A. Bleile

Calorimetric low-temperature detectors for high resolution x-ray spectroscopy on stored highly stripped heavy ions

The precise determination of the Lamb shift in heavy hydrogen-like ions provides a sensitive test of QED in very strong Coulomb fields, not accessible otherwise, and has also the potential to deduce nuclear charge radii. A brief overview on the present status of such experiments, performed at the storage ring ESR at GSI Darmstadt, is given. For the investigation of the Lyman-α transitions in Au78+- or U91+- ions with improved accuracy a high resolving calorimetric low temperature detector for hard x-rays (E⩽100u200akeV) 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 efficiency. The detectors are housed in a specially designed 3He/4He dilution refrigerator which fits to the geometry of the ESR target. The detector performance presently achieved is already close to fulfill the demands of the Lamb shift experiment. For a prototype detector an energy resolution of ΔEFWHM=75u200aeV is obtained for 60 keV x-...

Calorimetric low temperature detectors for low-energetic heavy ions and their application in accelerator mass spectrometry

The energy-sensitive detection of heavy ions with calorimetric low temperature detectors was investigated in the energy range of E=0.1-1 MeV/amu, commonly used for accelerator mass spectrometry (AMS). The detectors used consist of sapphire absorbers and superconducting aluminum transition edge thermometers operated at T approximately 1.5 K. They were irradiated with various ion beams (13C, 197Au, 238U) provided by the VERA tandem accelerator in Vienna, Austria. The relative energy resolution obtained was DeltaE/E=(5-9) x 10(-3), even for the heaviest ions such as 238U. In addition, no evidence for a pulse height defect was observed. This performance allowed for the first time to apply a calorimetric low temperature detector in an AMS experiment. The aim was to precisely determine the isotope ratio of 236U/238U for several samples of natural uranium, 236U being known as a sensitive monitor for neutron fluxes. Replacing a conventionally used detection system at VERA by the calorimetric detector enabled to substantially reduce background from neighboring isotopes and to increase the detection efficiency. Due to the high sensitivity achieved, a value of 236U/238U=6.1 x 10(-12) could be obtained, representing the smallest 236U/238U ratio measured at the time. In addition, we contributed to establishing an improved material standard of 236U/238U, which can be used as a reference for future AMS measurements.

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

The precise determination of the Lamb shift in heavy hydrogen-like ions provides a sensitive test of quantum electrodynamics in very strong Coulombelds, not accessible otherwise. For the investigation of the Lyman-a transitions in 208Pb81‘ or 238U91‘ with su

Precise Lamb Shift Measurements in Hydrogen‐Like Heavy Ions—Status and Perspectives

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

Calorimetric low temperature detectors for mass identification of heavy ions

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 fulll 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

High-precision x-ray spectroscopy of highly charged ions with microcalorimeters

The precise determination of the energy of the Lyman α1 and α2 lines in hydrogen‐like heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields. For the first time, a calorimetric low‐temperature detector was applied in an experiment to precisely determine the transition energy of the Lyman lines of lead ions 207pb81+ at the Experimental Storage Ring (ESR) at GSI. The detectors consist of silicon thermistors, provided by the NASA/Goddard Space Flight Center, and Pb or Sn absorbers to obtain high quantum efficiency in the energy range of 40–80 keV, where the Doppler‐shifted Lyman lines are located. The measured energy of the Lyman α1 line, E(Ly‐α1, 207Pb81+)u2009=u2009(77937±12stat±23syst)u2009eV, agrees within errors with theoretical predictions. The systematic error is mainly due to uncertainties in the non‐linear energy calibration of the detectors as well as the relative position of detector and gas‐jet target.

Precise Determination of the 1s Lamb Shift in Hydrogen-Like Lead and Gold Using Microcalorimeters

The energy sensitive detection of heavy ions with calorimetric low temperature detectors (CLTDs) is investigated for the energy range E=0.1–1u2009MeV/u, commonly used for accelerator mass spectrometry (AMS). Such measurements complement earlier investigations [1, 2] at higher energies (E=5–300u2009MeV/u) where an energy resolution of ΔE/E=1–2×10−3 was obtained for various ion species. The detectors used consist of sapphire absorbers and superconducting transition edge thermometers operated at T≈1.5u2009K. They were irradiated with various heavy ion beams (13C,u200a197Au,u200a238U) provided by the VERA tandem accelerator in Vienna, Austria. An energy resolution of ΔE/E=5–6×10−3 has been obtained even for heaviest ions like 197Au and 238U at E=0.1–0.3u2009MeV/u, thereby exceeding the resolution of conventional semiconductor detectors in this energy range by at least one order of magnitude. In addition, no evidence for pulse height defects has been observed. With the achieved performance, the present CLTDs bear a large potential fo...

Precise determination of the 1s Lamb Shift in hydrogen-like heavy ions at the ESR storage ring using microcalorimeters

The precise determination of the energy of the Lyman α1 and α2 lines in hydrogen-like heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields. To improve the experimental precision, the new detector concept of microcalorimeters is now exploited for such measurements. Such detectors consist of compensated-doped silicon thermistors and Pb or Sn absorbers to obtain high quantum efficiency in the energy range of 40–70 keV, where the Doppler-shifted Lyman lines are located. For the first time, a microcalorimeter was applied in an experiment to precisely determine the transition energy of the Lyman lines of lead ions at the experimental storage ring at GSI. The energy of the Ly α1 line E(Ly-α1, 207Pb81+) = (77937 ± 12stat ± 25syst) eV agrees within error bars with theoretical predictions. To improve the experimental precision, a new detector array with more pixels and better energy resolution was equipped and successfully applied in an experiment to determine the Lyman-α lines of gold ions 197Au78+.

First application of calorimetric low-temperature detectors in accelerator mass spectrometry

Quantum electrodynamics in very strong Coulomb fields is one scope which has not yet been tested experimentally with sufficient accuracy to really determine whether the perturbative approach is valid. One sensitive test is the determination of the 1s Lamb shift in highly-charged very heavy ions. The 1s Lamb shift of hydrogen-like lead (Pb81+) and gold (Au78+) has been determined using the novel detector concept of silicon microcalorimeters for the detection of hard x-rays. The results of eV for lead and eV for gold are within the error bars in good agreement with theoretical predictions. To our knowledge, for hydrogen-like lead, this represents the most accurate determination of the 1s Lamb shift.

First Experiments Aiming for Precise Lamb Shift Measurements on Hydrogen-Like Heavy Ions with Low Temperature Calorimeters

The precise determination of the energy of the Lyman α1 and α2 lines in hydrogen-like heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields. To improve the precision of such experiments, the new detector concept of microcalorimeters, which detect the temperature change of an absorber after an incoming particle or photon has deposited its energy as heat, is now exploited. The microcalorimeters for x-rays used in these experiments consist of arrays of silicon thermometers and x-ray absorbers made of high-Z material. With such detectors, a relative energy resolution of about 1 per mille is obtained in the energy regime of 50–100 keV. Two successful measurement campaigns to determine the 1s Lamb Shift in Pb81+ and Au78+ have been completed: a prototype array has been applied successfully for the determination of the 1s Lamb Shift of Pb81+ at the ESR storage ring at GSI in a first test experiment. Based on the results of this test, a full array with 32 pixels has been equipped and has recently been applied to determine the 1s Lamb Shift in Au78+ ions. The energy of the Lyman-α1 line agrees within error bars well with theoretical predictions. The obtained accuracy is already comparable to the best accuracy obtained with conventional germanium detectors for hydrogen-like uranium.