Thomas Krings

A self-triggering silicon tracking telescope for spectator proton detection

With the ANKE spectrometer at the COoler SYnchrotron COSY Juelich the mesonic structure of the nucleon will be studied in polarized proton-proton and proton-deuteron collisions. The identification and tracking of low energy protons permits using deuterium as an effective neutron target. For this purpose, modular self-triggering tracking telescopes built up by double-sided silicon strip detectors inside the accelerator ultra-high vacuum have been developed. Their basic features are /spl Delta/E/E proton identification from 2.5

Development of double-sided microstructured Si(Li)-detectors

40 MeV and particle tracking over a wide dynamic range, either 2.5 MeV spectator protons or minimum ionizing particles. By the use of self-triggering read-out chips, the telescopes identify a particle passage within 100 ns and therefore allow the possibility of a fast hit pattern recognition. In combination with a read-out pitch of /spl sim/200 /spl mu/m, they provide a high rate capability. The recent development of very thick (/spl ges/5 mm) double-sided microstructured Si(Li) and very thin (/spl les/65 /spl mu/m) double-sided Si-detectors provides the use of the telescopes over a wide range of particle energies.

Two-dimensional microstrip Germanium detector for the spectroscopy of hard X-ray transitions

A new technique for manufacturing double-sided structured Si(Li) detectors has been established. The position-sensitive structure on the implanted p/sup +/-contact can be made smaller than 100 /spl mu/m by photolithography followed by plasma etching of grooves to separate the position elements. By modifying this technique position-sensitive structures on a thin (/spl sim/30 /spl mu/m) Li-diffused contact were created. Areas of 50 mm /spl times/ 50 mm were divided into 50 or 100 strips with a pitch of 1 mm or 500 /spl mu/m, respectively. The strips were separated by /spl sim/35-/spl mu/m-deep and /spl sim/50-/spl mu/m-wide grooves. Measurements of the electrical resistance of the grooves and reverse current of the strips are presented. Charge splitting on the adjacent strips shows practically no charge loss through the groove. Small pixel effects are demonstrated on a Li-diffused contact (100 strips with the pitch of 500 /spl mu/m) and on the first double-sided Si(Li) detector (50 /spl times/ 50 strips with a pitch of 1 mm). By measuring the relative time distribution of the signal from both contacts it is possible to obtain some three-dimensional imaging capability.

Applications of position sensitive germanium detectors for X-ray spectroscopy of highly charged heavy ions

New possibilities are opened up utilizing position-sensitive germanium detectors in the X-ray spectroscopy of highly charged heavy ions at GSI-Darmstadt. The recent experiments revealed the need for two-dimensional strip detectors with their inherent advantages concerning spectroscopy and imaging capabilities as well as polarization sensitivity. For the first prototype a germanium diode (70 mmtimes41 mm, 11 mm thick) with a boron implanted contact and an amorphous Ge contact was prepared. A 128-strip structure on an area of 32 mmtimes56 mm with a pitch of 250 mum on the front contact (implanted) and a 48-strip structure with a pitch of 1167 mum on the rear contact (amorphous Ge) are realized with the help of plasma etching. The detector is mounted in a cryostat which will enable any orientation of the detector with respect to a photon source. The results of laboratory tests and planned applications at the ESR storage ring in Darmstadt are presented

First-generation hybrid compact Compton imager

The spectroscopy of atomic transitions in the hard X-ray regime above 15 keV utilizing position-sensitive solid state detectors is discussed. Special emphasis is given to the current detector developments for X-ray spectroscopy of heavy ions at the ESR storage ring where applications for precision spectroscopy as well as for polarization studies are of particular interest. For both cases, the advantages and new possibilities which are opened up by position and energy resolving solid state detectors are illustrated by the presentation of first experiments.

Microstructures on Ge detectors with amorphous Ge contacts

At Lawrence Livermore National Laboratory, we are pursuing the development of a gamma-ray imaging system using the Compton effect. We have built our first generation hybrid Compton imaging system, and we have conducted initial calibration and image measurements using this system. In this paper, we present the details of the hybrid Compton imaging system and initial calibration and image measurements

Reconstruction of the activity of point sources for the accurate characterization of nuclear waste drums by segmented gamma scanning.

