Irradiated Polymethylmethacrylate Research Articles

Interaction of Polymethyl Methacrylate with Boehmite-Filmed Aluminum Cladding Under Gamma Irradiation

This paper presents an overview of ongoing work to qualify the Advanced Test Reactor (ATR) driver fuel elements that have been affected by irradiation-degraded polymethyl methacrylate (PMMA) flux wands. Irradiation testing was performed on PMMA material in contact with aluminum clad material. The cladding was prefilmed with a boehmite oxide layer, an important feature of the ATR driver fuel. The effects on the boehmite layer due to gamma irradiation of the PMMA-aluminum clad system were investigated. PMMA embrittlement, followed by softening and degradation, occurred at high radiation levels. Adhesion between the cladding and irradiated PMMA was observed. Flow testing at prototypic ATR flow rates demonstrated the effective removal of the adhered material. Measurements of the boehmite layer thickness were performed, and Raman spectroscopy was utilized to detect the presence of boehmite in the irradiated PMMA material.

Incident beam current impact on space-charge retention in electron dynamitron irradiated polymethyl methacrylate

Dielectric charging aboard spacecraft and satellites is a persistent and pressing issue in materials design and applications. This study investigated the effect of electron irradiation on charge trapping and leakage properties in polymethyl methacrylate, which is necessary for determining the maximum permissible fluence of radiation before the material is pushed beyond its breakdown threshold in charged particle radiation-intense environments. It was observed that dielectric breakdown in the form of an electrostatic discharge event cannot be induced under the conditions of this experiment after an amount of time that is dependent on initial electron fluence. This time limit for which an electrostatic discharge can be induced was found to be longer for the lower beam current irradiations. The work presented here discusses the factors affecting charge leakage using a global electric field-driven model.

Feasibility of triple gamma ray imaging of 10C for range verification in ion therapy

Objective. In carbon ion therapy, the visualization of the range of incident particles in a patient body is important for treatment verification. In-beam positron emission tomography (PET) imaging is one of the methods to verify the treatment in ion therapy due to the high quality of PET images. We have shown the feasibility of in-beam PET imaging of radioactive 15O and 11C ion beams for range verification using our OpenPET system. Recently, we developed a whole gamma imager (WGI) that can simultaneously work as PET, single gamma ray and triple gamma ray imaging. The WGI has high potential to detect the location of 10C, which emits positrons with a simultaneous gamma ray of 718 keV, within the patient’s body during ion therapy. Approach. In this work, we focus on investigating the performance of WGI for 10C imaging and its feasibility for range verification in carbon ion therapy. First, the performance of the WGI was studied to image a 10C point source using the Geant4 toolkit. Then, the feasibility of WGI was investigated for an irradiated polymethyl methacrylate (PMMA) phantom with a 10C ion beam at the carbon therapy facility of the Heavy Ion Medical Accelerator in Chiba. Main results. The average spatial resolution and sensitivity for the simulated 10C point source at the centre of the field of view were 5.5 mm FWHM and 0.010%, respectively. The depth dose of the 10C ion beam was measured, and the triple gamma image of 10C nuclides for an irradiated PMMA phantom was obtained by applying a simple back projection to the detected triple gammas. Significance. The shift between Bragg peak position and position of the peak of the triple gamma image in an irradiated PMMA phantom was 2.8 ± 0.8 mm, which demonstrates the capability of triple gamma imaging using WGI for range verification of 10C ion beams.

