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  • Author or Editor: R. Silva x
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Abstract  

This work presents a new approach using nuclear track in solids methodology (NTSM) for the energy analysis of alpha-particles. This method is based on the quantitative relationship between the energy deposited in the polycarbonate by the geometrical parameters of the developed track after the chemical etching. We used separated calibrated sources of 239Pu and 241Am, and a mixed source with 239Pu, 241Am and 244Cm. CR-39 polycarbonate manufactured by Landauer Inc.® was selected as the detector material, because of its excellent response to these energies. The chemical etching was done in two steps: (a) pre-etching to avoid the irregularities on the surface of the material, and (b) chemical etching to develop the track. In both processes the temperature and pH of the solution need to be very controlled. The geometrical characteristics of the formed tracks were analyzed automatically by Digital Image System. The results show a distribution of track diameters as a function of the energies analyzed analogous to the pulses produced on the conventional electronic detection system.

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Abstract  

This work presents an alternative method to map the distribution of transuranic elements, which is characterized by its simplicity in both implementation and instrumentation. The method is based on the interaction of alpha particles in polymeric materials and the formation of tracks, which become visible after chemical etching. Nuclear track detectors are placed on the soil in order to evaluate the distribution of the radioactive material and its relative intensity for transuranic contaminants. CR-39 polycarbonate was used as a nuclear track detector in this study. Chemical etching was done with a 6.25M KOH solution in a closed system for 16 hours. The readings were performed in an automatic system using digital image analysis. The results show the distribution of the contaminants and their location, identifying the zones with large intensities. This method is attractive for use in areas contaminated with alpha particles, and specially transuranic elements, because it involves in situ measurements, generates very low amounts of radioactive waste, and the detectors are easily handled.

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Abstract  

Nuclear Track Detectors (NTD's) are used as passive systems to detect the alpha contamination on flat or semirough surfaces. The procedure for the application of these devices is simple because the detector needs only to be placed on the area to be surveyed for a short period of time, collected and chemically processed to develop the alpha tracks. For the quantification of the results, it is necessary to have a calibration procedure. This paper presents the response of CR-39 (allyl diglycol carbonate), from American Acrylics and Pershore Companies, to alpha particles from Pu-239 (5.15 MeV) and Am-241 (5.48 MeV). The methods of etching and counting are outlined, along with the achievable linearity, efficiency and reproducibility. The sensitivity to low activity levels is also discussed.

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Abstract  

Nuclear Track Detectors (NTD's) are a useful option forin situ measurements of the distribution of alpha contamination as a function of soil depth. The contamination profile of alpha emitting elements, e.g. Pu, Am and U, can be determined by detecting their alpha emission at varying depths. This paper discusses a stake type device, containing strips of CR-39 (allyl diglycol carbonate) that can be inserted into the soil up to ten centimeters or more, depending on the firmness of the soil. The CR-39 is exposed directly to the contaminated soil for a few hours. The stake is then withdrawn from the soil, the plastic detectors recovered and the alpha tracks developed by chemical etching with KOH. The distribution of tracks can be used to determine the alpha contamination depth profile as well as for detecting hot spots. It has a sensitivity of less than a pCi/g of soil.

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Abstract  

This paper presents a method for the energy analysis of alpha-particles emitted by transuranic elements via a novel technique using Nuclear Tracks. The method is based on the relationship between the energy deposited in the detection material and the diameter of the track, that is formed by chemical etching. The method involves CR-39 polycarbonate as the detector material, one-step chemical etching after irradiation, and a digital image analysis system for automatic reading of the track diameters. The experimental study included alpha-particles in the energy range 5.1 MeV to 5.8 MeV emitted by239Pu,241Am and244Cm. The quantitative results provide a clear signature to identify each one of the emitters based on a characteristic track diameter.

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Summary  

In this paper, a new radiation detection method is introduced which uses a commercial gel material for the measurement of radon (222Rn) gas. This method is based on the diffusion of radon gas into the gel material and the measurement of the radioactive daughters resulting from the radon decay. The 214Bi daughter gamma-ray, with an energy of 0.609 MeV, was chosen for these measurements, and the gamma-ray photopeak was analyzed via a HPGe multichannel system. The results indicate a linear relationship between the integrated area of the 214Bi photopeak and the concentration of radon that had diffused into the gel material. Two very well defined radon response levels were observed: (1) from 150 to 1500 Bq . m-3 and (2) from 1500 to 7400 Bq . m-3. This method gives highly reproducible and reliable results in the measurements of radon. This new technique opens the door to future studies of different gel materials in order to obtain better sensitivity and new applications in the measurement of radioactive gases.

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Abstract  

The effect of Ag additions on the reverse martensitic transformation in the Cu-10 mass% Al alloy was studied using differential thermal analysis (DTA), optical (OM) and scanning electron microscopies (SEM) and X-ray diffractometry. The results indicated that Ag additions to the Cu-10 mass% Al alloy shift the equilibrium concentration to higher Al contents, allow to obtain both β'1 and β' martensitic phases in equilibrium and that Ag precipitation is a process associated with the perlitic phase formation.

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Abstract  

The effect of 4 mass% Ag addition on the thermal behavior of the Cu-9 mass% Al alloy was studied using differential scanning calorimetry (DSC), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results showed that the presence of silver causes (Cu)-α+(α+g1)→ (Cu)-α+β transformation to occur in two stages. In the first one, part of the produced b phase combines with the precipitated Ag to give a silver-rich phase and in the second one the transformation is completed. The formation of this silver-rich phase seems to be enhanced at very low cooling rates.

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Abstract  

The thermal behavior of the Cu-10 mass%Al and Cu-10 mass%Al-4 mass%Ag alloys was studied using classical differential thermal analysis (DTA), optical microscopy (OM) and X-ray diffractometry (XRD). The DTA curves were obtained for annealed and quenched samples. The results indicated that the presence of silver introduces new thermal events, associated to the formation of a silver-rich phase, to the shift of the equilibrium concentration to higher Al contents and to the decomposition of the silver-rich phase in the same temperature range of the b1 phase decomposition.

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Abstract  

This paper presents a method for measuring indoor radon concentrations using a commercially available air-purifying respirator filter as a component of the radon monitor. The filter used was Survivair’s NIOSH (National Institute for Occupational Health and Safety)-approved 100800 model. The method is based on the diffusion of radon gas into the activated carbon of the filter and the measurement of the radioactive daughters resulting from the radon decay. The photopeaks of the 214Bi daughter gamma rays (0.609 MeV) were analyzed with a Hyper-Pure Germanium (HPGe) detector and a multichannel system. A monotonically increasing and very close to linear response relation between the integrated area under the 214Bi photopeak and the radon concentration of the activated carbon was found. A well-defined relation held for radon levels ranging from 15 to 4,700 Bq/m3. This procedure results in highly reproducible and reliable measurements of indoor radon levels. Interesting applications include the investigation of radiological accidents involving radon and the retrospective measuring of indoor radon concentrations by analyzing the filters of the respirators worn by personnel working during the relevant period.

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