Karakterizacija hitrostrjenih trakov zlitine Cu-Al-Ni z uporabo fokusiranega ionskega curka

This work investigates the possibilities for applying a focussed ion beam (FIB) for the metallographic preparation and characterization of Cu-Al-Ni melt-spun ribbons. Two alloys were selected for this reason: CuAl13Ni4 and CuAl15Ni4. The microstructure of the first alloy was fully martensitic and the microstructure of the second consisted of two phases: martensite and ▫$gamma_2$▫. It was discovered that with FIB-etching the microstructures of both alloys can be clearly revealed on polished cross-sections of the melt-spun ribbons, as well as on their wheel-side and air-side surfaces. However, better results were obtained when the etched surface was smoother, and finer details were visible when using smaller ion currents. In addition, a study was made into the influence of platinum deposition on the quality of 3D-cross sections. It was found that Pt-deposition is necessary when the edge of the trench should be straight and sharp, and the surface of the 3D cross-section smooth. However, in this case, the microstructure of the ribbons free surface cannot be seen.V tem delu smo raziskali mo.nosti uporabe fokusiranega ionskega curka (FIB) pri metalografski pripravi in karakterizaciji hitro strjenih zlitin Cu-Al- Ni. Izbrali smo dve zlitini: CuAl13Ni4 in CuAl15Ni4. Mikrostruktura prve zlitine je bila v celoti martenzitna, medtem ko je bila mikrostruktura druge zlitine sestavljena iz dveh faz: martenzita in ▫$gamma_2$▫. Ugotovljeno je bilo, da lahko pri jedkanju z ionskim curkom odkrijemo mikrostrukturo tako na poliranih prečnih prerezih trakov, kot tudi na obeh prostih površinah hitrostrjenih trakov. Mikrostruktura se je boljše odkrila, če je bila raziskana površina bolj gladka, medtem ko smo lahko razločili drobnejše mikrostrukturne sestavine pri uporabi manjših ionskih tokov. Poleg tega smo študirali tudi vpliv nanosa platine na kakovost 3D-prečnih prerezov. Ugotovili smo, da je nanos platine smiselno uporabiti, če želimo zelo ravne in ostre robove reza ter gladko površino prečnega reza, vendar pa v tem primeru ne moremo videti mikrostrukture proste površine

Neutron Halo Isomers in Stable Nuclei and their Possible Application for the Production of Low Energy, Pulsed, Polarized Neutron Beams of High Intensity and High Brilliance

We propose to search for neutron halo isomers populated via $\gamma$-capture in stable nuclei with mass numbers of about A=140-180 or A=40-60, where the $4s_{1/2}$ or $3s_{1/2}$ neutron shell model state reaches zero binding energy. These halo nuclei can be produced for the first time with new $\gamma$-beams of high intensity and small band width ($\le$ 0.1%) achievable via Compton back-scattering off brilliant electron beams thus offering a promising perspective to selectively populate these isomers with small separation energies of 1 eV to a few keV. Similar to single-neutron halo states for very light, extremely neutron-rich, radioactive nuclei \cite{hansen95,tanihata96,aumann00}, the low neutron separation energy and short-range nuclear force allows the neutron to tunnel far out into free space much beyond the nuclear core radius. This results in prolonged half lives of the isomers for the $\gamma$-decay back to the ground state in the 100 ps-$\mu$s range. Similar to the treatment of photodisintegration of the deuteron, the neutron release from the neutron halo isomer via a second, low-energy, intense photon beam has a known much larger cross section with a typical energy threshold behavior. In the second step, the neutrons can be released as a low-energy, pulsed, polarized neutron beam of high intensity and high brilliance, possibly being much superior to presently existing beams from reactors or spallation neutron sources.Comment: accepted for publication in Applied Physics

Production of Medical Radioisotopes with High Specific Activity in Photonuclear Reactions with γ\gamma Beams of High Intensity and Large Brilliance

We study the production of radioisotopes for nuclear medicine in $(\gamma,x{\rm n}+y{\rm p})$ photonuclear reactions or ($\gamma,\gamma'$) photoexcitation reactions with high flux [($10^{13}-10^{15}$)$\gamma$/s], small diameter $\sim (100 \, \mu$m$)^2$ and small band width ($\Delta E/E \approx 10^{-3}-10^{-4}$) $\gamma$ beams produced by Compton back-scattering of laser light from relativistic brilliant electron beams. We compare them to (ion,$x$n$+ y$p) reactions with (ion=p,d,$\alpha$) from particle accelerators like cyclotrons and (n,$\gamma$) or (n,f) reactions from nuclear reactors. For photonuclear reactions with a narrow $\gamma$ beam the energy deposition in the target can be managed by using a stack of thin target foils or wires, hence avoiding direct stopping of the Compton and pair electrons (positrons). $(\gamma,\gamma')$ isomer production via specially selected $\gamma$ cascades allows to produce high specific activity in multiple excitations, where no back-pumping of the isomer to the ground state occurs. We discuss in detail many specific radioisotopes for diagnostics and therapy applications. Photonuclear reactions with $\gamma$ beams allow to produce certain radioisotopes, e.g. $^{47}$Sc, $^{44}$Ti, $^{67}$Cu, $^{103}$Pd, $^{117m}$Sn, $^{169}$Er, $^{195m}$Pt or $^{225}$Ac, with higher specific activity and/or more economically than with classical methods. This will open the way for completely new clinical applications of radioisotopes. For example $^{195m}$Pt could be used to verify the patient's response to chemotherapy with platinum compounds before a complete treatment is performed. Also innovative isotopes like $^{47}$Sc, $^{67}$Cu and $^{225}$Ac could be produced for the first time in sufficient quantities for large-scale application in targeted radionuclide therapy.Comment: submitted to Appl. Phys.

