Effect of gamma ray irradiation on optical properties of Nd doped phosphate glass

The effect of gamma irradiation in the dose range of 5-500 kGy on the optical absorption and luminescence spectra of Nd doped phosphate glass is reported. The spectral absorption of this glass before and after gamma irradiation was measured in the spectral range 300-900 nm at room temperature using spectrophotometer and synchrotron beamline. Drastic increase in absorption was noted below 600 nm after gamma irradiation, which was dependent on the dose of irradiation. Additional absorption (AA) spectra of irradiated sample shows generation of two absorption bands below 600 nm, which finally became one very broad band peak with increased intensity at irradiation dose of 500 kGy. AA spectra also show the presence of negative peaks at the location of absorption peaks of Nd³⁺. Photoluminescence of Nd doped phosphate glass shows two strong bands which decreases to a very low intensity with a red shift after gamma irradiation. These results indicate that irradiation produces different kinds of defects in the glass material along with conversion of valence state of Nd³⁺ to Nd²⁺. This change was found irreversible at room temperature.     

Low and moderate dose gamma-irradiation and annealing impact on electronic and electrical properties of AlGaN/GaN high electron mobility transistors

To understand the effects of ⁶⁰Co gamma-irradiation, systematic studies were carried out on n-channel AlGaN/GaN high electron mobility transistors. Electrical testing, combined with electron beam-induced current measurements, was able to provide critical information on defects induced in the material as a result of gamma-irradiation. It was shown that at low gamma-irradiation doses, the minority carrier diffusion length in AlGaN/GaN exhibits an increase up to ～300?Gy. The observed effect is due to longer minority carrier (hole) life time in the material's valence band as a result of an internal electron irradiation by Compton electrons. However, for larger doses of gamma irradiation (above 400?Gy), deteriorations in transport properties and device characteristics were observed. This is consistent with the higher density of deep traps in the material's forbidden gap induced by a larger dose of gamma-irradiation. Moderate annealing of device structures at 200°C for 25?min resulted in partial recovery of transport properties and device performance.     

快重离子辐照对非晶态SiO2薄膜光致发光谱的影响

用湿氧化法在单晶硅表面生长了非晶态SiO2薄膜,再用高能Pb和Xe离子对薄膜进行辐照,最后用荧光光谱分析了辐照参数(剂量、电子能损值)与发光特性改变的相关性.研究发现,快重离子辐照能显著影响薄膜的发光特性,进一步分析显示,辐照导致了SiO2薄膜内O-Si-O缺陷、缺氧缺陷和非桥式氧空位缺陷的产生,且缺氧缺陷和非桥式氧空...     

Low dose 60Co gamma-irradiation effects on electronic carrier transport and DC characteristics of AlGaN/GaN high-electron-mobility transistors

The impact of internal irradiation with secondary Compton electrons, generated by gamma-photons, on the characteristics of III-N/GaN-based devices was explored. N-channel AlGaN/GaN high-electron-mobility transistors (HEMTs) were exposed to gamma-radiation from a ⁶⁰Co source for doses up to 600?Gy. Temperature-dependent electron beam-induced current (EBIC) was employed to measure minority carrier transport properties. For low doses below ～250?Gy, the minority carrier diffusion length in AlGaN/GaN HEMTs is shown to increase by about 40%. This increase is likely due to longer minority carrier lifetime induced by internal Compton electron irradiation. An associated decrease in activation energy, extracted from temperature-dependent EBIC, was also found. The obtained increase in transconductance and decrease in gate leakage current indicate an improvement in performance of the devices after low doses of irradiation. For high doses of gamma-irradiation, above ～300?Gy, the performance of HEMTs showed a deterioration. The deterioration results from the onset of increased carrier scattering due to additional radiation-induced defects, as is translated in a decrease of minority carrier diffusion length.     

