Petr Alexa

0+ states and collective bands in 228Th studied by the (p,t) reaction

The excitation spectra in the deformed nucleus 228Th have been studied by means of the (p,t)-reaction, using the Q3D spectrograph facility at the Munich Tandem accelerator. The angular distributions of tritons were measured for about 110 excitations seen in the triton spectra up to 2.5 MeV. Firm 0+ assignments are made for 17 excited states by comparison of experimental angular distributions with the calculated ones using the CHUCK3 code. Assignments up to spin 6+ are made for other states. Sequences of states are selected which can be treated as rotational bands and as multiplets of excitations. Moments of inertia have been derived from these sequences, whose values may be considered as evidence of the two-phonon nature of most 0+ excitations. Experimental data are compared with interacting boson model and quasiparticle-phonon model calculations and with experimental data for 229Pa.

Size distributions of nanoparticles from magnetotactic bacteria as signatures of biologically controlled mineralization

Abstract This paper addresses the problem of magnetite nanoparticle size distributions in magnetotactic bacteria. The methods described in the paper can be used to determine the origin of natural magnetite nanoparticle samples. We analyzed 36 histograms related to bacterial, inorganic, and biomimetic nanoparticle sizes. Using statistical software we concluded that the size of the nanoparticles in cultured magnetotactic bacteria follows an extreme value distribution. Magnetite in uncultured samples can be treated as a two-component mixture containing extreme value and/or log-normally distributed nanoparticles. Analysis of the time-dependent formation of bacterial magnetite revealed that the magnetite size distribution transforms from the initial log-normal (young bacterial culture) through normal-like toward the extreme value distribution (evolved culture). It seems that at a certain moment during bacterial magnetite formation, the bacterial system starts to behave as a closed system. The closing of the system must be followed by another unknown process, because restriction of the nutrient supply into magnetosomes is insufficient for the generation of the extreme value distribution. Based on our analysis, approximately 50% of the magnetite particles in the martian meteorite ALH 84001 follow an extreme value distribution

Hypothetical superparamagnetic magnetometer in a pigeon’s upper beak probably does not work

We reanalysed the role of superparamagnetic magnetite clusters observed in a pigeon’s upper beak to decide if this matter can be a component of some sort of pigeon magnetometer for Earth orientation. We investigated the mutual interaction of the magnetite clusters induced by the geomagnetic field. The force sensitivity of the hypothetical magnetometer in a pigeon’s upper beak was estimated considering the previously presented threshold magnetic sensitivity of pigeons, measured in electrophysiological and behavioural investigations. The typical intercluster magnetic force seems to be 10−19N well above the threshold magnetic sensitivity. To strengthen our results, we measured the magnetic susceptibility of superparamagnetic magnetite using a vibrating sample magnetometer. Finally we performed theoretical kinematic analysis of the motion of magnetite clusters in cell plasma. The results indicate that magnetite clusters, constituted by superparamagnetic nanoparticles and observed in a pigeon’s upper beak, may not be a component of a measuring system providing the magnetic map.Graphical abstract

Alpha decay of221Rn and217Po; level structure of217Po and the213Pb ground state

Alpha recoil sources of221Rn were used to study the level structure of217Po and the ground state of213Pb. The half-life of217Po was measured to be (1.6±0.2) s. When combined with unpublished data, an alpha-decay hindrance factor (HF) of 1.3 was obtained for the alpha-decay, strongly suggesting a g9/2 → g9/2 transition between217Po and213Pb ground states. Alpha-gamma coincidence studies confirm the previously observed 11/2+ band head in217Po. It is suggested that an unobserved 9/2+ ground state lies below the 11/2+ state in217Po and an attempt is made to observe connecting links between these two parts of the217Po level scheme.

