7 MeV dipole ground state transitions in 207Pb, 208Pb and 209Bi

The Doppler-broadened 7.117 MeV line from the ¹⁹F(p, αγ)¹⁶O reaction has been used to resonantly excite levels in ²⁰⁸Pb at 7071±2 and 7091±2 keV, in ²⁰⁷Pb at 7186±5 and 7206±5 keV and in ²⁰⁹Bi at 7179±5 and 7202±5 keV. On the basis of angular distribution measurements the 7071 and 7091 keV levels of ²⁰⁸Pb are assigned spins of 1 and assuming 100% ground state branching the widths are calculated to be 31±3 and 17±2 eV respectively. It is suggested that the states in ²⁰⁷Pb and ²⁰⁹Bi arise from the weak coupling of a $\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ neutron hole and an $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ proton respectively to one or the other of the ²⁰⁸Pb levels. The widths obtained in terms of _gΓ_o²/Γ are 15±4 and 25±5 eV for the 7186 and 7206 keV levels of ²⁰⁷Pb and 24±5 and 30±5 for the levels of ²⁰⁹Bi respectively. These values are consistent with the weak-coupling suggestion.     

Axially symmetric time-dependent Hartree-Fock study of the 208Pb + 208Pb reaction

A time-dependent Hartree-Fock calculation assuming axial and reflection symmetry constraints is performed for the head-on collision of ²⁰⁸Pb + ²⁰⁸Pb systems at E_lab≈1600 MeV. The calculation suggests the excitation of surface modes in the reaction and the energy loss characteristic of a deep inelastic process. An estimate of neck-radius and neck-formation time is given.     

Properties of single-particle states in the 208Pb region

The properties of single-particle states in the ²⁰⁸Pb region are obtained by subtracting from the empirical values the dressing effects of the multipole particle-hole and pairing phonons. Use is made of the particle-vibration formalism. Single-particle energies, one-body transfer spectroscopic factors and effective quadrupole charges are examined within this framework.     

Low-energy transitions in the 197Pb and 198Pb isotopes

The ¹⁹⁸Pb and ¹⁹⁷Pb isotopes are produced through the ¹⁸⁶W(¹⁶O, 4n, 5n) reactions. Conversion-electron, γ- and X-ray spectra are measured using the compound-nucleus recoil method. Conversion coefficients and multipolarities are deduced for a large number of transitions. Together with angular distribution measurements and the results of γγt multidimensional coincidences they lead to decay schemes for the two isotopes. Microscopic calculations, performed in the two- or three-quasiparticle approximation with a surface delta interaction, fail to reproduce completely the observed properties, showing similar defects for the odd and even isotope.     

Proton orbit sizes in 208Pb

The sub-Coulomb (t,α) reaction has been employed in the determination of the rms radii of the $\text{3s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{, 2}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{, 1}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$, and $\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ proton orbits in ²⁰⁸Pb. The experimental values are compared to the results of Hartree-Fock calculations.     

Molecular-orbital X-rays from 1 GeV 208Pb + 208Pb and 209Bi + 209Bi collisions

We have measured the spectra of continuum X-rays above the characteristic K lines for 4.5 to 4.8 MeV/N ²⁰⁸₈₂Pb → ²⁰⁸₈₂Pb, Pb → Bi, Bi → Pb and Bi → Bi collisions. Above ≈400 keV X-ray energy the spectral shape and intensity agree roughly with calculations of Kirsch et al. for the 1sσ molecular-orbital (MO) X-ray spectrum from Pb-Pb. Deviations from the theory below ≈400 keV suggest transitions to other MO's.     

Fully self-consistent description of high spin magnetic states in 208Pb

Magnetic transverse form factors of 12^? and 14^? states in ²⁰⁸Pb are calculated in a fully self-consistent manner utilizing the effective density dependent interaction D1. Reduction of the strength due to the RPA polarization and the ground state correlations is observed and found to be independent of the momentum transfer. Nuclear structure implications particular to two close lying 12^? states are discussed.     

Nuclear monopole polarization in muonic 208Pb

Nuclear polarization effects due to the presence of a muon in an atomic orbit are described in a self-consistent way. Within this framework the monopole part of the polarization energy is calculated by solving Hartree-Fock equations for the combined muon-nucleus system. The nuclear part is described by using the density dependent forces of both Skyrme and Moszkowski. The muon is assumed for the present to be in the 1s and 2s state, respectively, and is treated relativistically. The monopole part of the energy gain turns out to be -0.943 ± 0.070 keV for the 1s-muon and -0.169 ± 0.070 keV for the 2s-muon. The rms-charge-radii are decreasing by 0.20% and 0.036%, respectively.     

Radiative pion and muon capture on 208Pb

Partial and total rates for the (π^?,γ) and (μ^?,ν) capture reactions on ²⁰⁸Pb have been calculated within RPA.     

