Search

A procedure is described for finding nonpolarized transverse, longitudinal, and polarized longitudinal-transverse and longitudinal-transverse structure functions derived from data on the differential cross sections of exclusive channels of π+n and π0p electroproduction measured with the CLAS detector. The measured cross sections cover the wide kinematic range of W < 1.7 GeV in terms of invariant mass of a finite hadronic system and photon virtuality in the range of Q2 < 5.0 GeV2. The exclusive structure functions obtained from a single pion production channel play an important role in studying the structure of excited nucleon states.

We consider the possibility for using the method of local mass relations in the region of superheavy elements with nuclear charge Z > 106. Binding energies, α-decay energies, and half-lives of α-decay are found for isotopes Z = 107–110 and N = 152–161, using formulas for estimating residual np-interaction.

Experimental studies and theoretical calculations of photonuclear reactions on a natural mixture of palladium isotopes have been performed. The yields of photonuclear reactions on a natural mixture of Pd isotopes were measured for bremsstrahlung $$\gamma$$ radiation with a maximum energy of 55 MeV. The results are compared with calculations using the combined model of photonuclear reactions.

The data on photo- and electroexcitation amplitudes of most nucleon resonances in the mass range up to 2.0 GeV determined from the CLAS experiments on exclusive π+π−p photo-electroproduction off protons in collaboration between the Jefferson Lab and Moscow State University are presented. The first (and, currently, the only available) data on electroexcitation amplitudes from CLAS in a wide range of photon virtualities Q2

Different mass relations for estimating neutron–proton correlations are analyzed. The differences between the estimates indicate phenomenologocal distinction between the considered relations. Parametrization with a shell model is used to clarify the structure of different estimates and their correspondence to the real value of np-correlations.

A review of the theoretical studies of the 44Ti nuclear spectrum is given. In this example the diversity of nuclear degrees of freedom in complex nuclei and coexistence of excitation of different nature are demonstrated. The main attention is paid to the cluster model 40Ca + α and the shell model. In the latter case the calculation result and the detailed analysis of the role of nucleon pairing are presented. Similarities and differences in the spectra obtained in these approaches are considered. Rotational states and states of the molecular type are also briefly discussed. It is shown that many properties of the spectrum can be reasonably described in various models, which, therefore, are not completely independent and express the same physical phenomena in some cases.

The integrated cross sections of the ep → eπ+n, ep → eπ0p, ep → eK+Λ, and ep → eK+Σ0 reactions are evaluated in the energy range of nucleon resonance excitation at photon virtualities Q2 from 5 to 12 GeV2. These exclusive channels will be explored at photon virtualities Q2 > 5 GeV2 for the first time in future experiments with the CLAS12 detector. The cross-section evaluation is based on the extrapolation of exclusive contributions to the inclusive structure functions F1 and F2 from a region of Q2 < 5 GeV2, in which the experimental data are available, to the region of higher Q2. This evaluation of cross sections is of particular importance in the development of the program of experiments with the CLAS12 detector for studying the structure of the ground and excited nucleon states, which may reveal the dynamics of strong interactions in the nonperturbative regime.

Different estimates of the even–odd effect for the nuclear mass surface are discussed. The proton-number dependence of the energy gap is derived from the measured masses of the N = 20, 50, and 82 isotones with closed neutron shells. Its interrelation with the properties of external proton shells is demonstrated, and the effects of proton pairing are considered along with the microscopic nuclear structure.

Values of neutron–proton pairing based on mass relations are estimated. It is shown that substantially different formulas for calculating the np-pairing energy in self-conjugate nuclei yield similar results. Comparison of the obtained values and the structure of ground state multiplet spectra shows that mass relations can be used to describe the isovector (T = 1) component of np-pairing to sufficient accuracy, but provides little or no information on isoscalar component T = 0.

