


Vol 80, No 5 (2017)
- Year: 2017
- Articles: 25
- URL: https://journal-vniispk.ru/1063-7788/issue/view/12087
Proceedings of LXVI International Conference on Nuclear Spectroscopy and Atomic Nuclei Structure October 11–14, 2016, Sarov, Russia/Nuclei
Excitation of 111mCd, 113mIn, and 115mIn isomeric states by photons of energy up to 8 MeV
Abstract
Experimental results on the excitation of isomeric nuclear states in the reactions 111Cd(γ, γ′)111mCd, 113In(γ, γ′)113mIn, and 115In(γ, γ′)115mIn studied by the activation method at photon energies of up to 8 MeV are presented. The respective experiments were performed at the LUE-8 linear electron accelerator of the Institute for Nuclear Research (INR, Moscow). A method for calculating cross sections per equivalent photon was developed with the aid of a simulation on the basis of the GEANT-4 code. The data obtained in this way are discussed from the point of view of the possibility of studying collective nuclear excitations of various multipolarity near the threshold.



Use of (3He, t) charge-exchange reactions in determining radii of excited states of nuclei
Abstract
A method for determining the radii of excited states of nuclei by means of (3He, t) charge-exchange reactions was proposed. Two versions of a comparison of differential cross sections for (3He, t) reactions were considered. The first relies on a comparison with cross sections for inelastic-scattering processes leading to the formation of isobaric analog states, while the second involves (3He, t) reactions leading to the production of the ground state. The two versions in question yield similar results and make it possible to determine the radius of the first excited state of the 13N nucleus. This state has the excitation energy of E* = 2.37 MeV, lying above the proton-emission threshold. The resulting radius proved to be enhanced in relation to the ground state and is close to the radius of the 3.09-MeV isobaric analog state of the 13С nucleus, which has a neutron halo. This permitted drawing the conclusion that the 13N nucleus in the 2.37-MeV state has a proton halo. The possibility of revealing a proton halo in other states of light nuclei is considered.



Do analogs of the Hoyle state exist in 16O?
Abstract
The root-mean-square radii of short-lived 0+-states in 16O were obtained for the first time from an analysis of α+16O diffraction scattering. Data on elastic and inelastic α+16O scattering were analyzed on the basis of the modified diffraction model in the range of projectile energies between a few tens of MeV units to 400 MeV. No case of a significant enhancement of the radius with respect to its ground-state value was observed. In particular, this concerns the 15.1-MeV 06+ state, which lies near the threshold for breakup to four alpha particles and for which we did not confirm a giant radius predicted by the alpha-particle-condensate model. This result disproves the hypothesis that the 16O nucleus in the 06+ state has a rarefied structure and appears to be an analog of the known Hoyle state at 7.65 MeV (02+) in 12C.



Yields of hydrogen isotopes in stopped-pion absorption by light nuclei
Abstract
The spectra of p, d, and t charged particles produced in stopped-pion absorption by nuclei are analyzed. Respective measurements were performed for 17 nuclei by means of a semiconductor spectrometer. A phenomenological model developed previously for medium-heavy and heavy nuclei was applied to describing the spectra and yields of charged particles originating from light nuclei (6,7Li, 9Be, 10,11B, and 12C). The contribution of intranuclear clusters (such as pp and 3,4He) to pion absorption was estimated.



Decisive role of wriggling vibrations in the formation of angular and spin distributions of products originating from binary and ternary fission of oriented nuclei
Abstract
It is shown that the multiplicities and angular and energy distributions of neutrons and photons evaporated from thermalized fragments originating from the spontaneous and low-energy induced fission of nuclei, the relative yields of ground and isomeric states of final fragments, and the features of delayed neutrons emitted upon the beta decay of the above fragments can successfully be described by employing nonequilibrium distributions of spins and relative orbital angular momenta of fission fragments formed in the vicinity of the scission point for the fissile nucleus being studied. It is also shown that these distributions, which are characterized by large mean values of the spins and orbital angular momenta directed orthogonally to the symmetry axis of the fissioning nucleus are successfully constructed upon simultaneously taking into account zero-mode transverse wriggling and bending vibrations of a fissile compound nucleus in the vicinity of its scission point, the wriggling vibrations being dominant. It is confirmed that the zero-mode wriggling vibrations considered immediately above are directly involved in the formation of the angular distributions of fragments originating from the spontaneous and low-energy fission of nuclei. This makes it possible to describe successfully such distributions for photofission fragments.



