Supraleitung von Niob unter hohem Druck

The influence of allside pressure on the transition temperatureT _c of Nb is studied up to pressures of about 25 · 10³ kp/cm².T _c goes through a flat minimum at about 5 · 10³ kp/cm² and increases remarkably at higher pressures. The average slope of this increase between 10⁴ kp/cm² and 2 · 10⁴ kp/cm² equals 3,5 · 10^?5 °K cm²/kp.     

Die Supraleitung von Zinn und Blei unter sehr hohem Druck

The dependence of the critical temperatureT _c upon pressureP is measured in the pressure range up to 160 kbar. The experimental technique developed for very high pressure-low temperature experiments (preceding article) is improved by introducing a double-sample electrical resistance cell. An internal pressure calibration is therefore possible at some well-established room temperature pressure reference points commonly used. Both metals, tetragonal white tin and fcc-lead, show a monotonic decrease ofT _c vs.P with upward curvature. The results recommend the use of Pb as a secondary standard for very high pressure experiments at Helium temperatures. In addition, high pressure polymorphic modifications of Sn and Pb are found to show superconductivity withT _c =(5.30±0.10) ?K for Sn III atP=113 kbar andT _c =(3.55±0.10) ?K for Pb II atP=160 kbar.     

Bestimmung der Driftgeschwindigkeit von Elektronen in Wasserstoff und Stickstoff bei hohem Druck

By means of a time of flight method the electron drift velocity in hydrogen and nitrogen was determined for high pressure, at which no measurements were as yet available. The values are obtained in the range fromE/p=12 toE/p=0,03 V/cm Torr with an accuracy from 1% to 1,5%. The pressure range available (up to 31000 Torr) enabled an examination of the similarity rule. The measurements show that for constantE/p, in the rangeE/p<1, the drift velocities decrease with increasing pressure.     

Impulsformdiskrimination bei hohem Gamma-Untergrund

Two pulse shape discrimination circuits for a CsJ(Tl)-protonspectrometer were tested under high and low gamma-background. With low background both circuits behaved equally well, but with high background the circuit proposed byVarga is superior to the circuit according toOwen.     

Untersuchungen zur Supraleitung des Legierungssystems Zr-Rh

The transition temperatures of Zr-Rh alloys with small amounts of Rh are essentially higher than the transition temperature of pure Zr. Rhodium is not dissolved in the Zr lattice. In the unannealed specimens Rh stabilizes the body centered cubic phase which has aT _c of 6.4°K. After annealing an intermetallic compound is formed with aT _c of about 12°K. This compound is also formed in the unannealed specimens at higher Rh content.     

Der Übergang zur Supraleitung in Sinterproben des Systems Nb-Sn

For samples of the system Nb-Sn sintered between 700 and 1500°C with 20 and 25 percent Sn the inductive and resistive transition to superconductivity has been measured. Especially the influence of magnetic fields on the transition has been examined. The inductive transition is deduced from shielding currents, the anomalous rise of the transition temperature for the 4Nb∶1Sn-samples first found byJansen turns out to be a consequence of higher critical currents of these samples. At low sintering temperatures a rise of the critical fields has been observed.     

Supraleitung und elektrischer Widerstand von bei tiefen Temperaturen kondensierten Thalliumschichten mit Tl2Se-Zusatz

Tl-films with different additions of Tl₂Se were condensed upon a quartz plate at 4 K. The superconducting transition temperature and the normal resistance were studied as a function of the Tl₂Se-concentration. Approximately 25% of Tl₂Se in Tl increased the transition temperature up to 4.2 K. Annealing the films resulted in a pronounced maximum of the normal resistance versus temperature relation at about 240 K for Tl₂Se concentrations above 30%. From this maximum the resistance drops rapidly—within a temperature rise of 10 K — to a small value. This is explained by crystallisation of the Tl₂Se component which was supposed to be in a liquidlike state before.     

Das Neutralgasprofil und die Elektronentemperatur in der Freifallsäule bei hohem Ionisationsgrad

The neutral gas flux from the wall into the column - connected with the ion flux to the wall - and the anisotropy of the velocity distribution of the neutral gas are included into the theory of the steady-state positive column. d/l_n and v_n0/v₀ occur as characteristic parameters. d denotes the radius of the column, l_n the mean free path of the neutral atoms for ionization, v_n0 the mean velocity of the neutral atoms re-emitted from the wall, v₀ = (2kT_e/M)^1/2, M the ion mass, T_e the electron temperature. On the axis the neutral gas density N_n is decreasing, if d/l_n is rising. At the wall N_n is increasing for v_n0 ? v₀, but it is almost constant or decreasing for v_n0 ? v₀ at the same time. In the plasma the total number of the atoms and the ions is taken as constant. In the case of small v_n0 the degree of ionization is high only for d ? l_n. However, it is already high for d ≈ l_n in the case of high v_n0. Therefore, the radial profiles of the neutral gas densities of different gases in a column can differ from each other. Almost full ionization can be reached near the axis. These results hold, too, if the initial velocity of the ions and a magnetic field are taken into account. d/l_n, the degree of ionization, and the electron temperature are given as functions of the electric power input and of the total number of the neutrals and the ions. The velocities of the re-emitted atoms depend on the accomodation coefficient of the ions recombining at the wall. With rising d/l_n an increasing number of the neutral atoms is re-emitted with superthermal velocities and the total number of the neutrals and the ions can be decreased. The anisotropy of the velocity distribution of the neutral atoms and the ions must be taken into account for the interpretations of spectroscopical measurements.     

Das Neutralgasprofil und die Elektronentemperatur in der Freifallsäule bei hohem Ionisationsgrad

The formula for the ion density is corrected. Furthermore, for different accommodation coefficients at the wall numerical values of the neutral atom velocities in argon ion lasers are estimated. The neutral gas heating by electron collisions is relatively small in argon ion lasers.