Photonuclear reactions on a natural mixture of tin isotopes are studied by means of gamma activation. The experiment is performed using the bremsstrahlung γ-beam of an RTM55 racetrack microtron with a maximum electron energy of 55.6 MeV. The measured yields of photoproton and photoneutron reactions are compared to results from other experimental studies, and to calculations using the TALYS code and the combined model of photonucleon reactions (CMPR).

The emergence of the pairing effect of identical nucleons in the j = 9/2 state in low-lying excited states of nuclei near 90Zr (N = 50, Z = 40) is discussed. Multiplets of states with seniority s ≥ 2, the splitting of which is determined by the proton pairing energy, are clearly visible in the nuclear spectra for a chain of N = 50 isotones. A comparison of the spectra of ground state multiplets, calculated in the δ-interaction approximation, with experimental data and results from other theoretical calculations shows this approach can be used to describe the structure of spectra and level positions with high J values.

The Department of Accelerator Physics and Radiation Medicine of Moscow State University’s Faculty of Physics conducts experiments on the radiation processing of food products and the development of a new technology for the combined sterilization of bone implants, based on the joint action of different sterilizing factors (radiation and sterilization) in a gaseous medium. Radiation processing of potato tubers and bone implants is performed using accelerated electron beams with energies of 1 MeV. The results from experimental investigations along these lines are presented.

This review is devoted to the studies of heavy and superheavy elements and the methods of their synthesis and identification. Special attention is paid to the latest discoveries in the area of superheavy elements with Z = 107–112 in cold fusion reactions and Z = 113–118 in reactions between 48Ca and actinides.

A description is given and calculation results are presented for a high-intensity electron-beam source that can produce sequences of four electron bunches of 1 nC each, following at a frequency of 50 Hz. The root-mean-square normalized transverse beam emittance of the bunch does not exceed 4 mm mrad, the root-mean-square duration is 3 ps, and the energy can be adjusted in the 35–50 MeV range.

Peculiarities of electromagnetic interactions in silver isotopes are considered. Excited states of Ag isotopes are studied as a function of the mass number A = 95–117. Low-lying excited states reveal clear features that are specific for rotational spectra for the energies E < 4–5 MeV. In the energy domain above the nucleon separation threshold of 5–10 MeV, single-particle excited states overlap and produce a continuous spectrum. For energies E = 10–35 MeV, excitation of giant dipole resonance plays the most important role in Ag isotopes. Experimental data on the cross sections of photonuclear reactions in Ag isotopes are analyzed.

The pairing interaction of neutrons and protons in calcium isotopes and N = 28 isotones is considered. Ground state multiplets formed by neutrons and protons on the 1f 7/2 subshell with seniority values ν = 2, 3, 4 are investigated. Good agreement between the multiplet splitting value and nucleon pairing energies is shown not only for multiplets with seniorities ν = 2, but for higher seniority values as well.

The dependence of the properties of low-lying states of Mo isotopes on the mass number A = 83–117 is studied based on the collective and shell models of atomic nuclei. The variation of the nuclear shape with an increasing number of neutrons influences strongly the properties of excited states of Mo isotopes. Decay channels of isovector giant dipole resonance with emission of protons and neutrons are studied in the framework of the combined model. The basic mechanisms of the production of stable Mo isotopes in astrophysical nuclear reactions are described.

Methods for extracting nucleon resonance parameters from experimental data are reviewed. The formalism for the description of exclusive reactions of meson photo- and electroproduction off nucleons is discussed. Recent experimental data on exclusive meson production in the scattering of electrons and photons off protons are analyzed.

The pairing interaction between nucleons has a strong effect on the structure of an atomic nucleus. The most precise estimate of the magnitude of pairing forces is obtained by determining it for every isotope, based on the masses of the nuclei. The quality of this estimate is characterized by the degree of reconstruction for levels of the nucleus ground state multiplet (GSM). In this work, GSMs for even-even nuclei with pairs of identical nucleons over a filled core are considered on the basis of the delta interaction. Calculations of the GSM structure for isobar nuclei A = 42 and A = 134 show that analyzing GSM in the case of np pairing yields additional information on the correlation between isoscalar and isovector components in the structure of pairing forces.

