High Gamma Dose Research Articles

Ionisation density dependence of the optically stimulated luminescence dose–response of AL2O3:C to low-energy charged particles

The optically stimulated luminescence (OSL) response of Al2O3:C to high doses of gamma or beta irradiation can be used to predict the response of this material to charged particles as a function of particle fluence, particle energy and/or linear energy transfer (LET). In particular, it is predicted that track interaction effects at high particle fluences should result in linear-sublinear growth of the OSL signal. Similar considerations also predict a dependence of the fluence at which sublinearity starts upon the energy of the particles. In this work the OSL response of Al2O3:C to low-energy charged particles was investigated using protons (1, 2 and 4 MeV), carbon ions (13 MeV) and oxygen ions (10 MeV). The sublinear growth predicted above was qualitatively confirmed, but the energy dependence prediction was not. Furthermore, the efficiency of OSL production in the material after charged particle irradiation, compared to that obtained for gamma irradiation, is determined from the dose-response curves by fitting to a simple saturating exponential function. The efficiency values so obtained using this method are compared with those obtained from a conventional single-point measurement in the linear portion of the curve and found to be in good agreement. In general, the efficiency decreases as the LET of the particle increases. The present data are compared with published data obtained using high-energy charged particles and the results show that the efficiency is not a unique function of LET.

Evaluation of gamma and neutron irradiation effects on the properties of mica film capacitors

We present an investigation of gamma and neutron radiation effects on mica film capacitors from an electrical point of view. We have studied quantitatively the effects of gamma and neutron irradiation on mica film capacitors of thickness, 20 and 40 μm (0.7874 and 1.5748 mil) with two different areas, 01 and 04 cm2. The capacitance has been measured at room temperature in the frequency range 100 Hz-10 MHz. Negligible change in the capacitance due to high gamma dose of60Co, 15 kGy at dose rate 0.25 kGy/h, has been observed. However, appreciable change in the capacitance has been observed due to low doses of fast neutrons (cumulative dose, 115 cGy) with flux ∼ 9.925 x 107 neutrons/cm2 h from252Cf neutron source of fluence, 2.5 × 107 neutrons/s. We have also observed that the impact of gamma and neutron irradiation is more at frequencies higher than 10 kHz. These results show that the mica capacitors do not show any radiation response below 10 kHz. The study shows the radiation response of mica film capacitors to gamma and fast neutron radiations. Mica capacitors show low gamma radiation response in comparison to fast neutron radiation, because a total dose of kGy order has been given by gamma source and only few cGy dose has been given by fast neutron source.

Radiation Resistance Study of Semi-Insulating GaAs-Based Radiation Detectors to Extremely High Gamma Doses

In our previous paper [V. Necas et al.: Nucl. Inst. and Meth. A 458 (2001) 348-351] we reported on the study on radiation stability of semi-insulating (SI) LEG GaAs detectors to doses of photons from 60 Co up to 19.2 kGy. Later we presented a study, which covered radiation hardness to the same doses on the base of detector material itself, where strong dependence has been proved [T. Ly Anh et al., Proceedings of the XII th International Conference on Semiconducting and Insulating Materials (SIMC-XII-2002). Smolenice Castle, Slovakia (2002) 292-295 (0-7803-7418-5)]. In this paper we present both the key electrical and detection characteristics of SI GaAs radiation detectors prepared using substrates from four various supplies and two different types of contacts, which were exposed to several gamma doses from 60 Co up to the integral dose of about 1 MGy. The obtained results show that SI LEG GaAs detectors provide good spectroscopic performances and even their slight improvement after low to middle gamma irradiation doses (3 −10 kGy) was observed. Further dose exposure caused the degradation of detection properties with an extreme and following improvement depending on detector material properties. SI GaAs detector still retains its working capabilities even after very high doses applied, up to 1 MGy.

