Determination of Zn in high-purity GaAs with neutron activation analysis
Neutron activation analysis was used to analyse Zn concentrations in high-purity GaAs. A combination of chemical separation of the neutron-induced 65Zn from the GaAs-matrix with anion-exchange chromatography and ultra low-level gamma-ray spectrometry in an underground laboratory was applied. Zn concentration ranged from 2.1 to 51 ng g(-1), and detection limits from 0.018 to 0.059 ng g(-1) were obtained.
Instrumental neutron activation analysis of high-purity gallium, arsenic, and gallium arsenide
Instrumental neutron activation analysis (INAA) has been applied to obtain useful data on impurity concentrations in ultra-pure materials whose matrix elements are strongly activated and create severe interference for several weeks after irradiation. An analytical procedure has been developed and used to determine Sc, Fe, Co, Zn, Se, Zr, Ag, In, Sn, Sb, Te, and Hg in high-purity gallium, arsenic, and gallium arsenide. Detection limits ranged from 50 ng/g for iron to 0.001 ng/g for scandium. Problems of contamination control, blank level, and standardization are discussed.
Climatology of the cusp-related thermospheric mass density anomaly, as derived from CHAMP observations
We report on the thermospheric mass density anomaly in the vicinity of the ionospheric cusp. A systematic survey of the anomalies is presented, based on a statistical analysis of 4 years of data (2002–2005) obtained by the accelerometer onboard CHAMP. The anomalies are detected during all years and seasons in both hemispheres but with stronger signatures in the Northern Hemisphere. For the same geophysical conditions, solar flux and geomagnetic activity the anomalies in the north are larger by a factor of about 1.35. Over the course of the survey period the amplitude decreases by more than a factor of 5 while the level of solar flux reduces by a factor of 2. The anomaly strength also depends on the solar wind input. The merging electric field, E merg , is generally enhanced for about an hour before the anomaly detection. There is a quadratic response of the anomaly amplitude to E merg . For geophysical conditions of P10.7 E merg E merg , where the weight of E merg , in mV/m, is by about 50 times higher than that of the solar flux level. The solar zenith angle and the influence of particle precipitation are found to play a minor role as a controlling parameter of seasonal variation. The well-known annual variation of the thermospheric density with a minimum around June also influences the formation of the cusp anomalies. This leads to a clear hemispheric asymmetry with very weak anomalies in the south during June solstice, which is supposed to be a combined effect of the minimum in annual variation and the seasonal decrease of solar insolation in this region.