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[en] The Full Energy Peak (FEP) efficiencies of a large volume HPGe detector have been measured in several far geometries (of 17, 19 and 21 cm source-detector distances). The data points were obtained by using long-lived standard gamma sources for the energies from 40 to 2000 keV. Polynomial functions were well fitted to the measured points. A transformation function was obtained from the fitted functions and the solid angles subtended by the detector. Using the transformation function the FEP efficiencies in close geometry (of 1 cm source-detector distance) were derived. These results for close geometry were compared with those of previous measurements', following coincidence summing corrections. The agreement between the data sets is striking. In this way the FEP efficiencies derived from the far geometry data by using the transformation function provide an accurate method for determining the FEP efficiencies in any close geometry from far geometry measurements
[en] A brief discussion of the early history of unconventional uses of Ge detectors is given, followed by a more detailed discussion focusing on their uses for axion searches. The main purpose of this discussion is to explore the possibility of pushing the envelope of sensitivity of solar axion searches with future large Ge detector arrays applied to searches employing coherent Bragg-Primakoff conversion, as well as the axio-electric effect.
[en] Nuclear spectroscopic studies have provided a strong incentive to obtain γ-ray detectors with increasingly better energy resolution, higher full-energy peak efficiencies, and greater sensitivity or resolving power. A major step was the introduction of Ge detectors in the early 60's. But because of the low atomic number of Ge they have a poor response function; a majority of interacting gamma rays of moderate energy Compton scatter out of the detector leaving a large low-energy background. The remedy was to add a Compton-suppression shield made of NaI around the Ge crystal, and if interactions occurred simultaneously in the NaI scintillator and in the Ge detector to veto that event. Efficiencies also increased greatly when an English-Danish collaboration assembled five Ge detectors, each with a NaI suppressor, into the first array at the end of 1980. Obviously, a system of five such detectors gave much better statistics than the usual two bare detectors used for obtaining coincidence data (by a factor of 10). A few years later, another major improvement came with replacement of the NaI suppressors with shields made of the much denser bismuth germanate (BGO) as scintillator, as these could be thinner leading to arrays with of order 20 detectors. Use of such a large number of detectors led to the realization that for cascades of coincident gamma rays, as in going down a band, the improvement in the peak/background ratio observed and already appreciated in going from singles spectra to gated (double-) coincidence spectra continued when doubly-gated triple-coincidence data were compared for the first time to singly-gated double-coincidence ones. The higher-gated spectra were much cleaner and more selective, though with poorer statistics, and the advantages of higher folds and efficiencies led to the proposals for the larger 4π arrays of today, Eurogam and GASP in Europe and Gammasphere in the U.S
[en] Efficiency calibrations for Ge detectors are typically done with the use of multiple energy calibrations sources which are added to a bulk matrix intended to simulate the measurement sample, and then deposited in the sample container. This is rather easy for common laboratory samples. Bu, even there, for many environmental samples, waste assay samples, and operational health physics samples, accurate calibrations are difficult. For these situations, various mathematical corrections or direct calibration techniques are used at Canberra. EML has pioneered the use of mathematical calibrations following source-based detector characterization measurements for in situ measurements of environmental fallout. Canberra has expanded this by the use of MCNP for the source measurements required in EML. For other calibration situations, MCNP was used directly, as the primary calibration method. This is demonstrated to be at least as accurate as source based measurements, and probably better. Recently, a new method [ISOCS] has been developed and is nearing completion. This promises to be an easy to use calibration software that can be used by the customer for in situ gamma spectroscopy to accurately measure many large sized samples, such as boxes, drums, pipes, or to calibrate small laboratory-type samples. 8 refs., 8 figs., 5 tabs
[en] The GERDA experiment investigates the neutrinoless double beta decay of 76Ge and is currently running Phase I of its physics program. Using the same isotope as the Heidelberg Moscow (HDM) experiment, GERDA aims to directly test the claim of observation by a subset of the HDM collaboration. For the update to Phase II of the experiment in 2013, the collaboration organized the production of 30 new Broad Energy Germanium (BEGe) type detectors from original 35 kg enriched material and tested their performance in the low background laboratory HADES in SCK.CEN, Belgium. With additional 20 kg of detectors, GERDA aims to probe the degenerated hierarchy scenario. One of the crucial detector parameters is the active volume (AV) fraction which directly enters into all physics analysis. This talk presents the methodology of dead layer and AV determination with different calibration sources such as 241Am, 133Ba, 60Co and 228Th and the results obtained for the new Phase II detectors. Furthermore, the AV fraction turned out to be the largest systematic uncertainty in the analysis of Phase I data which makes it imperative to reduce its uncertainty for Phase II. This talk addresses the major contributions to the AV uncertainty and gives an outlook for improvements in Phase II analysis.
[en] Thanks to the design of the high purity germanium detectors, the use of this detector becomes more and more interesting for whole body counting systems. The advantage of this detector type over the conventional NaI(Tl) detectors is its superior resolution and peak to valley ratio. These features are especially useful for accurate whole body measurements. 6 figs.; 1 table
[en] While many Marinelli beaker geometries are in use, this standard specifies a single configuration for the sole purpose of characterizing germanium detector performance. This standardized sample geometry, and the measurement techniques described provide a meaningful assessment of detector performance when used in conjunction with the relative efficiency measurement standard specified in ANSI/IEEE Std 325-1971 (Reaffirmed 1977)