Delayed fission of atomic nuclei (To the 50th anniversary of the discovery)
Abstract
The history of the discovery of delayed nuclear fission is presented, and the retrospective of investigations into this phenomenon that were performed at various research centers worldwide is outlined. The results obtained by measuring basic delayed-fission features, including the fission probability, the total kinetic energy of fission fragments, and their mass distributions, are analyzed. Recommendations concerning further studies in various regions of nuclear map with the aim of searches for and investigation of atomic nuclei undergoing delayed fission are given. Lines of further research into features of delayed fission with the aim of solving current problems of fission physics are discussed.



Isospin in halo nuclei: Borromean halo, tango halo, and halo isomers
Abstract
It is shown that the wave functions for isobaric analog, double isobaric analog, configuration, and double configuration states may simultaneously have components corresponding to nn, np, and pp halos. The difference in the halo structure between the ground and excited states of a nucleus may lead to the formation of halo isomers. A halo structure of both Borromean and tango types can be observed for np configurations. The structure of ground and excited states with various isospins in halo-like nuclei is discussed. The reduced probabilities B(Mλ) and B(Eλ) for gamma transitions in 6−8Li, 8−10Be, 8,10,11B, 10−14C, 13−17N, 15−17,19O, and 17F nuclei are analyzed. Particular attention is given to the cases where the ground state of a nucleus does not have a halo structure, but where its excited state may have it.



Study of ground states of 3H, 3,4,6He, 6Li, and 9Be nuclei by Feynman’s continual integrals method
Abstract
The ground-state energies and the squared moduli of the ground-state wave functions are calculated for the 3H, 3,4,6He, 6Li, and 9Be nuclei by Feynman’s continual (path) integrals method. The results are in satisfactory agreement with experimental data.



Microscopic multichannel investigation of the 6Li + n seven-nucleon nuclear system at low energies
Abstract
The 6Li + n seven-nucleon nuclear system is studied at low energies within a microscopic approach based on the multichannel algebraic version of the resonating group model. The partial and total cross sections for the 6Li(n, t)4He reaction are calculated. The contributions of the various partial cross sections to the energy dependence of the total cross section are considered. The results of the calculations are found to be in a good agreement with experimental data.



Relationship between T-invariance and formation mechanisms for T-odd and T-even asymmetries in the angular distributions of fission fragments of oriented nuclei
Abstract
The T-invariance condition was analyzed for the amplitude Tb,a of multiparticle multistep elastic or inelastic a → b nuclear reactions. This condition leads to the equality of the amplitude Tb,a to the amplitude \({\tilde T_{\bar a,\bar b}}\) of \(\bar b \to \bar a\) time-reversed reaction, for which the reaction operator \(\tilde T\) coincides with the inverse-reaction (b → a) operator. It is shown that, in the case where the original, inverse, and time-reversed reactions are governed by a common T-invariant mechanism, the coefficients D of asymmetries appearing in the differential cross sections for these reactions can be represented in the form of a unified scalar (pseudoscalar) function of arguments equal to the momentum and spin vectors of particles of the initial and final channels of the reactions under analysis. It is also shown that the use of the T-invariance condition for the coefficients D of asymmetries in the differential cross section for the original nuclear reaction that are different in P- and T-parity makes it possible to separate mechanisms leading to nonzero coefficients D for a number of the asymmetries under analysis from the remaining mechanisms leading to zero coefficients D of these asymmetries. It is proven that there exist such asymmetries in the differential cross section for the original reaction whose coefficients vanish for all possible T-invariant mechanisms of their appearance, so that, upon proving experimentally the appearance of nonzero coefficients of these asymmetries in the differential cross section for the original reaction, this fact can be used to assess features of T-noninvariant interactions in nuclear systems.



Phenomenological features of two-proton virtual decay of the 45Fe nucleus
Abstract
On the basis of the theory of diagonal two-proton two-step virtual decays of spherical nuclei that was developed earlier and the superfluid model of the nucleus, the total and partial widths for the two-proton decay of the 45Fe parent nucleus in the ground state to the ground state of the 43Cr daughter nucleus were calculated along with the angular distribution of protons emitted in this decay. The calculated features of this mode of 45Fe decay were shown to be highly sensitive to the choice of form for nucleon shell potentials. It is also shown that there exists a potential such with which one can construct a successful simultaneous description of the experimental total width and the angular distribution of emitted protons for the aforementioned two-proton mode of decay of the 45Fe nucleus.



Single-particle properties of N = 12 to N = 20 silicon isotopes within the dispersive optical model
Abstract
Experimental neutron and proton single-particle energies in N = 12 to N = 20 silicon isotopes and data on neutron and proton scattering by nuclei of the isotope 28Si are analyzed on the basis of the dispersive optical model. Good agreement with available experimental data was attained. The occupation probabilities calculated for the single-particle states in question suggest a parallel-type filling of the 1d and 2s1/2 neutron states in the isotopes 26,28,30,32,34Si. The single-particle spectra being considered are indicative of the closure of the Z = 14 proton subshell in the isotopes 30,32,34Si and the N = 20 neutron shell.



