High-cycle fatigue tests with an evaluation of fatigue limit were carried out on large model components of bars with press fitted hubs of diameter 63/59
mm. Bars were made of three railway axle ...steels EA1N, EA4T and 34CrNiMo6 with considerable different strength from 586
MPa to 1041
MPa, respectively. Detection and measurement of crack growth under hubs by ultrasonic method was performed during the tests. In spite of the differences in strength and alloying of tested bars, differences in mean value of fatigue limit were not significant. This result was connected with specific damage mechanism and microcracks initiation under hubs with fretting effects. Short fatigue crack growth under hubs occurred at stress intensity factor range Δ
K considerably bellow threshold value Δ
K
th of long cracks. Simultaneous growth of main cracks from more than one point of surface circumferential area under hub was quite frequently observed.
Fabrics with metal threads were discovered in mediaeval well during excavations in the Mečová 2 Street in Brno. These are thin braids woven of metal threads using a small loom and sewed together into ...a broader strip. The textile materials are in a relatively good state, because the environment of the well preserved organic materials (fabrics, leather, wood). Furthermore, the positive effect of metal corrosion on the preservation of organic parts of the fabric occurred here. If metal threads are found in graves or dwelling backfills, only spiral-shaped metal fragments with microscopic relics of organic fibers are preserved. Based on microphotographs, we assume that metal threads were made by cutting or scissoring thin strips of metal sheets. The strips were spirally wound on a textile thread. The excavated fabric was deposited in a museum collection storage room for 20 years unnoticed, because its surface was covered with a layer of sediment and corrosion products. During the systematic research of mediaeval fabrics from Brno, it was found out that relics of gold are present in the ends of some of the threads. The fabrics were examined by non-destructive analytical methods. Metal threads covered with sediment and corrosion products were studied using X-ray fluorescence and radiography methods. The concentrations of elements in the individual layers show that the centre of the metal thread is formed by a silver strip. A thin layer of gold was laid on the silver strip. Silver was alloyed with copper, which corrosion products covered the whole metal strip and solidified the layer of sediments in the surface. XRF elemental mapping was employed to find out whether the metal threads pass through the whole braid. The results show that the braids are composed of silver threads with gold deposited on their rims and some central parts only.
•Mediaeval metal threads were investigated with non-invasive X-ray methods.•Gilding was identified on the outer side of the silver bands around the entire surface of metal threads.•Fire gilding with gold amalgam was disconfirmed due to the absence of mercury.
In this work we study the technological limits in the industrial scale growth of YAG:Ce by the Czochralski method in hydrogen-reducing atmosphere to speed-up its scintillation response using heavy ...codoping by magnesium. We present correlated experiments to characterize luminescence and scintillation properties focusing on light yield, scintillation decay incl. its rise time, and afterglow, and their dependence on magnesium content in the crystals. We show that an optimum amount of magnesium in combination with thermal treatment significantly improve the light yield, decrease afterglow and accelerate scintillation decay and its rise time.
•Major improvement of YAG:Ce scintillation performance on industrial scale is presented.•Doping by Mg2+ results in significant acceleration of the scintillation decay.•Simultaneously scintillation decay improved and light yield enhanced.
The RD48 (ROSE) collaboration has succeeded to develop radiation hard silicon detectors, capable to withstand the harsh hadron fluences in the tracking areas of LHC experiments. In order to reach ...this objective, a defect engineering technique was employed resulting in the development of Oxygen enriched FZ silicon (DOFZ), ensuring the necessary O-enrichment of about 2×10
17 O/cm
3 in the normal detector processing. Systematic investigations have been carried out on various standard and oxygenated silicon diodes with neutron, proton and pion irradiation up to a fluence of 5×10
14
cm
−2 (1
MeV neutron equivalent). Major focus is on the changes of the effective doping concentration (depletion voltage). Other aspects (reverse current, charge collection) are covered too and the appreciable benefits obtained with DOFZ silicon in radiation tolerance for charged hadrons are outlined. The results are reliably described by the “Hamburg model”: its application to LHC experimental conditions is shown, demonstrating the superiority of the defect engineered silicon. Microscopic aspects of damage effects are also discussed, including differences due to charged and neutral hadron irradiation.
