Precision Measurement of the First Ionization Potential of Nobelium.

One of the most important atomic properties governing an element's chemical behavior is the energy required to remove its least-bound electron, referred to as the first ionization potential. For the heaviest elements, this fundamental quantity is strongly influenced by relativistic effects which lead to unique chemical properties. Laser spectroscopy on an atom-at-a-time scale was developed and applied to probe the optical spectrum of neutral nobelium near the ionization threshold. The first ionization potential of nobelium is determined here with a very high precision from the convergence of measured Rydberg series to be 6.626 21±0.000 05 eV. This work provides a stringent benchmark for state-of-the-art many-body atomic modeling that considers relativistic and quantum electrodynamic effects and paves the way for high-precision measurements of atomic properties of elements only available from heavy-ion accelerator facilities.

Probing Sizes and Shapes of Nobelium Isotopes by Laser Spectroscopy.

Until recently, ground-state nuclear moments of the heaviest nuclei could only be inferred from nuclear spectroscopy, where model assumptions are required. Laser spectroscopy in combination with modern atomic structure calculations is now able to probe these moments directly, in a comprehensive and nuclear-model-independent way. Here we report on unique access to the differential mean-square charge radii of ^{252,253,254}No, and therefore to changes in nuclear size and shape. State-of-the-art nuclear density functional calculations describe well the changes in nuclear charge radii in the region of the heavy actinides, indicating an appreciable central depression in the deformed proton density distribution in ^{252,254}No isotopes. Finally, the hyperfine splitting of ^{253}No was evaluated, enabling a complementary measure of its (quadrupole) deformation, as well as an insight into the neutron single-particle wave function via the nuclear spin and magnetic moment.

Investigation of the Electromagnetic Radiation Emitted by Sub-GeV Electrons in a Bent Crystal.

The radiation emitted by 855 MeV electrons via planar channeling and volume reflection in a 30.5-µm-thick bent Si crystal has been investigated at the MAMI (Mainzer Mikrotron) accelerator. The spectral intensity was much more intense than for an equivalent amorphous material, and peaked in the MeV range in the case of channeling radiation. Differently from a straight crystal, also for an incidence angle larger than the Lindhard angle, the spectral intensity remains nearly as high as for channeling. This is due to volume reflection, for which the intensity remains high at a large incidence angle over the whole angular acceptance, which is equal to the bending angle of the crystal. Monte Carlo simulations demonstrated that incoherent scattering significantly influences both the radiation spectrum and intensity, either for channeling or volume reflection. In the latter case, it has been shown that incoherent scattering increases the radiation intensity due to the contribution of volume-captured particles. As a consequence, the experimental spectrum becomes a mixture of channeling and pure volume reflection radiations. These results allow a better understanding of the radiation emitted by electrons subjected to coherent interactions in bent crystals within a still-unexplored energy range, which is relevant for possible applications for innovative and compact x-ray or γ-ray sources.

Steering of a sub-GeV electron beam through planar channeling enhanced by rechanneling.

We report the observation of efficient steering of a 855 MeV electron beam at MAMI (MAinzer MIkrotron) facilities by means of planar channeling and volume reflection in a bent silicon crystal. A 30.5 µm thick plate of (211) oriented Si was bent to cause quasimosaic deformation of the (111) crystallographic planes, which were used for coherent interaction with the electron beam. The experimental results are analogous to those recorded some years ago at energy higher than 100 GeV, which is the only comparable study to date. Monte Carlo simulations demonstrated that rechanneling plays a considerable role in a particle's dynamics and hinders the spoiling of channeled particles. These results allow a better understanding of the dynamics of electrons subject to coherent interactions in a bent silicon crystal in the sub-GeV energy range, which is relevant for realization of innovative x-ray sources based on channeling in periodically bent crystals.

Note: Precise radial distribution of charged particles in a magnetic guiding field.

Current high precision beta decay experiments of polarized neutrons, employing magnetic guiding fields in combination with position sensitive and energy dispersive detectors, resulted in a detailed study of the mono-energetic point spread function (PSF) for a homogeneous magnetic field. A PSF describes the radial probability distribution of mono-energetic electrons at the detector plane emitted from a point-like source. With regard to accuracy considerations, unwanted singularities occur as a function of the radial detector coordinate which have recently been investigated by subdividing the radial coordinate into small bins or employing analytical approximations. In this note, a series expansion of the PSF is presented which can numerically be evaluated with arbitrary precision.

The experimental setup of the Interaction in Crystals for Emission of RADiation collaboration at Mainzer Mikrotron: Design, commissioning, and tests.

Silicon/germanium flat/bent crystals are thin devices able to efficiently deflect charged particle GeV-energy beams up to a few hundreds of µrad; moreover, high intensity photons can be efficiently produced in the so-called Multi-Volume Reflection (MVR) and Multiple Volume Reflections in One Crystal (MVROC) conditions. In the last years, the research interest in this field has moved to the dynamic studies of light negative leptons in the low energy range: the possibility to deflect negative particles and to produce high intensity γ sources via the coherent interactions with crystals in the sub-GeV energy range has been proved by the ICE-RAD (Interaction in Crystals for Emission of RADiation) Collaboration at the MAinzer MIkrotron (MAMI, Germany). This paper describes the setup used by the ICE-RAD experiment for the crystals characterization (both in terms of deflection and radiation emission properties): a high precision goniometer is used to align the crystals with the incoming beam, while a silicon based profilometer and an inorganic scintillator reconstruct, respectively, the particle position and the photon spectra after the samples. The crystals manufacturing process and their characterization, the silicon profilometer commissioning at the CERN PS T9 beamline, and the commissioning of the whole setup installed at MAMI are presented.

