[en] Irradiation of a solution of maleic acid in 2-propanol with ⁶⁰Co gamma rays (doses 1 - 10 x 10²⁰ eV/ml) produced terebic acid (3-carboxy-4-hydroxy-4-methylvaleric acid lactone) with a chemical yield up to 76% and a G-value of 17.4. As a by-product diaterebic acid, the non-lactonic form of terebic acid, was found by means of paper chromatography with a G-value of up to 5.1. Using the same method low yields of a number of further acids were identified: fumaric, succinic, methylsuccinic, ethylsuccinic, isopropylsuccinic, and 1,2,3,4-cyclobutanetetracarboxylic acids. These compounds originated partly from the addition of products of 2-propanol radiolysis, i.e. the alkyl radicals, to the maleic acid and partly by isomerization and dimerization of this acid. Thus in this case maleic acid also behaves as a radical scavenger. The influence of maleic acid concentration, radiation doses, dose rate and temperature was also studied. The addition of benzophenone or ammonia decreases only partly the production of terebic acid, whereas the addition of tetrabromomethane or hydrogen bromide slightly increases the yield of this acid and suppresses the diaterebic acid completely. From these results it is possible to make a conclusion that, unlike similar non-chain photoaddition, radiation addition is a chain reaction with 3 to 6 chain transfers. The reaction probably proceeds by means of two different mechanisms, of which the first is a radical-chain mechanism and the second, which predominates anionic-chain mechanism. The influence of temperature is very complex. (author)

[en] Facilities for neutron activation analysis (NAA) at the Nuclear Physics Institute (NPI) are described. Applications and developments of NAA achieved at NPI within the last five years are briefly discussed. These involve geochemistry, mycogeochemistry, food and agriculture, archaeometry, certification of new reference materials, and methodological development of k₀-INAA. The purpose of NPI participation in the interlaboratory testing organized by the IAEA and the lessons learned are reviewed, and future plans are outlined. (author)

[en] At the Czech Metrology Institute (CMI) we have developed a precision modular sinewave generator for impedance ratio bridges. The generator was developed to improve previously available designs regarding amplitude and phase accuracy, linearity, absolute stability, stability of the ratio between two outputs and harmonic distortion. It generates up to 7 V_rms in a frequency range from 1 mHz up to 20 kHz, extendable to 100 kHz with small changes to the filters. The amplitude resolution is better than 0.01 μV V⁻¹ of full scale with an output voltage stability of 0.05 μV V⁻¹/30 min and a stability for the ratio between two outputs of 0.02 × 10⁻⁶ over several hours. The generator can be powered from internal batteries and is controlled via optically isolated connections. The internal clock and voltage references can be replaced by external ones, optically coupled in the case of the clock. In this paper, we discuss experimental results obtained with the generator used as a signal source in digital impedance bridges with relative combined uncertainties from 10^–5 down to 10^–8. The generators have been used in a bridge to drive a quantum Hall resistor in the AC regime. The use of a generator with an AC quantum voltmeter will also be discussed. The generator is not only applicable in the field of AC impedance metrology but also for on-site comparisons of AC quantum voltage standards or, in general, where there is a need for precision voltage sources. (paper)

[en] We employed NAA with radiochemical separation (RNAA) for determination of ultra-low levels of ²³²Th and ²³⁸U in copper for SuperNEMO experiment aimed at searching for neutrinoless double beta decay. The RNAA procedures are based on sample dissolution in nitric acid and separation of ²³³Pa and ²³⁸U with TRU resin and extraction with tributyl phosphate, respectively. After purification of the separated fractions we obtained limits of detection (LOD) of 0.08 μBq and 0.2 μBq for ²³²Th and ²³⁸U, respectively. The RNAA procedures developed can be used not only for radiopurity testing of materials for the detection of rare nuclear processes, but also for analysis of environmental materials after an easy adaptation of the decomposition step. NAA can also be used for determination of ¹²⁹I, a long-lived fission product, using neutron capture and measurement of ¹³⁰I. We developed NAA with both preirradiation separation (sample combustion followed by trapping of the released iodine in a LiOH solution) and post-irradiation, radiochemical separation (RNAA) using extraction of elementary iodine in CHCl₃. We employed this method for ¹²⁹I determination in bovine thyroid and other biomonitors collected in the vicinity of Temelin nuclear power plant to study whether releases of ¹²⁹I occur into the environment during normal operation of the NPP. Using the above described procedure we obtained a LOD of 1.68 μBq for measurement of ¹²⁹I.

