Measurements have been made of the 7-7 and the conversion-electron-7 directional correlations of the 121-280-keV and the 136-265-keV cascades in As 75 following the decay of Se 76 . High-resolution Ge(Li) and Si (Li) detector systems were used exclusively, providing a significant degree of independence of these results from the effects of competing cascades. The Si (Li) electron spectrometer included a cooled fieldeffect transistor preamplifier to enhance its operation. The data are used to obtain the 7 multipole mixing ratios 8 and the internal-conversion particle parameters hi for transitions in As 75 . A precise definition of the mixing ratios in terms of reduced emission matrix elements is given in order to determine their sign unequivocally so that a comparison with theoretical predictions will be unambiguous. The results are 8 (280-keV 7) = -0.392±0.011,S(265-keV 7) --O.06±0.02, fc(JEl; 121-keV K e")= -1.96±0.04, b 2 (El; 136-keV K e~) --1.87=1=0.23. These values for the mixing ratios are discussed in light of those obtained in other experiments, and a comparison is presented of the results for the particle parameters with the theoretical predictions based on the point-and the finite-size-nucleus pictures.
Significant improvements in both the resolution and the precision of formation density logging tools are possible through the integration of a new "backscatter" gamma-ray detector into the traditional dual-spacing device. The spacing and the geometry of the new measurement permit intrinsic high resolution logging while much higher count rates provide increased precision.
Backscattering or single Compton Scattering in the formation complements standard attenuation logging by exhibiting a positive correlation between count rates and density. Statistical variations at higher densities are thus reduced. The reactions occur at short distances from the source dictating very short source-detector spacings and very high count rates. Such count rates have required adoption of a new crystal with attendant shielding and new count-rate electronics capable of digital treatment of the pulses. The backscatter detector is integrated into a skid that also carries more conventional short- and long-spacing detectors.
The energy spectra from the three detectors are binned into energy windows for data analysis. A nonlinear response model is established for each window count rate and the set of equations formed is solved for five unknowns—the formation density and photoelectric factor together with the mudcake density, thickness and photoelectric factor. This approach permits the optimal treatment of measurement errors and provides the best possible estimation of formation density and photoelectric factor available from the acquired measurements. The processing algorithms provide outputs at both standard and high resolution.
Field log examples show significant improvements in density precision and vertical resolution, and a dramatic improvement in the quality of the photoelectric factor (Pef) log.
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