TL and PTTL in natural fluorite previously irradiated with gamma rays and heavy ions

The effect of annealing temperature on the phototransfer thermoluminescence (PTTL) signal was studied to determine the appropriate annealing temperature for treating the natural powder before irradiation. The temperatures used to anneal virgin natural fluorite samples (only natural dose without giving the samples any artificial doses) were 150, 250, 350, 450, 550, 650 and 750°C for a duration of 1 h in each case. The results show that the PTTL response did not change for anneal temperatures up to 450°C, but at higher temperatures the signal decreased rapidly. The height of the 90°C peak decreased by two orders of magnitude as the anneal temperature increased from 450 to 750°C, whilst the height of the 180°C peak decreased by three orders of magnitude between the same two annealing temperatures. In order to investigate the effect of previous gamma rays and heavy ion irradiation on thermoluminescence (TL) and PTTL signals, powdered samples of natural fluorite from Cornwall, England, were annealed at 500°C and then irradiated (at GSI, Darmstadt, Germany) with ¹⁶¹Dy ions of energy 13 Mev/n; the range of fluences used was from 10⁴ to 10¹² ion cm⁻². Identical samples were given gamma doses in the range 1 Gy to 2.6 × 10⁴ Gy in order to compare the effects of gamma rays and heavy ions. The sensitivities of TL and PTTL were studied by giving the samples a gamma test dose of 1 Gy after annealing the samples at 500°C for 30 min in order to eliminate the TL resulting from previous gamma or heavy ion irradiation.     

Effect of processing temperature on the micro- and macro-interfacial properties of carbon fiber/epoxy composites

Three different temperature schemes were applied on carbon fiber/epoxy composite to elucidate the effect on interfacial shear strength (IFSS) and inter-laminar shear strength (ILSS). It showed that carbon fiber/epoxy IFSS was significantly influenced by the processing temperature, while ILSS was only slightly changed. Moreover, the mechanical properties revealed no necessary relationship between the micro- and macro-interfacial strengths with the properties of epoxy matrix. Among all the temperature schemes, Pro2 (the one-platform curing scheme with relatively rapid heating rate) produced highest IFSS and ILSS. Fourier transform infrared spectroscopy analysis demonstrated that the sizing agent can chemically react itself and also react with epoxy resin at temperature 180?°C. The resin rheological data showed that different temperature schemes can considerably impact diffusion behavior of the resin molecules. Hence, the highest interfacial strengths for Pro2 scheme were ascribed to large extent of chemical reactions and good inter-diffusion between components, at the interface region.     

In-phantom neutron dose distribution for bladder cancer cases treated with high-energy photons

This work presents an estimation of the neutron dose distribution for common bladder cancer cases treated with high-energy photons of 15 MV therapy accelerators. Neutron doses were measured in an Alderson phantom, using TLD 700 and 600 thermoluminescence dosimeters, resembling bladder cancer cases treated with high-energy photons from 15 MV LINAC and having a treatment plan using the four-field pelvic box technique. Thermal neutron dose distribution in the target area and the surrounding tissue was estimated. The sensitivity of all detectors for both gamma and neutrons was estimated and used for correction of the TL reading. TLD detectors were irradiated with a Co⁶⁰ gamma standard source and thermal neutrons at the irradiation facility of the National Institute for Standards (NIS). The TL to dose conversion factor was estimated in terms of both Co⁶⁰ neutron equivalent dose and thermal neutron dose. The dose distribution of photo-neutrons throughout each target was estimated and presented in three-dimensional charts and isodose curves. The distribution was found to be non-isotropic through the target. It varied from a minimum of 0.23 mSv/h to a maximum of 2.07 mSv/h at 6 cm off-axis. The mean neutron dose equivalent was found to be 0.63 mSv/h, which agrees with other published literature. The estimated average neutron equivalent to the bladder per administered therapeutic dose was found to be 0.39 mSv Gy^?1, which is also in good agreement with published literature. As a consequence of a complete therapeutic treatment of 50 Gy high-energy photons at 15 MV, the total thermal neutron equivalent dose to the abdomen was found to be about 0.012 Sv.     

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.     

Effect of halide ion concentration and irradiation dose dependent photostimulated luminescence investigation in the image screen phosphor CsBr1-xClx:Euy 2+

Photoluminescence(PL) characterization is carried out on CsBr_1-xCl_x:Eu_y²⁺ (x = 0.05, 0.1, 0.2, 0.3 y = 100 ppm, 200 ppm) crystals grown in vacuum with the Bridgman technique. PL studies show an increase in luminescence intensity with a decrease in bromide ion content. F(Br^–) and F(Cl^–) centers are formed due to -ray irradiation at room temperature. Photostimulated luminescence (PSL) emission is found to increase with an increase in irradiation dose from 7.5 Gy to 30 Gy at room temperature. From the results it is demonstrated that out of the different compositions studied, CsBr_0.9Cl_0.1:Eu²⁺ (200 ppm) phosphor has a linear PSL response with respect to irradiation dose.     

