TheL 1 subshell fluorescence and Coster-Kronig yields forZ=96

High resolution Si(Li)-Si(Li) and Si(Li)-Ge(Li) detector arrangements have been used to studyL x-ray spectra in coincidence withL-shell internal conversion electrons, gamma rays, andK x-rays emitted in²⁴⁹Cf decay. TheL ₁ subshell fluorescence and Coster-Kronig yields determined forZ=96 from these spectra are ω₁=0.25±0.06,f ₁₂≦0.10, andf ₁₃=0.69 ±0.08. The presence of theL ₁-L ₃ radiative transition is also further confirmed in this work.     

L 2 andL 3 subshell fluorescence and Coster-Kronig yields forZ=96 from the decay of249Cf

TheL ₂ andL ₃ subshell fluorescence and Coster-Kronig yields forZ=96 have been measured by theK-L x-ray coincidence method with high resolution Si(Li) and Ge(Li) x-ray detectors. The results ν₂=0.650±0.036, ω₂=0.552±0.032, ω₃=0.515±0.034, andf ₂₃=0.188±0.019 agree fairly well with theory. New measurements of theL x-ray singles spectra of²⁴⁴Cm and²³⁸Pu with a high resolution Si(Li) detector permitted reevaluation of the values of ω₂ andf ₂₃ forZ=92 and 94 reported by Byrneet al. The revised values atZ=92 are ω₂=0.529±0.035 andf ₂₃=0.23±0.12, and atZ=94, ω₂=0.523±0.023 andf ₂₃=0.24±0.08. These revised values are in much better agreement with theory and with current experiments.     

Inner-shell x-ray production in adiabatic iodine -Z 2 collisions withZ 1+Z 2≧100

For heavy collision systems withZ _UA ≧100 the excitation mechanism for electrons in molecular orbitals from 2p _{1/2 1/2} up to 3d_{3/2 1/2}, which end up inK andL levels of the collision partners, is investigated for Iodine projectile velocityv between 1.3 and 3.7 a.u. (i.e. 6.3 MeV≦E _i ≦45 MeV). For 2p _{1/2 1/2} excitation a prevailing radial coupling excitation mechanism is found. In a two state approximation coupling strengths are derived for decisive isolated crossings; for the strong variation of the projectileL x-ray spectra with targetZ and impact velocity a Landau Zener type model is suggested.     

Critical behaviour at the displacive limit of structural phase transitions

For a special critical point at zero temperature,T _c =0, which is called the displacive limit of a classical or of a quantum-mechanical model showing displacive phase transitions, we derive a set of static critical exponents in the large-n limit. Due to zero-point motions and quantum fluctuations at low temperatures, the exponents of the quantum model are different from those of the classical model. Moreover, we report results on scaling functions, corrections to scaling, and logarithmic factors which appear ford=2 in the classical case and ford=3 in the quantum-mechanical case. Zero-point motions cause a decrease of the critical temperature of the quantum model with respect to the classicalT _c , which implies a difference between the classical and the quantum displacive limit. However, finite critical temperatures are found in both cases ford>2, while critical fluctuations still occur atT _c =0 for 0<d≦2 in the classical case and for 1 <d≦2 in the quantum model. Further we derive the slope of the critical curve at the classical displacive limit exactly. The absence of 1/n-corrections to the exponents of the classical model is also discussed.     

139Sm,a new nuclide of relevance for the systematics of theN=77 isomers

The ground state and an isomeric state of¹³⁹Sm have been identified witht _1/2 ^m =9.5 ± 1.0 s andt _1/2 ^g =2.6 ± 0.3 min. The isomeric decay scheme is presented. It extends the chain of isomers withN=77. The distance between thed _3/2 andh _11/2-levels reaches a maximum forZ=60. This maximum is much more pronounced than expected from previous theoretical considerations and from systematic trends in theN=81 and 79 chains.     