Silicon as an unconventional detector in positron emission tomography Clinthorne, Neal; Brzezinski, Karol; Chesi, Enrico ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2013-Jan-01, Letnik:
699, Številka:
21
Journal Article
Recenzirano
Odprti dostop
Positron emission tomography (PET) is a widely used technique in medical imaging and in studying small animal models of human disease. In the conventional approach, the 511keV annihilation photons ...emitted from a patient or small animal are detected by a ring of scintillators such as LYSO read out by arrays of photodetectors. Although this has been successful in achieving ∼5mm FWHM spatial resolution in human studies and ∼1mm resolution in dedicated small animal instruments, there is interest in significantly improving these figures. Silicon, although its stopping power is modest for 511keV photons, offers a number of potential advantages over more conventional approaches including the potential for high intrinsic spatial resolution in 3D. To evaluate silicon in a variety of PET “magnifying glass” configurations, an instrument was constructed that consists of an outer partial-ring of PET scintillation detectors into which various arrangements of silicon detectors are inserted to emulate dual-ring or imaging probe geometries. Measurements using the test instrument demonstrated the capability of clearly resolving point sources of 22Na having a 1.5mm center-to-center spacing as well as the 1.2mm rods of a 18F-filled resolution phantom. Although many challenges remain, silicon has potential to become the PET detector of choice when spatial resolution is the primary consideration.
► We examine the use of position-sensitive silicon detectors in magnifying PET geometries. ► A demonstrator using silicon detectors and BGO scintillation detectors was constructed. ► Both single-slice and volume PET configurations were tested. ► For a 4.5cm field-of-view, resolutions <1mm were achievable. ► Resolution will improve further with higher resolution silicon detectors.
Characterization of 3D thermal neutron semiconductor detectors Uher, J.; Fröjdh, C.; Jakůbek, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2007, Letnik:
576, Številka:
1
Journal Article
Recenzirano
Neutron semiconductor detectors for neutron counting and neutron radiography have an increasing importance. Simple silicon neutron detectors are combination of a planar diode with a layer of an ...appropriate neutron converter such as
6LiF. These devices have limited detection efficiency of not more than 5%. The detection efficiency can be increased by creating a 3D microstructure of dips, trenches or pores in the detector and filling it with a neutron converter. The first results related to the development of such devices are presented. Silicon detectors were fabricated with pyramidal dips on the surface covered with
6LiF and then irradiated by thermal neutrons. Pulse height spectra of the energy deposited in the sensitive volume were compared with simulations. The detection efficiency of these devices was about 6.3%. Samples with different column sizes were fabricated to study the electrical properties of 3D structures. Charge collection efficiencies in silicon columns from 10 to 800
μm wide and 80–200
μm high were measured with alpha particles.
The neutron detection efficiency of a full 3D structure was simulated. The results indicate an increase in detection efficiency by a factor of 6 in comparison with a standard planar neutron detector.
Simulation indicates that PET image could be improved by upgrading a conventional ring with a probe placed close to the imaged object. In this paper, timing issues related to a PET probe using ...high-resistivity silicon as a detector material are addressed. The final probe will consist of several (four to eight) 1-mm thick layers of silicon detectors, segmented into 1 × 1 mm2 pads, each pad equivalent to an independent p + nn+ diode. A proper matching of events in silicon with events of the external ring can be achieved with a good timing resolution. To estimate the timing performance, measurements were performed on a simplified model probe, consisting of a single 1-mm thick detector with 256 square pads (1.4 mm side), coupled with two VATAGP7s, application-specific integrated circuits. The detector material and electronics are the same that will be used for the final probe. The model was exposed to 511 keV annihilation photons from an 22Na source, and a scintillator (LYSO)–PMT assembly was used as a timing reference. Results were compared with the simulation, consisting of four parts: (i) GEANT4 implemented realistic tracking of electrons excited by annihilation photon interactions in silicon, (ii) calculation of propagation of secondary ionisation (electron–hole pairs) in the sensor, (iii) estimation of the shape of the current pulse induced on surface electrodes and (iv) simulation of the first electronics stage. A very good agreement between the simulation and the measurements were found. Both indicate reliable performance of the final probe at timing windows down to 20 ns.
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