Angular distributions of photoprotons from 208Pb

Angular distributions of photoprotons following the (e, e′p) reaction in ²⁰⁸Pb have been measured at incident energies of 25.0 MeV and 40.0 MeV. The proton energy distributions were measured at several angles and the angular distributions were obtained for several proton energy ranges. Proton groups at around 11.0 MeV and 15.3 MeV are separated for the angular distributions and the results show almost isotropic distributions, which indicate that these proton groups are emitted through IAR. The angular distributions for other slowly varying parts of the proton spectra proved strongly asymmetrical, indicative of interference between E1 and E2 transition.     

Electroexcitation of high spin states in 208Pb

The formfactors for the electroexcitation of the collective states of ²⁰⁸Pb have been calculated within the Model of Separable Residual Interaction (MSI); the results for the even parity states up to J^π = 10⁺ agree nicely with recent measurements. It turns out, that the energies of the lowest collective states of positive parity follow rather closely a J(J + 1) law.     

The 207Pb(d,p)208Pb reaction with high resolution

The reaction ²⁰⁷Pb(d, p)²⁰⁸Pb has been studied at E_d = 18.0 MeV using the MPI Heidelberg Emperor tandem accelerator and multiple-gap spectrograph. The average resolution of 18 keV was better than previous measurements, and this, combined with the long beam exposure, allowed many finer details of the neutron particle-hole structure of ²⁰⁸Pb to be examined. In all, 45 levels were seen up to E_x = 6.3 MeV, many of which had never been seen before. A DWBA analysis of the stripping transitions angular distributions is made, and values of (2J + 1)S_ij, energy centroids, and summed strengths are given. An interesting cluster of 1i_{$\text{11}\text{2}$} and 2g_{$\text{9}\text{2}$} levels at E_x ≈ 4.2 MeV are resolved and are compared to recent isobaric analog state data. A search for weak stripping strength to known pairing vibrations in ²⁰⁸Pb gave essentially negative results and points to the need for improved ultra-resolution measurements.     

Heavy-ion transfer reactions on 208Pb above the coulomb barrier

The selective excitation of single-particle and hole states in stripping and pick-up reactions induced by ¹¹B ions of 113.5 MeV on ²⁰⁸Pb is interpreted on the basis of a semi-classical theory. The excitations of outgoing ions and the continuum are also discussed.     

Proton yields from quasielastic pion scattering on 27Al and 208Pb

A singles measurement of the quasielastic scattering of 255 MeV pions by ²⁷Al and ²⁰⁸Pb has been made. The measured values for the ratio R of π⁺ and π^? induced cross section, averaged over all measured angles of 2.2 ± 0.2 and 1.5 ± 0.1 for ²⁷Al and ²⁰⁸Pb respectively are substantially below the classical impulse approximation value of 11. A semiclassical nucleon charge exchange model is described for singles and coincidence measurements and is compared with the measured proton spectra. The comparison indicates that the singles proton spectra are dominated by events other than the quasielastic process whereas the coincidence data reported earlier and compared with the present calculations support the quasielastic interpretation. A strongly decreasing dependence of R on A for coincidence measurements may be interpreted as supporting the view that recoil nucleon charge exchange plays an important role in the quasielastic knockout process.     

RPA-calculations in 208Pb with a density dependent interaction

Excitation energies and excitation probabilities of the low lying states of ²⁰⁸Pb are calculated within the theory of Finite Fermi System (FFS), using a density dependent residual interaction. A strong M2-transition at 7.51 MeV is predicted.     

A microscopic description of inelastic 12C scattering from 208Pb

Heavy-ion inelastic scattering is described microscopically by using an effective nucleon-nucleon interaction and RPA hole-particle wave functions. The relative cross sections for different multipoles can be sensitive to the range of the interaction. The strength is determined by fitting elastic scattering. The model is used to analyze 98 MeV ¹²C ions exciting ²⁰⁸Pb. The range required is shorter than that for the bare interaction between nucleons. Collective model fits are also presented for comparison.     

Q值效应对多核子转移反应136Xe+208Pb的影响

基于改进的量子分子动力学(ImQMD)模型,模拟了136Xe+208Pb在质心系入射能量为$E_{rm{c.m.}}$=617 MeV的多核子转移反应。为了研究这个特殊的反应体系,将不同核子数转移前后形成的类弹与类靶对应的$Q$值的指数概率分布引入模型中考虑$Q$值效应,并将计算结果与实验探测的总动能损失分布和质量分布进行了比较。我们发现考虑$Q$值效应后的计算结果更好地再现了实验数据。在少于10个核子的转移过程中,核子的转移明显受到了$Q$值效应的驱动。在更多的核子转移过程中,$Q$值效应明显压低了反应产物的生成截面。这是因为大量的核子转移主要发生在小碰撞参数,对应的复合体系的寿命由于$Q$值效应明显减小。在ImQMD与ImQMD+Q的计算结果比较中,我们还发现,$Q$值效应明显增加了比208Pb更丰中子的中子数为126的初级碎块生成截面。