Silicon drift detectors with enlarged sensitive areas

The silicon drift detector is a compact, high‐resolution and energy‐dispersive x‐ray detector. The differences between the conventional silicon drift detectors with an active area of 5 mm² and new detectors with larger areas are outlined. Several constraints from fundamental physical and electronic properties are given, which limit the achievable energy resolution and size of the active area. The expected characteristics of larger upcoming devices are calculated. The deterioration of the energy resolution at very high count rates is quantitatively explained. Some limitations are eliminated if the chip is segmented into several cells with individual read‐out nodes. Copyright © 2004 John Wiley & Sons, Ltd.     

The dipole operator for exotic atoms and molecules

This note clarifies the role of the Fried-Martin factor in the calculation of dipole matrix elements for transitions between muonic and hardronic states. Formulae are given which are appropriate for exotic atoms or molecules and which take account of screening.     

On the formation of exotic atoms

A general disagreement exists between theory and experiment in the field of formation and decay of muonic and pionic atoms. Allowing for collisional processes in the deexcitation of heavy exotic atoms can substantially change the interpretation of experimental Coulomb-capture ratios, particularly of those measured by the muonic X-ray method.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.The author is grateful to Prof. F. Measday (Univ. of British Columbia, Vancouver, Canada) and Dr. J. Révai (C. R. I. P., Budapest) for illuminating discussions.     

Hyperfine structure of light exotic atoms

Recoil corrections to the hyperfine structure of light exotic atoms, including the effect of the anomalous magnetic moment are calculated for light muonic and baryonic atoms. In the case of muonic atoms, the effects of recoil and finite nuclear size are significant in view of the presently attainable experimental precision.     

Interference between multi-step transitions in exotic atoms

We discuss the interference effects due to coherent transitions involving more than one photon in exotic atoms. It is found that the populations are not influenced by this interference. In the case of muonic atoms there is an influence on the polarizations under specific conditions.     

Novel high‐resolution silicon drift detectors

Silicon drift detectors (SDDs) are used as energy‐dispersive detectors for x‐ray fluorescence analysis in commercial systems. Because of the low capacitance of the readout anode, achieved by the device topology and by the integration of the first FET on the chip, noise contributions are very small, allowing good energy resolution at low shaping times and high count rates. Typical energy resolution is better than 147 eV FWHM at 5.9 keV (Mn Kα), at ?10°C. This allows the chips to be cooled with a thermoelectric element, avoiding the use of liquid nitrogen. SDD chips are produced at MPI‐Halbleiterlabor in Munich with different geometries and areas. Recently, a new SDD has been developed which places the anode and the integrated JFET at the margin of the chip where it can easily be shielded from direct irradiation with the use of a collimator. The new layout allows the design of a readout anode with smaller area and therefore reduces the capacitance to values of about 120 fF compared with 200–250 fF with standard SDDs. The result is an improvement in energy resolution down to 128 eV at ?15°C. A second effect is the enhancement of the peak‐to‐background values to 6000 homogeneously across the active area of the detector. Copyright © 2004 John Wiley & Sons, Ltd.     

Unified approach to nuclear densities from exotic atoms

Parameters of nuclear density distributions are derived from least-squares fits to strong interaction observables in exotic atoms. Global analyses of antiprotonic and pionic atoms show reasonably good agreement between the two types of probes regarding the average behaviour of root-mean-square radii of the neutron distributions. Apparent conflict regarding the shape of the neutron distribution is attributed to different radial sensitivities of these two probes.     

Scattering of light exotic atoms in excited states

The differential and total cross-sections for the scattering of muonic, pionic, kaonic and antiprotonic hydrogen in excited states from atomic hydrogen have been calculated for the purpose of atomic cascade calculations. The scattering problem is treated in a fully quantum mechanical framework which takes the energy shifts and, in the case of the hadronic atoms, the widths of the ns states into account. The validity of semiclassical approximations is critically examined. Received 4 December 2001 and Received in final form 4 February 2002     

