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This work mainly depends on the assumption or hypothesis which exploits the tendency of natural rubber latex (NRL) to cross-link under irradiation in the presence of Alginate and CMC biopolymer and form (ALG/NRL and CMC/NRL) films containing polar/charged functional groups which offer them hydrophilicity, and consequently water absorption capacity. CMC/NRL and ALG/NRL (v/v) blend films prepared first by latex compounding followed by casting technique. The prepared ALG/NRL and CMC/NRL blend films characterized then, by various techniques such as IR, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Equilibrium swelling properties and gel percent GF% of prepared films also studied in details. GF% studies revealed that the GF% increased with increasing both NRL content and irradiation dose for both ALG/NRL and CMC/NRL. Thermal analysis shows the increased thermal stability of the irradiated samples due crosslinking effect of NRL. The improved gel content percentage obtained paved the way for the application of various films in the removal of toxic dyes such as acidic, direct, and basic dyes from waste water where in this study, the films exhibited high affinity toward basic blue dye. KEYWORDS alginate, carboxymethyl cellulose, gamma radiation, latex compounding, natural rubber latex, 1 | INTRODUCTION The interactions of gamma radiation with matters induce ionizations leading to the formation of ions and expelled fast-moving electrons. The interactions of the energetic electrons take place [...]

Radiation technology has been recognized as a potential tool to modify starches in order to enhance their solubility and enzymatic digestion, hence improving their applicability in food industry. In the present study, the local cassava starch was irradiated under 60Co gamma source with the absorbed dose ranging from 1 to 10 kGy, and the obtained radiation-modified starches were characterized. The microstructure of the initial cassava starch was not much changed although several starch granules were deformed or even fragmented by gamma irradiation as observed in the scanning electron microscopy images. Water solubility of the irradiated starch was significantly increased, and their viscosity was much reduced by radiation degradation. Gamma radiation broke glycosidic bonds in starch chains into smaller molecules with lower molecular weight, whereby increased the water solubility of cassava starch. Radiation scission also partly decreased the crystallinity of the starches irradiated with dose higher than 5 kGy as indicated in their X-ray diffraction patterns. The Fourier transform infrared spectra of irradiated starches revealed the reduction in intensities of stretching vibration characterized for OH, CH, and COC groups of starch molecules. Thus, gamma irradiation can be used to modify cassava starch for further applications. KEYWORDS cassava starch, irradiation modification, morphology, structure and properties, viscosity average molecular weight, water solubility, 1 | INTRODUCTION Cassava has been cultivated as a major crop and used as staple food over the world for a long time. While fresh cassava is directly cooked or [...]

