Nature of radiation resistance of LFS oxyorthosilicate crystals doped with Ce,Sc, Ca,and Y ions

Optical and luminescence characteristics of Lu_2+2ySi_1-yO_5+y (LFS) scintillation crystals are studied before and after irradiation with doses to 45 Mrad from a ⁶⁰Co source. LFS crystals were doped with Ce³⁺, Sc³⁺, Ca²⁺, and Y³⁺ ions with various concentrations. The dependence of the radiation resistance of LFS crystals on Ce ion concentration is detected. For the crystal of composition Ce:Sc:Ca:Y:LFS, it was found that its optical transmission (OT) and pulsed cathodoluminescence (PCL) spectra before irradiation do not differ from the spectra measured after irradiation with a dose of 45 Mrad within experimental error. The nature of the radiation resistance of rare-earth lutetium oxyorthosilicates (LFS) is discussed.     

Spectroscopic and thermal studies of gamma irradiated polypropylene polymer

Thin films of polypropylene have been irradiated with different doses of gamma radiation from a ⁶⁰Co source. IR, UV-VIS spectra of this polymer before and after irradiation have been recorded and from the spectral data some modifications in the properties have been investigated. The spectra indicated that polypropylene film was oxidised at the dose of 10⁶ Gy. Due to the removal of additives, total destruction of the polymer takes place at this dose. Isotactic arrangement of the polymer is no longer present after irradiation. Growth of carbon cluster takes place above a gamma dose of 10² Gy. Thermal stability of the polymer changes due to irradiation and the polymer seems to decompose in four different steps at the highest dose of 10⁶ Gy.     

Influence of 60Co gamma irradiation on the structural and optical properties of 2-aminopyridinium 4-nitrophenolate 4-nitrophenol crystals

In this article, effect of gamma irradiation on the structural and optical properties of 2-aminopyridinium 4-nitrophenolate 4-nitrophenol (2AP4N) has been reported. The grown crystals of 2AP4N were exposed to ⁶⁰Co gamma rays with a dose of 50 kGy and 100 kGy. The radiation-induced effects were analyzed using X-ray diffraction, FT-IR, UV–visible, photoluminescence techniques. The refractive index was determined using a long arm spectrometer. The structural properties of the pristine and irradiated crystals were studied using powder XRD. The peak intensity decrease after irradiation may be attributed to the formation of point defects. The UV visible study reveals that the energy gap has decreased after irradiation and then has increased for the higher dose. The intensity variation in the PL spectra is due to colour center mechanism. The SHG efficiency of 2AP4N crystals was found to be unaffected by gamma irradiation.     

Long-lived excited states and photoluminescence excitation spectra in single crystals of fullerene C60

Photoluminescence, optical absorption spectra, and photoluminescence excitation spectra were measured on large (2–3 mm), very pure crystals of fullerene C₆₀ at 5 K. It is shown that the main contribution to the photoluminescence of these crystals is from singlet and triplet excitons captured on crystal defects. The concentration of these defects does not exceed 10¹⁸ cm⁻²³, and the lifetime of triplet excitons on these defects is about 3 ms. It is shown that the symmetry distortion of the C₆₀ molecules at the defects is rather large and causes the oscillator strength of the zero-phonon optical transitions to be comparable to the most intense optical transitions with the participation of intramolecular vibrations. Zh. éksp. Teor. Fiz. 113, 734–746 (February 1998)     

Effect of irradiation on ethyl 2‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐3‐carboxylate: an ESR study

Ethyl 2‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐3‐carboxylate [C₁₁H₁₅NO₂S] was synthesized by the Gewald method. Its single crystals were grown from an alcohol/ethyl acetate solution at 15 °C and characterized using IR and ¹H‐NMR. These single crystals were irradiated for 72 h at 298 K by a ⁶⁰Co gamma source with a dose speed of 0.864 kGy/h. After irradiation, electron spin resonance (ESR) measurements were carried out to study radiation‐induced radicals in the temperature range from 120 to 450 K. Additionally, for the single crystal, ESR angular dependencies were measured in the xy, xz and yz planes of the substance. This irradiated single crystal was analyzed based on the ESR spectra. Analysis of the spectra revealed that the radical was formed by a C–H bond fission at the carbon end of the substance. It was also observed that the color of the sample changed after irradiation. The hyperfine and g parameters were determined from the experimental spectra. It was inferred from these results that the hyperfine parameters and g value exhibited anisotropic behavior. The average values of these parameters were calculated as follows: g = 2.0088, A_H1=H2 = 20.70 G, A_H3=H4 = 10.80 G, A_Ha = 4.59 G, A_Hb = 3.24 G and, A_N = 6.10 G. Copyright © 2011 John Wiley & Sons, Ltd.     

