H. Gobrecht
Technical University of Berlin
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Featured researches published by H. Gobrecht.
Solid State Communications | 1967
H. Gobrecht; H. Nelkowski; J.W. Baars; M. Weigt
Abstract The diffusion of S-35 in ZnS crystals was studied for temperatures between 740 and 1100°C by an autoradiography technique. For a sulphur pressure of 0.5 atm a diffusion coefficient of D = 8 × 10-5 exp (2.2 eV/kT) cm2 sec-1 was obtained. D increases with increasing sulphur pressure.
Solid State Communications | 1966
H. Gobrecht; A. Tausend; P. Brätter; G. Willers
Abstract By means of neutron activation analysis a sensitive determination of chlorine traces in selenium was developed. The nuclide used for detection is Cl38. Its half-life of 38 min requires a rapid chemical separation from the matrix. The calculated limit of detection is 0.01 ppm. The Cl concentration of three different specimens of high purity selenium and of single crystals of different growth was determined. The effectiveness of vacuum distillation for deliverance of Se from chlorine was tested.
The International Journal of Applied Radiation and Isotopes | 1965
H. Gobrecht; W. Bock-Werthmann; A. Tausend; P. Brätter; G. Willers
Abstract A non-destructive determination of Cl and Na traces in selenium by means of γ-scintillation spectrometry is described. The influence of these elements on the semiconductor properties of selenium is mentioned. The nuclear data of the matrix is discussed. The best activation and measurement conditions for the BER (Berlin Reactor), which allowed the determination of 0·01 ppm Na and 10 ppm Cl, are indicated. It was necessary to apply a method of spectrum subtraction to the determination of low Cl concentrations.
Solid State Communications | 1966
H. Gobrecht; A. Tausend; P. Brätter; G. Willers
Abstract A method for the sensitive determination of sulphur and antimony in selenium is described. The trace elements are activated by epithermal neutrons inducing the reactions S 32 (n,p) P 32 and Sb 121 (n,γ) Sb 122 . The thermal flux is screened by cadmium. The limit of detection is 0.05 ppm S and 0.001 ppm Sb respectively (effective neutron flux about 10 12 cm −2 sec −1 , irradiation time 36 hr, sample mass 1 g).
Solid State Communications | 1967
H. Gobrecht; U. Schlichting
Abstract Conductivity measurements on PbSe single crystals with a natural p-n junction were carried out at various temperatures. Only at temperatures below 150° K the p-n junction shows an effect of rectification. From the mean width of the rectifying p-n junction the diffusion length of the minority carriers is found to exceed 0.3 mm at low temperatures.
Solid State Communications | 1975
H. Gobrecht; P. Kersten
Abstract The ultrasonic absorption of trigonal selenium single crystals has been measured in the frequency range from 137–465 MHz for longitudinal waves parallel to the c-axis. The results can be understood by phonon-phonon coupling.
Solid State Communications | 1967
H. Gobrecht; A. Tausend; J. Danckwerts
Abstract Helicon oscillations were investigated in HgSe. The proportionality between the frequency of the oscillations and the static magnetic field is well confirmed in our experiments. The Hall coefficient was determined. The evaluation of the decay time in various magnetic fields leads to the determination of the magnetoresistance effect in HgSe.
Solid State Communications | 1972
H. Gobrecht; F. Mahdjuri
Abstract Liquid selenium shows above 720°C a detectable anomalous (positive and negative) magneto-resistance, which is dependent on the applied electric field. A positive magneto-resistance could be observed too below 720°C after switching to high conductance. Liquid selenium shows after switching to low conductance a relative high negative magneto-resistance with saturation. In order to explain these effects a model is suggested.
Journal of Radioanalytical and Nuclear Chemistry | 1970
H. Gobrecht; P. Brätter; G. Willers; S. Baum
A sensitive method for determination of oxygen in selenium is described. Oxygen is converted into the gaseous compound sulfur dioxide labelled with35S. The β-radiation of35S is measured by liquid scintillation counting. The detection limit is 0.02 ppm. The efficiency of vacuum distillation in the purification of selenium, and the influence of air, dry oxygen and water on the absorption of oxygen by selenium have been investigated.
Solid State Communications | 1969
H. Gobrecht; J. Danckwerts
Abstract The transverse permeability of HgSe was measured at 4.2K in magnetic fields up to 45 kG. In high magnetic fields ( B > 23 kG) quantum oscillations are superposed on the helicon resonance curve. The oscillations are periodic in 1/ B . The carrier concentration was gained from the measured period of the quantum oscillations. Its value is in good agreement with the Hall coefficient obtained by direct observation of the helicon oscillation.