The evaluation of the agreement between calculated and measured dose plays an essential role in the quality assurance procedures of intensity-modulated radiation therapy (IMRT). This study aimed to compare gamma analysis using portal dosimetry (PD), Epiqa, and 2D array detector for dose verification of radiotherapy treatment plans. Five field stepand-shoot IMRT plan was performed for 20 prostate IMRT patients using the dual-energy DHX linear accelerator (Varian Medical System, Palo Alto, Calif., USA). The treatment plans were created using Varian DHX Eclipse treatment planning system (TPS) version 15.1. All measurements were performed by aS500 EPID integrated into Varian DHX linear accelerator and 2D array detector. The dose distribution was evaluated with gamma area histograms (GAHs) generated using different g criteria (1%/1 mm, 2%/2 mm, 3%/2 mm, and 3%/3 mm) for dose agreement and distance to agreement parameters. Statistical analyses were evaluated by using Mann-Whitney U test and Kruskal-Wallis test, and p-value of p < 0.01 was considered to be significant. The average pass rate for 20 IMRT plans was above 95 for all devices with 2%/2 mm, 3%/2 mm, and 3%/3 mm. The mean and standard deviation pass rates ([gamma] [less than or equal to] 1) were found to be 99.80 [+ or -] 0.19, 99.35 [+ or -] 0.34, and 97.53 [+ or -] 0.71 for PD, Epiqa, and 2D array, respectively. All IMRT plans passed 2%/2 mm, 3%/2 mm, and 3%/3 mm gamma by more than 95 of three dosimetric systems. They are all in good agreement with the literature. All three devices are acceptable for quality control of IMRT. Due to the simplicity and fast evaluation process, PD can be preferred for quality control. Key words: gamma analysis, PD, Epiqa, IMRT, 2D array detector. La validation de l'accord entre les doses calculees et les doses mesurees joue un role essentiel dans les procedures de verification de la qualite (VQ/QA) en therapie par radiations a modulation d'intensite (TRMI/IMRT). Cette etude vise une analyse gamma utilisant la dosimetrie portale (DP/PD), Epiqa et un reseau 2D de detecteurs pour verifier la dose dans les procedures de traitement de radiotherapie. Nous utilisons une procedure de TRMI a un pas/un tir (step and shoot) a cinq champs pour traiter la prostate de 20 patients irradies a l'aide de l'accelerateur lineaire DHX a deux energies (Varian Medical System, Palo Alto, Calif., USA). Nous generons les procedures de traitement a l'aide du systeme de planification de traitement (SPT/TPS) DXH Eclipse de Varian, version 15.1. Toutes les mesures se font par un EPID aS500 integre dans l'accelerateur DHX de Varian et le reseau 2D de detecteurs. La distribution de la dose est evaluee par les histogrammes gamma generes en utilisant differents criteres g (1 %/1 mm, 2 %/2 mm, 3 %/2 mm et 3 %/3 mm) pour accord de dose et distance. Les analyses statistiques sont faites en utilisant les tests de Mann-Whitney et de Kruskal-Wallis, et une valeur p < 0.01 est consideree etre significative. Le taux de passage du test pour les 20 procedures TRMI est au-dessus de 95 pour tous les dispositifs avec 2 %/ 2 mm, 3 %/2 mm et 3 %/3 mm. Nous trouvons que la moyenne et l'ecart type des taux de passage ([ganna] [less than or equal to] 1) sont 99,80 [+ or -] 0,19, 99,35 [+ or -] 0,34 et 97,53 [+ or -] 0,71 pour DP, Epiqua et le reseau 2D respectivement. Toutes les procedures TRMI passent 2%/2 mm, 3 %/2 mm et 3 %/3 mm par plus de 95 des trois systemes dosimetriques. Ils sont tous en bon accord avec les resultats dans la litterature. Les trois dispositifs sont acceptables en controle de qualite TRMI. A cause de la simplicite et de la rapidite d'utilisation, on peut preferer le controle de qualite DP. [Traduit par la Redaction] Mots-cles : analyse gamma, therapie par radiation a modulation d'intensite, reseau 2D de detecteurs, dosimetrie portale, Epiqa., Introduction Prostate cancer is the second most common cancer in men worldwide. Radiotherapy has a crucial role in the treatment of prostate cancers [1]. The prostate is close to the [...]

This investigation focused on the opportunity of devulcanizing waste Rubber (WR) by ultrasonication to study the possibility of utilized as an added substance to replace with styrene-butadiene rubber (SBR) in preparation process with the final aim of preparation new composites. The present work expects to compare the ultrasonic technique and the previous work on devulcanization by mechano-chemical method. The influence of the ultrasonication treatment on the WR was explored by Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy analysis revealed that ultrasonication was observed to be the best factor impacting the devulcanization procedure, this procedure suggests that use of specific levels of ultrasonic waves to the vulcanized rubber with a specific aim to accomplish a particular breaking of compound connections: scission of C-S and S-S bonds without break carbon-carbon (C-C) bonds. Various blends of devulcanized WR with SBR was treatments with gamma ray then investigated and compared with find out the rubber giving the highest compatibility for compounding and revulcanization. In addition, a comparison of these results was made with the ones of raw SBR rubber compound., INTRODUCTION Waste rubber (WR) represents a potential 'green' source of rubber, replacing the raw natural and synthetic rubber. The increasing quality requirements of rubber products and the high costs of [...]

Abstract: Amorphous chromium-containing solid nanoparticles and hollow spheres were formed as the intermediate product during the synthesis of [Cr.sub.2][O.sub.3] by gamma radiolysis of dichromate solution. Scanning transmission X-ray microscopy (STXM) [...]