A new method for structuring germanium detectors with amorphous Ge contacts (a-Ge contacts) is presented. The method is based on the established technique for performing position sensitive structures by, means of photolithography and subsequent plasma etching of grooves through implanted contacts. First prototype was manufactured from n-type germanium. The p/sup +/-contact was performed by boron implantation and the amorphous Ge contact by, evaporation of germanium. The 0.30 /spl mu/m thick germanium layer was then covered with 0.27 /spl mu/m thick layer of evaporated aluminium. A simple 50 strip structure with a pitch of 615 /spl mu/m was produced on the a-Ge contact. The grooves between the strips were 13 /spl mu/m deep and 56 /spl mu/m wide. The coincidental spectra of adjacent strips indicate that practically no charge losses were caused by the existence of the groove between these strips. Further investigations are going on like test of structured a-Ge contacts on p-type germanium and improving the energy resolution of the strips on the a-Ge contacts using the cooled first stage of a preamplifier. But already the first results prove, that good functioning structures on the a-Ge contacts can be created by means of plasma etched grooves. Narrow grooves, even below 10 /spl mu/m, can be easily fabricated. Energy measurements with practically no energy losses influenced by the grooves can be performed.

Reconstruction of the isotope activity content of heterogeneous nuclear waste drums

This work improves the reliability and accuracy in the reconstruction of the total isotope activity content in heterogeneous nuclear waste drums containing point sources. The method is based on χ(2)-fits of the angular dependent count rate distribution measured during a drum rotation in segmented gamma scanning. A new description of the analytical calculation of the angular count rate distribution is introduced based on a more precise model of the collimated detector. The new description is validated and compared to the old description using MCNP5 simulations of angular dependent count rate distributions of Co-60 and Cs-137 point sources. It is shown that the new model describes the angular dependent count rate distribution significantly more accurate compared to the old model. Hence, the reconstruction of the activity is more accurate and the errors are considerably reduced that lead to more reliable results. Furthermore, the results are compared to the conventional reconstruction method assuming a homogeneous matrix and activity distribution.

Detection Characteristics of Ge detectors with microstructured amorphous Ge contacts

Radioactive waste must be characterized in order to verify its conformance with national regulations for intermediate storage or its disposal. Segmented gamma scanning (SGS) is a most widely applied non-destructive analytical technique for the characterization of radioactive waste drums. The isotope specific activity content is generally calculated assuming a homogeneous matrix and activity distribution for each measured drum segment. However, real radioactive waste drums exhibit non-uniform isotope and density distributions most affecting the reliability and accuracy of activities reconstruction in SGS. The presence of internal shielding structures in the waste drum contributes generally to a strong underestimation of the activity and this in particular for radioactive sources emitting low energy gamma-rays independently of their spatial distribution. In this work we present an improved method to quantify the activity of spatially concentrated gamma-emitting isotopes (point sources or hot spots) in heterogeneous waste drums with internal shielding structures. The isotope activity is reconstructed by numerical simulations and fits of the angular dependent count rate distribution recorded during the drum rotation in SGS using an analytical expression derived from a geometric model. First results of the improved method and enhancements of this method are shown and are compared to each other as well as to the conventional method which assumes a homogeneous matrix and activity distribution. It is shown that the new model improves the accuracy and the reliability of the activity reconstruction in SGS and that the presented algorithm is suitable with respect to the framework requirement of industrial application.

Analytical calculation of the collimated detector response for the characterization of nuclear waste drums by segmented gamma scanning

The established technique for performing position sensitive structures by means of photolithography and subsequent plasma etching of grooves through detector contacts was applied for amorphous germanium contacts (a-Ge contacts). A simple 50 strip structure with a pitch of 615 /spl mu/m was produced. Charge sharing between two adjacent strips (33 mm long) was investigated with the help of 60 keV photons and 5.8 MeV /spl alpha/-particles. No charge losses could he detected irradiating the front (structured) contact of the 16 mm thick detector by 60 keV photons. The same was concluded for /spl alpha/-particles hitting the rear, not structured p/sup +/-contact made by boron implantation. Moreover, excellent position information for a-particles, with an accuracy of about 30 /spl mu/m, could be extracted in this case. Surprising results were obtained for /spl alpha/-particles impinging on the front contact. No coincidental signals from the two adjacent strips caused by a-particles could be observed. But a normally positive signal from one of the strips coincided occasionally with a negative signal from the other strip and vice versa. Using a cooled FET assembly mounted near a strip an energy resolution of 0.78 keV [FWHM] for 60 keV photons was achieved and slightly better for lower energies. Even better energy resolutions will be probably possible, because the measuring set up was far from being optimized.