Search results for "IRRADIATION"
showing 10 items of 1012 documents
X-ray versus Ultraviolet Irradiation of Astrophysical Ice Analogs Leading to Formation of Complex Organic Molecules
2019
In astrochemistry, complex organic molecules (COMs) are defined as species with at least one C atom and six or more atoms in total. More than 70 COMs were detected toward various interstellar and c...
Numerical and Experimental Analysis of Convection Transfer During Melting by a Mono-Pulsed Laser
2010
This paper presents a comparison between simulation and experimental results of the melting process of metallic material by a pulsed laser source Nd-YAG. Variations of the thermophysical properties were considered. Furthermore, the model included the effects of the surface-tension gradient on the fluid surface and the buoyancy force. The keyhole effect induced strong surface deformations and often formed cavities, which arre undesirable in the surface treatment process. An experimental study of the surface profile of the melted zones was also conducted to seek a relationship between the so-called keyhole effect and the laser triangulation measurements. The predicted Laser Melted Zone (LMZ) …
A review of colour center and nanostructure creation in LiF under heavy ion irradiation
2015
A study of radiation damage in LiF crystals under irradiation with MeV–GeV energy ions, from 12C to 238U, at temperatures varying from 8 to 300 K, depending on the ion energy, energy loss and irradiation temperature, is presented. For light ions (12C, 14N) at low fluences, it is mainly color centers that are created. Increasing the fluence leads to the overlapping of tracks and the creation of more complex color centers, defect aggregates and dislocations. For ions with an energy loss above a threshold value (dE/dx = 10 keV nm−1) the tracks exhibit a central core damage region with a radius of 1–2 nm, surrounded by an extended halo which mainly contains single color centers. In this case, i…
X‐irradiation induced photo‐ and thermostimulated luminescence of CsCdF 3 :Mn crystals
2005
Photo- and thermostimulated luminescence (PSL and TSL respectively) of previously X-irradiated CsCdF3 crystal doped with Mn were investigated. After X-irradiation of CsCdF3 crystal at 8 K PSL bands at about 300 nm and 550 nm appear. Several stimulation bands can be revealed for luminescence at 300 nm and 550 nm. The stimulation band at 340 nm is related to an F-type centre absorption band in accordance with the Mollwo-Ivey relation for halide crystals. Subsequent heating of the crystal after X-irradiation at 8 K shows TSL peaks in the temperature regions 8 K – 90 K and 200 K – 300 K. The spectral composition of the TSL involves both bands at 300 nm and 550 nm. Experiments performed allow us…
Radiation defects in undoped and Nd‐doped LaGaO 3 crystals
2005
Radiation induced defects have been studied in undoped and Nd-doped (6 mol% and 12 mol%) LaGaO3 crystals. Wide absorption band (2.2–2.8 eV) was observed after crystal irradiation with X-rays at 300 K. Induced defects have been annealed in air at ∼450 K. Similar absorption band was observed in transient absorption spectra after ns-pulsed electron beam excitation. The radiation defect creation efficiency is higher in undoped LaGaO3 crystal. It is shown that small concentration of Nd-doping increases the LaGaO3 crystal radiation hardness. In transient absorption spectra along with 2.7 eV band the absorption bands at 1.5 eV and 2.2 eV were observed. The decay process of transient absorption has…
<title>Photostimulated recombination processes in x-irradiated CsCdF<formula><inf><roman>3</roman></inf></form…
2005
Fluoride crystals with the perovskite structure doped with rare-earth ions and other activators are interesting materials for laser hosts, scintillators, and detectors of ionizing radiation. Therefore, an actual task is to clarify the structure of the radiation-induced defects and recombination processes in these crystals. Compared to other fluoroperovskites, considerably less information is available concerning to the radiation-induced processes in the CsCdF3 crystals. We present a study of photostimulated luminescence (PSL) in the previously x-irradiated CsCdF3 crystal doped with Mn (0.05%). After the x-irradiation of the crystal, optical stimulation at 320 nm leads to the appearance of 3…
Photoluminescence excited by ArF and KrF lasers and optical absorption of stishovite mono-crystal
2008
Two photoluminescence bands were found in a stishovite (silicon dioxide) mono-crystal sample under ArF (193 nm) and KrF (248 nm) excitation. The blue band is situated at 3.17 ± 0.02 eV in the case of ArF and at 3 ± 0.2 in the case of KrF. The UV band is at 4.55 ± 0.05 eV in the case of ArF and at 4.5 ± 0.05 eV in the case of KrF. The position of the UV emission band correlates with that excited by x rays. This position is 4.6 ± 0.05 eV with FWHM 0.8 ± 0.05 eV (Truhins et al 2003 Solid State Commun. 127 415). The blue band possesses slow decay kinetics with time constant 16 ± 2 µs and the UV band is fast on the level of 2 ± 0.5 ns, similarly for both lasers. Thermal quenching of both bands b…
Annealing of Radiation Defects in X-Irradiated LiBaF3
2002
AbstractResults of application of the glow rate technique GRT for analysis of the activation energy of thermostimulated annealing of X-ray created F-type color centers in LiBaF3 crystals, pure and containing hetero-valence oxygen centers are presented. It is shown that depending on impurity composition in crystal two alternative mechanisms are involved in annealing of color centers. It is proposed that either the anion vacancy governed migration of F- centers resulting in recombination with complementary defects, or the thermal delocalization of radiation created fluorine (Fi) interstitials captured by anti-structure defects followed by recombination with all kinds of complementary F- type …
<title>Formation of dislocations and hardening of LiF crystals irradiated with energetic Au, Bi, Pb, and S ions</title>
2003
The irradiation of LiF crystals with Au, Pb, Bi, and S ions in the range of 400 - 2200 MeV leads to a remarkable increase of the hardness. The effect appears for Bi and Pb ions at fluences above 109 ions/cm2 and for S ions above 1010 ions/cm2. The increase of hardness follows the energy loss and is related to the formation of defects along the ion path. Defect complexes, clusters and aggregates with nanoscale dimensions serve as strong obstacles for dislocations and cause dispersion strengthening. Structural investigations reveal the generation of long-range stress in the adjacent non-irradiated part of the crystal. Close to the implantation zone, the stress exceeds the yield strength, caus…
Tracks induced in TeO2 by heavy ions at low velocities
2000
On the basis of its thermal properties, TeO2 crystal was selected as an insulator with low threshold electronic stopping power for track formation Set. The crystals were irradiated by S, Zn, Mo, Kr, Te and Pb ions and the optical absorption and track formation were studied. Comparison is made with the published results on LiNbO3 ,Y 3Fe5O12 and SiO2 quartz. Good quantitative agreement is found with the predictions of the thermal spike model of Szenes with respect to Set and the variation of the track size with the electronic stopping power Se. It is shown that TeO2 has a high eAciency g at low ion velocities, which is a characteristic feature of the damage cross-section velocity eAect. ” 200…