To improve the oxidative efficiency of polyacrylonitrile (PAN) precursors, modification of PAN precursors was employed by gamma ray irradiation. Effects of irradiation on the structure and properties of PAN precursors were investigated. The results showed that cyclized structure in the precursors was formed after γ-ray irradiation. Meanwhile, irradiation could reduce the heat evolved, relax the exothermic behavior, decrease the mechanical properties and enhance the density of PAN fibers. It is supposed that the modification of γ-ray irradiation could remarkably accelerate the stabilization process of PAN precursors and reduce the production cost of resulting carbon fibers., INTRODUCTION Carbon fibers are the most successful new carbon products to be commercialized in past 50 years. Their high strength and stiffness, combined with their light weight, make carbon fibers [...]

Films of poly(vinyl alcoholj/cadmium sulphide (PVA/CdS) nanocomposite containing various concentrations of [Cd.sup.2+] ions were prepared using gamma radiation at different doses from 50 up to 200 kGy. The UV/VIS spectra revealed that the CdS/PVA nanocomposites showed blue shift for the absorption peak as compared with bulk CdS. As the irradiation dose increased, a gradual red shift in the wavelength accompanying with broadening of the absorption peak was observed. The estimated optical band gap energies and the calculated CdS particle sizes of (PVA/CdS) showed correlation between their values and the variable parameters (irradiation dose and [Cd.sup.+2]:[S.sup.-2] molar ratio). Transmission electron microscopy images showed that the CdS/PVA nanocomposites were dispersed as spherical CdS nanoparticles with homogeneity at either lower concentration of Cd[Cl.sub.2] or irradiation dose. The nano-rod structures of CdS was accompanied with small agglomeration at either higher Cd[Cl.sub.2] concentration or irradiation dose. A cubic phase and mixture of cubic and hexagonal phases of the prepared CdS nanoparticles were formed at lower and higher Cd[Cl.sub.2] concentrations, respectively. Fourier Transform Infrared spectra confirmed the coordination of CdS nanoparticles with the hydroxyl groups of PVA matrix. POLYM. ENG. SCI., 55:2583-2590, 2015. [C] 2015 Society of Plastics Engineers, INTRODUCTION Semiconductor nanoparticles polymer composites have attracted considerable interest in recent years because of their size dependent properties and great potential for many applications such as nonlinear optics, optoelectronic device, [...]

Poly [2-(dimethylamino) ethyl methacrylate], PDMAEMA, was synthesized by heterophase polymerization at 70°C using sodium dodecylsulfate (SDS) as stabilizer and potassium persulfate (KPS) as the initiator. Conversions were 60%, polymer content 18%, and intensity average particle diameter, [D.sub.p], 32 nm. γ-rays irradiation of PDMAEMA nanolatexes and DMAEMA/ [H.sub.2]O/SDS microemulsions using ethyleneglycol dimethacrylate produced nanogels responding to temperature and pH. Nanogels shrinked as temperature increased, swelled excessively in acidic solutions (maximum [D.sub.p]: 498 nm) and deswelled (minimum [D.sub.p]: 257 nm) in basic solutions for the case of the nanogels obtained from PDMAEMA nanolatexes. pH response to swelling is due to protonation of amine groups in the backbone of PDMAEMA in acidic conditions leading to electrostatic interactions in the nanogel., INTRODUCTION Polymers which can react adjust or modulate their physicochemical character, that is, their water-solubility, shape, volume, optical properties, and so forth, in response to an external stimulus, are generally [...]

In the present article, the effect of γ-ray irradiation of doses 14.85, 30, and 45 kGy on the thermomechanical and tensile properties of blends of cis-polyisoprene and trans-polyisoprene have been investigated. The results on thermomechanical properties show that glass transition temperature increases and height of tan δ of material decreases with increasing radiation dose. Tensile measurements reveal that all the tensile properties like tensile strength, Young's modulus, and toughness also show an increasing trend with increasing dose of radiation. This increasing behavior of both thermomechanical and tensile properties has been explained through crystallinity and crosslink density induced by radiation. POLYM. ENG. SCI., 53:443-451, 2013. [C] 2012 Society of Plastics Engineers, INTRODUCTION Trans-polyisoprene (TPI) is one of the widely used polymers for various products with some specific properties different from those of cis-polyisoprene (CPI) (1). CPI, a natural polymer, suffers from [...]