Inner-shell ionization by relativistic electron impact

K-, L andM-shell ionization cross sections have been measured for 23 elements, 12≦Z≦92, after bombardment with relativistic electrons, 15≦E ₀65MeV, by means of high resolution semiconductor detectors and a recently developed gas-scintillation proportional counter. For constant electron bombarding energyE ₀ the ionization cross sections follow a power law dependence,σ∽Z ^?α, and forE ₀=50MeV we deducedα =2.45±0.02 for theK shell andα=3.00 ±0.09 for theL shell. The observedZ dependence exhibits significant systematic deviations from theoretical predictions which exceed the experimental values up to 15 % at lowZ elements for theK shell and on the average about 11% for theL andM shell. The same behaviour of too low experimental values, i.e. an overestimation by the theory, is observed for the energy dependence of the cross sections for all shells. A scaling behaviour describing theZ andE ₀ dependence for allK-, L andM-shell data points is observed which also predicts the experimental values by other groups at lower and higher energies correctly. The comparsion of the measuredLΒ/Lα, andLγ/Lα intensity ratios for highZ elements with the values obtained by other groups in the energy range 0.3≦E₀≦1,000 MeV exhibits an increase with bombarding energy that cannot merely be explained by the energy dependence of the subshellionization cross sections for theL shell. An attempt to explain this effect with the change of the Coster-Kronig transition probability is described.     

TDPAC studies of Hf doped YBCO

Time differential perturbed angular correlation measurements of the 133–482 keVγ-γ cascade of¹⁸¹Ta in Hf-doped YBa₂Cu₃O_7−x are presented. The¹⁸¹Hf precurser nuclei are incorporated into the sample by thermal neutron irradiation. Two quadrupole interaction frequencies are observed in the as-irradiated sample:v _Q1=161±10 MHz with intensityf ₁=75%, asymmetry parameterη ₁=0.32 and damping parameter Λ₁=0.42, andv _Q2=1108±40 MHz withf ₂=25%,η ₂=0.62, and Λ₂=0.60. On annealing the sample in air at various temperaturesT _a and quenching to room temperature,f ₁ remained nearly constant forT _a<600°C andv _Q1 for all annealing temperatures indicating that these are insensitive to oxygen stoichiometry. This frequency is interpreted to be due to¹⁸¹Hf substitutingY sites. BeyondT _a=600°C,f ₁ increased and reached a constant value of 90% forT _a=800°C. The value ofv _Q2 showed a slight variation between 1086 and 1160 MHz, whilef ₂ remained nearly constant at 25% forT _a<600°C. This component is identified to be due to¹⁸¹Hf substituting Cu 1 sites in the Cu-O chains of YBCO. Above 600°Cv _Q2 decreased and reached a value of 808 MHz beyond 750°C.     

Electron screening in thed+3He fusion reaction

Cross section measurements of thed(³He,p)⁴He reaction have been extended to an energy as low asE _cm =5.4 keV. The data have an improved accuracy compared with previous work and confirm the existence of electron screening. The combined analysis of the present and previous data leads to an electron screening potential ofU _e =123 ± 9 eV. A similar analysis of previous data for³He(d, p)⁴He leads toU _e =186 ± 9 eV. Both screening potentials differ due to the molecular and atomic aggregate state of the targets involved in these investigations and are significantly larger than expected from available atomic physics models, supporting the general trend in studies of electron screening.     

Deep levels in gallium arsenide by capacitance methods

The three capacitance methods, i.e., TSCAP, PHCAP, and transient capacitance measurements, are applied to determine electronic properties of deep levels inn-GaAs. In the boat-grown wafer detected are the 0.30 eV electron trap withN _T =3.6×10¹⁶ cm^?3 andS _n =2.4×10^?15 cm², and the 0.75 eV electron trap withN _T =2.0×10¹⁶ cm^?3 andS _n =1.2×10^?14 cm². In the epitaxial wafer, the 0.45 eV hole trap is detected withN _T >1.5×10¹³ cm^?3 andS _p =1.4×10^?14 cm² as well as the 0.75 eV electron trap withN _T =2.4×10¹³ cm^?3.     