New radiation resistant scintillator LFS-3 for electromagnetic calorimeters

The results of the study of optical and luminescence characteristics of new LFS-3 heavy scintillation crystals are presented. Advantages of these crystals in comparison with conventional scintillators are discussed. The radiation resistance of LFS-3 scintillation crystals is studied using an intense ⁶⁰Co radioactive source and a proton beam with an energy of 155 MeV. No changes in the optical transmission of LFS-3 crystals after their irradiation with a dose of 23 Mrad are detected.     

Simulation of the xenon gamma spectrometer for analyzing radioactive materials

The results of the calculation of the detection efficiency of gamma-rays for the xenon gamma spectrometer (XGS) obtained using the GEANT4 Monte Carlo simulation are presented. The gamma spectra of the set of basic standard gamma-sources (OSGI) are analyzed for a real detector, and the calculated and actual detection efficiencies are compared. The XGS spectra are analyzed to determine the minimum concentration of the ¹⁵²Eu radio nuclide in the ¹³⁷Cs and ⁶⁰Co mixture. It is shown that the xenon gamma spectrometer is capable of detecting the isotope at concentrations above 40% in the mixture.     

Influence of the defect state of samples on the luminescence spectra of CdS single crystals irradiated by electrons

The photoluminescence spectra of CdS single crystals irradiated by electrons (E = 1.2 MeV, Φ = 2×10¹⁷ cm^?2) are investigated in the visible and near-infrared regions of electromagnetic radiation. Some samples of the CdS single crystals are preliminarily irradiated by neutrons (E = 2 MeV, Φ = 2 × 10¹⁸ cm^?2) with the aim of increasing the concentration of initial structural defects. From analyzing the peak intensities of photoluminescence in the irradiated single crystals at the wavelengths λ_m = 0.720, 1.030, and 0.605 μm, it is concluded that the CdS samples with a low concentration of structural defects in the initial state possess the highest resistance to electron radiation. It is assumed that the observed transformation of the photoluminescence spectra of the imperfect CdS single crystals subjected to electron irradiation is determined by either the mechanisms of subthreshold defect formation or the transformation of the defect complexes in elastic and electric fields near the large structural damages of the crystal lattice.     

Effect of cobalt-60 gamma irradiation on graphene: Raman and field emission investigations

Electrophoretically deposited graphene (HG) on silicon is irradiated using a cobalt-60 gamma radiation source with the radiation dose up to 22.7 kGy. The effect of gamma irradiation on the field emission current noise behavior of HG is investigated. The power spectra of pristine and irradiated HG exhibit 1/f^α type of noise, with α ～ 0.8. The magnitude of noise power is observed to increase with the radiation dose. The variations in the turn on field and noise power in the emission current are attributed to the structural modifications of HG, as revealed from the field emission scanning electron microscopic and Raman spectroscopic studies.     

Effets produits par l'irradiation avec des neutrons et avec des rayons gammas sur la série jaune et la série verte du spectre d'absorption excitonique de la cuprite

The effects of irradiations in a reactor and in a Cobalt 60 source on the green and yellow series of the excitonic absorption spectrum of cuprous oxide are studied. In the reactor irradiation experiments, the effects of fast neutrons are separately studied from those of thermal neutrons and of gamma rays. It is shown that the perturbations of the absorption spectra of Cu₂O by fast neutrons are very similar to those produced by an external electric field. They are also similar to those produced by quenching which creates probably internal strains. Charged defects occur probably in the crystal during bombardment and these charged defects produce an internal electric field and strains. It is not possible to study separately the effects of the electric field and the effects of strains. The electric field can be evaluated by comparison of its effects on the excitonic spectrum with those of an external field. An evaluation of the rate of creation of defects by fast neutrons in the crystal is deduced. It is also shown that the effects of gamma-rays are very different from those of fast neutrons. It is possible with gamma-ray irradiations to decrease residual internal fields which may exist in a crystal.     

Luminescence enhancement by gamma irradiation of nanocomposites for UV dosimetry devices

The aim of this work is to evaluate the influence of gamma radiation on a material constituted by a photonic complex used in a UV dosimetry device embedded in a polymeric composite with multiwalled carbon nanotubes (MWCNT). Films of CNT-free and MWCNT-containing composites were exposed to a gamma radiation beam of ⁶⁰Co. Characterization was performed by X-ray powder diffraction (XRD), thermogravimetric curves (TGA), and luminescence spectroscopy. The results indicate that the presented self-standing hybrid films show improvements to act as a better light conversion molecular device (LCMD) for UV dosimetry applications. Best results are attained after 50 kGy of gamma irradiation (⁶⁰Co) for CNT-free composites, and 5 kGy for MWCNT-containing films.     

