Search results for "IRRADIATION"

EFFECTS OF GAMMA IRRADIATION ON THE ALFA TOCOPHEROL AND FATTY ACIDS CONTENT IN RAW UNPEELED ALMOND KERNELS (PRUNUS DULCIS)

2011

Fast and blister-free irradiation conditions for cross-linking of PMMA induced by 2MeV protons

2013

For soft lithography, the conventional negative tone resists, such as SU-8, that are used to create the mold have a number of drawbacks. PMMA, which is normally used as a positive tone resist, can be used as a negative resist by using high-fluence irradiation conditions. In this report, we outline optimization of the irradiation conditions for PMMA thin films using 2MeV H^+ ions to exploit their ability to work as a negative tone resist at ion fluences above 1.0x10^1^5ionscm^-^2. The main aim was to induce cross-linking while maintaining the exposed regions free of blisters and maintaining short irradiation times. We found that by using a two-step process with a low-flux irradiation, follow…

<title>Hardening in LiF, induced by fast Kr and Ni ions, and recovery of the structure and properties under annealing</title>

2005

The recovery of optical and mechanical properties of LiF crystals irradiated with 790 MeV 78Kr and 640 MeV 58Ni ions at 10l2 ions/cm2 under annealing at temperatures up to 810 K is investigated. The optical absorbance and depth profiles of hardness before and after annealing were measured. A marked recovery of hardness and change in the optical absorption spectra were observed at temperatures above 520-530 K. An activation energy of 0.15±0.02eV, which is close to that for the thermal migration of H centers, is obtained from the annealing data. The results indicate a significant role of the H-center aggregates in the hardening and annealing processes. The maximum hardening is created and the…

Irradiation effects on the OH-related infrared absorption band in synthetic wet silica.

2007

The effects of b-irradiation on the OH-related infrared (IR) absorption band in synthetic wet silica samples have been investigated by Fourier transform infrared spectroscopy. Depending on the accumulated doses, b-irradiation affects different zones of the IR composite band at about 3670 cm 1 , assigned to the OH stretching modes of silanol groups. These modifications are independent of the original OH content. The results are discussed considering possible radiation-induced changes of the silanol bonding configuration and of the glass network. These are monitored by revealing the IR band a 2260 cm 1 , which is related to the distribution of Si–O–Si bond angle. We have identified the existence of…

Modifications of optical absorption band of center in silica

2005

Abstract We report an experimental study of the modifications induced by gamma ray irradiation and by thermal treatment of both the electron paramagnetic resonance (EPR) and the optical absorption spectra of the E γ ′ center in silica. Our data show that the main g-values of E γ ′ EPR signal change as a function of the irradiation dose together with a red shift of the peak position of the absorption band around 5.8 eV attributed to the same center. Changes in the opposite direction are observed in both signals after thermal treatments. The peak position change of the optical absorption band is in quantitative agreement with the g-values shift. This strict correlation is evidence for the exi…

<title>Influence of radiation defects on exciton-magnon interactions in nickel oxide</title>

2005

Influence of radiation defects on the optical absorption spectrum of nickel oxide (NiO) was studied at 6 K in the near-IR energy range of 7750-8300 cm-1 corresponding to the magnetic-dipole transition 3A 2g(F )->3T 2g(F ) at nickel sites. NiO single crystals grown by the method of chemical transport reactions on the MgO(100) substrates were irradiated by the neutron fluences up to 5x1018 cm-2. Two sharp lines were observed at the low-energy side of the band: the peak at 7805 cm-1 is assigned to the pure exciton transition, whereas the peak at 7845 cm-1, to the exciton-magnon excitation that occurs at the Brillouin zone-center (BZC). An increase of the defect concentration at higher fluences…

An increased F2-laser damage in ‘wet’ silica glass due to atomic hydrogen: A new hydrogen-related E′-center

2006

Abstract A dramatic increase of F2-laser induced room temperature-stable point defects in ‘wet’ synthetic silica glass occurs when irradiation temperature is lowered to 80 K. Contrary to the predictions based on the established models of defect processes, a large part of defects induced at 80 K remains stable also at the room temperature. The intensities of the laser-induced optical absorption bands of the non-bridging oxygen hole centers (2.0 and 4.8 eV) and E′-centers (5.8 eV) are comparable to those created by neutron irradiation (1018 n/cm2). A growth of infrared absorption peak at 2237 cm−1 indicates creation of silicon hydride (SiH) groups. A study of irradiation dose dependences and …

Effects of high pressure thermal treatments in oxygen and helium atmospheres on amorphous silicon dioxide and its radiation hardness

2009

The effects of thermal treatments at similar to 400 degrees C in oxygen or helium atmospheres at similar to 180 baron the radiation hardness of amorphous SiO(2) are studied. The generation efficiency of several point defects under gamma irradiation is compared to that of the untreated material. All the effects on point defects generation here observed can be explained in terms of changes in the precursor sites. In particular it has been observed that the thermal treatments can change the precursors sites of point defects both through temperature and pressure related processes, not depending on the atmosphere, and through oxygen related processes creating oxygen excess sites. The presence of…

Optical properties of natural topaz

2013

The results of investigation of infrared, Raman and UV-Visible absorption spectra of natural topaz crystals from Ukraine before and after fast neutron irradiation are presented. We assume that the ~ 620 nm band in topaz crystals is associated with the presence of Cr 3+ , Fe 2+ and Mn 2+ impurities. The broad band with maxima at 650 cm -1 observed in Raman spectra for topaz irradiated by fast neutrons may be connected with lattice disorder. Exchange interaction between radiation defect and impurity ions during neutron irradiation leads to appearance of additional absorption band in UV-VIS spectra and bands broadening in infrared and Raman spectra of investigated crystals.

In-situ observation of beta-ray induced UV optical absorption in a-SiO2: radiation darkening and room temperature recovery

2006

International audience; We studied the optical absorption in the 3.0-6.2 eV range induced in bulk amorphous SiO2 by beta-ray irradiation up to similar to 1 MGy at room temperature. The induced absorption was measured in situ both during irradiation and in the post irradiation time. Our data evidence E', center as the main defect induced by irradiation and the partial decay of their absorption band at about 5.8 eV after irradiation. A quantitative analysis of the time evolution of the induced absorption shows that the transmission recovery observed after irradiation is compatible with the reaction of radiation-induced defects with H-related (H-2, H2O) species diffusing in the amorphous matrix