Single Ge Detector Research Articles

Analyzing the high-momentum part of positron annihilation Doppler spectra with a single germanium detector

We present a novel way for recording and mathematically analyzing the Doppler-broadening of the 511 keV annihilation line to obtain the momentum distribution of the annihilating electron–positron pair. A necessary precondition is employing either background free positron beams or e.g. a 68Ge-source, instead of the widely used positron emitter 22Na. The 68Ge-source emits positrons with an end-point energy of about 1.9 MeV, while the contribution of gamma quanta having higher energies than the annihilation radiation at 511 keV is negligible low. Compared to 22Na, this results in a significant lower background in the photo peak. Employing such a 68Ge-source allows an analysis of the high-momentum part of the annihilation radiation. However, this part contains valuable chemical information about the annihilation site of the positron, originating from high momentum electrons. Providing an adequate mathematical analysis in determining the remaining background and its subsequent subtraction, we are able to obtain the contribution of these high electron momenta to the annihilation peak using only a single Ge-detector. After background subtraction, the same information contained in the momentum range up to 35×10 −3 m 0 c can be extracted by analyzing spectra from metals and semiconductors as if measured employing a coincidence setup with two Ge-detectors. With the method presented here it is possible to obtain the whole information of a positron annihilation Doppler spectrum employing just a single Ge-detector.

Chemical sensitivity in positron annihilation with just one single Ge detector

AbstractWe present a novel method for analyzing the data from momentum distribution measurements employing positron annihilation, using just one single Ge‐detector, but employing a mathematically sufficiently well suited model for background subtraction. For a variety of high purity metals the resulting momentum distributions have exactly the same shapes up to 35 × 10–3 m0c as those obtained with coincidence Doppler broadening of the annihilation radiation using a two‐detector system. This data analysis applies to any positron source without high energy gammas or a slow positron beam system with just a single Ge‐detector and enables the possibility of analysing the chemical surrounding at the positron trapping site without any additional hardware. In particular, in combination with a slow positron microbeam, it allows a spatially resolved measurement of the electron's momentum distribution. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Studies of the interaction of slow very highly charged ions with solid surfaces using the LLNL EBIT facility

A summary of the present status of the LLNL EBIT based research program on highly charged ion-solid surface interaction is presented. New results for coincidence measurements of K α−K β X-ray emission for Fe 26+ incident on Al, using two Ge detectors are presented. It is shown that excellent resolution of the satellite and hypersatellite lines are achieved, in excess of what is possible with single Ge detector measurements. Recent results from ongoing investigations on electron emission, sputtered ion and energy loss phenomena are presented. Results from charge-state analysis of grazing incidence specular scattering of highly charged ions off atomically flat surfaces of gold, carbon and mica indicate that the incident ion essentially reaches ground state of its electronic distribution within the ion-surface interaction time of ∼ 100 fs. Atomic force microscopy is used to investigate the formation of a new type of ion induced surface defect, peculiar to highly charged ion-surface interactions. A linear correlation, between the defect volume and the incident ion charge, supports a mechanism of defect formation due to potential energy induced electron emission and subsequent collective displacement due to local charge imbalance.

Compton-suppression spectrometer for in-beam coincidence measurements and proposal for a detector configuration consisting of systems with a large solid angle

A γ-γ coincidence apparatus consisting of a Compton-suppression spectrometer with a large solid angle of 54 msr and a single Ge detector is described, and examples of experimental results obtained in in-beam spectroscopy of heavy-ion induced reactions are presented. Furthermore, a γ-γ coincidence Compton-suppression spectrometer consisting of three veto systems for three Ge-detectors is described. By using one integrated Compton-suppression shield consisting of a NaI(Tl) detector optimally divided into four parts for the Ge detectors, an extraordinarily large solid angle of 100 msr is obtained for each of Compton-suppression spectrometer. At the same time the total solid angle of the NaI(Tl) veto shield is minimized, which is the central problem when measuring γ cascades of high multiplicity.