Gamma-photon induced modifications in Polyvinylchloride (PVC) film

Gamma photon induced modifications in Polyvinylchloride (PVC) polymer have been studied in the dose range of 10¹-10⁶Gy at room temperature. Polyvinylchloride films have been irradiated with different doses of gamma radiation from a ⁶⁰Co source. To monitor the chemical and structural changes caused by gamma radiation IR and UV-Vis spectroscopy of pristine and irradiated PVC have been performed and using the spectral data some changes in the properties have been investigated. The spectral studies have indicated that at a dose of 10⁶Gy scissioning of the C-a bonds takes place. This scissioning of the chain initiates decomposition at a lower temperature. Thermal stability of the polymer reduces due to irradiation but the decomposition patterns remain the same. The optical band-gap is found to decrease due to irradiation at doses bigher than 10³Gy.     

Modification of Mössbauer reflection spectra of group AIIBVI single crystals with Fe<Superscript>57</Superscript> nuclei under influence of infrared radiation

Interaction of Mössbauer gamma radiation with ultrasound vibrations in group AIIBVI single crystals of CdS and CdSe with Fe⁵⁷ impurity nuclei under action of infrared radiation is investigated. It is shown that the infrared irradiation excites a phonon field in single crystals. Similar to the case of optical irradiation of single crystals the shape of their Mössbauer spectrum is modified. The effect of double modulation of resonant gamma radiation by infrared radiation has been observed.     

Thermoluminescent properties of a Li2O-B2O3-Al2O3 glass system doped with CaF2 and Mn

A Li₂O-B₂O₃-Al₂O₃ glass system doped with CaF₂ and Mn was synthesized by fusion and its physical properties were investigated using thermoluminescence (TL) and differential thermal analysis (DTA) techniques. The TL glow curve peaks, resulting from this analysis, are characteristic of metastable levels intrinsic to CaF₂ crystals that have undergone γ-ray irradiation from a colbalt-60 (⁶⁰Co) source. This provides evidence of CaF₂ crystal formation in the glass system. Furthermore, the TL glow peak at about 480 K was stable at room temperature, sensitive to ⁶⁰Co γ-rays and showed good linearity with doses ranging from 3 Gy to approximately 100 Gy, and consequently could be used to quantify radiation doses. High quality synthesis of these crystals permits control of their thermoluminescent properties.     

Multiwalled boron nitride microtubes (BNMTs) shielding in thermal neutron absorbing

In this study, multiwalled boron nitride microtubes (BNMTs) were synthesised from amorphous boron powder in pure nitrogen atmosphere controlled graphite furnace at 1300°C for 6?h with amorphous boron/manganese (IV) oxide (MnO₂) catalyst mass ratio of 1/1. It was found that the synthesised BNMTs outer diameters and the lengths vary between 0.68 and 1.57?µm and between 6.79 and 31.23?µm, respectively, by the scanning electron microscope analysis. The surface layer of AISI 1040 steel material was coated with multiwalled BNMTs at 950°C for 4?h in a foundry furnace. Transport phenomena of BNMT molecules on surfaces of the steel were considered by diffusion. Neutrons from obtained ²⁴¹Am-Be source were irradiated on the ⁵⁸Fe nuclei. The irradiation properties of the without and with BNMT coated steel materials were studied in the field of gamma emitted by ⁶⁰Co. The radiation exposure rate of gamma radiation sources used at 1099 and 1291?keV, respectively. The higher peak area was obtained in steel coated with BNMT according to non-coated steel from irradiation results of samples. These results show that BNMT coated steel was more capable for radiation shielding.     

