Untersuchung der beiden ersten angeregten Zustände des Li6-Kernes durch Elektronenstreuung

Inelastic electron cross sections for Li⁶ were measured using the facilities at the 300 MeV linear accelerator of the Institut für Kernphysik in Mainz. The form factor for theC 2 transition to the 2.184 MeV level is given in the region of momentum transfer 0.4 fm^?1<q<1.9 fm^?1. It was possible to determine the form factor for the 3.562 MeVM 1 transition up toq=1.2 fm^?1.     

Inelastic electron scattering from 6Li near the α-d threshold

The form factor for the alpha-deuteron continuum in ⁶Li has been measured in the excitation region within 2 MeV of threshold, for momentum transfers q < 1.2 fm^?1. The results are interpreted in terms of an α-d cluster model. The monopole breakup appears to be predominant near threshold, but the influence of the J = 2⁺ (4.31 MeV) quadrupole resonance becomes important a few MeV above threshold. The form factor for the C2 transition to the 3⁺ (2.185 MeV) state is also presented.     

Calculations of mass and moment of inertia for neutron stars

Masses and moments of inertia for slowly-rotating neutron stars are calculated from the Tolman-Oppenheimer-Volkoff equations and various equations of state for neutron-star matter. We have also obtained pressure and density as a function of the distance from the centre of the star. Generally, two different equations of state are applied for particle densities n > 0.47 fm^?3 and n < 0.47 fm^?3.The maximum mass is, in our calculations for all equations of state except for the unrealistic non-relativistic ideal Fermi gas, given by 1.50 M_⊙ < M < 1.82 M_⊙, which agrees very well with “experimental results”. Corresponding results for the maximum moment of inertia are 9.5 × 10⁴⁴ g · cm² < I < 1.58 × 10⁴⁵ g · cm², which also seem to agree very well with “experimental results”. The radius of the star corresponding to maximum mass and maximum moment of inertia is given by 8.2 km < R < 10.0 km, but a smaller central density ρ_c will give a larger radius.     

Variational calculations of asymmetric nuclear matter

We report on variational calculations of the energy E(ρ, β) of asymmetric nuclear matter having ? = ?_n + ?_p = 0.05 to 0.35 fm^?3, and β = (?_n ? ?_p/g9 = 0 to 1. The nuclear h used in this work consists of a realistic two-nucleon interaction, called v₁₄, that fits the available nucleon-nucleon scattering data up to 425 MeV, and a phenomenological three nucleon interaction adjusted to reproduce the empirical properties of symmetric nuclear matter. The variational many-body theory of symmetric nuclear matter is extended to treat matter with neutron excess. Numerical and analytic studies of the β-dependence of various contributions to the nuclear matter energy show that at ? < 0.35 fm^?3 the β⁴ terms are very small, and that the interaction energy EI(ρ, β) defined as E(ρ, β) ? T_F(ρ, β), where T_F is the Fermi-gas energy, is well approximated by EI₀(?) + β²EI₂(ρ). The calculated symmetry energy at equilibrium density is 30 MeV and it increases from 15 to 38 MeV as ? increases from 0.05 to 0.35 fm^?3.     

Dependence of nuclear dissipation upon deformation or temperature: analysis of the data using a Langevin-Monte-Carlo approach

We investigate the dynamical formation of clusters in nuclear matter. The model is based on classical nucleation theory and describes the time evolution of clusters by repeated condensation and evaporation of nucleons. We numerically calculate the growth of clusters with A <- 10 at temperatures of T = 2 MeV and T = 6 MeV and densities of ρ = 0.01fm^?3 and ρ = 0.05fm^{t -.} Equilibration times are rather long, 30 -2 100fm/c, and it is unlikely that clusters with A >- 10 observed in heavy-ion collisions arise from the nucleation process.     

