays a small electric field shift, to the red at low T, changing over to a blue shift at higher temperatures.