Calculation of nucleon densities in calcium, nickel, and molybdenum isotopes on the basis of the dispersive optical model
Abstract
The radial distributions of proton and neutron densities in the even–even isotopes 40−70Cа and 48−78Ni and the analogous distributions of neutron densities in the even–even isotopes 92−138Mo were calculated on the basis of the mean-fieldmodel involving a dispersive optical potential. The respective root-mean-square radii and neutron-skin thicknesses were determined for the nuclei under study. In N > 40 calcium isotopes, the calculated neutron root-mean-square radius exhibits a fast growth with increasing N, and this is consistent with the prediction of the neutron-halo structure in calcium isotopes near the neutron drip line.



Peculiarities in total cross sections of reactions with weakly bound nuclei 6He, 9Li
Abstract
The energy dependence of the total cross sections for the 6He + Si and 9Li + Si reactions was measured at beam energies between 5 and 20 MeV per nucleon. The results agree with experimental data published for the 6He + Si reaction. New data are obtained for the 9Li + Si reaction in the vicinity of a local enhancement of the total cross section. A theoretical analysis of the possible reasons behind the appearance of this peculiarity in the case of collisions of 6He and 9Li nuclei with silicon target nuclei is performed. In particular, the enhancement may owe its origin to the effect of loosely bound projectile nucleons.



Analysis of p10B scattering within Glauber theory
Abstract
The differential cross sections for p10B scattering are calculated at the energies of 197, 600, and 1000 MeV within Glauber theory. The contributions of single and double collisions are taken into account in the multiple-scattering operator. The contributions of proton collisions with nucleons belonging to various (1s, 1p) shells are estimated in the single-scattering cross sections. A comparison with experimental data and with the result of calculations in the distorted-wave Born approximation (DWBA) at 197 MeV showed that the differential cross sections for p10B scattering are adequately described in the region forward scattering angles.



Differential cross section for the 16O(t, p)18O reaction and determination of the size of the two-neutron periphery in the 18O nucleus
Abstract
Within the theoretical formalism that combines a four-body problem with themultiparticle shell model, it is shown that the cross section for the dineuteron-stripping mechanism is consistent with the experimental angular distribution of protons from the 16O(t, p)18O reaction. This makes it possible to find the wave function for the relative motion of the dineutron and 16O and to obtain thereby the probability density W(r) for the dineutron in 18O, the nn–16O interaction potential, and the root-mean-square distance 〈L〉nn between the dineutron and 16O. The respective calculations reveal that, at r ≈ 8 fm, the dineutron probability density and a rather deep nn–16O potential become negligible, which leads to the absence of a dineuntron periphery in 18O. It seems that one can explain this fact by a rather large value (12.19 MeV) of the dineutron binding energy in this nucleus. Thus, the 18O nucleus is quite compact an object, despite the excess of two neutrons, and has a neutron skin rather than a periphery.



Modern status of photonuclear data
Abstract
The reliability of experimental cross sections obtained for (γ, 1n), (γ, 2n), and (γ, 3n) partial photoneutron reactions using beams of quasimonoenergetic annihilation photons and bremsstrahlung is analyzed by employing data for a large number of medium-heavy and heavy nuclei, including those of 63,65Cu, 80Se, 90,91,94Zr, 115In, 112−124Sn, 133Cs, 138Ba, 159Tb, 181Ta, 186−192Os, 197Au, 208Pb, and 209Bi. The ratios of the cross sections of definite partial reactions to the cross section of the neutron-yield reaction, Fi = σ(γ, in)/σ(γ, xn), are used as criteria of experimental-data reliability. By definition, positive values of these ratios should not exceed the upper limits of 1.00, 0.50, 0.33,... for i = 1, 2, 3,..., respectively. For many nuclei, unreliable values of the above ratios were found to correlate clearly in various photon-energy regions Fi with physically forbidden negative values of cross sections of partial reactions. On this basis, one can conclude that correspondent experimental data are unreliable. Significant systematic uncertainties of the methods used to determine photoneutron multiplicity are shown to be the main reason for this. New partial-reaction cross sections that satisfy the above data-reliability criteria were evaluated within an experimental–theoretical method [σeval(γ, in) = Fitheor (γ, in) × σexpt(γ, xn)] by employing the ratios Fitheor (γ, in) calculated on the basis of a combined photonuclear-reaction model. It was obtained that cross sections evaluated in this way deviate substantially from the results of many experiments performed via neutron-multiplicity sorting, but, at the same time, agree with the results of alternative activation experiments. Prospects of employing methods that would provide, without recourse to photoneutron-multiplicity sorting, reliable data on cross sections of partial photoneutron reactions are discussed.