Implementation of a preamplifier-amplifier system for radiation detectors used in Mössbauer spectroscopy

We report the assembly and testing of a preamplification and amplification system for pulses produced by gaseous radiation detectors commonly used in Mössbauer spectroscopy. The system is composed by a pair of commercial integrated circuits A203 and A206, which operate as charge sensitive preamplifier-shaping amplifier and linear amplifier-low level discriminator, respectively. The integrated circuits were interconnected in the unipolar output mode and placed inside a metallic shielding, which prevents noise amplification for a suitable signal-noise ratio. The system was tested by irradiating a proportional counter LND-45431 with characteristic X rays of 6.3 keV and gamma rays of 14.4 keV emitted by a Mössbauer radioactive source of ⁵⁷Co (Rh). Unipolar pulses with Gaussian profile were obtained at the output of the linear amplifier, whose amplitudes were close to 0.4 V for 6.3 keV X rays and 1.4 V for 14.4 keV gamma rays. Pulse height spectra showed that the system allows a satisfactory identification of the X-rays and gamma rays emitted by the ⁵⁷Co source, giving the possibility to make a good selection of the 14.4 keV peak for having a suitable signal-noise ratio in the Mössbauer spectra. Absorption percentages of 14 % were found by taking the Mössbauer spectra of a natural iron absorber. The assembly and tests of the system are presented through this paper.     

Radiation effect studies on some glycine derivatives in solid state

Five glycyl derivatives, glycyl-L-histidine, L-alanyl-glycine, glycine hydrochloride, gly-gly hydrochloride and, gly-gly-glycine in powder form were exposed to 20?kGy doses of ⁶⁰Co gamma radiation to study the effects of ionizing radiation. In these compounds, the paramagnetic centers formed after irradiation were attributed to the R─NHCH─?O^?OH, ?H₂CHNH, H₂NCH₂?O^?OHHCl, NH₂?HCONHCH₂COOHHCl and HNCH₂?O^?OH radicals, respectively. The effect of gamma irradiation to the radical structures and time stability of the radicals were investigated by EPR spectroscopy. The spectra were computer simulated and the hyperfine coupling constants were determined.     

Radiation-induced formation of ZnO nanoparticles on the ZnSe single-crystal surface

The possible formation of ZnO nanocrystals was studied as a result of radiolysis of a ZnSe crystal surface exposed to zinc vapor and irradiated with gamma rays and in producing ZnSe-ZnO heterostructures. Under ⁶⁰Co gamma radiation in air, nanocrystals ～27 nm in size are formed from nanoscopic ZnO nuclei. Under a mixed flux of gamma rays and thermal-neutron radiation, a twin structure is formed in the host ZnSe lattice and ZnO is removed. The oxide layer is also destroyed under proton irradiation in vacuum. It is found that the growth of ZnO nanocrystallites causes a manyfold increase in the luminescence intensity in the ～600-nm band and in microhardness and also a decrease in the resistance and blocking and threshold voltages irrespective of polarity. Thus, gamma irradiation brings about the formation of light-emitting ZnSe-ZnO: Zn semiconductor structures with a p-n junction.     

Investigation of photoradiation resistance of polystyrene scintillators in vacuum

Maximum permissible absorbed doses of ⁶⁰Co ionizing radiation were first measured in thin (1 mm) polystyrene scintillator samples at simultaneous irradiation by 0.01–1 Gy s^?1 gamma radiation and ～10¹⁶ cm² s^?1 light in vacuum. It was shown that photoradiation resistance (unlike radiation resistance) is not increased if samples are placed into vacuum and all other conditions are preserved the same. The process of formation in the polymer of unsaturated conjugated structures, whose fraction is independent of oxygen content and supply, is probably responsible for the loss of light yield.     

Thermoluminescence and dosimetric aspects of topaz from Yono Shigar mine in Pakistan

Topaz shows thermoluminescence (TL) on heating after exposure to ionising radiation. A study was carried out to explore the possibility to design and develop a TLD (thermoluminescence dosimeter) from locally occurring topaz. Topaz was collected from a mine in Yono Shigar valley in northern Pakistan. The samples were identified as topaz by neutron irradiation, X-ray diffraction and X-ray fluorescence. The crystals of topaz were cut into chips of dimensions compatible to the commercial TLD readers. The chips were exposed to ⁶⁰Co and/or ¹³⁷Cs gamma irradiators. The investigation features included glow curve, dose and energy responses, sensitivity, fading, reproducibility and mechanical stability. The TL glow curves revealed a stable peak at about 250 °C, whose height rose linearly with increase of irradiation dose. The TL response versus dose (calibration curve) showed the linear behaviour between 10^?2 and 10² Gy. The dose response was independent of gamma energies of ⁶⁰Co and ¹³⁷Cs. The response of topaz chips remained constant within 10% deviation from the initial value after 30 cycles of reuse. The rate of fading of topaz was very fast just after irradiation and slowed after a few days. Mechanical stability of the chips remained constant during handling in all investigation experiments. The topaz from Yono Shigar mine may be recommended as a TLD for gamma dose within 10^?2–10² Gy.