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Register a new userPlanar LAAPDs: Temperature Dependence, Performance, and Application in Low Energy X-ray Spectroscopy
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An experiment measuring the 2S Lamb shift in muonic hydrogen mup is being performed at the Paul Scherrer Institute, Switzerland. It requires small and compact detectors for 1.9 keV x rays (2P-1S transition) with an energy resolution around 25% at 2 keV, a time resolution better than 100 ns, a large solid angle coverage, and insensitivity to a 5 T magnetic field. We have chosen Large Area Avalanche Photodiodes (LAAPDs) from Radiation Monitoring Devices as x-ray detectors, and they were used during the last data taking period in 2003. For x-ray spectroscopy applications, these LAAPDs have to be cooled in order to suppress the dark current noise, hence, a series of tests were performed to choose the optimal operation temperature. Specifically, the temperature dependence of gain, energy resolution, dark current, excess noise factor, and detector response linearity was studied. Finally, details of the LAAPDs application in the muonic hydrogen experiment as well as their response to alpha particles are presented.
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We have measured the intricate temperature dependence of the Co L2,3 x-ray absorption spectra (2p-3d excitations) of CoO. To allow for accurate total electron yield measurements, the material has been grown in thin film form on a metallic substrate in order to avoid charging problems usually encountered during electron spectroscopic studies on bulk CoO samples. The changes in spectra due to temperature are in good agreement with detailed ligand-field calculations indicating that these changes are mostly due to thermal population of closely lying excited states, originating from degenerate t2g levels lifted by the spin-orbit coupling. Magnetic coupling in the ordered phase, modeled as a mean-field exchange field, mixes in excited states inducing a tetragonal charge density. The spin-orbit coupling induced splitting of the low energy states results in a non-trivial temperature dependence for the magnetic susceptibility.
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We use narrow spectral lines from the x-ray spectra of various highlycharged ions to measure low-energy tail-like deviations from a Gaussian responsefunction in a microcalorimter x-ray spectrometer with Au absorbers at energiesfrom 650 eV to 3320 eV. We review the literature on low energy tails in othermicrocalorimter x-ray spectrometers and present a model that explains all thereviewed tail fraction measurements. In this model a low energy tail arises fromthe combination of electron escape and energy trapping associated with Bi x-rayabsorbers.
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