Spectroscopic Investigations of Optical Bandgap and Search for Reaction Mechanism Chemistry Due to γ-Rays Irradiated PMMA Polymer

Radiation damage and the product formation chemistry in Polymethyl methacrylate (PMMA) due to γ-irradiation have been studied by SEM, XRD, FTIR, and UV-Vis spectroscopy. Co-60 gamma source with a dose rate of 1.707 kGy/hr has been used for irradiation to a total 570 kGy dose. No significant changes in morphology upon such irradiation. Crystallinity decreases at a lower dose and then increases for a higher dose. Crosslinking dominates at lower doses, and chain scission overwhelms at higher doses in the irradiated polymer. Two isosbestic points are formed, and the absorption maxima shift towards a higher wavelength. The optical bandgap energy decreases with the addition of radiation dose. A new FTIR peak at 1638 cm-1 appeared, suggesting the formation of an unsaturation center in the irradiated polymer. Up to a dose of 409 kGy, FTIR absorption peak intensity increases and decreases with further irradiation.

Influence of momentum acceptance on range monitoring of 11C and 15O ion beams using in-beam PET

In heavy-ion therapy, the stopping position of primary ions in tumours needs to be monitored for effective treatment and to prevent overdose exposure to normal tissues. Positron-emitting ion beams, such as 11C and 15O, have been suggested for range verification in heavy-ion therapy using in-beam positron emission tomography (PET) imaging, which offers the capability of visualizing the ion stopping position with a high signal-to-noise ratio. We have previously demonstrated the feasibility of in-beam PET imaging for the range verification of 11C and 15O ion beams and observed a slight shift between the beam stopping position and the dose peak position in simulations, depending on the initial beam energy spread. In this study, we focused on the experimental confirmation of the shift between the Bragg peak position and the position of the maximum detected positron-emitting fragments via a PET system for positron-emitting ion beams of 11C (210 MeV u−1) and 15O (312 MeV u−1) with momentum acceptances of 5% and 0.5%. For this purpose, we measured the depth doses and performed in-beam PET imaging using a polymethyl methacrylate (PMMA) phantom for both beams with different momentum acceptances. The shifts between the Bragg peak position and the PET peak position in an irradiated PMMA phantom for the 15O ion beams were 1.8 mm and 0.3 mm for momentum acceptances of 5% and 0.5%, respectively. The shifts between the positions of two peaks for the 11C ion beam were 2.1 mm and 0.1 mm for momentum acceptances of 5% and 0.5%, respectively. We observed larger shifts between the Bragg peak and the PET peak positions for a momentum acceptance of 5% for both beams, which is consistent with the simulation results reported in our previous study. The biological doses were also estimated from the calculated relative biological effectiveness (RBE) values using a modified microdosimetric kinetic model (mMKM) and Monte Carlo simulation. Beams with a momentum acceptance of 5% should be used with caution for therapeutic applications to avoid extra dose to normal tissues beyond the tumour when the dose distal fall-off is located beyond the treatment volume.

Photoluminescence and reflectivity studies of high energy light ions irradiated polymethyl methacrylate films

The self-standing films of non-conducting polymethyl methacrylate (PMMA) were irradiated in vacuum using high energy light ions (HELIs) of 50 MeV Lithium (Li+3) and 80 MeV Carbon (C+5) at various ion dose to induce the optical changes in the films. Upon HELI irradiation, films exhibit a significant enhancement in optical reflectivity at the highest dose. Interestingly, the photoluminescence (PL) emission band with green light at (514.5 nm) shows a noticeable increase in the intensity with increasing ion dose for both ions. However, the rate of increase in PL intensity is different for both HELI and can be correlated with the linear energy transfer by these ions in the films. Origin of PL is attributed to the formation of carbon cluster and hydrogenated amorphous carbon in the polymer films. HAC clusters act as PL active centres with optical reflectivity. Most of the harmful radiation like UV are absorbed by the material and is becoming opaque after irradiation and this PL active material are useful in fabrication of optoelectronic devices, UV-filter, back-lit components in liquid crystal display systems, micro-components for integrate optical circuits, diffractive elements, advanced materials and are also applicable to the post irradiation laser treatment by means of ion irradiation.

