Strong Interference Luminescence of Mixed Modes in the Neighborhood of the Critical Value of Exciton Decay

Optics and Spectroscopy - The results of a numerical calculation of the dispersion and luminescence spectra of mixed exciton modes of crystals of the CdS ( $${{A}_{{n = 1}}}$$ ) type are analyzed...     

Influence of exciton decay on the polariton luminescence spectra of CdTe crystal

The polariton luminescence spectra of CdTe crystals have been numerically calculated with allowance for the decay of mechanical excitons and compared with the known experimental low-temperature photoluminescence spectra of these crystals. The mechanism of formation of polariton luminescence in dependence of the optical parameters of crystal for the exciton resonance A _n=1 is discussed.     

Experimental investigation of high-energy photon splitting in atomic fields

Data analysis of an experiment in which photon splitting in atomic fields was observed is presented. The experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M collider. In the energy region of 120-450 MeV, statistics of 1.6x10(9) photons incident on the BGO target was collected. About 400 candidate photon-splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the calculated exact atomic-field cross section. The predictions obtained in the Born approximation differ significantly from the experimental results.     

Determination of 41Ca with LSC and AMS: method development, modifications and applications

Despite the emission of only low energy Auger electrons (ca. 3.6 keV) and the difficulty of obtaining a certified standard, Liquid scintillation counting (LSC) determinations are still reasonable options for a radioanalytical laboratory involved in nuclear installation decommission. Besides, accelerator mass spectrometry (AMS), being the most sensitive analytical technique not only for ⁴¹Ca, is gaining increasingly broader accessibility and applicability. Herein, we present a radiochemical separation procedure developed for ⁴¹Ca determination with LSC and AMS in varying materials (i.e. water, concrete, sediment, soil, and biota). The radioanalytical isolation consists of anion exchange and extraction chromatography as well as carbonate precipitation and recrystallization from organic solvents. Thereby, interfering radionuclides as ⁵⁵Fe, ⁶⁰Co, ¹⁵²Eu, U or actinides are removed with decontamination factors of 10²–10⁴. Quench curves for determining the measurement efficiency is generated with a ⁴¹Ca solution gained from the ⁴¹Ca/⁴⁰Ca certified reference material ERM-AE701. In routine application the procedure is characterized by chemical yields of 67–86 %, measurement efficiencies of 1–10 % and detection limits of 0.05 Bq g^?1 and 0.3 Bq L^?1. Aliquots of the digestion solutions of LSC can be easily converted into CaF₂–AMS targets by successive oxsalate and fluoride precipitation. Pros and cons for both measurement techniques are addressed based on ⁴¹Ca results from LSC and AMS for the same material.     

Nanoindentation of ion-irradiated reactor pressure vessel steels – model-based interpretation and comparison with neutron irradiation

Ion-irradiation-induced hardening is investigated on six selected reactor pressure vessel (RPV) steels. The steels were irradiated with 5 MeV Fe²⁺ ions at fluences ranging from 0.01 to 1.0 displacements per atom (dpa) and the induced hardening of the surface layer was probed with nanoindentation. To separate the indentation size effect and the substrate effect from the irradiation-induced hardness profile, we developed an analytic model with the plastic zone of the indentation approximated as a half sphere. This model allows the actual hardness profile to be retrieved and the measured hardness increase to be assigned to the respective fluence. The obtained values of hardness increase vs. fluence are compared for selected pairs of samples in order to extract effects of the RPV steel composition. We identify hardening effects due to increased levels of copper, manganese-nickel and phosphorous. Further comparison with available neutron-irradiated conditions of the same heats of RPV steels indicates pronounced differences of the considered effects of composition for irradiation with neutrons vs. ions.     

On the low-temperature photoluminescence and photovoltaic properties of fine-grained CdTe films

In the low-temperature (T = 4.2 K) photoluminescence spectrum of a fine-grained (the grain size is smaller than 1 μm) obliquely sputtered CdTe thin film, the dominant intrinsic emission band caused by potential barriers at grain boundaries and the edge doublet band representing the LO-phonon replica of the dominant band are observed. Doping of the film with an In impurity quenches the doublet band and subsequent heat treatment activates the intrinsic emission band. The full-width at half maximum and the short-wavelength shift of the red edge of the latter correlate with a maximum anomalously high photovoltage of 2 × 10²–10³ V generated by the film.     

The post-ionisation of Pb ions from a molten Sn host field-ion emitter

A tin liquid metal ion source contaminated with lead has been studied. From a detailed analysis of the source mass spectra as a function of emission current, it is established that while Sn⁺, Sn⁺⁺ and Pb⁺ are directly field evaporated from the liquid surface, Pb⁺⁺ forms by the post-ionisation of Pb⁺. Moreover, our results for the Pb⁺⁺/Pb⁺ ratio are in excellent agreement with those of Komuro obtained with a pure lead LMIS. PACS 07.77.Ka; 33.15.Ta; 61.25.Mv     

An in-depth investigation into the temperature dependence of the mass spectra of an Au82Si18 liquid metal field emitter

The mass spectra of the beam emitted by a Au₈₂Si₁₈ eutectic molten metal ion source are investigated in detail as a function of emitter temperature. At the conclusion of the work it emerges that while Au⁺, Si⁺, and Si⁺⁺ are the result of direct field-evaporation from the liquid surface, Au⁺⁺ forms by the post-ionisation of Au⁺. Cluster ions are most probably the product of droplet break-up. PACS  07.77.Ka; 32.10.Bi; 61.25.Mv     

Investigation of a tin liquid metal ion source

In view of its importance in materials research, tin is a metal worth studying in a liquid metal ion source configuration, even if results complement or extend previous work. This is the more so if the new work corrects misconceptions of the past and adds to current thinking. We, therefore, prepared a Sn liquid metal ion source employing a Ni needle to anchor the liquid, cone-shaped, emitter. Source properties, such as the current–voltage curve, the mass spectra of the beam and the energy spread of the main ionic species, were studied in detail. The mass spectra show a considerable amount of Sn clusters, apart from the dominant species, Sn⁺ and Sn⁺⁺. The source was stable down to 1-A emission current, corresponding to an energy spread for the singly charged ions of 7 eV. Theoretical arguments, involving the peak energy deficit of the ion-energy distribution, strongly suggest that both Sn⁺ and Sn⁺⁺ are emitted by direct field evaporation from the liquid surface. The same conclusion is reached from a careful examination of the beam mass spectra of the source. PACS 07.77.Ka; 33.15.Ta; 61.25.Mv     

Surface-Radiative Modes and Longitudinal Excitons in the Spectra of Exciton–Polariton Luminescence

A cascade fiber-optic system that generates pulses of high spectral density by using the effect of nonlinear spectral compression is proposed. It is demonstrated that the shape of the pulse envelope substantially influences the degree of compression of its spectrum. In so doing, maximum compression is achieved for parabolic pulses. The cascade system includes an optical fiber exhibiting normal dispersion that decreases along the fiber length, thereby ensuring that the pulse envelope evolves toward a parabolic shape, along with diffraction gratings and a fiber spectral compressor. Based on computer simulation, we determined parameters of cascade elements leading to maximum spectral density of radiation originating from a subpicosecond laser pulse of medium energy.