Environmental effects of ozone depletion, UV radiation and interactions with climate change : UNEP Environmental Effects Assessment Panel, update 2017

Peer reviewe

Mechanical properties and related substructure of TiNi shape memory alloys

Vol. 5, C8 (1995): International Conference on Martensitic Transformations : ICOMAT 95, Lausanne, Switzerland, August 20-25, 1995The mechanical properties of binary near equiatomic TiNi shape memory alloys were investigated after different types of mechanical and heat treatments. The changes of deformation behaviour are explained on the basis of substructure differences after work hardening. The ''elastic moduli'' of both the high-temperature phase B2 and the martensite B19' as well as the ''easy stage of deformation'' are dependent on the work hardening intensity and these changes are related to the mobility of B2/B19' interfaces. The martensite changes its morphology after work hardening. In contrast to a twinned martensite, typical for annealed alloys, the internally slipped martensite was detected after work hardening

Physics of hydroxyapatite plasma coatings on TiNi shape memory materials

The microstructure of hydroxyapatite (HAP) ceramics coatings on TiNi shape memory alloy substrates was investigated. From the point of view of adherence, these coatings posses higher strength than approx. 30 MPa. The three levels of power input parameters were applied during the spraying process (55, 50 and 45 V). At lower voltage, the prepared HAP coatings contained pure Ca-10(PO4)(6)(OH)(2) with a Ca/P ratio of 1.65. At the highest voltage (55 V), the transition phase Ca-10(PO4)(6)(OH)(0.5)O-0.75 was detected. The observed good metal/ceramic interface strength is given by the formation of chemical bonding and by the energy dissipation due to stress induced martensite formation (SIM) and/or martensite reorientation (RE) during stressing the investigated composite

In-situ monitoring of internal oxidation of dillute alloys

This paper presents a non-destructive measurement method that enables identification and characterization of phenomena during internal oxidation of metallic materials as well as monitoring the kinetics of internal oxidation using "in-situ" electrical resistance measurements. A special laboratory device, based on the unique measurement cell, for the electrical resistance measurements at high temperatures and the model for electrical resistance transformation into an instantaneous microstructure were developed. To accomplish this, the process of internal oxidation was divided into the sequence of the key partial reactions that were presented in the model as the parallel andžor serial connected time variable resistors in the electrical circuit. The validity of the transformation model was experimentally confirmedby internal oxidation of Ag-Sn (2 at.% Sn) alloy at different oxidation temperatures in air atmosphere. The comparison of the results obtained by "in-situ" electrical resistance measurements with those obtained by metallographic analysis and Wagnerćs theory shows that the novel method presents a more effective tool for monitoring of internal oxidation kinetics. The method identifies also the microstructural defects and their influences onthe kinetics of internal oxidation

Physical-metallurgy properties of hydroxyapatite plasma coating on TiNi shape memory alloy

V práci je studována mikrostruktura hydroxylapatitového (HAP) keramického nástřiku na substrátu z tvarově paměťové slitiny TiNi. Současně. byla sledována i tzv. duplexní varianta typu TiNi/TiO2/TiO2+HAP/HAP. U nástřiku HAP je pevnost rozhraní TiNi/HAP vyšší než 30 MPa. V případě duplexního nástřiku je z hlediska pevnosti kritická smíšená oblast Ti02 + HAP. V některých případech zde bylo zjištěno porušení za nižšího napětí než 30 MPa. Vzhledem k možnosti dosáhnout vyšší spolehlivosti v pevnostní úrovni a vzhledem k jednodušší technologii byl preferován nástřik typu TiNi/HAP. Příznivou úroveň fázového rozhraní je možno spojit s disipací energie související se vznikem napěťově indukovaného martenzitu (SIM) a reorientací martenzitu (RE) během porušení. Velikost zrn nanášených částic HAPu ovlivňuje jak pórovitost, tak i rozvoj precipitačních procesů v keramickém nástřiku.Microstructure of plasma sprayed ceramic coatings on a TiNi shape memory alloy substrate was investigated. Hydroxyapatite (HAP) or so called "duplex" TiNi/TiO2/TiO2 + HAP/HAP coatings were applied. From the adherence point of view, the interface TiNi/HAP possesses higher strength than 30 MPa. In the case of duplex coating, the mixed TiO2 + HAP region was found as critical and the failure was detected at strength lower than 30 MPa in this region. Hence, the hydroxyapatite coating with higher strength reliability and relatively simple process technology was preferred. The observed favourable strength of metal/ceramic interface was attributed to the energy dissipation due to stress induced martensite formation (SIM) and/or martensite reorientation (RE) before and during a failure. Grain size of the deposited HAP particles influences porosity and precipitation processes in ceramics