Pb Nuclei Research Articles

Isotopic effect in the energy dependence of the total fission cross section of lead and 209Bi nuclei for protons with energies up to 1 GeV

The results from measurements of the total fission cross sections of 206Pb, 207Pb, and 208Pb nuclei for protons with energies from 207 to 1000 MeV and a step of ≈100 MeV. These results complemented by our data for 209Bi and the data of the EXFOR world base allow determination of absolute and relative contributions of the isotopic effect.

Asymmetric nuclear matter and neutron skin in an extended relativistic mean-field model

The density dependence of the symmetry energy, instrumental in understanding the behaviour of the asymmetric nuclear matter, is investigated within the extended relativistic mean field (ERMF) model which includes the contributions from the self and mixed interaction terms for the scalar-isoscalar ($\sigma$), vector-isoscalar ($\omega$) and vector-isovector ($\rho$) mesons upto the quartic order. Each of the 26 different parameterizations of the ERMF model employed are compatible with the bulk properties of the finite nuclei. The behaviour of the symmetry energy for several parameter sets are found to be consistent with the empirical constraints on them as extracted from the analyses of the isospin diffusion data. The neutron-skin thickness in the $^{208}$Pb nucleus for these parameter sets of the ERMF model lie in the range of $\sim 0.20 - 0.24$ fm which is in harmony with the ones predicted by the Skyrme Hartree-Fock model. We also investigate the role of various mixed interaction terms which are crucial for the density dependence of the symmetry energy.

Trapped Hole Center at a Pb++Vacancy in γ-Irradiated PbCl2Crystals

In PbCl 2 crystals irradiated with γ-rays and then pulse annealed, a new ESR spectrum appeared. The spectrum could be interpreted in terms of a hole trapped at a Pb 2+ vacancy. The hole interacts mainly with four 207 Pb nuclei around the center. The g factor was found to be anisotropic and the g values are g x = 2.117, g y = 2.021, and g z = 2.098. The z-axis of the g tensor corresponds to the crystallographic c-axis, and the x- and γ-axes make angles of about 18° with the a- and b-axes, respectively. Hyperfine interactions with four 207 Pb nuclei are nearly isotropic and two of these nuclei are identical. Hyperfine constants were found to be about 53, 53, 300, and 526 G. The trapped hole center is the antimorph of the F center.

Investigation of Deuteron Emission Spectra at 62 MeV Proton Incident Energy

In this study, deuteron emission cross sections for 27Al, 54,56Fe, 89Y, 120Sn, 197Au, 208Pb and 209Bi target nuclei have been calculated at 62 MeV proton incident energy. In these calculations, the pre-equilibrium and equilibrium effects have been investigated. The pre-equilibrium calculations involve the geometry dependent hybrid model and hybrid model. Equilibrium effects are calculated according to the Weisskopf–Ewing model. The calculated results are compared with the experimental data taken from the literature and found to be in good agreement.

10.1007/s11450-008-3010-7

A combination of the exciton and evaporation models is used to describe photonucleon reactions induced in heavy and medium-mass nuclei by photons of energy in the range 7 ≤ E γ ≤ 140 MeV. The formation of a giant dipole resonance and quasideuteron absorption are considered as two mechanisms that are responsible for the photoexcitation of a nucleus in the energy regions E γ ≲ 20 MeV and E γ ≳ 40 MeV, respectively. As is well known, the densities of particle-hole states are employed in the exciton model, and these quantities are calculated on the basis of the Fermi gas model. This makes it possible to take into account the effect of the energy dependence of single-particle and single-hole densities of states on the rate of emission and intranuclear processes. The model in question is applied to describing partial photonucleon cross sections for 119Sn, 140Ce, 181Ta, and 208Pb nuclei.