Thermally stimulated currents depolarization study of gamma ray irradiated PMMA

ABSTRACTWe will investigate the effect of γ-irradiation on the polymethyl methacrylate (PMMA) properties. The Fourier transform infrared spectroscopy technique in attenuated total reflexion mode (FTIR-ATR) results allowed us to show that the irradiated PMMA undergoes a scission in its lateral chain combined to an oxidation phenomenon. In fact, a decrease in the carbonyl index, versus the radiation dose, is observed. The differential scanning calorimetry and the thermostimulated depolarization currents revealed that the scission in the lateral chain provides a better flexibility to the PMMA chain and an increase in the free volume of the material. The consequences of these phenomena appear in the decrease of the activation energy of PMMA and the appearance of a local order in the material at a temperature Tc which decreases versus the radiation dose.

Ion Etching Induced Surface Patterns of Blend Polymer (Poly Ethylene Glycol – Poly Methyl Methacrylate) Irradiated with Gamma Rays

Abstract The pattern surface structure of a thin blend polymer film of Poly methyl methacrylate (PMMA) – Poly ethylene glycol (PEG) induced by Ar+ ion etching (5 keV) has been investigated by scanning electron microscopy. Blend polymer films have been obtained consisting of a hydrophilic PEG and a hydrophobic PMMA distributed in co-continuous phases. Four different compositions of the two polymers are dissolved in chloroform and irradiated with gamma rays (60Co) at 20 kGy to produce transparent films of blend polymer PMMA-PEG after casting. Self-assembled of PMMA-PEG film is obtained because of the high contrast between the two polymers. Ion-polymer interaction with a hydrophilic polymer (Ar+ +PEG) rather than the high etch resistance of hydrophobic polymer (Ar+ −PMMA) was observed. The results are discussed in terms of significant destruction of bonds in the blend polymer films as a result of which one polymer undergoes rapid dissociation rather than the other one. This means that etching with Ar+ ions of the PMMA domains are stable and PEG can be selective. The ATR-FTIR spectrum shows the absence of hydrogen bonds and XRD/DSC curves show the crystanility of PMMA depending on the PEG contents and gamma radiation effect, irradiated blend polymer PMMA/PEG has shown more resistant at thermal degradation than irradiated PMMA. This indicates that the PEG contents have an effect on the thermal stability of PMMA/PEG as detected by TGA. Finally, the pattern surface of irradiated blend polymer (PMMA-2%PEG) was plated with two coaxial layers subsequently of copper (Cu) and silver (Ag) using sputter technique.

High energy (MeV) ion fluence dependent nano scale free volume defects studies of PMMA films

A systematic study on the dependence of the free volume at nanoscale in carbon ions irradiated polymethylmethacrylate polymer samples was carried out by means of positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy (DBS). An investigation about the evolution of cross-linking in the polymeric chains after ion irradiation was carried out from the calculated values of hole radius, free volume and fractional free volume using Tao-Eldrup Model. The role of rise in temperature on the growth of free volume was observed at higher fluences. The results were supported by variations in the S parameter of DBS study. The structural analyses were carried out using XRD to investigate for the modification in the structural nature, degree of crystallinity and average crystallite size of the polymer after ion irradiation. Additional information on the modifications of optical and chemical properties was extracted by means of UV–visible and FTIR spectroscopy respectively.

Experimental characterisation of charge distribution and transport in electron irradiated PMMA

For studying the space charge distribution and transport in poly-methyl-methacrylate (PMMA) polymer material, the specimens were submitted to electron irradiation using a scanning electron microscope (SEM). An arrangement adapted to the SEM for measuring the leakage and displacement currents have been used. Measurements help in estimating the charge quantity and studying trapping processes during and after the electron irradiation. The properties of the dynamic trapping of PMMA and the time constants of charge processes were evaluated. Many physical processes are involved in the charging and discharging mechanisms; among them surface conduction is outlined. The effective resistivity of the sample is measured and compared with that of classic and standardized methods. The strength of the electric field initiating surface discharge is also estimated.