Annihilation kinetics of color center in polycarbonate (PC), irradiated with gamma ray at elevated temperatures, was investigated. The transmission loss in the PC was monitored in the ultraviolet and visible wavelength range. The transmittance decreased with increasing gamma-ray dose. The loss was attributed to the presence of annealable and permanent color centers. The absorbance in situ data were detected at the wavelength of 450 nm and found in good agreement with the theoretical model in which the annealable color center followed a first-order kinetic process. The rate constant satisfies the Arrhenius equation, with the activation energy of the color centers decreasing with increase of the gamma-ray dose. The results were compared with the early findings reported in the literature. POLYM. ENG. SCI., 52:2391-2395, 2012. © 2012 Society of Plastics Engineers, INTRODUCTION Polycarbonate (PC) is a high performance engineering thermoplastic, which has found broad applications in many industrial fields due to its high toughness, high impact strength, excellent optical clarity, heat [...]

The National Institute of Standards and Technology (NIST) has developed new gamma-ray and neutron emitting sources for testing radiation detection systems. These radioactive sources were developed for testing of detection […]

We have constructed a prototype, rapid-deployment portal monitor that uses visible-light and gamma-ray imaging to allow simultaneous monitoring of multiple lanes of traffic from the side of a roadway. Our Roadside Tracker uses automated target acquisition and tracking (TAT) software to identify and track vehicles in visible light images. The field of view of the visible camera overlaps with and is calibrated to that of a one-dimensional gamma-ray imager. The TAT code passes information on when vehicles enter and exit the system field of view and when they cross gamma-ray pixel boundaries. Based on this information, the gamma-ray imager 'harvests' the gamma-ray data specific to each vehicle, integrating its radiation signature for the entire time that it is in the field of view. In this fashion we are able to generate vehicle-specific radiation signatures and avoid source confusion problems that plague nonimaging approaches to the same problem. Index Terms--Coded-aperture imager, gamma-ray detectors, gamma-ray imagers, nuclear imaging, radiation portal monitor.

Due to the widespread use of polymeric insulating materials in radiation environments, there is an increasing demand to evaluate the radiation effects on the surface dielectric characteristics of polymeric insulating materials. This paper presents a recurrence plot approach to analyze the surface discharge of gamma-ray irradiated polymeric insulating materials based on the tracking test described in IEC60112. Because the resulting comparative tracking index has wide variation, an attempt has been made to evaluate the resistance to tracking more consistently. In this research, for different dosages of gamma-ray irradiation, the discharge currents are detected when the discharge occurs on the sample surface. Recurrence plots of the discharge currents are derived. It is found that the resistance to tracking could be projected on a map as a function of the dosage of irradiation. The recurrence plots are sensitive and give visual methods for identification of the dosage of irradiation effects on the resistance to tracking. Results obtained show that with the increase of dosage of irradiation, the resistance to tracking of polybutylene terephthalate decreases, but increases for polyethylene terephthalate. Index Terms--Polymeric materials, gamma-ray irradiation, tracking test, surface discharge, dielectric breakdown, recurrence plot, fractal dimension.

Gamma-ray attenuation is used to measure cryogenic mixture density. Parameters axe optimized for specific space application. A simple error formula is established. The feasibility of the measurement is demonstrated. The effect of container's walls is measured. An automatic measurement device is built. A theoretical calculation is made for the geometry of Ariane V launcher. Index Terms--Cryogenics, density measurement, gamma rays, space vehicle propulsion.

The effect of total dose on SEU hardness is investigated as a function of temperature and power supply voltage to determine worst-case hardness assurance test conditions for space environments. SRAMs from six different vendors were characterized for single-event upset (SEU) hardness at proton energies from 20 to 500 MeV and at temperatures of 25 and 80[degrees]C after total dose irradiating the SRAMs with either protons, Co-60 gamma rays, or low-energy x-rays. It is shown that total dose irradiation and the memory pattern written to the memory array during total dose irradiation and SEU characterization can substantially affect SEU hardness for some SRAMs. For one SRAM, the memory pattern made more than two orders of magnitude difference in SEU cross section at the highest total dose level examined. For all SRAMs investigated, the memory pattern that led to the largest increase in SEU cross section was the same memory pattern that led to the maximum increase in total-dose induced power supply leakage current. In addition, it is shown that increasing the temperature during SEU characterization can also increase the effect of total dose on SEU hardness. As a result, worst-case SEU hardness assurance test conditions are the maximum total dose and temperature of the system environment, and the minimum operating voltage of the SRAM. Possible screens for determining whether or not the SEU cross section of an SRAM will vary with total dose, based on the magnitude of the increase in power supply leakage current with total dose or the variation in SEU cross section with power supply voltage, have been suggested. In contrast to previous works, our results using selective area x-ray irradiations show that the source of the effect of total dose on SEU hardness is radiation-induced leakage currents in the memory cells. The increase in SEU cross section with total dose appears to be consistent with radiation-induced currents originating in the memory calls affecting the output bias levels of bias level shift circuitry used to control the voltage levels to the memory cells and/or due to the lowering of the noise margin of individual memory cells caused by radiation-induced leakage currents. Index Terms--Hardness assurance, proton irradiation, single-event upset.