The energy dependence of 18O(π+, π−)18Ne(gs)

Eight angular distributions measured for ¹⁸(π⁺, π^?)¹⁸Ne(gs) across the Δ₃₃ resonance show the details of the energy dependence of the reaction. At higher energies, the maximum is at q ? 0.85 fm^?1, in agreement with simple sequential scattering models, but a lower energies it is at q ? 0.5 fm^?1, with the transition occuring over a narrow energy range.     

Study of electric monopole transitions between the ground state and the first excited 0+ state in 40, 42, 44, 48Ca with high resolution inelastic electron scattering

Monopole transitions from the 0₁⁺ ground states to 0₂⁺ excited states at 3.353 MeV (⁴⁰Ca), 1.837 MeV (⁴²Ca), 1.884 MeV (⁴⁴Ca) and 4.272 MeV (⁴⁸Ca) have been investigated with high resolution inelastic electron scattering (FWHM ≈ 30 keV) at low momentum transfer (0.29 ≦ q ≦ 0.53 fm^?1). The respective monopole matrix elements are 2.53 ± 0.41 fm², 5.24 ± 0.39 fm², 5.45 ± 0.41 fm² and 2.28 ± 0.49 fm². These results are used together with known ground state charge radii and the average number of holes in the sd shell in the ground state to estimate the number of particle-hole excitations in the wave functions of the excited 0⁺ states.     

New determination of the 127I and 129I Mössbauer isomer shift calibration constants

New experimental data on the chemical changes δλ/λ of the probabilities λ of electron capture by ¹²³I and ¹²⁵I nuclei are treated taking into account the dependence of the exchange and overlap effect on the state of the electronic shell of the atom. The change δ?(0) in the electronic charge density at the iodine nucleus is evaluated and used for determination of the changes δ〈r²〉 in the mean square charge radius of the ¹²⁷I and ¹²⁹I nuclei on transition from the ground state to the first excited state. The δ〈r²〉 values determined, ?(10.0 ± 1.0) × 10^?3 fm² for ¹²⁷I and (13.0 ± 1.3) × 10^?3 fm² for ¹²⁹I, are in excellent agreement with the “best” values, recommended by Ruby and Shenoy.     

Electron scattering studies of magnetic isovector transitions in 12C at high momentum transfer

The inelastic electron scattering cross sections for the M1 transition to the 15.11 MeV (1⁺, T = 1) level and for the M2 transition to the 16.58 MeV (2^?, T = 1) level in ¹²C have been measured in the momentum transfer region q = 0.4–3.0 fm^?1, with emphasis on precise data at high momentum transfers. Additionally, a broad state near 15.4 MeV excitation has been observed and its excitation energy and natural width have been established as 15.44 ± 0.04 MeV and 1.5 ± 0.2 MeV, respectively. The Fourier-Bessel technique for determining the Mλ transition current density has been applied to the M1 and M2 transitions. Particular attention has been paid to the Coulomb corrections required to deduce the PWBA form factors. The M1 radiative width is Γ_γ0 = 38.5 ± 0.8 eV.     

Vibrational band structure in 184W populated in the decay of 184Re

The decay of ^184mRe has been investigated through γ-ray and conversion electron studies. The band head of the K^π = 2^? octupole band has been established at 1130.0 keV. The E2/M1 mixing ratios of three transitions from the γ-vibrational band to the ground state band have been determined by angular correlation measurements. A mixing of El, M2 and E3 multipolarity has been derived for the 921 keV transition combining angular correlation and conversion electron data. A value B(E3, 0⁺ → 3^? = (25 ± 5) × 10⁴e² · fm⁶ was obtained from the measured E2/M1 mixing of the 91 keV 3^? → → 2^? transition and γ-branchings. The data are discussed in terms of the collective model taking into account band mixing.     