Physical and chemical response of 145 MeV Ne6+ ion irradiated polymethylmethacrylate (PMMA) polymer

Characterization of ion induced modifications in the physical, chemical and structural properties of polymethylmethacrylate (PMMA) polymer induced by 145MeV Ne6+ ions has been carried out by FTIR, UV–Visible, Differential scanning calorimetry (DSC) and X-ray diffraction. Heavy ion irradiation was carried out under a vacuum of ∼10−6 torr at Variable Energy Cyclotron Centre, Kolkata, India using a low beam current (∼15nA). Ion fluences of 1010, 1011, 1012, 1013 ions/cm2 were used. The optical band gap (Eg), calculated from the absorption edge of the UV–Vis spectra of these films in 200–800nm region varied from 2.167eV to 1.512eV for virgin and irradiated samples. In FTIR spectra appreciable changes have been observed after irradiation, indicating the molecular fragmentation, cross-linking, formation of unsaturated groups and free radicals. DSC thermograms give information about the thermal stability and type of thermal reactions (exothermic/endothermic) on the application of heat to the polymer. XRD analyses show slight shift of peak position and significant changes in peak intensity. XRD results show a decrease of ∼4.12% in crystallite size of irradiated sample at the higher fluence of 1012 ions/cm2.

Commentary: Nano- and micromachining using laser plasma soft X-rays

Investigating interactions of intense soft X-rays with solid surfaces and resulting phenomena is still challenging. One could expect material removal from the surfaces (ablation) caused by soft X-ray irradiation at a precision as high as the diffraction limit of the soft X-rays. The X-ray ablation technique could enable us to fabricate nano- and micro-structures on sufaces of even transparent materials such as silica glass, polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS), which are highly valued for their use in the fields of nanometric chemical analysis and chemical reactions in medicine and biotechnology. For machining at high resolution, light with a short wavelength is preferable because of the diffraction limit. In the X-ray region, however, most of the materials have less optical absorption at shorter wavelengths, resulting in no energy transfer of the light to the materials, that is, no ablation. Therefore, photons in the range of 100 eV–1 keV are suitable for micromachining. So far, synchrotrons have been utilized for extensive studies on interaction of soft X-rays with inorganic materals such as silica glass. However, silica surfaces are etched at a low rate and the exposed surfaces are modified to Si-rich ones. In contrast, photo-etching of polymers has been realized. PMMA surfaces can be removed (etched) by X-ray irradiation without further chemical treatment. PMMA can also be etched by chemicals after X-ray irradiation, which is applied to fabricate micro-molds of PMMA and metals in the Lithographie Galvanoformung und Abformung (LIGA) process. In addition to synchrotrons radiation, soft X-rays from laserproduced plasma have been applied to PMMA ablation [1,2]. Barkusky et al. irradiated PMMA with focused laser plasma soft X-rays (LPSXs), using a Schwaltzschild objective that reflects X-rays at 13.5±1.0. Although they achieved high energy as high as 1 J/cm 2 , X-rays out of the

Optical transmission of PMMA optical fibres exposed to high intensity UVA and visible blue light

Optical transmission of PMMA (polymethylmethacrylate) POF (polymer optical fibre) in the spectral range from 280 to 450 nm is investigated with a high radiation emission source comprising a mercury lamp delivering 40 W/cm 2 at the PMMA POF launch face. The heat generated from the radiation source causes a sudden drop in the launched radiation due to thermal-oxidation and photo-degradation of the launch face of the PMMA POF; this results in a loss of 53% of the total launched power within 13 min of exposure to the source. The thermal-oxidation degradation is controlled by a cooling device which improves the transmission stability of the fibre. However, photo-degradation is still active and causes a loss in power of 7% in 13 min. The spectral output of the transmitted radiation through the PMMA POF was monitored and indicates the variation in optical loss with wavelength. High rates of nominal absorption for the irradiated PMMA POF are found below 320 nm wavelength. From the Beer–Lambert law, the photo-degradation effect with time of a fixed path length of PMMA POF is described by the absorption coefficient ( α λ , cm −1) . The nominal absorption coefficient α λ values in the range 335–368 nm wavelength are found to be higher after 1 h of irradiation than the values in the range 406–438 nm. However, the relative change in the nominal absorption coefficient Δ α λ is greater at 438 nm than at 335 nm, 368 or 406 nm. After 1 h of irradiation with the cooling device in place, the PMMA POF transmission was reduced to 44.8% of its initial value; this recovered to a maximum of 86% of the original transmission of the total launched power after 5 weeks in ambient conditions.