The use of polarized gamma-ray beams or high energy photons as superior probes of protons, neutrons and nuclei is examined. These photons are easily created by directing laser light at a high-energy electron beam.

Abstract: Radiation induced grafting of vinyl pyrrolidone onto cellulose wood pulp was carried out in heterogeneous and homogenous media using gamma radiation. Cellulose wood pulp was used in different forms; [...]

Resistance to tracking of insulating materials has been studied by many investigators using the test method of IEC Publication 112. This method has now been applied to materials selection. There is no internationally recommended method for determining dc resistance to tracking because the experimental values of the comparative tracking index (CTI) are obtained only under ac voltage. The environmental factors affecting dc resistance to tracking of organic insulating materials are still far from being well understood. This paper presents a study of the effects of gamma-ray irradiation, atmospheric pressure, and sample temperature on the dc resistance to tracking of polyethylene. Samples were irradiated in air up to 1 MGy with a dose rate of 10 kGy/h using a [sup.60] Co gamma source. The resistance to tracking on applying dc or ac voltage was examined. We found that the dc resistance to tracking is lower than the ac resistance. As the total radiation dose is increased, the dc and ac resistance to tracking both increase. The erosion depth, weight loss and contact angle affected by the radiation have been studied under combined environmental conditions. A nonlinear correlation was observed. As the total irradiation dose was increased, the dc resistance to tracking decreased with decreasing pressure from 100 kPa to 50 kPa. When the samples were above room temperature the dc resistance to tracking decreased. Index Terms--Polyethylene, dc resistance to tracking, gamma-ray irradiaion, atmospheric pressure, temperature, erosion depth, weight loss.

Comparative analysis of the soft-electron method and irradiation method used to sterilize soybeans is presented.

A study analyzing the combined effect of gamma irradiation and edible coatings on strawberries, to preserve their quality during storage, is presented.

We present the first observation of total dose effects of gamma-ray irradiation on enhancement mode 6H-SiC p-channel MOSFETs. Electrical characterization of these transistors was performed before and after irradiation up to a total dose of [10.sup.8] rad(Si[O.sub.2]) by measuring the drain-source current ([I.sub.ds]) as a function of gate voltage ([V.sub.g]) and drain-source voltage ([V.sub.ds]). These transistors were compared to 6H-SiC n-channel MOSFETs. The p-channel devices remain fully functional up to [10.sup.6] rad(Si[O.sub.2]), while the n-channel devices are fully functional through [10.sup.8] rad(Si[O.sub.2]). We found that the generation of radiation-induced interface states in the n-channel transistors is substantially lower than that of the p-channel devices. Index Terms--Interface traps, mobility, MOSFET, oxide-trapped charge, silicon carbide.

We are developing a liquid xenon ionization chamber for single-photon radioisotope imaging in nuclear medicine. The chamber has a mini-strip plate made of glass substrate with metal strips deposited along two perpendicular directions. Here, we report on a version of this chamber with an additional grid, improved trigger capability and the development of the multichannel readout system based on highly integrated low-noise front-end electronics and dedicated data acquisition system. The average root mean square (rms) noise between 250 and 350 electrons has been achieved with the front-end electronics operated at the temperature of -100[degrees]C. The whole system was tested with 122 keV [gamma]-rays from [sup.57]Co. Index Terms--Data acquisition, nuclear imaging, xenon.