Short-term variations in 7Be wet deposition in the eastern part of the Czech Republic

Weighted multiple regression analysis was used to study the relationship between 7Be wet deposition and selected characteristics of rainfall events and concentrations of pollutants and 7Be in air for the first time. We sampled 24 individual rain events (September 2013–March 2014) and simultaneously collected relevant meteorological data. 7Be content in the collected water was determined by gamma spectrometry. A dominant negative correlation was observed between 7Be volume activity and rainfall amount. The influence of PM10 and PM2.5 concentrations and weekly values of 7Be volume activity in aerosols on 7Be volume activity in rainwater was found to be statistically insignificant.

Microscopic analysis of low-lying states in odd-A Tm isotopes

Low-lying states in odd-A 159–169Tm isotopes are analyzed in the framework of the quasiparticle-plus-phonon model (QPM) taking into account the coupling between the odd proton and RPA phonon vibrations of the even–even core of each odd-A isotope. For detail comparison of calculated energies of the low-lying states with corresponding experimental values the χ2 test is used. Model parameters are discussed within a broader context of other microscopic approaches for nuclear structure.

Opportunity to observe an M0 transition

It seems that the best opportunity to observe a low-energy 0+ ? 0? M0 transition would be in the most strongly octupole deformed nucleus 224Ac having the known 0? ground state and parity doublet bands with splittings of only ~7 keV. Based on the rigid rotor model fit to available experimental data a 0+ excited state at ~2 keV is suggested and possible mechanisms of the M0 transition to the ground state discussed.

Infrared thermographic measurement of the surface temperature and emissivity of glossy materials

Determination of the surface temperature and emissivity of glossy materials is a complicated task due to the relatively wide range of emissivity values and the reflection of infrared radiation from surrounding objects. As a consequence, standard methods used in infrared thermography are not applicable. In this article, an alternative method is proposed for the measurement of the surface temperature and emissivity of glossy materials used in the external structures of buildings that is based on an external source of thermal radiation. It is shown that the method gives quite accurate values of emissivity of both low- and high-emissivity glossy materials, whereas the surface temperature of low-emissivity glossy materials is less accurate and strongly depends on the accuracy of the used thermal camera.

GAMMA RADIOACTIVITY OF THE JANUARY 2013 RAINFALL IN OSTRAVA GAMA RADIOAKTIVITA DEŠTĚ V LEDNU 2013 V OSTRAVĚ

Abstract Gamma radioactivity of an 8 mm thick ice layer formed after a modest rain on 21 January 2013 in the VŠB-Technical University of Ostrava campus was analyzed and gamma-ray emissions from primordial 40K have been found. Cosmogenic 7Be produced mainly in galactic cosmic-ray spallation processes on atmospheric nitrogen and oxygen and 226Ra, 235U and 137Cs have been also observed. Abstrakt Při analýze gama radioaktivity 8 mm silné vrstvy ledu, která se vytvořila při dešťových srážkách v areálu VŠB-Technické univerzity Ostrava 21.1.2013, bylo detekováno gama záření z izotopu 40K. Rovněž bylo pozorováno kosmogenní 7Be vznikající především v tříštivých reakcích galaktického kosmického záření s atmosférickým dusíkem a kyslíkem a také 226Ra, 235U and 137Cs.

The First Test of the New Neutron Generator at the Všb / Technical University of Ostrava První Test Nového Neutronového Generátoru Na Všb-Tu Ostrava

Abstract The compact neutron generator MP320 (Thermo Scientific Inc.) operating on the principle of a deuterium-tritium reaction was tested before its planned application as the neutron source for the purpose of Fast Neutron Activation Analysis applications. Plates made from Al, Fe, Sn and Si were irradiated by a 14 MeV neutron beam and typical neutron induced reactions were identified. Abstrakt Kompaktní neutronový generátor MP320 (Thermo Scientific Inc.) pracující na principu deuterium-tritiové reakce byl testován před plánovaným využitím jako zdroj neutronů pro neutronovou aktivační analýzu pomocí rychlých neutronů. Destičky vyrobené z Al, Fe, Sn a Si byly ozářeny svazkem neutronů s energií 14 MeV a byly identifikovány reakce indukované neutrony typické pro uvedené prvky.