Differential elastic cross-sections of excited exotic hydrogen atoms

Differential cross-sections for the elastic scattering of excited exotic hydrogen atoms by hydrogenic atoms are calculated for the first time. The calculations are performed for exotic atoms (μ a,π a; a=p,d,t) in the states with the principal quantum numbers n=2-10 at relative motion energies E=0.001-15 eV and at scattering angles ϑ =0–180^00B0;. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of Debye plasma on compressed exotic atoms

The effect of plasma environment on the energy levels and structural properties of exotic atomic systems p⁺μ⁻ and μ⁺μ⁻ bound by Coulomb force and confined at the centre of an impenetrable spherical box has been thoroughly studied. The plasma environment is assumed to produce a Debye type of screening in the potential energy. Compression is generated by confining the exotic system in a spherical box. The effect of plasma and compression on system properties like orbital energies, excited states, dipole polarizabilities, oscillator strength and transition probabilities has been studied using time dependent variation perturbation theory. Ionisation pressures at different plasma screening have been estimated. The data obtained may be useful in the astrophysical context where different plasma environments exist.     

Formation of fast exotic atoms by radiative Coulomb capture

Interesting surprises in some exotic atom kinetics have been reported recently. These involve muonic atom transfer cross sections, nuclear pion capture and theq 1s effect in CF. These can be explained if the exotic atom population contains a contributing fast component. Such fast atoms can be formed by radiative continuum to bound transitions of fast (keV) muons or pions. Cross sections for formation of such fast pionic and muonic atoms and their velocity distributions are reported. The possibility of these processes competing with the thermalisation channels and contributing effectively to the exotic atom population is discussed.     

Ultracold metastable helium: from atoms to exotic molecules

We have written this article in the honor of our friend Vladilen Lethokov, who has produced so many brilliant ideas and results in the field of atomic and molecular physics and with whom we have had frequent unlightening discussions. We hope that the work described here will contribute to illustrate the richness of the field.     

Experiments with exotic atoms and exotic nuclei at GSI, recent developments and future prospects

Results and new developments with exotic atoms and exotic nuclei are presented from recent experiments at GSI. The proposed European inflight facility at GSI will open up new fields of outstanding research and will simultaneously access unknown regions of nuclei with new properties. A new generation of precision experiments will be performed with stored exotic nuclei, whereby nuclear reactions with an internal target and electron scattering in a small electron-ion collider will be a great challenge.     

Recoil corrections to the hyperfine splitting of exotic atoms

All recoil corrections to the hyperfine structure to orderα ⁴ are given, for arbitrary nuclear spins.     

On the interaction of exotic atoms with their environment

A theoretical study is made of the effect of collisions on the two-photon 2s → 1s transition of the fully-ionized muonic boron migrating in helium. Data on atomic processes are indicated which may be extracted from measurements of the yield of this transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

High-velocity components in exotic atoms,their origin and effects

The evolution of the kinetic energy distribution during the cascade is shown to play an important role for pionic and muonic atoms in hydrogen and deuterium. The kinetics of muon transfer in excited states is studied with a new cascade code and the results are compared with recent experimental data.     

Collisional deexcitation of exotic hydrogen atoms in highly excited states

The atomic cascades in μ^- p and p atoms have been studied in detail using new results for the cross-sections of the scattering of highly excited exotic atoms from molecular hydrogen. The cascade calculations have been done with an updated version of the extended standard cascade model that computes the evolution in the kinetic energy from the beginning of the cascade. The resulting X-ray yields, kinetic energy distributions, and cascade times are compared with the experimental data.     

Collisional deexcitation of exotic hydrogen atoms in highly excited states

The deexcitation of exotic hydrogen atoms in highly excited states in collisions with hydrogen molecules has been studied using the classical-trajectory Monte Carlo method. The Coulomb transitions with large change of principal quantum number n have been found to be the dominant collisional deexcitation mechanism at high n. The molecular structure of the hydrogen target is shown to be essential for the dominance of transitions with large Δn. The external Auger effect has been studied in the eikonal approximation. The resulting partial wave cross-sections are consistent with unitarity and provide a more reliable input for cascade calculations than the previously used Born approximation. Received 28 May 2002 Published online 15 October 2002 RID="a" ID="a"e-mail: thomas@physik.unizh.ch