Preliminary results from analyzing π+π− pair electroproduction on a proton bound in a deuteron are presented. Procedures for considering the Fermi motion of the initial proton in the deuteron and assessing the effects of interaction in the final states are developed. The yield of the reaction ep(n) → e′p′(n′)π+π− is obtained for the first time.

This review considers the history and meaning of the phenomenon of configurational splitting of giant dipole resonance in light nuclei, which was first discovered a quarter of a century ago and induced profound changes in the commonly accepted understanding of the structure of light nuclei and the mechanisms of their high-energy excitations. The experiments that led to the discovery of this phenomenon are described. The present status of the phenomenon of the configurational splitting of nuclear giant dipole resonance is discussed and directions of its future studies are outlined.

The nature of the excited states of the 40–48Ca isotopes is analyzed in the region of energies below the nucleon separation threshold. A peculiar feature of the 40–48Ca isotopes is the predominant filling of the 1f 7/2 neutron shell. Interaction between the neutrons of the 1f 7/2 shell and the nucleons of the 1d2s core results in formation of multiparticle excited states with a few vacancies in the 1d2s shell. The energies of single-particle proton states in the 40–48Ca isotopes are calculated using the Hartree-Fock potential with the Skyrme potential. The manner in which the energy of single-particle states varies, the magic numbers N = 20, 28 are formed, and the charge and nucleon density vary in the 40–48Ca isotopes as the neutron number increases from 20 to 28 is shown. Coherent interactions of the 1f 7/2 shell and 1d2s core nucleons also manifest themselves in the region above the nucleon separation threshold, leading to the configuration and isospin splitting of the GDR.

The yield of radioisotopes formed during photonuclear reactions in a natural mixture of titanium isotopes is measured at an electron energy of ≈15 MeV using a slot microtrone.

Yields of photonuclear reactions on the natural mixture of titanium isotopes were measured under exposure to a beam of bremsstrahlung γ-quanta with the end-point energy of 55 MeV. The results are compared with computations based on the TALYS model. It is shown that description of cross sections of photonuclear reactions on Ti isotopes requires the proper account for isospin and configuration splitting of the giant dipole resonance.

Existing experimental data allow us to study the behavior of nuclear shell structure by analyzing characteristics of different nature. In this work, one of the most striking phenomena of nuclear dynamics is examined: nucleon pairing. Nucleon pairing for different nuclei chains as a function of the number of protons or neutrons in a nucleus explains why high numbers of states with positive parity in even-odd nuclei are observed for excitation energies E* < 4 MeV that form the multiplet of a nucleus’s ground state.

Experimental data on single-particle neutron energies of Cd isotopes are analyzed within a dispersive optical model. Parameters of the potential are extrapolated to the region of unstable isotopes with a neutron excess. The evolution of calculated single-particle spectra and occupation probabilities of single-particle orbits corresponds to formation of magic features in Cd isotopes with N = 50, 82. The results from calculations agree with the concept that the 174Cd isotope with N = 126 forms the end of the peninsula at the neutron drip line.

Doses of ionizing radiation generated by a luggage simulator are measured. The luggage simulator is irradiated under conditions that occur when luggage is inspected by photonuclear detectors for explosive materials. It is shown that the ionizing radiation caused by induced radiation is not dangerous either to passengers or to airport stuff.

The possibility of production and separation of the 18F medical radioisotope at a race-track microtron with an accelerated electron energy of 55 MeV in the 23Na(γ, αn) photonuclear reaction is studied. Ion-exchange chromatography is used to separate 18F from irradiated NaOH targets.

Evaluation of fully integrated double pion electroproduction cross sections of protons was carried out at 1.4 < W < 2.0 GeV, 5 < Q 2 < 12 GeV2. The cross-section evaluation was obtained from an approach based on extrapolation of the double pion component of inclusive structure functions F 1 and F 2 from photon virtualities Q 2 < 5 GeV2 towards 5 < Q 2 < 12 GeV2. Q 2-parameterization compatible with restrictions from the Operator Product Expansion was used to conduct the extrapolation. The results will be used to extract double pion electroproduction cross sections of protons in future experiments with the new CLAS12 detector.