Charge transportation and permittivity in electron beam irradiated polymethyl methacrylate

The charging phenomenon in the insulating dielectrics often occurs in the radiative environments such as in the outer space and in the nuclear reactor. Both surface charging and bulk charging have various influences on the dielectric properties. Understanding electrical properties of e-beam irradiated dielectrics is of great significance in order to maintain the stability and reliability of the related operating system. In this work, the effect of electron beam irradiation on the permittivity of polymethyl methacrylate (PMMA) samples was investigated. It was found that the variance of permittivity in e-beam irradiated PMMA is mainly determined by two factors. One is the porosity of the material. The irradiating process could increase the porosity of PMMA due to the escape of the small molecule (e.g., CO, CO2, and CH4) produced during material degradation caused by e-beam irradiation. The enhanced higher porosity corresponds to lower permittivity. The distribution of the implanted charge is the other factor that influences the permittivity. When the distribution of electric field generated by the accumulating charge is asymmetric for the middle thickness of the sample, the PMMA sample with polar groups would be subjected to extra polarization by the field, which could lead to the increase in permittivity. Combining with the model of Wakino et al. [J. Am. Ceram. Soc. 76, 2588 (1993)] on permittivity of mixture materials, the Clausius–Mosotti equation was utilized to analyze the variation in permittivity in the e-beam irradiated PMMA samples.

Effect of applied mechanical stress on space charge breakdown in electron beam irradiated polymethyl methacrylate

The role of applied mechanical stress on space charge breakdown in electron beam irradiated polymethyl methacrylate (PMMA) is investigated. Space charge is implanted into PMMA sheets by electron beam. Space charge is measured by laser induced pressure pulse technique to investigate injection, trapping and detrapping of charge. Mechanical stress is applied on PMMA sheet to study its influence on space charge behavior. Experimental results show that applied electric field is not a necessary condition for breakdown of insulating materials. The breakdown can be triggered during space charge detrapping. The detrapping of space charge can result in tree-like breakdown, wherein this phenomenon is termed as space charge breakdown. Effect of applied mechanical stress on the initiation of breakdown and the development of tree-like breakdown is discussed in this paper.

Radiation dose measurements in irradiated PMMA using ultrasonic technique

Polymethylmethacrylate (PMMA) samples of 20 mm thickness and 50 mm diameter were prepared by machining from a half a metre rod and exposed to γ -ray dose for different durations in an irradiation chamber with Co-60 source. Prominent radiation induced colouration as function of absorbed dose was observed in the irradiated samples. Precise ultrasonic velocity measurements were made in the irradiated samples using 2 MHz longitudinal ultrasonic wave contact type transducer. Measurements indicate that up to 89 kGy of absorbed dose there is no pronounced change in the ultrasonic velocities. Further exposure of samples up to 267 kGy decreases the ultrasonic velocity continuously. From the experimental data points, a graph was drawn with measured velocity as function of absorbed dose. A quantitative linear correlation was obtained between ultrasonic velocity and the absorbed dose for the γ -ray dose range 50–250 kGy. Present study suggests that a reliable radiation dosimeter can be developed employing precise ultrasonic velocity measurements in commercially available PMMA as the medium for propagation of ultrasonic waves.

