Zerfallsschemata, β-Matrixelemente und γ-Multipolordnungen für die Übergänge Co56→Fe56 und J131→Xe131

In the decay of Co⁵⁶ the following quantities have been measured:γ-ray intensities,β-γ directional correlation, andβ-(circularly polarizedγ) correlation. The directional correlation anisotropy was found to be, forβ energies above 300 keV,A ₂=0.5±0.4 per cent, corresponding to small or vanishing twice forbidden contributions to the allowed decay. The asymmetry parameterA of theβ-(circularly polarizedγ) correlation was measured to beA=?0.01±0.05 which implies a ratiox between Fermi and Gamow-Teller contributions to the decay ofx=?0.10±0.07, in agreement with the isospin selection rule. In the decay of J¹³¹ the following quantities have been measured: shape of the 606 keVβ-ray group,γ-ray intensities, conversion coefficients, andβ-(circularly polarizedγ) correlations. The measuredK/L ratio of the 364 keVγ-transition,K/L=6.0±0.2, is compatible with the conversion tables of Sliv and Band only. The multipolarities of theγ rays of 364, 637, and 723 keV were deduced. The 606 keVβ-364 keVγ cascade was used as a new calibration standard for analysers of circularly polarizedγ-rays.     

Verzweigungsverhältnisse undβ +-Maximalenergie beim Zerfall von Ag108

The branching ratios of Ag¹⁰⁸ have been remeasured with scintillation spectrometers. There is evidence for a weak 177 keV-β ^?-branch going to the 1473 keV level of Cd¹⁰⁸, followed by aγ-γ-cascade of (841+632)keV. Spin and parity 2+ of this level are supported by logft=4.7 of theβ ^?-branch. Theβ ⁺-spectrum has been measured for the first time yielding an end point energy of (880±25)keV, in agreement with the value derived from theK/β ⁺ratio.     

DasK/β+-Verhältnis beim Zerfall J128→T128

In the decay of J¹²⁸ the intensity of a weak positron activity was measured to be (3.1±0.7)·10^?5 per disintegration. The remeasurement of the totalK capture was found to be 0.059±0.007 in agreement with the results of other authors. From this theK/β ⁺-ratio of the decay to the ground state of Te¹²⁸ is 1800±400. Theoretical calculations ofK/β ⁺ for allowed transitions show that the maximum energy of the positrons is 245±12 keV. In the decay of Rh¹⁰⁴ and Lu^176m no positrons more than 5·10^?6 could be detected.     

Messung von fünf β-γ-Zirkularpolarisationskorrelationen beim Zerfall Eu152→Gd152

In the decay Eu¹⁵²→Gd¹⁵² fiveβ(circularly polarizedγ) correlations have been measured (Table). The Fermi matrix element of the 3^?–3^? β transition is small or vanishing. The levels of 344 and 755 keV (I=2⁺ and 4⁺, respectively) seem to be collective states.     

Zum Zerfallπ→e+ν+γ

The radiative decay of the chargedπ-mesonπ→e+ν+γ is calculated using dispersion relation techniques. It is assumed that the weak interaction producing the decay has a V-A structure. The decay through the vector variant has been reinvestigated and found to be different from the result ofVaks andIoffe. The theoretical prediction of this paper is in agreement with a preliminary experiment recently performed at CERN.     

Die Koeffizienten der Inneren Paarbildung bei den γ-Übergängen nach Co60→Ni60 und Pr142→Nd142

The coefficients ε of internal pair formation of the 1.17 and 1.33 MeV transitions in Ni⁶⁰ and of the 1.57 MeV transition in Nd¹⁴² were measured by detecting the annihilation radiation of the positrons. We obtained the values ε=(3.7±0.6)·10^?5 for Ni⁶⁰ and ε=(10.8±1.8)·10^?5 for Nd¹⁴². The results for Ni⁶⁰ are in good agreement with theoretical calculations. The 1.57 MeV transition in Nd¹⁴² is identified as electric quadrupole and the first excited level of Nd¹⁴² is determined to be 2⁺. By further measurements the partial transition from Pr¹⁴² to the first excited level of Nd¹⁴² was found to be (3.7±0.4)% per disintegration. NoK capture of Pr¹⁴² more than 2·10^?4 could be detected.     

Isomerieverschiebung und Quadrupolaufspaltung beim Mößbauer-Effekt von Fe57 in Eisenverbindungen

Data from previous measurements are discussed from the point of view of isomeric shift and quadrupole splitting. For a comparison of isomeric shifts the magnitude of temperature shifts have to be regarded. Information about electric field gradients arises from the magnitude and the temperature dependence of quadrupole splittings. After putting the data into a suitable form, characteristic regions of the value of line shift, quadrupole splitting and temperature dependence of the splitting for different bond types are obtained. Besides this, influences of the crystal field are to be considered. Different types of contributions to the electric field gradient are discussed. The main features of field gradients in iron ions and molecules with and without closed electron shells are derived and compared with the experimental results. The result that the isomeric shifts for covalent bond iron in the oxydation states 0, +2, +3 and metallic bond iron are distributed over the same region whilst the ions Fe²⁺, Fe³⁺ and [Fe^VIO₄]^2? each have characteristic values is discussed.π-bonds in addition to σ-bonds and partially ionic bonds have to be considered. Based on the foregoing discussion the connection between the strength ofπ-bonds and the value of isomeric shifts and quadrupole-splittings and the sign of field gradients is regarded for iron ions and molecules, where ligands have been exchanged. Finally examples for the interdependence of the structure of multicenter-molecules and -ions and the data are given.     