As for standard positron emission tomography (PET) scanners, MR-compatible PET scanners will require gamma shielding to suppress the influence of activity outside the PET field of view (FOV). Suitable materials must have very specific properties, including magnetic properties close to those of water, high density, high atomic number, and ideally a low conductivity. In order to identify potential suitable materials, we have selected several heavy-metal-based candidates based on the available data for magnetic and shielding properties. These materials include several nonferromagnetic metals and metal oxides, two scintillating crystals (bismuth germanate and lead tungstate) and two metal/epoxy compounds. The magnetic resonance imaging (MRI) compatibility of these materials was assessed under various conditions, both on a human and a small-animal MRI scanner. In parallel, we assessed the shielding efficiency at 661 kev of the most promising candidates. These experiments showed that there is a range of possibilities for the design of MR-compatible gamma shields. Lead has acceptable magnetic compatibility but can induce significant conductivity-related artefacts. Heavy-metal-based minerals are fully insulating and hot-pressed lead monoxide showed good MR compatibility combined with good shielding properties. Other possibilities include the use of lead based powders and heavy-metal oxide composites. Index Terms--Magnetic resonance imaging (MRI), positron emission tomography (PET), shielding.

In this paper, we report on the investigation of silicon avalanche photodiodes (APDs) for high-energy photon imaging applications. This includes a new APD design that provides X-ray and [gamma]-ray imaging with significant reduction in electronic readout requirements. This new APD design, referred to as position-sensitive avalanche photodiode (PSAPD), involves charge sharing amongst the electrodes that enable determination of position of interaction. PSAPDs with 14 x 14 [mm.sup.2] area have been fabricated using planar processing. The performance of these devices has been evaluated for energy resolution, timing resolution (4 ns full-width at half-maximum), and spatial resolution (~300 [micro]m intrinsic spatial resolution). The potential of these APDs in high-energy physics and medical imaging is addressed. Index Terms--Avalanche photodiode, imaging, nuclear, position-sensitive detector.

The report stated that control of the relative humidity of the plasmid DNA sample has made it possible to study systematically the effect of hydration on the induction of damage by direct energy deposition in the DNA-water complex, using enzymatic approaches to reveal base lesions. It is also stated that the nucleobases are oxidized by H(sub 2)O(one dot)(super +) in competition with its conversion to hydroxyl radicals, which if formed do not produce ssb's presumably due to their scavenging by Tris present in the samples.

Gamma-ray imaging using quasi-monochromatic and energy-tunable photon beam was performed. The photon was produced by the laser-Compton backscattering of 300-800 MeV electrons with laser photons. Radiographs of several objects were measured using 3-20 MeV quasi-monochromatic photons. Index Terms--Compton scattering, gamma ray, imaging, laser, radiography.

Three-dimensional gamma-ray computer tomography offers oceanographers an advantage over traditional X-ray computer tomography, as it significantly extends capabilities for quantitative analysis. The technique is applied to polymetallic nodules in the Pacific Ocean's Clarion-Clipperton region for illustration.

Byline: M. A. Rahman (1), P. N. Bhat (2), B. S. Acharya (1), V. R. Chitnis (1), P. Majumdar (1), P. R. Vishwanath (1) Keywords: atmospheric attenuation; atmospheric Cerenkov technique; Cerenkov photon growth curve; Cerenkov spectrum; UV component in Cerenkov radiation; VHE I3-rays Abstract: We study the propagation of Cerenkov photons generated by Very HighEnergy I3-rays and hadrons in the atmosphere. The photon productionheight distributions are estimated from semi-empirical methods andcompared with those derived by standard simulation techniques. Incidentspectra at various observation altitudes are then derived after applyingwavelength dependent corrections due to photon attenuation in theatmosphere during the propagation of photons from the height of productionto the height of observation. These are generated both for I3-ray and hadron primaries of various energies. The derivedproduction height distributions agree very well with those generated bythe simulation package `CORSIKA' at all energies and for both I3-ray and proton primaries. The incident photon spectra are found to beboth altitude and primary energy dependent. The peak ofthe incident spectrum shifts towards the shorter wavelength withincreasing altitude of observation for a given primary. Also the peak ofthe photon spectrum shifts towards the shorter wavelength withincreasing energy of the primary at a given altitude. The fraction of the UVcomponent in the incident Cerenkov spectrum is estimated both forI3-ray and hadronic primaries at various observation altitudes andenergies. Hadron generated Cerenkov spectra are marginally richer in UVlight and the difference increases slightly at higher altitudes. The fraction of the UV to the visible light in the Cerenkov spectrum could be a usefulparameter to separate I3-rays from cosmic ray background only if onecan measure this fraction very accurately. Author Affiliation: (1) Tata Institute of Fundamental Research, Colaba, Mumbai, 400 005, India (2) Tata Institute of Fundamental Research, Colaba, Mumbai, 400 005, India Article History: Registration Date: 12/10/2004