Observation of optical Smith-Purcell radiation at an electron beam energy of 855 MeV.

Smith-Purcell radiation, generated when a beam of charged particles passes close to the surface of a diffraction grating, has been studied in the visible spectral range at wavelengths of 360 and 546 nm with the low emittance 855 MeV electron beam of the Mainz Microtron MAMI. The beam focused to a spot size of 4 microm (full width at half maximum) passed over optical diffraction gratings of echelle profiles with blaze angles of 0.8 degrees, 17.27 degrees, and 41.12 degrees and grating periods of 0.833 and 9.09 microm. Taking advantage of the specific emission characteristics of Smith-Purcell radiation a clear separation from background components, such as diffracted synchrotron radiation from upstream beam optical elements and transition radiation, was possible. The intensity scales with a modified Bessel function of the first kind as a function of the distance between electron beam and grating surface. Experimental radiation factors have been determined and compared with calculations on the basis of Van den Berg's theory [P.M. Van den Berg, J. Opt. Soc. Am. 63, 689 (1973)]. Fair agreement has been found for gratings with large blaze angles while the measurement with the shallow grating (blaze angle 0.8 degrees ) is at variance with this theory. Finally, the optimal operational parameters of a Smith-Purcell radiation source in view of already existing powerful undulator sources are discussed.

Total knee replacement infection after 2-stage reimplantation: results of subsequent 2-stage reimplantation.

Twelve patients who underwent salvage of an infected total knee replacement with removal, debridement, 6 weeks of parenteral antibiotics, and reimplantation subsequently acquired another infection in the same knee. These patients were again treated with the same protocol followed by reimplantation or arthrodesis and were observed for an average of 31 months. Nine of the patients underwent reimplantation surgery and 3 of the patients underwent arthrodesis. At followup the average Hospital for Special Surgery knee score for the reimplantation group was 84, the average Knee Society knee score was 79, and the average functional score was 73. The 3 patients who did not undergo reimplantation surgery had solid fusions in good position but were dissatisfied with their stiff limb. No knee to date has shown signs of recurrent infection.

Post-traumatic spinal cord cysts evaluated by magnetic resonance imaging.

In order to determine a more accurate prevalence of post-traumatic spinal cord cysts (PTSCC) in spinal cord injured (SCI) patients, we retrospectively reviewed magnetic resonance scans from symptomatic imaging and asymptomatic SCI patients. We found the incidence of PTSCC to be 51% in our patient population. The only symptom that correlated to the presence of a cyst was spasticity. The cyst develops at the site of injury and appears to be a common sequela of SCI. We believe that conservative treatment is indicated in most patients with a PTSCC.

[Epidemiology of hantaviruses in Baden-Wurttemberg]. / Epidemiologie von Hantaviren in Baden-Württemberg.

Hantavirus, originally named after the Hantaan River in Korea, is the aetiologic agent for the Hemorrhagic Fever with Renal Syndrome (HFRS) in the asian region, in the Americas for the Hantavirus Pulmonary Syndrome (HPS). In Middle Europe hantaviruses are responsible for the "Nephropathia Epidemica" (NE), a mild form of HFRS. Hantaviruses belong to the family of Bunyaviridae. Like other members of this family their genome consists of three segments of single stranded RNA (ss-RNA) leading to various subtypes, strongly associated with different rodent hosts. There are two major groups, the hantaan lineage harbored by murine rodents and the Puumala lineage harbored by arvicolidae ("old world") and sigmodontidae ("new world"). Infected rodents may develop chronic infections for months or even life-long and may shed infectious virus with urine and feces. The primary mode of infection of man occurs by inhaling contaminated aerosols or soil particles. The collection of epidemiologic data in the state of Baden-Württemberg was realized in three different steps: Collection and localisation of clinical cases (n = 62): A concentration of clinical cases in the middle of the state was found. The examination of the seroprevalence of exposed persons: By the examination of 4000 sera from forest workers, a seroprevalence with an average of 2.1% was found. In the districts of Reutlingen and Tübingen seroprevalences up to 9% were found. This leads to the assumption that there are endemic areas. Epidemiologic studies of reservoir hosts: Serologic surveys of rodents (n = 1150) in the described areas yielded to a seroprevalence up to 10-30%. Virus carriers were determined with RT-PCR and nested-PCR testing. The prevalence in the rodent population showed an average of 10%. The isolated subtypes were all identified as members of the Puumala-lineage. The origin of sporadic infections with Hantavirus of the Hantaan-lineage in Baden-Wuerttemberg is still unknown.

First observation of atomic levels for the element fermium (Z=100).

The atomic level structure of the element fermium was investigated for the first time using a sample of 2.7x10(10) atoms of the isotope 255Fm with a half-life of 20.1 h. The atoms were evaporated from a filament and stored in the argon buffer gas of an optical cell. Atomic levels were sought by the method of resonance ionization spectroscopy using an excimer-dye-laser combination. Two atomic levels were found at wave numbers (25 099.8+/-0.2) and (25 111.8+/-0.2) cm(-1). Partial transition rates to the 5f(12)7s(2) (3)H(e)(6) ground state have been determined from their saturation characteristics. Multiconfiguration Dirac-Fock calculations suggest that the leading orders of these levels could be the 5f(12)7s7p (5)I(o)(6) and 5f(12)7s7p (5)G(o)(5) terms.