Relaxor properties and the mechanism of conduction in TlInS<Subscript>2</Subscript> crystals exposed to gamma irradiation

The density of states at the energy levels associated with radiation-induced defects, the localization length of a defect center, and the hopping distance of charge carriers are determined in a TlInS₂ crystal. It is demonstrated that, by varying the dose of gamma irradiation, it is possible to control the dielectric properties of ferroelectrics and to attain a stable relaxor state. In the temperature range of existence of this state, charge carriers execute tunneling from electron levels in the band gap through potential barriers created by an incommensurate superstructure of the TlInS₂ crystal.     

Effect of gamma irradiation on high temperature hardness of low-density polyethylene

Gamma irradiation can cause the change of microstructure and molecular structure of polymer, resulting in the change of mechanical properties of polymers. Using the hardness measurement, the effect of gamma irradiation on the high temperature hardness of low-density polyethylene (LDPE) was investigated. The gamma irradiation caused the increase in the melting point, the enthalpy of fusion, and the portion of crystallinity of LDPE. The Vickers hardness of the irradiated LDPE increases with increasing the irradiation dose, annealing temperature, and annealing time. The activation energy for the rate process controlling the reaction between defects linearly decreases with the irradiation dose. The process controlling the hardness evolution in LDPE is endothermic because LDPE is semi-crystalline.     

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.     

Gamma ray induced sensitization of 110°C TL peak in quartz separated from sand

We have investigated the gamma ray induced sensitization of the 110°C TL peak in quartz, separated from sand, in the dose range 30–750 Gy. A pre-dose of 100 Gy followed by annealing at 500°C for 1 h yielded an optimum sensitization factor of 14.2 for a test gamma dose of 0.5 Gy; this factor decreases slowly up to the studied pre-gamma dose of 750 Gy. From ESR studies carried out in the temperature range 25–550°C, the formation of E′₁-centres and their subsequent decay (at temperatures >400°C) have been observed. The released charge carriers (electrons) may lead to elimination of competitors (as a result of their filling up). Thus, the radiation-induced sensitization of the 110°C TL peak could be due to elimination of the competing deep traps.     

Optical and electron beam studies of gamma-irradiated AlGaN/GaN high-electron-mobility transistors

The impact of ⁶⁰Co gamma-irradiation on n-channel AlGaN/GaN high-electron-mobility transistors was studied by means of temperature-dependent electron beam-induced current (EBIC) and cathodoluminescence (CL) techniques. For the doses up to ～250?Gy, an enhancement of minority carrier transport was observed as evident from the EBIC measurements. This enhancement is associated with internal electron irradiation induced by the primary gamma photons. For the doses above ～250?Gy, deterioration in minority carrier transport was explained by carrier scattering on radiation-induced defects. It is shown that calculated activation energy from the EBIC and CL measurements follows exactly the same trend, which implies that the same underlying phenomenon is responsible for observed findings.     

Structural and optical investigation of nonpolar α-plane GaN grown by metalben organic chemical vapour deposition on r-plane sapphire by neutron irradiation

Nonpolar (1120) α-plane GaN films are grown by metal-organic chemical vapour deposition (MOCVD) on r-plane (1102) sapphire. The samples are irradiated with neutrons under a dose of 1 × 10¹⁵ cm^-2. The surface morphology, the crystal defects and the optical properties of the samples before and after irradiation are analysed using atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD) and photoluminescence (PL). The AFM result shows deteriorated sample surface after the irradiation. Careful fitting of the XRD rocking curve is carried out to obtain the Lorentzian weight fraction. Broadening due to Lorentzian type is more obvious in the as-grown sample compared with that of the irradiated sample, indicating that more point defects appear in the irradiated sample. The variations of line width and intensity of the PL band edge emission peak are consistent with the XRD results. The activation energy decreases from 82.5 meV to 29.9 meV after irradiation by neutron.     