Line shape and excitation strength of the first excited state in9Be

The line shape and the excitation strength of the very weak first excited J ^π =1/2⁺ state at E_x=1.684 MeV in Zeitschrift für Physik Zeitschrift für Physik⁹Be has been investigated with high-resolution inelastic electron scattering at E₀=45 and 49 MeV and scattering angles θ=105°, 117°, 129° and 165°, and with high-resolution inelastic proton scattering at E₀=13MeV and θ=15° and 18°. Due to lying just above the neutron threshold the level has a strongly asymmetric line shape which in both experiments can be described consistently with a Breit-Wigner expression modified on the low energy side by the threshold behaviour of the cross section. The resonance energy is E_R=1.684 ± 0.007 MeV and the width T=217± 10 keV in thec.m. system. A single particle potential model calculation reproduces the line shape and the resonance parameters fairly well. In addition, the inelastic electron scattering form factor has been measured. In the range of momentum transfersq =0.24-0.46 fm^?1 it is dominated by a 0p_3/2→ 1s_1/2 particle-hole transition. The transition is mainly longitudinal and of isoscalar nature with a strength of B (E1)↑ =0.027 + 0.002 e² fm², but a small M2 contribution ofB(M2)↑=8.8 ±1.5 μ _N ² fm² has also been detected.     

Cluster-model calculations of the electrodisintegration of lithium

Extending previously derived cluster-model treatments of the lithium isotopes to continuum states, we calculate (longitudinal) electrodisintegration cross-sections in the energy loss range 1.5 to 7.5 MeV, for momentum transfers q² = 0 to 1.5 fm^?2.     

Änderung des quadratischen Kernladungsradius bei Rotationsanregung

Isomer shifts ofγ rays from rotational bands of deformed nuclei have been determined in Mössbauer effect measurements. The following changes of the mean square nuclear charge radii have been deduced:Δ〈r ²〉(¹⁵⁶Gd, 89keV)=(+2.6±0.8)·l0^?3fm²,Δ〈r ²〉(¹⁷⁰Yb, 84keV)=(+1.2±0.3)·10^?3fm²,Δ〈r ²〉(¹⁷¹Yb, 67keV)=(+1.1±0.2)·10^?3fm². The results are compared with theoretical calculations and additional experimental data, to study the effect of the Coriolis and centrifugal forces in rotational excitation on the motion of the nucleons.     

Constraints on the properties of the massive neutron star PSR J0348+0432 from the f0(975) and φ(1020) mesons

The effect of the f ₀(975) and φ(1020) mesons on the properties of the massive neutron star PSR J0348+0432 is examined in the framework of the relativistic mean-field theory by choosing the suitable hyperon coupling constants. It is found that, compared with that without the f ₀(975) and φ(1020) mesons, the radius of the neutron star PSR J0348+0432 increases from R = 12.072 km to R = 12.08 km (i.e. by 0.07%), the central energy density ? _c decreases from 5.6695 fm^?4 to 5.6492 fm^?4 (i.e. by 0.36%), the central pressure decreases from 1.585 fm^?4 to 1.58 fm^?4 (i.e. by 0.32%), the moment of inertia increases from 1.4592 × 10⁴⁵ g · cm² to 1.4615 × 10⁴⁵ g · cm² (i.e. by 0.16%) and the surface gravitational redshift decreases from z = 0.4026 to z = 0.4022 (i.e. by 0.1%). Our results show that the effect of the f ₀(975) and φ(1020) mesons on the properties of the massive neutron star PSR J0348+0432 is very small (i.e. no more than 0.5%) and therefore they do not play a major role.     

N1−3H configurations in 4He

Wavefunctions for N¹?³H configurations in ⁴He are calculated using NN → N¹N transition potentials V and ³HN → N¹³H transition potentials from a two-nucleon exchange mechanism. The radial N¹?³H momentum distributions peak at ～ fm^?1 which is much lower than the short-ranged V. For (πN) S-wave isobars, e.g. N¹(1535) and N¹(1700), N¹?³H probabilities are estimated to be ～2‰ each, while those for N¹'s in higher (πN) partial waves are much smaller.     