Gamma radiation induced effects on silica and on silica–polymer interfacial interactions in filled polysiloxane rubber

We report in our studies to assess the impact of gamma radiation on silica and on the silica–polymer interface in filled polysiloxane rubber. Electron spin resonance (ESR) and solid-state nuclear magnetic resonance (NMR) studies have been performed on samples exposed to gamma radiation. In an effort to probe directly the effect of gamma radiation on the silica surface, we employed 1H and 29Si NMR. Our ESR studies show trapped paramagnetic species (positive holes and/or trapped electrons) within the host silica matrix for all samples exposed to gamma radiation. A sample of pure cab-o-sil irradiated to a dose of 50 kGy also shows an ESR signal. Our studies on real-time aged samples (derived from field trials) also show ESR signatures indicative of silica based trapped paramagnetic species. The growth of trapped paramagnetic species as a function of gamma dose was investigated. This shows that the build up of trapped species occurs rapidly at low gamma dose before reaching saturation at about 20–30 kGy. Radiation induced band gap excitation is the likely process leading to the creation of these paramagnetic species which may be trapped in regions of local charge deficit within the silica matrix. Species that are not trapped may take part in silica surface reactions leading to changes in filler–polymer interfacial interactions. NMR studies combined with ammonia modified swell studies have shown increased polymer segmental chain mobility (softening) at low gamma dose indicative of a possible reduction in filler–polymer interfacial interactions. For those samples exposed to high gamma dose, our ammonia modified swell studies suggest increased polymer–filler interactions presumably through silica–polymer crosslinking effects. Our 1H and 29Si NMR studies on irradiated silica suggest that the silica surface is sensitive to gamma radiation. Our observations are important as they highlight the need to better control the quality (size, purity, etc.) of the silica constituent in filled polymer components used in gamma radiation environments.

High temperature ultrasonic transducers for imaging and measurements in a liquid Pb/Bi eutectic alloy

In some nuclear reactors or accelerator-driven systems (ADS) the core is intended to be cooled by means of a heavy liquid metal, for example, lead-bismuth (Pb/Bi) eutectic alloy. For safety and licensing reasons, an imaging method of the interior of ADS, based on application of ultrasonic waves, has thus to be developed. This paper is devoted to description of developed various ultrasonic transducers suitable for long term imaging and measurements in the liquid Pb/Bi alloy. The results of comparative experimental investigations of the developed transducers of different designs in a liquid Pb/Bi alloy up to 450 degrees C are presented. Prototypes with different high temperature piezoelectric materials were investigated: PZT, bismuth titanate (Bi4Ti3O12), lithium niobate (LiNbO3), gallium orthophosphate (GaPO4) and aluminum nitride (A1N). For acoustic coupling with the metal alloy, it was proposed to coat the active surface of the transducers by diamond like carbon (DLC). The radiation robustness was assessed by exposing the transducers to high gamma dose rates in one of the irradiation facilities at SCK x CEN. The experimental results proved that the developed transducers are suitable for long-term operation in harsh conditions.

Natural radioactivity in the high background radiation area at Erasama beach placer deposit of Orissa, India

The newly discovered Erasama beach placer deposits in southeastern coast of Orissa state has a high natural radiation environment. The concentrations of radioactive elements such as 232Th, 238U and 40K were measured by gamma ray spectrometry, using a High Purity Germanium detector. The studies show that these placer deposits have high natural radioactivity and external gamma dose rate levels.

EPR dosimetry using commercial glasses for high gamma doses

Commercial transparent and colored (bronze, brown, and green) glasses were studied as possible dosimeters for high gamma doses using electronic paramagnetic resonance (EPR). All EPR spectra showed the characteristic Fe 3+ signals, g = 4.27 and 2.01. The signal at g = 2.01 presented a more useable behavior for the calibration curve. All samples showed their usefulness as high dose dosimeters.