Thermoluminescence Kinetic Parameters of TLD-600 and TLD-700 after ~(252)Cf Neutron+Gamma and ~(90)Sr-~(90)Y Beta Radiations

The thermoluminescent(TL) properties such as glow curve structure, relative thermoluminescence sensitivity,dose response linearity of lithium fluoride thermoluminescent dosimeters 6 LiF:Ti,Mg(TLD-600) and 7 LiF:Ti,Mg(TLD-700) are investigated after irradiation ~(252)Cf neutron+gamma and ~(90)Sr-~(90)Y beta sources at room temperature and then the obtained results are compared. The kinetic parameters, namely the order of kinetics b,activation energy Ea and the frequency factor s,are calculated using the computerized glow curve deconvolution(CGCD) program. The effect of heating rate on the glow curves of dosimeters is also investigated. The maximum TL peak intensities and the total area under the glow curves decrease with the increasing heating rate. There is no agreement with the kinetic parameters calculated by the CGCD program for both radiation sources.     

Gamma effect on track properties of PADC detector

Effect of high gamma irradiation on track properties of PADC (Homalite) has been studied in the dose range of 10¹–10⁶ Gy. The properties like bulk-etch rates and track-etch rates of the detector are found to increase due to gamma exposure. Etching efficiency of the detector increases due to exposure and it is significant at the dose higher than 10³ Gy. Another track property, the critical angle, is also influenced by gamma exposure and is found to decrease with increasing dose. In all cases it is observed that the post-gamma exposure has greater effect than the pre-gamma exposure. The experimental results are presented and discussed in details.     

Structural,electrical and optical properties of gamma irradiated methyl para-hydroxy benzoate single crystals

ABSTRACT

Nonlinear optical materials (NLO) have been garnering attention due to their role in optical data storage, optical communication and laser technology. Organic crystals have emerged as an extremely important class of NLO materials, since their NLO properties compare very well with traditional inorganic NLO materials like KCl, LiNbO₃, KDP (potassium dihydrogen phosphate), etc. They offer the additional advantage that they can be grown relatively inexpensively from solution close to room temperature, unlike the inorganic NLO materials which are grown from high temperature melts. In the present work, organic transparent single crystals of methyl para-hydroxy benzoate (MHB) were grown by slow evaporation solution growth technique (SEST) from aqueous solution at room temperature. The changes in structural, electrical and optical properties of gamma irradiated MHB single crystals were studied using X-ray diffraction (XRD), UV–Visible absorption spectroscopy, Photo-luminescence (PL), Fourier transform infrared (FTIR) spectroscopy and AC conductivity measurements at room temperature. The polished MHB single crystals were irradiated with gamma rays of doses 10 and 15 kilogray (kGy). From the XRD analysis, it was observed that gamma irradiation for these doses drastically decreases the crystallinity. The optical absorption constants were examined by UV-Visible absorption spectroscopy, measured over the wavelength range of 200–800?nm, at normal incidence. The optical band gap as estimated from the Tauc plot ((αhν)² vs hν) was found to be reduced with increasing gamma irradiation doses. PL spectra showed emission at wavelengths of 361?nm (3.43?eV) and 452?nm (2.74?eV), with enhanced intensities for the irradiated crystals. FTIR spectroscopy was utilised to identify the functional groups of MHB and indicated the rupture of specific types of bonds with gamma irradiation. Apart from that, the enhancement of AC conductivity with gamma irradiation was also observed for the gamma irradiated crystals.     

Defects generated by irradiation with gamma rays in lead doped KCl–KBr mixed single crystals

In this work we report the behavior of solid solutions of lead-doped KCl–KBr mixed single crystals subjected to gamma irradiation. Various composition of KCl_1−xBr_x (x=0.02, 0.35, 0.50, 0.65, 0.85) doped with 20–40 ppm of Pb²⁺ were used and exposed to ionizing radiation. The defect production seems to be correlated with the observed increasing integrated thermoluminescence glow curve as a function of irradiation at high 10 kGy dose as well as in the low 2.2–130 dose Gy range. The analysis shows the potential use of these mixed crystals as radiation detector. The defects generated by irradiation were monitored by the optical absorption spectrum and the thermally stimulated luminescence.     

Study of neutron irradiation effect on Morin transition in hematite

It is established by Mössbauer spectroscopy and slow neutron diffraction that temperature range of Morin transition in hematite changes depending on neutron irradiation dose, and above some critical values the transition is not observed at all. A fraction of iron ions with high-temperature orientation of moments which cause the sample weak-ferromagnetic characteristics decreases with temperature fall but does not disappear completely, and near 4 K it even rises. It is established that radiation defects causing the changes in Morin transition disappear at annealing of hematite on air at temperatures of 400–500 K.