X-ray and gamma-ray spectrometers are being developed with high absorption efficiency and high energy resolution.

The results of investigation of gamma irradiated blends of high-density polyethylene (PE) with thermotropic polymer liquid crystal (PLC) are presented. The PLC used was a copolyester of 40% poly(ethylene terephthalate) with 60% p-(hydroxybenzoic acid). The PLC content in the blends was 0, 5, and 10 wt%. The constituents were blended with the use of a single screw extruder. The specimens were prepared by compression molding. The irradiation of the samples was performed by a [Co.sup.60] [Gamma]-radiation source in inert atmosphere (argon) up to absorbed relatively low doses (up to 200 kGy; 1 Mrad = 10 kGy). The morphological, thermal, and mechanical properties were investigated for irradiated and unirradiated samples. The influence of gamma irradiation and addition of PLC on the temperature dependence of the elastic modulus as well as the effect of a 'form memory' of the materials examined are discussed. It was found that an addition of the PLC affects substantially the stress-strain relationship in tension at temperatures above the melting point of PE for the irradiated samples. The features of thermomechanical behavior of the PE + PLC blends, previously irradiated and oriented, at isometrical heating and cooling were also established. The results obtained testify that the addition of PLC to PE makes it possible to improve considerably the thermosetting properties of the heat-shrinkable polymeric products., INTRODUCTION High energy irradiation (gamma or electron beams) is the well-known technique for the modification of polymers (1-5). The radiation processing of polymers can successfully compete with the chemical processing [...]

Depth of interaction (DOI) measurement is an important capability for a detector suitable for use in a small PET scanner designed for breast imaging or small animal imaging. We have investigated a different scheme to determine DOI by using a position sensitive PMT (PS-PMT) at one end of an LSO crystal array for positioning and timing, and a single channel PMT connected to the other end through bent optical fibers with the ratio of the two signals to determine DOI. The main advantage of this approach is that both the PS-PMT and PMT can provide high signal-to-noise ratio outputs (improving DOI resolution) and that the necessary technology is available with easy readout electronics. Therefore, the design permits a relatively simple and practical solution to measure DOI while still maintaining good detector performance. We have successfully bent optical fibers, with a light loss due to fiber bending less than 12% for bending angles from 90 to 130 degrees and for a radius of curvature from 2 to 10 mm. Preliminary measurements for a detector with 2x2x21 [mm.sup.3] LSO scintillators and a Hamamatsu R5900-C8 PS-PMT reveal good DOI measurement capability with this design, with the measured DOI resolution ranging from 4.2 to 6 mm. It also provides excellent crystal identification and coincidence timing performance. The attenuation and scatter effects introduced by using optical fibers were also studied.

We are developing a small gamma camera for scintimammography with [Tc.sup.99m] (140 keV). The camera is based on coupling wavelength-shifting fibres (WSF) to the surface of an inorganic scintillation crystal - CsI(Na) - in order to obtain information about the position of interaction of the gamma rays. We have performed experimental measurements on the light output of 1 mm round multi-clad WSFs coupled to two CsI(Na) slabs, 3 and 5 mm thick. The results show a mean of 3.8 photoelectrons per gamma ray interaction of [Co.sup.57] 122 keV, with a mean of 1 photoelectron at the fibre located nearest the collimated beam of gamma rays, for the 3 mm thick crystal. Simulations based on the single electron response of Photomultiplier Tubes show that a 1.7 mm FWHM spatial resolution can be achieved with this camera design. The camera can be shaped to suit any application, it is compact and has low cost, which, together with its predicted performance in terms of spatial resolution, makes this concept very promising as a small gamma camera for 140 keV.