Dosimetric properties of KNO 3 pellets mixed with sensitizing compounds

Potassium nitrate (KNO 3) in pellet form has been used as dosimetric material for high-gamma dose measurements in the industrial applications of radiation. The evaluation technique is based on the changes observed in the optical properties of solutions prepared with irradiated and non-irradiated pellets, respectively, by means of spectrophotometric analysis. Aiming to increase the applicable dose range, by retarding the decomposition of the nitrate ions (NO 3 −) to nitrite ions (NO 2 −), sensitizing compounds like Ba(NO 3) 2, KBr and MnO 2 were mixed with pure KNO 3 before preparing the pellets and the dosimetric properties of the new compounds were then evaluated. The following parameters were studied: absorption spectra before and after irradiation, sensitizer concentration, signal stability, linear dose range and dose rate dependence between 1.70 and 5.65 kGy/h. Using this method the dose range could be extended from 150 kGy, obtained using KNO 3 to 600 kGy, or more, using MnO 2 (40%).

Response of piezoresistive MEMS accelerometers and pressure transducers to high gamma dose

Several piezoresistive microelectromechanical (MEMS) sensors are operated in a gamma ray environment to doses of 800 kGy. The pressure transducers and accelerometers are micromachined silicon-on-insulator (SOI) and bulk silicon devices, respectively. Both sensor types experienced similar performance degradation: a drift in offset voltage with a slight increase in sensitivity. We explain the drift in offset voltage for all sensors tested by correlating the change in resistance of the silicon piezoresistors to the formation of oxide and interface trapped hole charges. We demonstrate how these charges effectively reduce the volume for current flow through the piezoresistors due to the creation of a depletion region surrounding the periphery of the gage resistors. Differences in the magnitude of the output voltage drift of the two sensor types are determined to be related to the unique construction of each sensor.

Toward the development of radiation-tolerant instrumentation data links for thermonuclear fusion experiments

Thermonuclear reactors will require permanent monitoring under high-gamma dose rates and high neutron flux. We propose to get rid of the digital data transmission limitations in highly radioactive environments by implementing an analog fiber-optic link based on directly modulated vertical-cavity surface-emitting laser (VCSELs). In this paper, we introduce an architecture for highly radiation-tolerant instrumentation data links based on the intrinsic wavelength division multiplexing capabilities of fiber-optic data transmission. The potential radiation acceptance level of the analog fiber-optic link is estimated on the basis of irradiation results on individual COTS photonic components such as VCSELs, fiber-optic passive multiplexers, and optical fibers.

Gamma radiation resistant Fabry–Perot fiber optic sensors

The Nuclear Regulatory Commission (NRC) in 1998 completed a study of emerging technologies that could be applicable to measurement systems in nuclear power plants [H. M. Hashemian et al., “Advanced Instrumentation and Maintenance Technologies for Nuclear Power Plants,” NUREG/CR-5501 (1998)]. This study concluded that advanced fiber optic sensing technology is an emerging technology that should be investigated. It also indicated that there had been very little research related to performance evaluation of fiber optic sensors in nuclear plant harsh environments, although substantial research has been performed on nuclear radiation effects on optical fibers in the last two decades. A type of Fabry–Perot fiber optic temperature sensor, which is manufactured by Fiso Technologies in Canada, is qualified to be a candidate for potential applications in nuclear radiation environment due to its unique signal processing technique and its resistance to power loss. The gamma irradiation effects on this type of sensors are investigated in this article. Two sensors were irradiated in a gamma irradiation field and one of them was irradiated up to a total gamma dose of 133 Mrad. The sensor on-line performance was monitored during each gamma irradiation test. Furthermore, the sensor static and dynamic performance before and after each irradiation test were evaluated according to the Standard ISA-dS67.06.01 (“Performance Monitoring for Nuclear Safety-Related Instrument Channels in Nuclear Power Plants”, Standard ISA-dS67.06.01, Draft 7, Instrument Society of America, 1999). Although several abnormal phenomena were observed, analysis shows that gamma irradiation is not accredited to the abnormal behavior, which implies that this type of sensor is suitable to a gamma irradiation environment with a high gamma dose.

Suppression of tumor angiogenesis through the inhibition of integrin function and signaling in endothelial cells: which side to target?