Influence of Pb(II) Ions on the EPR Properties of the Semiquinone Radicals of Humic Acids and Model Compounds: High Field EPR and Relativistic DFT Studies

X-band (9.76 GHz) and high field (416.00 GHz) electron paramagnetic resonance spectroscopy (EPR) was used to study the interactions between Pb(II) ions and semiquinone radicals of natural humic acids and their simple models. The EPR experiments were performed on powder samples. The formation of Pb(II) complexes with the radicals was accompanied by a significant decrease of g parameters as compared to those observed for parent radicals. Two types of complexes were identified depending on the initial concentration of Pb(II) ions. For one of them the anisotropic hyperfine coupling with the (207)Pb nucleus was observed. Systematic DFT calculations were carried out for complexes with different forms of radical ligands (L(2)(-*), HL(-*), and H(2)L*) derived from 3,4-dihydroxybenzoic acid representing different ligation schemes. The g parameters calculated for the structure characterized by a significant accumulation of spin density on the Pb atom are strongly deviated from the values observed experimentally. Moreover, a decrease of the spin population on all oxygen atoms as a result of complexation of Pb(II) via carboxyl oxygens and protonation of hydroxyl oxygens is required to reproduce the experimental g parameters.

Self-consistent calculations within the quasiparticle time blocking approximation with exact account taken of the single-particle continuum

A self-consistent version of the model based on the method of Green’s functions which takes into account conventional phonons of the random phase approximation, complex configurations like 2 quasiparticles⊗phonon ones, and exact single-particle continuum is used to describe many discrete natural-parity states and giant resonances in the 123Sn and 208Pb nuclei. The quasiparticle-phonon interaction is shown to be important not only for low-lying and high-lying collective states but also for low-lying noncollective states.

Isotopic dependence of the cross section for the induced fission of heavy nuclei

The cross sections for the induced fission of 211−223Ra, 203−211Rn, and 221−231Th nuclei undergoing peripheral collisions with 208Pb nuclei are calculated on the basis of the statistical model. The role of the N = 126 neutron shell is studied. The level density in excited nuclei is determined within the Fermi gas model and a model that takes into account the collective enhancement of the level density. The inclusion of a particle—hole excitation in addition to a collective Coulomb excitation makes it possible to obtain a satisfactory description of experimental cross sections for the fission of radium isotopes. The calculated ratios of the cross sections for the induced fission of 236U (237U) and 238U (239U) nuclei agree with experimental data.

Semimicroscopic description of charge-exchange giant spin-monopole resonances

The quantitative analysis of the main properties of charge-exchange giant spin-monopole resonances is performed for closed-shell parent nuclei within the semimicroscopic approach based on the continuum version of the random phase approximation and phenomenological treatment of the spreading effect. For the first time the description of direct neutron decay of the spin-monopole resonances in the β+-channel is given together with taking into account the resonance energy shift due to the spreading effect. The results of the joint analysis of the main properties of the above-mentioned giant resonances are given for the parent nuclei 48Ca and 208Pb.

Nuclear Data Sheets for A = 187

Evaluated spectroscopic data and level schemes from radioactive decay and nuclear reaction studies are presented for 187Hf, 187Ta, 187W, 187Re, 187Os, 187Ir, 187Pt, 187Au, 187Hg, 187Tl, 187Pb, 187Bi, and 187Po. This evaluation for A = 187 supersedes the earlier one by R.B. Firestone (1991Fi02) published in Nuclear Data Sheets 62, 159 (1991) and the 187Tl evaluation by C.M. Baglin (1999Ba24) published in Nuclear Data Sheets 86, 487 (1999). Highlights of this publication are the following: This evaluation includes first identifications of 187Hf, 187Ta (1999Be63, 2000PoZY) and 187Po (2006An11) nuclides. A B(E2)↑ = 0.080 12 was determined by 1967Bi10 for the 9/2+ state at 845 keV in 187Re Coulomb Excitation. Using this B(E2) value and the adopted 845γ ray properties, a T 1 / 2 = 54 fs 34 can be deduced for the 845 keV level of 187Re. This T 1/2 yields a large B(E2)(W.u.) ≈ 1.3 × 105 for the 263γ (depopulating the same level) indicating either substantial unobserved feeding or incorrect g-ray branching intensities of this level. The decay of g.s. and isomer of 187Tl are poorly known (please see 187Tl ε decay (51 s+15.60 s)). Based on 191Po α decay studies, 2002An19 establishes a 187Pb isomeric level energy at 2(15) keV and assigns J π = 13 / 2 + for the 187Pb g.s. and J π = 3 / 2 − for the isomeric state (inverse of the systematics of odd-mass Pb nuclei in this region). From 187Pb and 187Pb m mass measurements, 2005We11 determined the isomeric level energy at 33(13) keV.

Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions

We have studied the low-lying magnetic spectra of {sup 12}C, {sup 16}O, {sup 40}Ca, {sup 48}Ca, and {sup 208}Pb nuclei within the random phase approximation (RPA) theory, finding that the description of low-lying magnetic states of doubly-closed-shell nuclei imposes severe constraints on the spin and tensor terms of the nucleon-nucleon effective interaction. We first used four phenomenological effective interactions, and we obtained good agreement with the experimental magnetic spectra and, to a lesser extent, with the electron scattering responses. Then we made self-consistent RPA calculations to test the validity of the finite-range Gogny D1 interaction. For all the nuclei under study, we found that this interaction inverts the energies of all the magnetic states forming isospin doublets.

Attenuation of the neutron spin–orbit splitting in a relativistic Hartree–Fock calculation in the 48Ca and 208Pb nuclei with the removal of the s1/2 protons

On the basis of a relativistic Hartree–Fock (RHF) calculation, we describe the reduction of the neutron and proton spin–orbit (SO) splittings when passing from the 48Ca and 208Pb nuclei to the nuclei characterized by the πs−21/2 configuration with respect to the starting double magic nuclei (in their ground states). As in earlier relativistic mean field calculations by several authors, we have observed a correlation between the magnitude of the SO splitting in p-doublets and the density of protons in the nuclear core, which is modified by the proton hole created with the removal of the s1/2 protons near the Fermi surface in the double magic nuclei studied. The SO interaction, in our model, due to the strong effect of the Fock terms, does not have a perturbative character. The contribution of the SO potential to the SO splitting is negative and increases in magnitude when going from the magic nuclei considered to the 46Ar and 206Hg nuclei. The specific values of the SO splittings, in our case, arise as a consequence of a fine adjustment of the central and the SO potentials (which are strongly state dependent), and of the kinetic energy also, rather than induced by just the change of the SO potential owing to the modification of the charge density inside the nucleus. From the magic nucleus to the πs−21/2 configuration nucleus, in the p-doublets, it happens that the more bound SO partner with j+ is shifted up more so than its less bound partner with j−, bringing about a minor SO splitting or even an incipient inversion of the relative position of the two SO partners. Pions slightly enhance this different behaviour of the two SO partners and, consequently, favour the quenching of the SO splitting.

Shears bands in 112In

A new level scheme of 112In have been established up to 6.8 MeV in excitation energy and to a tentative spin of (21+) through the reaction 110Pd(7Li,5n)112In at a beam energy of 50 MeV. In-beam measurements involving γ-γ coincidences and directional correlation of oriented states were performed. M1 bands consisting of ΔI = 1 dipole transitions have been observed. Possible quasiparticle configurations suggest that these bands are similar to the shears bands observed in Pb nuclei.

Level density andγ-decay properties of closed shell Pb nuclei

The level densities and $\ensuremath{\gamma}$-ray strength functions of $^{205\ensuremath{-}208}\mathrm{Pb}$ have been measured with the Oslo method, using the $(^{3}\mathrm{He},^{3}\mathrm{He}{}^{'}\ensuremath{\gamma})$ and $(^{3}\mathrm{He},\ensuremath{\alpha}\ensuremath{\gamma})$ reactions on the target nuclei $^{206}\mathrm{Pb}$ and $^{208}\mathrm{Pb}$. The extracted level densities are consistent with known discrete levels at low excitation energies. The entropies and temperatures in the microcanonical ensemble have been deduced from the experimental level density. An average entropy difference of $\ensuremath{\Delta}S~0.9{k}_{B}$ has been observed between $^{205}\mathrm{Pb}$ and $^{206}\mathrm{Pb}$. The $\ensuremath{\gamma}$-ray strength functions in $^{205\ensuremath{-}208}\mathrm{Pb}$ have been extracted and compared with two models; however, none of them describe the data adequately. Intermediate structures have been observed in the $\ensuremath{\gamma}$-ray strength functions for $\ensuremath{\gamma}$-ray energies below neutron threshold in all the analyzed Pb nuclei. These structures become less pronounced while moving from the doubly magic nucleus $^{208}\mathrm{Pb}$ to $^{205}\mathrm{Pb}$.