Mittlere Energien und Driftgeschwindigkeiten von Elektronen in Stickstoff,Argon und Xenon,ermittelt aus Bildverstärkeraufnahmen von Elektronenlawinen

Local and temporal development of electron avalanches in a pulsed discharge gap (d=3,00 cm) are investigated in N₂, Ar, Xe and mixtures of N₂ and CH₄ by simultaneously applying high gain image intensifier- and photomultiplier techniques. Electron drift velocities are obtained from time-of-flight and way-of-flight measurements in these gases. The mean energy of agitation of the electrons is derived both from electron mobility and avalanche image trace profile (diffusion broadening). The results obtained (for 20°C), being in fair agreement with one another, read N₂: (4·6...5·0) eV forE/p=50...200 V/cm Torr; Ar: (9·0...9·5) eV forE/p=24... 45 V/cm Torr; Xe: (4·8...5·0) eV forE/p= 40... 90 V/cm Torr; CH₄(10% N₂): 6·3 eV forE/p= 89 V/cm Torr. The mean energy of agitation does not change very much withE/p in the ranges investigated. Some results concerning the radiation properties of these gases are included such as lifetime of the excited states, quenching pressure etc.     

Improved Thomas-Fermi interaction potential for atoms with very dissimilar nuclear charges

The interaction potential,U(R), for atoms with nuclear chargesZ ₁ andZ ₂ (Z ₁?Z ₂) is discussed. It is shown that within the linear approximation inZ ₂/Z ₁ this potential is determined by the atomic screening function,?(R;Z), alone. On the basis of the Thomas-Fermi model allowing for quantum corrections, several universal expressions for?(R; Z) are suggested. They permit reliable estimates ofU(R) up toR～2 a.u. and forZ ₂/Z ₁?1/5.     

Investigation of inclusive production ofK 0 andK * (892)0 mesons inK + A interactions at 11.2 GeV

Inclusive production ofK ⁰ andK ^* (892)⁰ mesons inK ⁺ A-interactions (A=Be, Cu, Pb) at the energy 11.2 GeV has been investigated to study hadronisation of the leading \(\bar s\) -quark; the results are presented. Double differential cross sections d²σ/dx _f dp _t ² were measured in the region of incident particle fragmentation (0.4≦x _f ≦1,p _t ≦0.5 GeV/c). The experimental data obtained were analysed on the basis of the Lund model FRITIOF and a quark-gluon model that takes into account colour screening and hadron formation length effects. The experimental data confirm the picture of hadronisation of the leading \(\bar s\) -quark developed in the latter model.     

Conversion coefficient for internal pair creation

The conversion coefficient for internal electron-positron pair formation is calculated for arbitrary electric and magnetic multipolarity. Analytical expressions for the differential conversion coefficientdβ/dE _p can be derived in the range 0≦Z≦118, if one employs relativistic Coulomb wave functions according to pointlike nuclei for the electron. Especially forML-transitions in the high-Z-region we found large deviations from results obtained within the Born approximation.     

Electromagnetic contributions to proton- and neutron-4He scattering

A proper treatment of various electromagnetic contributions toN-⁴He scattering enables one to determinen(p)-⁴He observables fromp(n)-⁴He data. Several calculations ofn-⁴He observables considering different electromagnetic effects are presented. It is shown that the contribution of thep-⁴He Coulomb corrections ton-⁴He polarizations and differential cross sections dominates over other electromagnetic effects forθ _c.m.≧30°. For smaller scattering angles, neutron magnetic scattering is important and produces a divergingn-⁴He differential cross section atθ=0° and a large peak (Mott-Schwinger effect) in the polarization. The influence of thep- andn-⁴He vacuum polarizations on then-⁴He observables is found to be small.     

L-subshell fluorescence and coster-kronig yields atZ=92 and the decay of235Np

TheK andL x-rays emitted in the decay of²³⁵Np have been studied with high resolution Ge(HP) and Si(Li) detectors in coincidence, in order to obtain theL ₂ andL ₃ subshell fluorescence and Coster-Kronig yields atZ=92. The results are:v ₂=0.630±0.036, ω₂=0.560±0.033,f ₂₃=0.147±0.010, and ω₃=0.481±0.029. Results for theL ₁ subshell were derived from singles spectra, by assuming a value off ₁₃ of 0.67, and are:v ₁=0.54±0.04, ω₁=0.21±0.04, andf ₁₂<0.07. With the same assumption, theL ₁/K electron capture ratio and decay energyQ _ec for²³⁵Np were found to be 29.0±3.6 and 123.6±0.7 keV, respectively. RelativeL x-ray intensities forZ=92 also were measured and are compared with the theory of Scofield and with recent diffraction experiments. Electron ejection from theL shell during²³⁵Np decay has been studied byL x-ray-L x-ray coincidences and found to occur with a probability of (1.3±1.0) × 10^?4 per disintegration.     