The process of photodisintegration of molybdenum isotopes was studied using the induced activity method. The yields of isotopes produced as a result of photonuclear reactions on a natural mixture of molybdenum isotopes were determined at an electron accelerator energy of 67.7 MeV. A comparison of the experimental results with the theoretical calculation carried out using the combined model of photonucleon reactions shows that the model gives a fair description of the experimental yields of photonucleon reactions on all molybdenum isotopes except for 92Mo. The high yields of the proton channels of photonuclear reactions on the 92Mo isotope and low yields of the corresponding neutron channels are interpreted based on the shell structure of molybdenum isotopes.

The nucleon pairing effect that is analyzed in the present paper is one of the striking manifestations of nuclear dynamics. Nucleon pairing for different chains of nuclei dependent upon the number of protons or neutrons in the nucleus allows one to explain the emergence of a great number of positive-parity states, which form a ground state multiplet, in even-even nuclei in the excitation energy range E* < 4 MeV. The interaction of paired nucleons with vibrational and rotational degrees of freedom of a nucleus produces a wide variety of excitation spectra of positive-parity states in even-even nuclei.

The mass distribution of the 238U photofission fragments formed under γ-quanta action is analyzed in the range of excitation energies of a fissile nucleus from 5 to 20 MeV. The influence on the ratio of asymmetric and symmetric photofission of the 238U structure and excitation energy of a fissile nucleus is discussed. A combined analysis and the comparison of the behavior of the asymmetric and symmetric modes of photofission were conducted for the first time. The results we obtained are compared with the prediction of the multimode model of the dependence of fission modes on the nuclear excitation energy.

The possibility of using radioactive sources to measure atomic number Z and the amount of substance nD of unknown objects is considered. An experiment is performed with test samples of different materials exposed to γ-rays from Cs-137 and Co-60 sources. The range of the method’s applicability in measuring atomic number Z and amount of substance nD is shown.

This paper describes a software package that is designed to simulate experiments to study photonucleon reactions by measuring residual activity. Calculations of the cross sections and yields of photonucleon reactions, the number of photonucleon reactions product-nuclei and their decay products, the spectrum of gamma rays produced in the irradiated sample, and the spectrum that is measured by the detector are described in detail. A comparison of the simulation results with the results of experiments is given.

Photofission of 238U by bremsstrahlung photons is studied at four energies of an electron accelerator: 19.5, 29.1, 48.3, and 67.7 MeV. The yields of the fission fragments after the emission of prompt neutrons are obtained using the gamma-ray spectroscopic technique. The mass distributions of photofission are obtained at different upper energies of the bremsstrahlung spectrum. The ratio the symmetric-fission mode to the asymmetric mode is obtained from the mass distribution. The symmetric mode becomes 3–4 times greater than the asymmetric as the excitation energy of the 238U nucleus increases from 12 to 16 MeV.

The history and modern state of the development of electron-beam accelerators at the Skobeltsyn Institute of Nuclear Physics at Moscow State University and investigations with their use are considered.

The activity of 18F that was produced in the 23Na(γ,αn)18F reaction with the maximum bremsstrahlung energy E b = 55 MeV was measured.

Yields of photonuclear reaction on natural mixture of Sn isotopes irradiated by bremsstrahlung beam with maximum energy of 29.1 MeV are studied via the residual activity method. Using the TALYS code and a combined model, the cross sections of the photonucleon reaction in stable isotopes of Sn are calculated. Measured yields are compared with the yields calculated using theoretical, experimental, and estimated cross sections.