Proceedings of LXVI International Conference on Nuclear Spectroscopy and Atomic Nuclei Structure October 11–14, 2016, Sarov, Russia/Elementary Particles and Fields
Application of cyclotrons in beam technologies
Abstract
Some currently developed applications of cyclotrons (beam technologies) are discussed. They include new methods for producing radioisotopes for medical purposes and investigations into the radiation strength ofmaterials and the wear of units of variousmachines and devices bymeans of beams of radioactive nuclei.



Phenomenological description of relativistic-quark interaction on the basis of the Dirac equation with the Cornell potential
Abstract
Relativistic-quark interaction is described phenomenologically on the basis of the Dirac equation with the Cornell potential. A general form of the initial equation involving the vector and scalar components of the Cornell potential is used for the case of an arbitrary relation between them. The Hamiltonian in the Foldy–Wouthuysen representation is derived in a general form with allowance for electromagnetic interaction. In contrast to earlier investigations, it is relativistic and exact for the zeroth- and first-order terms in the Planck constant and also for those second-order terms that describe contact interactions. General quantum-mechanical equations of motion for the momentum and spin are derived, and the classical limit of the Hamiltonian and for the equations of motion is found for the first time. A relation between the angular velocity of quark spin precession and the force acting on the quark is obtained. The energy of spin–orbit interaction is rather high (on the order of 100 MeV). Terms that describe spin–orbit and contact interactions have opposite signs for the vector and scalar components of the Cornell potential. The evolution of the quark helicity and the spin–spin interaction of the quarks are also calculated.



XIX International Moscow School of Physics (44th ITEPWinter School of Physics) and International School of Physics “QCD and Exotic Hadrons” February 16–23, 2016, Serpukhov, Russia/Elementary Particles and Fields
Search for a massive invisible particle X0 in B+ → e+X0 and B+ → μ+X0 decays
Abstract
We present a search for a non-Standard-Model invisible particle X0 in the mass range 0.1–1.8 GeV/c2 in B+ → e+X0 and B+ → μ+X0 decays. The results are obtained from a 711 fb−1 data sample which corresponds to 772 × 106\(B\bar B\) pairs, collected at the Υ(4S) resonance with the Belle detector at the KEKB e+e− collider. One B meson is fully reconstructed in a hadronic mode to determine the momentum of the lepton of the signal decay in the rest frame of the recoiling partner B meson. We find no evidence of a signal and set upper limits on the order of 10−6.



Beasts in Lambda-CDM zoo
Abstract
Recent astronomical discoveries of supermassive black holes (quasars), gamma-bursters, super-novae, and dust at high redshifts, z = (5−10), are reviewed. Such a dense population of the early universe is at odds with the conventional mechanisms of its possible origin. Similar data from the contemporary universe, which are also in conflict with natural expectations, are considered too. Two possible mechanisms are suggested, at least one of which can potentially solve all these problems. As a by-product of the last model, an abundant cosmological antimatter may be created.



Exotic quarkonium states in CMS
Abstract
The studies of the production of the X(3872), either prompt or from B-hadron decays, and of the J/ψϕ mass spectrum in B-hadron decays have been carried out by using pp collisions at \(\sqrt s \) = 7 TeV collected with the CMS detector at the LHC. The cross-section ratio of the X(3872) with respect to the ψ(2S) in the J/ψπ+π− decay channel and the fraction of X(3872) coming from B-hadron decays are measured as a function of transverse momentum (pT), covering unprecedentedly high values of pT. For the first time, the prompt X(3872) cross section times branching fraction is extracted differentially in pT and compared with NRQCD predictions. The dipion invariant-mass spectrum of the J/ψπ+π− system in the X(3872) decay is also investigated. A peaking structure in the J/ψϕ mass spectrum near threshold is observed in B± → J/ψϕK± decays. The data sample, selected on the basis of the dimuon decay mode of the J/ψ, corresponds to an integrated luminosity of 5.2 fb−1. Fitting the structure to an S-wave relativistic Breit–Wigner lineshape above a three-body phase-space nonresonant component gives a signal statistical significance exceeding five standard deviations. The fitted mass and width values are m = 4148.0 ± 2.4(stat.) ± 6.3(syst.) MeV and Γ = 28+15 − 11(stat.) ± 19(syst.) MeV, respectively. Evidence for an additional peaking structure at higher J/ψϕ mass is also reported.









On thermodynamics and gravity
Abstract
A new entropic gravity inspired derivation of general relativity from thermodynamics is presented. This generalizes the “Thermodynamics of Spacetime” approach by T. Jacobson, which relies on the null Raychaudhuri evolution equation. Here the rest of the first law of thermodynamics is incorporated by using the null Damour–Navier–Stokes equation, known from the membrane paradigm for describing the tangential flow of deformations along a horizon.