AtomicL-subshell yields from the electron capture decays of 65 157 Tb and 65 158 Tb

Sources of the mass and chemically separated terbium isotopes,A=157 and 158, have been used to study inner shell phenomena atZ=64. In coincidence experiments employing high resolution Ge and Si(Li) detectors photon spectra characteristic of 2s,2p _1/2, and 2p _3/2 vacancies have been measured. The following results were obtained:f ₁₂=0.20±0.03,f ₁₃=0.289±0.015,f ₂₃=0.14±0.02,v ₁=0.179±0.014,v ₂=0.21±0.02,ω ₃=0.183±0.015. From thisω ₁=0.084±0.016 andω ₂=0.185±0.020 were deduced. Generally good agreement with the calculations is found, while larger discrepancies pertain to an overall fit of previous experimental results. The electron capture decay energy of¹⁵⁷Tb was inferred from the measured 2s-fluorescence yield to be 62.2±0.6 keV.     

Valence and inner proton hole states in119in via the (d,3He) reaction

Proton holes states have been studied up toE _x=17 MeV andE _x=3.5 MeV in the¹¹⁹In nucleus via the¹²⁰Sn(d,³He)¹¹⁹In reaction respectively atE _d=108.4 MeV andE _d=51 MeV. DWBA analysis of angular distributions has allowedl attributions for a large number of new levels and the determination of valence and inner hole strength distributions. The first 1g _9/2, 2p _1/2 and 2p _3/2 levels only exhaust 40%, 60% and 32% of their respective sum rule limits. The missing strengths are shared among several low lying levels and significant higher lying contributions. The 1f strength, not identified in the previous experiments is spread fromE _x=1 MeV to about 17 MeV. The low lying levels aroundE _x=2.4 MeV could exhaust some 40% of the 1f _5/2 sum rule. The higher lying strength with a flat maximum aroundE _x=7.5 MeV could account for the 1f _7/2inner hole strength and the missing 1f _5/2 valence strength. The experimental strength functions compare rather well with the predictions of the quasiparticle-phonon model.     

On the time evolution of generator coordinates

Collective potential energy surfaces were determined in the mass region with 50<(N, Z)<82 by fitting experimental level spectra andB(E 2)-values on the basis of the generalized collective model of Gneuss and Greiner. While the nuclides withN=80 and withZ=52 are rather soft vibrators we find an abrupt transition to asymmetric rotators forN=78 and forZ=54 tending to more symmetric shapes further away from the closed shells. The results predict the position of levels not yet observed andB(E 2)-values.     

Non-perturbative renormalization group for field theories with scalars and fermions

An approximate, but non-perturbative, RG equation is derived for theories involving scalars and fermions, ind dimensions withn _f flavours. The approximation consists in restricting the parameter space to interactions without derivatives. In a numerical study of the equation ind=3 andd=4, in the range of parameter space explored, no evidence is found of new fixed points generated by the inclusion of fermions.     

L 1 subshell yields atZ=73 from the electron capture decay of181W

The TaL x ray spectrum from the electron capture decay of¹⁸¹W is analyzed into components characteristic of the threeL-subshells and theL ₁ subshell yields atZ=73 are determined to beΩ ₁=0.15±0.02,f ₁₂=0.23±0.05 andf ₁₃=0.32±0.02. A revised decay scheme for the decay of¹⁸¹W is proposed from measurements of x-ray and gamma intensities. A value of 0.97±0.08 for theK-conversion coefficient of the 153 keV transition is obtained and itsE ₂/M ₁ multipolarity mixing ratio,δ ²(0.25) is deduced.