Tumor angiogenesis is an essential step in tumor progression and metastasis formation. Suppression of tumor angiogenesis results in the inhibition of tumor growth. Recent evidence indicates that vascular integrins, in particular alpha V beta 3, are important regulators of angiogenesis, including tumor angiogenesis. Integrin alpha V beta 3 antagonists, such as blocking antibodies or peptides, suppress tumor angiogenesis and tumor progression in many preclinical tumor models. The potential therapeutic efficacy of extracellular integrin antagonists in human cancer is currently being tested in clinical trials. Selective disruption of the tumor vasculature by high doses of tumor necrosis factor (TNF) and interferon gamma (IFN-gamma), and the antiangiogenic activity of nonsteroidal anti-inflammatory drugs are associated with the suppression of integrin alpha V beta 3 function and signaling in endothelial cells. Furthermore, expression of isolated integrin cytoplasmic domains disrupts integrin-dependent adhesion, resulting in endothelial cell detachment and apoptosis. These results confirm the critical role of vascular integrins in promoting endothelial cell survival and angiogenesis and suggest that intracellular targeting of integrin function and signaling may be an alternative strategy to extracellular integrin antagonists for the therapeutic inhibition of tumor angiogenesis.

Radiation-resistant WDM optical link for thermonuclear fusion reactor instrumentation

The future International Thermonuclear Experi- mental Reactor (ITER) is a complex installation that will require permanent monitoring and frequent maintenance operations. The high-gamma dose rates, the high neutron fluence, and other radiological hazards call for the use of remote-handled equipment. The management of heavy umbilicals connecting the control systems with the remote tools is therefore a key issue. Multiplexing signals can relieve the cable-handling difficulties. In this respect, the intrinsic wavelength division multiplexing (WDM) capabilities of fiber-optic technology make it a very promising candidate for integration in ITER instrumentation links. However, the radiation hardness of a complete WDM optical link still needs to be assessed. In this paper, as a first step toward the development of a rad-hard WDM optical link, we report on irradiations of different parts of a typical WDM optical link. We present our irradiation results on COTS fiber-optic devices, including WDM single-mode couplers, which remain operational up to MGy dose levels while the channel drift observed in narrow-band couplers compromises their use in WDM multiplexers. The intrinsic wavelength encoding of fiber Bragg grating (FBG) sensors makes them ideal candidates for WDM fiber-optic sensor networks. Therefore, we also investigated the -radiation response of FBGs written in germanosilicate fibers. We irradiated such sensors up to MGy dose levels. At a total dose of 0.1 MGy, saturation of the radiation-induced Bragg peak shift has been observed, evidencing the potential radiation hardness of FBG-based devices in highly radioactive environments. To illustrate wavelength multiplexing in sensing, we discuss our preliminary results on a new multicomponent force sensor design based on eight multiplexed FBG sensors intended for use at the end effector wrist of remote-controlled robots. Finally, we present the in-reactor irradiation results of standard Corning Ge-doped fiber up to GGy dose levels. Index Terms—Fiber Bragg grating (FBG) sensor, gamma radia- tion, International Thermonuclear Experimental Reactor (ITER), nuclear robotics, optical fiber sensor, radiation effects, wavelength division multiplexing (WDM).

Preparation, thermoluminescent and electron spin resonancecharacteristics of LiF:Mg,Cu,P phosphor

A highly sensitive and tissue equivalent LiF:Mg,Cu,Pthermoluminescent (TL) phosphor in powder form has been developed. The TLsensitivity of this phosphor is about 1.5 times that of Harshaw-BicronLiF:Mg,Cu,P (TLD100-H) by peak height measurements. Its dose against TLresponse is linear up to 10 Gy. The annealing temperature was found to affectthe glow curve shape and sensitivity.Defect centres formed in the LiF:Mg,Cu,P phosphor after high gamma dose werestudied using electron spin resonance. Two centres assigned to (PO4)2-and an F-centre were observed at room temperature. Step annealing measurementsindicate possible association between the (PO4)2- centre and the TLpeak at 120 °C. Phosphorus appears in the form ofthe (PO4)3- moiety in the lattice and is responsible for the high TLsensitivity.