Homogenitätsuntersuchungen an neutronenaktivierten Eisen-Mangan-Mischoxiden durch Messung der γ-Strahlung des 59Fe

In neutronenaktivierten Eisen-Mangan-Mischoxiden, deren Komponenten in Mengen gleicher Gröβenordnung vorlagen, wurde von einer statistisch ausreichenden Probenzahl die γ-Strahlung des ⁵⁹Fe gemessen. Zur Beurteilung der Homogenität warden die Standardabweichungen der Meβreihen mit der des Meβverfahrens verglichen und die Zahl der Meβwerte, die auβerhalb des Streu-bereichs des Meβverfahrens lagen, bestimunt. Es konnte gezeigt werden, daβ Messungen dieser Art zur Homogenitätsprüfung gut geeignet sind.     

Ein richtungsempfindliches Zählrohr und seine Anwendung beim Li8→Be8*-Zerfall

A new type of proportional counter having a directional dependent efficiency has been used to measure the angular distribution of the α-particles of Be⁸ in the reaction Li⁸→Be^8*. From the experiment an upper limit of 10% for the amount of the Fermi contribution in the Li⁸ beta-decay is deduced.     

Quadrupolaufspaltung und Isomerieverschiebung der 14,4 keV γ-Linie von Fe57 in metall-organischen Eisenverbindungen

The Mößbauer absorption of the 14.4 keVγ-ray of Fe⁵⁷ was investigated in Ferrocene, Fe(C₅H₅)₂, and in a Ferriciniumcation [Fe(C H₅)₂]BF₄. The resonance absorption spectra reveal a quadrupole splitting and an isomeric shift of the 14.4 keV level in both compounds. The data give some evidence of the occupation of the molecular orbits formed in these complexes.     

~(59)Co(n,p)~(59)Fe,~(59)Co(n,α)~(56)Mn,~(59)Co(n,2n)~(58)Co反应截面的测量

本实验用活化法测量了中子能量在12.8MeV到17.8MeV的~(59)Co(n,p)~(59)Fe,~(59)Co(n,α)~(56)Mn,~(59)Co(n,2n)~(58)Co三个反应道的反应截面值,实验的测量误差在3.3％—6.9％范围内. 本文还计算了反应截面测量误差的协方差矩阵,并将实验测量值与理论计算值进行了比较.另外,还对上述三个反应道的截面进行编评,给出了推荐的激发曲线.     

Excited levels and isobaric analogue states in55Co investigated with the54Fe(p, γ)55Co reaction

The yield curve for the⁵⁴Fe(p, γ)⁵⁵Co reaction in the energy regionE _p=1.5–2.9 MeV has been recorded and the decay of ten resonances has been investigated. For six of the resonances the strengths have been determined. The angular distributions of the gamma rays have been recorded for four resonances to obtain spins or spin limitations for excited levels. In addition the lifetimes of 10 bound levels were determined with the Doppler Shift Attenuation Method. The isobaric analogues of the ground state and five excited states in⁵⁵Fe are discussed.     

Zur räumlichen Ausbreitung einer Entladung beim Generationen- und beim Kanalaufbau

The spatial expansion of a discharge was investigated under homogeneous field conditions, using an anode with a small central area separated from the remainder and wide band double beam oscillographic techniques. The discharge currents were initiated by electrons released along traces of single α-particles in the gas between the electrodes. The α-particles enter the gap volume through a small hole in the middle of the separated center of the anode. The measurements have shown that a secondary photon emission from the cathode causes a spreading over the total gap volume within the first few electron generations (N₂, air, CO₂ at lower pressures). If streamer mechanism occurs (O₂, CO₂ at higher pressures), the discharge remains localized to the trace of the α-particle, in which the avalanches yielded by the primary electrons have produced a high density of positive ions. — New details of streamer mechanism are revealed by analysing the rapid increase of the current during streamer formation.     

Form factor π0 → γ* + γ* at different photon virtualities

The π⁰ γγ vertex for virtual photons of squared masses q ₁ ² and q ₂ ² plays a vital rôle in several physical processes; for example for q ₁ ² < 0, q ₂ ² < 0, in the two-photon physics reaction e ⁺ e ^? → e ⁺ e ^?π⁰, and for q ₁ ² > 0, q ₂ ² > 0, in the annihilation process e ⁺ e ^? → π⁰ l ⁺l^?. It is also of interest because of its link to the axial anomaly. We suggest a new approach to this problem. We have obtained a closed analytic expression for the vertex in the limit in which at least one of ¦q ₁ ² ¦ and ¦q ₂ ² ¦ is large for arbitrary fixed values of the ratio q ₁ ² /q ₂ ² . We compare our results with those obtained previously by Brodsky and Lepage. It should be straightforward to test our predictions experimentally.