Model dependence of charge densities determined from electron scattering

A new method is used to analyze recent experiments on electron scattering on ³He in the high momentum transfer region. The accuracy of the new measurements is very high so that the charge density can be determined with much higher accuracy than before. We find that further reduction of the error in charge density can only be achieved by a more accurate measurement of the region 3 < q < 6 fm^?1. Continuing the previous work of Hetherington and Borysowicz, a very useful approximate relation is derived between the error of charge density and the error of measurements of form factor. We find that linear expansion methods lead to similar results as the present method. They require, however, stronger asymptotic assumptions about ?(r).     

Transition charge densities of low-lying collective states in even Zn isotopes

The inelastic electron scattering cross sections for the quadrupole transitions to the 2₁⁺ and 2₂⁺ states in the even Zn isotopes ⁶⁴Zn, ⁶⁶Zn and ⁶⁸Zn and for the hexadecapole transition to the 4⁺₁ state in ⁶⁴Zn have been measured in a momentum transfer range up to q = 2.2 fm^?1. In the frame-work of the vibrational model these states are considered as one- and two-quadrupole-phonon states. The measurements are characterized by high statistical accuracy and by an overall resolution of δE/E₀ = 10^?3 which permitted separation of almost all members of the two-phonon triplet. The measured cross sections are analyzed with phenomenological models as well as with a Fourier-Bessel expansion of the transition charge density. The latter analysis yields realistic error bands for the transition charge densities and model-independent values for the reduced transition probabilities and transition radii.     

Electron scattering from the 3.65 MeV (0+, T = 1) state in 6Li at high momentum transfer

The form factor ofthe 3.56MeV(0⁺, T = 1) state of ⁶Li has been measured for momentum transfers q = 1.0–3.0 fm^?1, and the $\text{2.18}\text{MeV}\text{(3}{}^{\mathrm{+}}\text{, T = 0)}$ and $\text{5.37}\text{MeV}\text{(2}{}^{\mathrm{+}}\text{, T = 1)}$ states have been measured up to q = 2.5 fm^?1. The 3.56 MeV form factor is analysed in terms of a phenomenological shell model with l = i valence nucleons. The radial wave functions are found to have a greater radial distribution than given by the harmonic oscillator, more closely resembling Woods-Saxon functions. The M1 form factor is found to decrease at high momentum transfer somewhat more slowly than the models predict. A technique for determining the Mλ transition current density based on the Fourier-Bessel analysis is developed and applied to the M1 transition. The M1 transition current density is obtained within a moderate error band and compared with the harmonic oscillator and Woods-Saxon densities. The M1 radiative width is 8.18 ± 0.25 eV, in agreement with previous measurements.     

Electrodisintegration of 3He

Double differential cross sections for electron-³He scattering leading to continuum states were measured between break-up threshold and the region of quasi-free interaction in a momentum transfer range of $\text{1}\text{fm}{}^{\mathrm{?2}}\text{< ¦}\text{q}\text{¦}{}^2\text{< 2.5}\text{fm}{}^{\mathrm{?2}}$. The cross sections for the quasi-free scattering calculated in plane-wave impulse approximation were found to be in good agreement with the experimental results for momentum transfer $\text{¦}\text{q}\text{¦ > 1.5}\text{fm}{}^{\mathrm{?1}}$.     

Unelastische Elektronenstreuung am4He bei kleinem Impulsübertrag

Using a liquid helium target, inelastic electron scattering from⁴He was investigated at momentum transfers below 0.5 fm^?1 with improved resolution. The assignment 0⁺ for the state at (20.10±0.05) MeV (measured excitation energy) has been confirmed, and new values for the monopole matrix element (1.10±0.16) fm² and the total width (270±50) keV were derived. The giant resonance region shows evidence for theM2-resonance at 24 MeV.