Beginning in 1911, starting from the instant of the discovery of the atomic nucleus by Rutherford, physicists have made attempts to gain an understanding of the constitution of the atomic nucleus. Each nucleus is a complex unique object that consists of a finite number of neutrons and protons. It is shown in this review that the concept of the atomic nucleus changed as a large amount of experimental data was accumulated, understood, and theoretically analyzed. As a result, new types of interactions that were previously unknown in physics, such as the strong and weak interactions, were discovered; new phenomena associated with the mutual transformation of the particles were revealed; new types of symmetry, particularly spatial symmetry, were found; and new experimental methods were developed. As well, accelerators, which made it possible to observe the variations of separate atomic nuclei for the first time, were designed. Investigation of the properties of atomic nuclei opened a new world, viz., the subatomic quantum world. This knowledge is important in natural sciences, from the investigation of living organisms to astrophysics.

A comparative study of the results of the simulations of the photodisintegration of heavy nuclei in the energy range corresponding to the giant dipole resonance by the TALYS software package and by a combined model of is carried out. The cross sections of photoabsorption, photoneutron, and photoproton reactions and of the excitation of isomeric states for Hg and 208Pb isotopes are calculated. The results of the calculations are compared with the known experimental data.

Yields of photonucleon reactions of different multiplicity of natural isotopic mixture of Pb were measured on a bremsstrahlung photon beam with a maximum energy of 67.7 MeV using gamma-activation methods. Cross-sections of photonucleon reactions of different multiplicity were calculated on stable Pb isotopes within the bounds of the combined model. The calculated cross sections are compared to those measured in experiments on quasimonochromatic photon beams. They are also used to split the measured yields into yields of particular photonucleon reactions.

Yields of photonuclear reactions of several Hg isotopes are measured on a bremsstrahlung photon beam with a maximal energy of 19.5 MeV using a gamma-activation analysis. Cross sections of photonuclear reactions on stable Hg isotopes are calculated within bonds of the collective model taking isospin splitting of giant dipole resonance into account. The experimental results are compared with the results of theoretical calculations and earlier experimental studies.

A combined analysis of experimental data on total and partial photoneutron reaction cross sections, obtained using bremsstrahlung γ-radiation and quasi-monoenergetic annihilation photon beams, was performed for nine Sn isotopes. The partial reactions σeval(γ, nX) and σeval(γ, 2nX) cross sections were evaluated using an approach free of the shortcomings of experimental neutron multiplicity sorting methods. This approach involves calculations within the photonuclear reaction model, based on Fermi gas densities and considering the effects of nucleus deformation, the isospin splitting of its giant dipole resonance (GDR), and experimental data on the total photoneutron cross sections σexp(γ, xn) = σexp(γ, nX) + 2σexp(γ, 2nX) = σexp(γ, n) + σexp(γ, np) + … + 2σexp(γ, 2n) + 2σexp(γ, 2np) + …. The evaluated σeval(γ, nX) and σeval(γ, 2nX) reactions cross sections were obtained using the introduced transition multiplicity functions Ftheor = σtheor(γ, 2nX)/σtheor(γ, xn) = σtheor(γ, 2nX)/[σtheor(γ, nX) + 2σtheor(γ, 2nX) + …]; and σeval.(γ, 2nX) = Ftheor.σexp.(γ, xn) = σeval(γ, nX) = (1 − 2Ftheor)σexp(γ, xn). The evaluated partial reaction cross sections were used to assess the total photoneutron reaction cross sections σeval(γ, sn) = σeval(γ, nX) + σeval(γ, 2nX) + … as functions of the mass number A. The GDR features of 112, 114, 116, 117, 118, 119, 120, 122, 124Sn isotopes were studied and are discussed here.

The dynamics of the shell parameters of 64, 66, 68, 70Zn nuclei close to the Fermi energy, obtained by the joint evaluation of data from the stripping and pick-up reaction of a nucleon on one and the same nucleus, demonstrates how the difference between the neutron single-particle spectra of the levels of 70Zn and 68Ni nuclei with the number N = 40 arises. The experimental data are analyzed within a mean field model with dispersive optical potential. The calculation results describe very well the dimunution of the energy gap between the 1g9/2 and 2p1/2 levels in Zn isotopes, in comparison with Ni isotopes.