Comparison and limitations of three different bulk etch rate measurement methods used for gamma irradiated PM-355 detectors

Samples of Nuclear Track Detectors (PM-355) were exposed to high gamma doses from 1×10 5 Gy (10 Mrad) up to 1.2×10 6 Gy (120 Mrad) at an incremental dose of 1×10 5 Gy (10 Mrad ). The gamma source was a 9.03 PBq ( 244 kCi ) Co-60 source used for sterilization of medical syringes. The bulk etch rate ( V b) was measured for various high gamma doses by three different methods: 1—thickness change method; 2—mass change method; 3—fission track diametric method. The study gives a comparison and limitations of these three methods used for bulk etch rate measurements in the detectors as a function of high gamma doses. The track etch rate ( V t) and the sensitivity ( V) of the detector were also measured using the fission track diametric method. It was observed that V b increases with the increase of the gamma absorbed dose at a fixed etching time in each bulk etch measuring method. The bulk etch rate decreases exponentially with the etching time at a fixed gamma absorbed dose in all three methods. The thickness change and mass change methods have successfully been applied to measure V b at higher gamma doses up to 1.2×10 6 Gy (120 Mrad ). The bulk etch rate determined by the mass change and thickness change methods was almost the same at a certain gamma dose and etching time whereas it was quite low in the case of the fission track diametric method due to its limitations at higher doses. Also in this method it was not possible to measure the fission fragment track diameters at higher doses due to the quick disappearance of the fission tracks and therefore the V b could not be estimated at higher gamma doses.{

Effect of high gamma doses on the etching behaviour of different types of PADC detectors

Polyallyldiglycol carbonate (PADC) detectors were exposed to different doses of gamma radiation ranging from 10 1 to 10 6 Gy from a 60Co source. The effect of gamma doses on etch-rates were studied. Etch-rate values were found to increase at the dose of 10 6 Gy for all types of PADC detectors. The influence of gamma exposure on sensitivity and etching efficiency of these detectors was also determined. The experimental results are presented and discussed.

Diagnosis of acute localized irradiation lesions: review of the French experimental experience.

In the last 50 years several radiation accidents occurred in which industrial radiographers and others suffered severe radiation injuries from inadvertent contact with radiation sources. Such accidents involving acute localized injuries are characterized by a severe initial reaction progressing through erythema to skin necrosis with a spontaneous resolution of the lesion over a 2-mo period for the lower doses. However, the early symptoms observed on the skin give no indication as to the in-depth pathology, and cutaneous and muscular radionecrosis started generally from early epithelial, microvascular, and vascular lesions and from delayed muscular and connective tissue lesions. In a case of acute localized irradiation, different biophysical techniques are able to give real responses in biological dosimetry. More numerous are the methods, especially imaging methods, that make it possible for the clinician to evaluate the extent of the early injuries and to manage the medical intervention. We have developed animal experimental models of acute localized irradiation: overexposure to the gamma rays of a 192Ir industrial radiographic collimated source (in the pig and the rabbit) and overexposure to the beta rays of a 90Sr-90Y collimated source (in the pig). In these experimental models, most of the imaging techniques used in clinical practice, as infra-red thermography, microwave thermography, cutaneous and tissular vascular scintigraphy (beta or gamma emitters), cutaneous blood flow measurements by cutaneous laser Doppler, x ray computed tomography, nuclear magnetic resonance imaging, and skin topography, were correlated with clinical evaluation and histopathological observations, after high doses of gamma or beta irradiations ranging from 4 to 340 Gy at the skin surface. All these techniques are not for isolated use and the present review indicates that their combination is necessary to give an improved diagnostic and prognostic picture of early and late delayed radiation damage to the skin and subcutaneous tissues.

Pulse treatment of human vascular endothelial cells with high doses of tumor necrosis factor and interferon-gamma results in simultaneous synergistic and reversible effects on proliferation and morphology.