[en] Mercury is an essential component of fluorescent lamps. Not all fluorescent lamps are recycled, resulting in contamination of the environment with toxic mercury, making measurement of the mercury mass used in fluorescent lamps important. Mercury mass measurement of lamps via instrumental neutron activation analysis (NAA) was tested under various conditions in the LVR-15 research reactor. Fluorescent lamps were irradiated in different positions in vertical irradiation channels and a horizontal channel in neutron fields with total fluence rates from 3×10⁸ cm⁻² s⁻¹ to 10¹⁴ cm⁻² s⁻¹. The ²⁰²Hg(n,γ)²⁰³Hg nuclear reaction was used for mercury mass evaluation. Activities of ²⁰³Hg and others induced radionuclides were measured via gamma spectrometry with an HPGe detector at various times after irradiation. Standards containing an Hg₂Cl₂ compound were used to determine mercury mass. Problems arise from the presence of elements with a large effective cross section in luminescent material (europium, antimony and gadolinium) and glass (boron). The paper describes optimization of the NAA procedure in the LVR-15 research reactor with particular attention to influence of neutron self-absorption in fluorescent lamps. - Highlights: • Mercury is an essential component of fluorescent lamps. • Fluorescent lamps were irradiated in neutron fields in research reactor. • ²⁰³Hg induced radionuclide activity was measured using gamma spectrometry. • Mercury mass in fluorescent lamps can be measured by neutron activation analysis.

[en] In a series of recent papers we have established a semiempirical model for quantum transport in a nanotransistor. Here we apply this model to characterize four industrial transistors with gate lengths ranging between 22 nm and 30 nm finding excellent quantitative agreement between theory and experiment. Adjusting our semiempirical model to the experimental output traces, three calibration parameters are found: First, the height of the source–drain barrier, second, the device temperature, and, third, the overlap parameter. The overlap parameter describes the wave function overlap between the source/drain contact and the conduction channel. With the aid of the calibration parameters the considered devices can be classified in three groups: A first group (G1) with good contact-channel coupling and a high saturation current, a second group (G2) with intermediate values and a third group (G3) with poor contact-channel coupling and a small saturation current. We calculate the gate capacitance of the transistors: At threshold voltage a peak of the gate capacitance is observed which is associated with a jump in the overlap parameter. This finding is most pronounced in G1, weaker in G2 and absent in G3. We attribute it to favorable screening conditions in G1 leading to a smooth transition between the contacts and the conduction channel. Our results indicate that this screening effect is favored by an efficient release of the Ohmic heat. - Highlights: • Semiempirical model for nano-scale field effect transistors • Quantitative description of seven experimental I-V-traces • Contact-channel coupling in transistor and peak in gate capacitance • Screening in the conduction channel of a nanoFET

[en] Knowledge of the content of natural radionuclides in bricks can be important in some cases in dosimetry and application of ionizing radiation. Dosimetry of naturally occurring radionuclides in matter (NORM) in general is one of them, the other one, related to radiation protection, is radon exposure evaluation, and finally, it is needed for the thermoluminescence (TL) dating method. The internal dose rate inside bricks is caused mostly by contributions of the natural radionuclides ²³⁸U, ²³²Th, radionuclides of their decay chains, and ⁴⁰K. The decay chain of ²³⁵U is usually much less important. The concentrations of ²³⁸U, ²³²Th and ⁴⁰K were measured by various methods, namely by gamma-ray spectrometry, X-ray fluorescence analysis (XRF), and neutron activation analysis (NAA) which was used as a reference method. These methods were compared from the point of view of accuracy, limit of detection (LOD), amount of sample needed and sample handling, time demands, and instrument availability. - Highlights: • Contents of naturally occurring radionuclides U, Th and K in bricks were determined. • Homogeneity was tested by neutron activation analysis and X-ray fluorescence analysis. • Distribution of particle size was evaluated after two types of grinding. • X-ray fluorescence appeared to be the least suitable for the determination. • Gamma-ray spectrometry can give results comparable to neutron activation analysis.

[en] An empirical multiorbital (spd) tight binding (TB) model including magnetism and spin–orbit coupling is applied to calculations of magnetic anisotropy energy (MAE) in CoPt L1₀ structure. A realistic Slater–Koster parametrisation for single-element transition metals is adapted for the ordered binary alloy. Spin magnetic moment and density of states are calculated using a full-potential linearised augmented plane-wave (LAPW) ab initio method and our TB code with different variants of the interatomic parameters. Detailed mutual comparison of this data allows for determination of a subset of the compound TB parameters tuning of which improves the agreement of the TB and LAPW results. MAE calculated as a function of band filling using the refined parameters is in broad agreement with ab initio data for all valence states and in quantitative agreement with ab initio and experimental data for the natural band filling. Our work provides a practical basis for further studies of relativistic magnetotransport anisotropies by means of local Green's function formalism which is directly compatible with our TB approach. - Highlights: • Calculations of electronic structure properties of bulk ordered CoPt alloy using tight-binding (TB) and density functional theory (DFT) approach. • Refinement of existing single-element TB parameters for a binary alloy based on a comparison of band structure and spin magnetic moment per atom to DFT results. • Quantitative agreement of magnetic anisotropy energy (MAE) obtained by TB and DFT on a range of band fillings. • Successful description of ground state spin–orbit coupling phenomena using an extended TB model suitable for subsequent magnetotransport simulations