Spin-Isospin Resonances: A Self-Consistent Covariant Description

For the first time a fully self-consistent charge-exchange relativistic RPA based on the relativistic Hartree-Fock (RHF) approach is established. The self-consistency is verified by the so-called isobaric analog state (IAS) check. The excitation properties and the nonenergy weighted sum rules of two important charge-exchange excitation modes, the Gamow-Teller resonance (GTR) and the spin-dipole resonance (SDR), are well reproduced in the doubly magic nuclei 48Ca, 90Zr and 208Pb without readjustment of the particle-hole residual interaction. The dominant contribution of the exchange diagrams is demonstrated.

On the contribution of the pair Coulomb interaction of protons to the IAR energy

The energy of isobaric analog resonances (IARs) has been quantitatively interpreted within the isospin-self-consistent approach and based on the continuum random-phase approximation. Analysis is performed on the assumption that the Coulomb interaction of protons is the main source of violation of isobaric symmetry in nuclei. The new element in the analysis is the consideration of the contribution of virtual excitation of isovector multipole giant resonances (due to the pair Coulomb interaction of protons) to the IAR energy. The approach proposed is implemented by the example of an analog of the ground state of the 208Pb nucleus. Satisfactory description of the experimental energy of the corresponding IAR is obtained.

Dissociation of deuteron, 6He and 11Be from Coulomb dissociation reaction cross-section

The fragmentation of deuteron, 6He and 11Be have been studied during interaction with the 208Pb nucleus at various projectile energies. The Coulomb dissociation cross-sections and the momentum distribution of the break-up fragments have been analysed within the framework of the direct fragmentation model. The post-acceleration effect of deuteron during break-up and the halo structures of both the 6He and 11Be have been investigated.

Preequilibrium model of photonucleon reactions that is based on Fermi gas densities

A combination of the exciton and evaporation models is used to describe photonucleon reactions induced in heavy and medium-mass nuclei by photons of energy in the range 7 ≤ Eγ ≤ 140 MeV. The formation of a giant dipole resonance and quasideuteron absorption are considered as two mechanisms that are responsible for the photoexcitation of a nucleus in the energy regions Eγ ≲ 20 MeV and Eγ ≳ 40 MeV, respectively. As is well known, the densities of particle-hole states are employed in the exciton model, and these quantities are calculated on the basis of the Fermi gas model. This makes it possible to take into account the effect of the energy dependence of single-particle and single-hole densities of states on the rate of emission and intranuclear processes. The model in question is applied to describing partial photonucleon cross sections for 119Sn, 140Ce, 181Ta, and 208Pb nuclei.

Nuclear-spin relaxation ofPb207in ferroelectric powders

Motivated by a recent proposal by O. P. Sushkov and co-workers to search for a P,T-violating Schiff moment of the $^{207}$Pb nucleus in a ferroelectric solid, we have carried out a high-field nuclear magnetic resonance study of the longitudinal and transverse spin relaxation of the lead nuclei from room temperature down to 10 K for powder samples of lead titanate (PT), lead zirconium titanate (PZT), and a PT monocrystal. For all powder samples and independently of temperature, transverse relaxation times were found to be $T_2\approx 1.5 $ms, while the longitudinal relaxation times exhibited a temperature dependence, with $T_1$ of over an hour at the lowest temperatures, decreasing to $T_1\approx 7 $s at room temperature. At high temperatures, the observed behavior is consistent with a two-phonon Raman process, while in the low temperature limit, the relaxation appears to be dominated by a single-phonon (direct) process involving magnetic impurities. This is the first study of temperature-dependent nuclear-spin relaxation in PT and PZT ferroelectrics at such low temperatures. We discuss the implications of the results for the Schiff-moment search.

Lifetimes of intruder states in 186Pb, 188Pb and 194Po

Lifetimes of prolate intruder states in 186Pb and 188Pb and oblate intruder states in 194Po have been determined through recoil distance Doppler-shift lifetime measurements. Deformation parameters of | β 2 | = 0.29 ( 5 ) and | β 2 | = 0.17(3) have been extracted from experimental B ( E 2 ) values for the prolate and the oblate bands, respectively. The present study addresses the phenomenon of shape coexistence typical for the nuclei near Z = 82 and N = 104 , providing information on configuration mixing of intrinsic structures of the nuclei of interest. The results are compared with the available lifetime data and theoretical results for neutron-deficient Po, Pb, Hg and Pt nuclei. Furthermore, new self-consistent mean-field calculations have been carried out for 194Po.