Messung von thermischen Aktivierungs-Wirkungsquerschnitten mit hoher Genauigkeit

Activation cross sections have been determined for some isotopes which are important for flux monitoring or which have rarely been measured sofar. The following reactions were investigated: Sc⁴⁵(n, γ)Sc⁴⁶, In¹¹⁵(n,γ)In^116m , La¹³⁹(n,γ)La¹⁴⁰, Hf¹⁷⁹(n,γ)Hf^180m and Hf¹⁸⁰(n, γ)Hf¹⁸¹. The activations were performed in a purely thermal neutron spectrum (Cd ratio > 1100) using one of the bent neutron guide tubes at the FRM. The isotopes were irridiated in the form of foils sandwiched with gold foils as flux monitor. The flux ratio between measuring and monitor foil was corrected for self-absorption, self-scattering and scattering from neighbouring foils. The activities were measured in a 5×5″ well type NaJ-detector by integral counting ofγ-pulses exceeding 22 kev. The NaJ-detector was calibrated for singleγ-energies to better than 0.3%, the accuracy being even better in the case ofγ-γ-cascades. Because of the high accuracy in the activation measurement, the total error of the cross sections measured is smaller by a factor of 5 to 10 compared to previous data. An analysis of all contributions to the total error is given in detail.     

Messung der Energieverlustspektren von Aluminium- und Silberfolien mit hoher Auflösung

The energy loss spectra of polycrystalline aluminium and silver foils have been measured with high resolution. For the plasmon energy of aluminium 14.97 eV is obtained. The half width of the plasmon peak is 0.60 eV corresponding to a relaxation time τ=1.1×10^?15 sec in fair agreement with optical data. In silver films of certain thicknesses the surface plasmon peak and the plasmon peak can be separated in the energy loss spectrum. The values of the energy losses are 3.64 and 3.78 eV respectively.     

Ionenlaser hoher Leistung

Investigations on ion lasers with large bored tubes (7 ... 15 mm I.D.) without additional axial magnetic field are performed. An axial magnetic field is shown to be not necessary to achieve high laser power. By absence of additional magnetic fields the laser construction is considerably simplified. Experimental criterions for maximum laser power are derived by means of a previously published theoretical paper. 120 W total power summed up over the 4p-4s Argon II transitions in the visible part of the spectrum, and 1.5 W ultraviolet power in Argon (3638 Å, 3511 Å) and Krypton (3507 Å) are obtained in continuous mode operation. High inversion densities of 7 · 10⁹ cm^?3 give rise to non-resonant laser oscillations. By multipass amplification the spontaneous emission is amplified up to 20 W/cm², having a beam divergence of about 10^?4 rad. All results are pointing out the influence of radiation trapping effects on the laser power to be smaller than estimated and measured by other authors using conditions deviating from our optimum conditions for maximum laser power.     

Die Strahlungsverluste einesz-Pinches hoher Dichte

The radiative losses of a high densityz-pinch (n _e=10¹⁹cm^?3) were investigated experimentally. When the compressed column has a temperature of 10 eV, the radiative losses were determined by a special measuring method in which the vacuum UV radiation was resolved in time and recorded by means of an open photocell. This method also involved absolute, but time integrated measurement of the radiation by means of a thermopile. It was possible to achieve a certain resolution of the radiation wavelength by filling a volume between the light source and the detectors with various absorbing gases in succession. It was found that the major part of the internal energy of the plasma was lost by radiation.     

Wirkungsquerschnittsbestimmung von14N(n,p)14C für 14,7 MeV-Neutronen über eine Aktivitätsmessung von14C

The¹⁴N(n, p)¹⁴C cross-section for 14.7 MeV neutrons has been evaluated by the measurement of the activity of the formed¹⁴C. The value is 38±3 mb. This result was compared with calculations based on the statistical model for nuclear reactions.     

Optische Messung der Elektronenstoß-Anregung von Xenon und molekularem Stickstoff im Schwellenbereich mit hoher Energieauflösung

Relative optical excitation functions of Xe and N₂ have been measured in the threshold region. The inciting electron beam had a FWHM of 50 meV. The threshold behaviour of the excitation functions ofp-levels of Xenon is strongly influenced by resonances. The onset is step-like, in some cases resonance structure is to be seen just above threshold. In some excitation functions resonance structure is found immediatly above the ionization limit. This is believed to be caused by two compound states the parent states of which could be the 6d′ and the 8s′ autoionizing state of Xenon. In nitrogen, the excitation functions of two bands of the second positive group have been measured (3371 and 3755 Å), the upper levels of which are thev=0 and thev=1 levels of theC ³Π _u state. The excitation raises linear from threshold. In the 3371 Å excitation function a resonance maximum at 11.50 eV is observed, where the cross section is increased due to resonance population by about 100%, as measured with a FWHM of 50meV of the electron beam. The broad absolute maximums of the excitation functions are found to lie at 14.0±0.1 eV in the case of the 3371 Å- and at 14.3±0.1 eV in the 3755 Å-band.     

Synthesen von 14C-CH3O-markierten phosphoroganischen Insektiziden aus 14C-CH3OH

Es werden Halbmikrosynthesen im 1—5 mmol-Maβstab mit ¹⁴C-CH₃OH als Ausgangsprodukt beschrieben für die Wirkstoffe Trichlorphon (und Derivate), Methylparathion und Bromophos (und deren Oxone) sowie Dimethoat.     

Optische Messung der Elektronenstoß-Anregung von Helium,Neon und Krypton im Schwellenbereich mit hoher Energieauflösung

The optical electron-impact excitation functions ofp-levels of He, Ne and Kr show a sharp increase at threshold which is limited by the resolution of the apparatus (appr. 50 meV). Some ten meV above threshold most of them have a first resonance which is followed by several further ones. In Neon there are two strong “W”-profile double resonances the parent states of which could be the 2p ⁵ np (n=4, 5) states of the Ne-atom.     

Diagnostik des Xenon-Plasmas bei hoher Leistung

Several experimental methods for temperature measurements are discussed with respect to their qualities as diagnostic tool for xenon plasmas in the pulsed mode. In this work the continuum radiation intensity corrected for infinite optical thickness is used for the determination of plasma temperature. An uncertainty δT = 1,5% follows from a detailed error calculation. Results are given for p = 6 ?20 at and i = 1 ?3,5 kA/cm². It is proposed to use a xenon pulse discharge as an calibaration standard for black body radiation at T ≈ 11000 ºK in a special pressure range where the plasma temperature is nearly independent on pressure.     

Zum Einfluß der Versetzungsdichte auf die Primärrekristallisation von Kupfer und Silber nach extrem hoher plastischer Verformung

The isochronal and isothermal recovery of the electrical resistivity after large homogeneous compression of copper and silver was measured with a low frequency eddy current method. Two relations between the recovery data and the flow stress were found: 1. For high purity copper and silver the recovery of the electrical resistivity with recrystallization is proportional to the square of the flow stress. 2. The temperature at which half of the resistivity decrease with recrystallization is reached may be related to the flow stressσ by the equation \(\sigma ^2 e^{ - a/T_R } = const\) . The present experiments indicate that a simple relation between the quantitya and the activation energy for recrystallization cannot be given.