An experiment measuring the 2S Lamb shift in muonic hydrogen (μ-p) is being performed at the Paul Scherrer Institute (PSI), Switzerland. It requires small detectors for 1.9 keV X-rays (2P-1S transition) with an energy resolution around 25%, a time resolution better than 100 ns, a large solid angle coverage, and insensitivity to a 5 T magnetic field. We used large area avalanche photodiodes (LAAPDs) from radiation monitoring devices (RMD) for the latest data taking period in 2003. For soft X-ray spectroscopy applications, they have to be cooled, hence, a series of tests were performed to choose the optimal operation temperature. 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 our experiment as well as their response to alpha particles are presented.
[Show abstract][Hide abstract] ABSTRACT: The Lamb shift in muonic hydrogen continues to be a subject of experimental
and theoretical investigation. Here my older work on the subject is updated to
provide a complementary calculation of the energies of the 2p-2s transitions in
Physical Review A 10/2004; 71(3). DOI:10.1103/PhysRevA.71.032508 · 2.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Position-sensitive avalanche photodiodes (PSAPDs) have recently been proposed as optical light detectors in scintillation based gamma cameras. They are compact solid-state devices that provide high quantum efficiency and gain, and they can achieve precise positioning over relatively large surfaces with few readout channels. In previous studies, PSAPDs were coupled to scintillator arrays and the imaging task consisted in identifying the crystal of interaction. In this paper, we investigate the possibility of using a PSAPD to read the light of a single continuous crystal. Such a configuration has the potential to reduce the cost and simplify the construction of a PSAPD-based gamma camera while maintaining good overall performance. The spatial resolution of a small imaging unit having a continuous scintillator coupled to an 8×8 mm<sup>2</sup> PSAPD was evaluated at different energies for CsI:Tl and LaBr<sub>3</sub>:Ce crystals. After correcting the images for the distortion and the minification associated with this camera, spatial resolution values of 0.62, 0.72, 0.99, and 1.25 mm (FWHM) were obtained for <sup>99m</sup>Tc (140 keV), <sup>57</sup>Co (122 keV), <sup>241</sup>Am (60 keV), and <sup>125</sup>I (30 keV) respectively for an 8×8×1 mm<sup>3</sup> CsI:Tl crystal. Corresponding values of 0.55, 0.64, 0.92 and 1.10 mm (FWHM) were obtained from a 1 mm thick LaBr<sub>3</sub>:Ce crystal. These results, reproduced by Monte Carlo simulations, suggest that the continuous crystal configuration is an attractive approach to develop a PSAPD-based high-resolution gamma camera and is especially well suited for a small-animal imaging system.
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