Experimental single-particle energies and occupation probabilities for neutron states near the Fermi energy in 58,60,62,64Ni nuclei were obtained from joint evaluation of the data on nucleon stripping and pickup reactions on the same nucleus. Degeneracy of the 2p 3/2,1/2 and 1f 5/2 subshells was demonstrated. The resulting data were analyzed within a mean-field model with dispersive optical-model potential. Good agreement was obtained between the calculated and experimental single-particle energies of the subshells.

Studying the interaction mechanism between gamma-quanta and atomic nuclei in the giant dipole resonance energy region gives us significant information about atomic nuclei. A large number of experiments for studying giant dipole resonance structure were accomplished using bremsstrahlung gamma-quanta. In such experiments cross sections of interactions are retrieved from reaction yields. To retrieve cross sections one needs to know the shape of the bremsstrahlung spectrum and to choose the optimal characteristics of the bremsstrahlung target. The purpose of this article is to choose the optimal characteristics of the bremsstrahlung target for experiments in the energy region E < 30 MeV. The analysis that was carried out based on numerical simulation showed that the optimal bremsstrahlung target consists of two parts. The first part is a tungsten plate 2.5 mm thick. The second part is aluminum plate 3 cm thick.

Evaluated and experimental neutron single-particle energies of the 88, 94, 96Sr and 90, 96, 98Zr nuclei near the Fermi energy are compared. A possibility of formation of a considerable particle-hole gap in the 94, 96Sr typical of traditional magic nuclei is investigated. Agreement is obtained between the single-particle energies calculated within the mean field model with the dispersive optical potential and the evaluated energies for the 94, 96Sr nuclei.

The contributions of exclusive π+n, π0p, and π−π+p channels to the inclusive structure function F 2(x, Q 2) are determined from the CLAS collaboration data analysis. Reliability of the CLAS data on the inclusive structure function and single-pion electroproduction channels is verified. The total contribution of the uninvestigated π+π0n and π0p channels to this function and the integrated cross sections of these channels at photon virtualities Q 2 = 0.4 and 0.5 GeV2 are predicted.

Several large relational databases (DBs) containing various atomic nucleus parameters and nuclear reaction features were produced at the Centre for Photonuclear Experiments Data (Centr Dannyh Fotoyadernykh Eksperimentov (CDFE)) of the Skobeltsyn Institute of Nuclear Physics, Moscow State University). The sources are numerical data founds maintained by International Nuclear Data Centers Network of the International Atomic Energy Agency (IAEA) and produced by CDFE. The original CDFE product is the electronic “Chart of Quadrupole Nuclear Deformations” which includes ∼2000 sets of data on nuclei quadrupole moments Q and quadrupole deformation parameters β2 for ∼1500 nuclei. At last time, in the frame of joint research with the Joint Institute for Nuclear Research (JINR) that electronic Chart was supplemented with the data on nuclear mean-root-square (MRS) charge radii (∼900 isotopes of 90 elements (Z = 1–96, N = 0–152)) and therefore transformed into the “Chart of Nucleus Shape and Size Parameters”—complete collection of data under discussion. New Chart allows one to investigate the isotopic and isotonic behavior of nuclei quadrupole moments, parameters of quadrupole deformation and charge radii, and study the R(Z, N) surface structure and R(A) dependence of the fine structure.

On the basis of the most reliable experimental information about the single-particle energies of neutron and proton states in 20 48 Ca28, 22 50 Ti28, 24 52 Cr28, and 26 54 Fe28 nuclei, single-particle energies in mirror 28 48 Ni20, 28 50 Ni22, 28 52 Ni24 and 28 54 Ni26 nuclei have been evaluated. The evaluated single-particle energies are compared with the energies calculated within the dispersive optical model. Good agreement between the calculated and experimental single-particle energies is demonstrated.