6533b826fe1ef96bd1284f7b

RESEARCH PRODUCT

Low-temperature X-ray detectors for precise Lamb shift measurements on hydrogen-like heavy ions

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The precise determination of the Lamb shift in heavy hydrogen-like ions provides a sensitive test of quantum electrodynamics in very strong Coulomb"elds, not accessible otherwise. For the investigation of the Lyman-a transitions in 208Pb81‘ or 238U91‘ with su$cient accuracy a high resolving calorimetric detector for hard X-rays (E)100 keV) is presently developed. The detector modules consist of arrays of silicon thermistors and of X-ray absorbers made of high Z material to optimize the absorption e$ciency. The detectors are housed in a specially designed 3He/4He dilution refrigerator with a side arm which "ts to the geometry of the internal target of the storage ring ESR at GSI Darmstadt. The detector performance presently achieved is already close to ful"ll the demands of the Lamb shift experiment. For a prototype detector pixel with a 0.3 mm2]66 lm Sn absorber an energy resolution of *E FWHM "75 eV is obtained for 60 keV X-rays. ( 2000 Elsevier Science B.V. All rights reserved. 1. Motivation The precise experimental test of the theoretical predictions of quantum electrodynamics (QED) on corrections to the classical Coulomb interaction potential is still } at least for high Z systems } one of the outstanding and most challenging problems of atomic physics. In the hydrogen atom, or in hydrogen like ions, the QED corrections give rise to the so-called Lamb shift, which is a small deviation of the binding energies from those predicted by the relativistic Dirac}Coulomb energy (see Fig. 1). Whereas in light systems, where QED