Das Größenspektrum des natürlichen atmosphärischen Aerosols

The size distribution of natural occuring aerosol particles with a radius between 10^?5 and 10^?6cm was measured simultaneously by two different methods: Firstly the measurement of the current, caused by the natural distribution of electric charges on the particles, which move along the axis of a cylindrical condenser; secondly the distribution of thoron decay products on the size spectrum of the aerosol. The both methods have their maximum sensitivity in different regions of the size spectrum. The distributions obtained with the two methods are in rather good agreement. The small deviation of the two spectra is ascribed to systematic differences of the measuring methods.     

Die Temperaturabhängigkeit des magnetischen Barkhausen-Effekts. II

The size distribution of Barkhausen discontinuities was measured during “thermal idealisation” of a hard drawn nickel specimen. Thermal idealisation means the magnetization by increasing temperature in a constant magnetic field. The sensitivity of the apparatus covered a range of magnetic moment between 1.3 and 17.3·10^?6 e.m.u. The results are in good agreement with investigations ofGerlach andTemesváry on the irreversible part of thermal idealisation. The average volume of Barkhausen discontinuities of the measured size was found to be nearly independent of temperature in a range from ?150 to+200°C, while above 200°C the volume increases markedly with temperature. By means of the average Barkhausen volume the temperature dependence ofNéels thermal fluctuation field was calculated. The results are in good agreement with those ofPescetti andBarbier on the temperature dependence of magnetic after effect.     

Die Verteilung der natürlichen Radioaktivität auf das Größenspektrum des natürlichen Aerosols

The apparatus described allows to measure the distribution of natural radioactivity on aerosol particles. Careful measures were taken that the aerosol concentration and its size spectrum were not altered before being examined. To increase the accuracy of the measurements the natural aerosol was charged with thoron decay products. The resulting electric charge-distribution by ion diffusion on dust particles is known, therefore the radii of these particles could be calculated by mobility measurements. By means of the law, governing attachment of emanation decay products on dust particles — as derived byLassen orWieser andStierstadt (afterBricard), it is possible to calculate the size spectrum of natural aerosol from the measured activity spectrum. Until now we have onlyion spectra for the range of size 6×10^?7 to 10^?5 cm. With the quoted apparatus however it is possible to measure thesize spectrum of natural aerosol. So we have a simple size-spectrometer, that covers a large range of particles. Among other things can be deduced from these measurements, that the natural radioactivity of air is attached to particles of radii from 10^?6 up to 10^?5cm, — the main part of the activity being carried by aerosols with radii between 4 and 6×10^?6cm. From the calculated aerosol spectrum (r from 6×10^?7 to 10^?5 cm) follows a mean particle radius ofr=2,5×10^?6cm at a particle concentration of 3×10⁴cm^?3.     

Die Temperaturabhängigkeit der magnetischen Jordan-Nachwirkung von Nickel

The magnetic after effect of pure polycristalline nickel and of a single crystal was measured between ?196 and +340 °C by a Förster second harmonic magnetometer. The viscosity constantS _v is shown to be proportional toB(T)·H_c(T) with an increasing functionB(T) for specimens of different magnetic hardness. The temperature dependence S_v(T) atH _c is rather complex in comparison to the simpleT- or √T-behaviour of former theoretical models. The latter is observed only forT??100 °C, whileS _v is nearly independent ofT between ?100 and +300 °C, and drops abruptly to zero forT?300 °C.     

Zusammensetzung und Eigenschaften des natürlich radioaktiven Aerosols

The influence of an electrical field, acting on the deposition of natural radioactive aerosols was investigated. At an over-all aerosol concentration of 10⁴ particles pro cm³ only 3% of the Ra-A-activity exists in an atom-disperse state. 90% of the radon-decay-products are attached on particles with a radius <10^?5 cm. The size-spectrum of natural occurring radioactive aerosol was calculated. The result is in good agreement with experience.     

Low-frequency susceptibility of single-domain nickel particles from 2 K up to the Curie point

The magnetic susceptibility of small single-domain nickel particles chemisorbed on a silica carrier has been studied as a function of temperature in the range 1.7 < T < 700K. The mean particle size was obtained from the blocking temperature in good agreement with results deduced from magnetization measurements. A slightly sintered specimen shows the typical behaviour of bulk nickel. The remarkable thermostability of the small particles seems to be of considerable interest.     

Stress-induced crossover phenomena in nickel above its Curie point

The temperature dependence of the anisotropic critical scattering of neutrons from a nickel single crystal was observed under the influence of elastic uniaxial mechanical stress of 140 g/mm². The temperature was varied between 10^-4 < τ = [T ? T_c(Δ)]/T_c(0) < 10^-2, and the momentum transfer between 1.4 × 10^-3 < $\text{q = (2π/λ) sin θ < 6.6 × 10}{}^{-3}\text{A}\text{?}{}^{\mathrm{-I}}$. The expected crossover from isotropic (Heisenberg) to anisotropic (XY) behaviour should occur between 10^-5 < τ < 10^-3, in good agreement with the experimental result.     

Magnetoviscosity of concentrated ferrofluids

We investigated a concentrated hydrocarbon base magnetite ferrofluid (saturation magnetization 2.9·10⁴ A/m) and present experimental data for magnetization and magnetoviscosity. The results can be understood after some straightforward modifications of the standard theory of dilute ferrofluids.