Raman studies of nonlinear phenomena in fullerene crystallites

The resonant Raman scattering of C₆₀ crystallites is monitored as a function of excitation intensity at 514.5 nm. At low intensities, a strong line at 1468 cm^–1 is observed. No feature at 1459 cm^–1 is observable. With increasing intensities, the 1468 cm^–1 line shifts continuously and reversibly to lower frequencies. The mode softening is nonlinearly dependent on the input intensity and is accompanied by a nonlinear increase in the Raman intensity. The spectral changes are discussed in terms of a nonlinear reduction in force constant and increase in bond polarisability as a result of an increased intermolecular delocalisation of the -electron cloud. The nonlinear changes are associated with the nonlinear luminescence and photoconductive response observed in fullerenes and are contrasted to the irreversible phototransformation recently discussed.     

Magnetomechanical training of single crystalline Ni-Mn-Ga alloy

A 5M Ni-Mn-Ga single crystal was investigated, supplied by Adaptamat Ltd, Finland. Especially low temperature magnetic actuation as well as cyclic tensile-compression tests revealed promising properties, which provide useful insights for training concepts in polycrystalline materials. Successive compressions lead to a significant reduction of the twinning stress by a factor of two.     

Low-energy dipole strength and the critical case of Ca

Recent theoretical work has not led to a consensus regarding the nature of the low-energy E1 strength in the ^40,44,48Ca isotopes, for which high-resolution (γ,γ^′)$(\gamma ,{\gamma }^{\prime })$ data exist. Here we revisit this problem using the first-order quasiparticle random-phase approximation (QRPA) and different interactions. First we examine all even Ca isotopes with N=14–40$N=14\text{–}40$. All isotopes are predicted to undergo dipole transitions at low energy, of large and comparable isoscalar strength but of varying E1 strength. Provided a moderate and uniform energetic shift is introduced to the results, QRPA with the Gogny D1S interaction is able to account for the (γ,γ^′)$(\gamma ,{\gamma }^{\prime })$ data, because, up to N=28$N=28$, it yields a rather pure isoscalar oscillation. A neutron-skin oscillation is anticipated for N?30$N?30$. This contradicts existing predictions that ^44,48Ca develop a neutron-skin mode. Which theoretical result is correct cannot be resolved conclusively using the available data. We propose that alpha-scattering, possibly followed by an electroexcitation experiment, could resolve the situation and thereby help to improve the different models aspiring to describe reliably the low-energy dipole strength of nuclei.     

Internal Biokinetic Behaviour of Molybdenum in Humans Studied with Stable Isotopes as Tracers

Abstract

Although molybdenum is considered to be an essential trace metal for humans, the knowledge about its metabolism is rather limited. The present study was aimed at the assessment of biokinetics following intravenous injection of trace amounts of ⁹⁵Mo or ⁹⁶Mo into five healthy volunteers. In a total of 11 investigations, the plasma clearance up to eight hours and the urinary excretion for at least three days after the injection were evaluated. The tracer concentrations were determined by proton nuclear activation analysis in blood plasma and by thermal ionization mass spectrometry in urine samples respectively. In all subjects, the plasma clearance is much faster than expected from the literature. The data obtained for the plasma clearance of the tracer can reasonably be fitted by a two exponential equation. The half times of the fast component range between 4 and 70 minutes and for the slow component between 3 and 30 hours. The urinary excretion of the injected tracer seems also to be faster than expected and the fractions lost are higher for larger doses administered. For the smallest dose given, 34% of the injected tracer were excreted within one day whereas for the four times larger dose about 60% were lost. These findings on urinary excretion are in agreement with recently published results.     

Proton-neutron interaction at N≅Z — First observation of the Tz=1 nucleus 46 94 Pd48 in-beam

The neutron deficient nucleus⁹⁴Pd was identified and studied for the first time by in-beam spectroscopy. An I=(14⁺) isomer with t_1/2=0.8 (2) s was observed in a recoil catcher setup inside the multi-detector -array OSIRIS. Filter detectors for neutrons and charged particles were used to identify the (2p2n) exit channel of the reaction⁵⁸Ni+⁴⁰Ca, populated with only 0.06% of the total evaporation residue cross section. The structure of the isomer is discussed within the frame work of shell model calculations in the (p_1/2,g_9/2) model space with emphasis on the g ₉ ^2/2 T=0, I=1,9 pairing two-body matrix elements.Communicated by: D. Schwalm     

<Emphasis Type="Italic">Ab initio</Emphasis> nuclear structure calculations with transformed realistic interactions

We discuss three elements of modern ab initio nuclear structure theory with an emphasis on the role of correlations in the nuclear many-body problem. Starting from the QCD-motivated construction of a realistic nuclear interaction we review two methods to derive phase-shift equivalent tamed interactions, the Unitary Correlation Operator Method and the Similarity Renormalization Group. Eventually we use these interactions for ab initio calculations within the importance truncated no-core shell model.     

Direct dark matter search with CRESST and EURECA

The current status of the direct Dark Matter experiments CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) and the planned EURECA (European Underground Rare Event Calorimeter Array) is presented. Both experiments are aimed at the direct detection of WIMPs (Weakly Interacting Massive Particles), potential candidates for the Dark Matter in the universe. New design developments of the cryogenic detectors operated at mK temperatures are investigated to optimize detector performance and to simplify mass production. Thus, CRESST is also providing a basis for the EURECA project, aimed at a ton of cryogenic detectors with a multi-material target.     

The A-emission of KBr : Tl

The line shapes and relative efficiencies of A_T and A_X emission bands of KBr : Tl have been studied over a wide temperature range (10–500 K). The behavior of A_T and A_X emissions has been described phenomenologically in terms of the coexistence of two different kinds of minima on the adiabatic potential energy surface of the ³T_1u relaxed excited state. The line shape parameters and the A-emission temperature dependence show that T and X minima belong to distortions of different symmetry. A model considering the emission processes from T and X minima separately, in spaces of different distortions, is shown to account well for the experimental results. The emission at very low temperatures (below 50 K) was found to be sensitive to trace impurities.