Regional administration of high doses of tumor necrosis factor (TNF), interferon gamma (IFNgamma) and melphalan to patients with advanced cancers of the limbs, results in rapid and specific tumor necrosis, while the normal adjacent tissues remain unaffected. The tumor vasculature is selectively destroyed by this treatment, and neovascular endothelial cells appear to be an early and specific target of TNF and IFNgamma. To further understand some of the cellular events underlying these in vivo effects, we have investigated the response of human macro- and microvascular endothelial cells in vitro, after exposure to high doses of TNF and IFNgamma (up to 40 x 10(3) U/ml each). TNF and IFNgamma synergistically inhibited endothelial-cell proliferation by up to 80% after 72 hr of treatment. Achievement of synergy required the simultaneous presence of both cytokines. A cytokine pulse as short as 30 min was sufficient to induce maximal growth inhibition measured after 48 hr. Both cytokines also induced progressive and dose-dependent elongation of the endothelial-cell morphology. The effects on endothelial-cell proliferation and morphology were reversible upon removal of the cytokines. Moreover, replating of treated cells onto a fresh substrate immediately resulted in re-acquisition of their normal shape. In contrast to the effect on cell proliferation, there was little or no effect on the rate of endothelial-cell apoptosis. The presented data extend reports on the effects of TNF and IFNgamma on human endothelial cells in vitro, and suggest that the in vivo disruption of the tumor vasculature caused by high doses of TNF and IFNgamma is not due to a direct cytotoxic effect on endothelial cells but occurs through an indirect mechanism.

The effects of irradiation on the expression of a tumour rejection antigen (heat shock protein gp96) in human cervical cancer

Purpose: Studies were designed to analyse the effects of high doses of gamma -irradiation on the expression of a tumour rejection antigen (heat shock protein gp96) in human cervical carcinoma cell lines. Materials and methods: The expression of heat shock protein gp96 was evaluated at the transcriptional (Northern blot) and posttranscriptional levels (Western blot) in two human cervical carcinoma cell lines following exposure to high doses of gamma -irradiation. Results: Doses of gamma -irradiation ranging from 25 to 100 Gy significantly and consistently increased the expression of heat shock protein gp96 on CaSki and HT-3 cervical cancer cells. The increase in the amount of protein was due to transcriptional up-regulation of this gene. Radiation doses unable to inhibit completely cell replication in the totality of tumour cells (i.e. 25 Gy), as well as higher (fully lethal) doses of irradiation (i.e. 50 to 100 Gy), were shown to up-regulate significantly the expression of heat shock protein gp96 mRNA in a dose-dependent manner. Conclusions: Recently, gp96 molecules have been implicated in the presentation of endogenous and viral antigens. A number of key elements in this pathway, including major histocompatibility complex (MHC) class I molecules as well as adhesion/costimulation molecules such as ICAM-1, are known to be sensitive to irradiation effects. The results show that radiation can also increase the expression of other immunologically important cell molecules such as a tumour rejection antigen (heat shock protein gp96) in human cervical cancer. Such findings may partially explain the increased immunogenicity of tumour cells following irradiation and further support a role for local radiation therapy as a powerful biologic response modifier.

Effect of high gamma dose on the PADC properties

The effect of the properties of PADC nuclear track detectors after exposure to high doses of gamma absorbed doses up to 5×10 5 Gray (50 Mrad) were studied. The gamma source was a 9.03 PBq (244 KCi), Co-60 source. Results indicate that each of the bulk etch rate (V b), the tracks etch rate (V t) and the sensitivity (V) of the detectors increases with the high gamma absorbed dose, but there is a drop in these parameters at the low gamma absorbed dose. Signs of surface roughness were observed by increasing the gamma absorbed doses and changes in color observed for doses larger than 2×10 5 Gray. The temperature of detectors during irradiation time reached 41°C. The fission fragment tracks (from Cf-252 source) disappeared quickly within the etching time (minutes) for total absorbed doses greater than 3×10 5 Gray due to their high bulk etch rate.