Irradiated polymethylmethacrylate studied by positron annihilation spectroscopy

AbstractThe effect of gamma irradiation dose on microscopic structure of polymethylmethacrylate (PMMA) has been studied using positron annihilation lifetime (PAL) and Doppler broadening of annihilation radiation (DBAR) techniques. The measurements were performed at room temperature as a function of the γ‐irradiation doses from 60‐1200 kGy. The observed lifetime spectra were resolved into three components. The size and the fraction of the o‐Ps hole volume were estimated from the positron annihilation parameters. The effect of γ‐irradiation was identified at lower doses to be cross‐linking while at higher doses the chemical degradation of the polymer was observed. Moreover, the distribution of the free volume shifts from a large to small size as the irradiation increases and has very similar Gaussian‐like distribution. The PAL results were confirmed with X‐ray measurement. A correlation between the macroscopic mechanical properties Hv and positron annihilation parameters has been demonstrated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Development of Polymer Films Containing Tris(sulfonyloxy)benzene Analogs for .GAMMA. Rays Detection

For development of γ rays detection system using acid sensitive dyes and photo-acid generators, sensitivity and stability of the photo-acid generators, 1,2,3-tris(sulfonyloxy)benzenes (1a-e), N-p-toluenesulfonyloxyphthalimide (2), diphenyliodonium salts (3a,b), were investigated. Heating of acetonitrile solution of the photo-acid generators in the presence of 3'-methoxy-6'-diethylamino-spiro[isobenzofuran-1(3H)-9'-[9H]xanthene]-3-one (4a) as an acid sensitive dye indicated that 1,2,3-tris(sulfonyloxy)benzenes were more thermally stable than N-p-toluenesulfonyloxy-phthalimide and diphenyliodonium salts. The acetonitrile solutions of 1a-c showed no absorbance change even after bearing for 168 hours. The photo acid generators 1a-c showed good thermal stability. The solid-state γ rays detection systems containing 1a, 1b, or 3a as an acid generator and an acid sensitive dye 4a were prepared by dispersion of these particles in polymethyl methacrylate (PMMA) or polystylene (PS). The prepared films were tinged with red by γ irradiation. The color change of the irradiated PMMA films containing 1a and 4a could be distinguished at a glance from non-irradiated films after an irradiation dose of 50 Gy.

Photo-induced synthesis of amorphous SiO 2 film from tetramethoxy-silane on polymethylmethacrylate at room temperature

A new technique, formation of an SiO 2 film on polymethylmethacrylate (PMMA) with tetramethoxysilane (TMOS) as a starting material, by irradiation with a Kr 2 excimer lamp (8.5 eV, 146 nm), and at room temperature was reported. Two photo-induced reactions are involved in this process; the scission of side chains of PMMA and the photochemical reaction of TMOS. The scission of side chains of PMMA with the first irradiation is an essential procedure to fabricate a transparent PMMA coated with TMOS. TMOS coating on PMMA was carried out between the first irradiation and the second irradiation. With the second irradiation, TMOS liquid on the irradiated PMMA turned into a solid which was harder than aluminum. The refractive index of the film is 1.48 ± 0.03 at 633 nm which is almost the same value as the refractive index of SiO 2 fabricated with the thermal oxidation of silicon (1.46). In the infrared spectrum all bands related to alkyl groups disappeared and the line shape was close to that of thermal SiO 2. Though etching rate of the film is 10 times faster than that of thermal SiO 2, we propose that photo-induced formation of SiO 2 having organic impurities of less than 1% succeeded.

The anomalous treeing resistance of proton-irradiated PMMA

This paper is dedicated to the description of an interesting experimental phenomenon that was discovered in irradiated polymethyl methacrylate (PMMA). The breakdown voltage and electric-tree inception (initiation) time in PMMA were investigated under 50 Hz AC voltage after inhomogeneous proton irradiation. An anomalous relationship among , and the proton free length (the depth of irradiation) R in PMMA was found.