A new method is presented to calculate with improved accuracy the absolute peak efficiency of cylindrical Ge and Ge(Li) detectors
for point, disk and cylinder sources, positioned at any source-detector distance. Moreover attention was paid to true-coincidence
effects. The method is extensively tested and applied for the analysis of reference materials. The accuracy turned out to
be 3% or better.
Research associate of the “Nationaal Fonds voor Wetenschappelijk Onderzoek”. 相似文献
A pre-irradiation separation procedure, for gallium determination in biological and environmental materials by neutron activation analysis (NAA) is reported. The proposed method, based on ion-exchange chromatography, allows to eliminate the radiation risk, while taking the advantages of high sensitivity of NAA. The single comparator method is employed for gallium quantitative evaluation. Since no standard reference materials with certified gallium contents were available, the reliability of the proposed method was extensively investigated by various approaches. Four biological and one environmental standard reference materials, with gallium contents ranging from 54 g/g-3 ng/g, have been analyzed. 相似文献
A novel silicone and phosphate modified acrylate (DGTH) was synthesized and characterized by 1H NMR and FTIR. It was found that DGTH could be cured both by UV radiation and moisture mode with FTIR. The flammability and thermal behavior of the cured film were studied by the limited oxygen index (LOI), thermogravimetric analysis (TG) and real time Fourier transform infrared (RT-FTIR). The LOI value of the cured film is 48 and the TG data shows that the cured film has three characteristic degradation temperature regions, attributing to the decomposition of phosphate and polyurethane to alcohols and isocyanates, thermal pyrolysis of alkyl chains, and decomposition of unstable structures in char, respectively. The RT-FTIR data implies that the degraded products of phosphate form poly(phosphoric acid) further catalyse the breakage of carbonyl groups to form an intumescent char, preventing the samples from further burning. 相似文献
The amount of silicon sample used in instrumental neutron activation analysis (INAA) is generally less than twenty grams and the detection limits are in the range of ppb to ppt. The detection limits can be decreased further in several ways. Increasing neutron flux density, extending irradiation period and/or using more effective detector can improve the detection limits to some extent. Increasing sample weight, however, is a more feasible way to decrease the detection limits by a factor of hundreds with no new investment in existing irradiation/counting systems. In this work, two 8-inch high-purity silicon samples were analyzed by INAA to evaluate the validity and limitations of this concept in respect to neutron flux inhomogeneity, neutron shielding and -ray counting efficiency. 相似文献
The k0-values were determined for five high Q0(n,γ) reactions, including 74Se(n,γ) 75Se, 109Ag(n,γ) 110mAg, 114Cd(n,γ) 115Cd–115mIn, 130Ba(n,γ) 131Ba, and 152Sm(n,γ) 153Sm. These determinations were carried out under favorable experiment conditions: the irradiations were performed in a highly thermalized neutron flux, the irradiated target samples were counted at a far distance from HPGe detector with an efficiency carefully calibrated, and the k0-values were calculated against an internal comparator. When compared to the new values from this work, the 2003 recommended 110mAg k0-values are confirmed. The other confirmed recommended k0-value is that of 75Se 400.7 keV line. However, for the other 75Se γ-lines, the new k0-values are 4–10 % higher. It is assumed that an inaccurate efficiency calibration was used when the recommended k0-values were measured. For the other three nuclides, the new k0-values are higher by 4 % for the 115Cd–115mIn γ-lines, lower by 6–8 % for the 131Ba γ-lines, and lower by 8.8 % for the 153Sm 103.2 keV γ-line. 相似文献
The application of chitosan (CS) in new materials is a hot research topic. In this paper, CS was used alone as flame retardant to prepare thermoplastic polyurethane elastomer (TPU) composites. Then, the flame retardancy and thermal decomposition behavior of TPU/CS composites were intensively investigated using cone calorimeter test (CCT), scanning electron microscope (SEM), microscale combustion colorimeter (MCC) test, thermogravimetric analysis/infrared spectrometry (TG‐IR), and gas chromatography‐mass spectrometry (GC‐MS). The results showed that CS can reduce the fire risk of TPU; 2.0‐wt% CS could make the peak value of heat release rate (pHRR) decreased to 457.2 kW/m2, reduced by 65.9% compared with TPU. And the peak value of smoke production rate (pSPR) and total smoke release (TSR) of the same sample was decreased by 79.4% and 54.2%, respectively. The TG‐IR and GC‐MS results confirmed that CS could promote TPU decomposition in advance, reacting with the decomposition products of TPU. Therefore, the production of combustible gas was reduced. The GC‐MS results showed that the production of isocyanates and ethers was reduced with the addition of CS. The digital photographs of SEM for the samples after CCT were shown that the char residue layer of the sample containing 2.0‐wt% CS was fibrous in shape. It could be speculated that the thermal decomposition products from TPU could react with CS at low temperature, which reduced the production of flammable gases. So CS had a good prospect in reducing the fire hazard for TPU. 相似文献
CaCO3-containing oil sludge (OS) is a by-product from petroleum industry, with great amount of production. Therefore, an effective processing methods for CaCO3-containing OS is urgently needed. Herein, ethylene-vinyl acetate (EVA) composites based on CaCO3-containing OS and carbon black (CB) were prepared by melt blending method. The combustion behavior and thermal stability of flame-retardant EVA/OS/CB composites were investigated by cone calorimeter test, limiting oxygen index (LOI), scanning electron microscopy (SEM), smoke density test (SDT), and thermogravimetry-Fourier infrared spectrometry. The heat release rate and smoke production rate of the ternary composites containing 3% CB significantly decreased compared with the EVA/OS composites and pure EVA. Moreover, addition of a certain amount of CB could evidently increase LOI values. The morphologies and structures of the residues, revealed by SEM, ascertained that a better carbonaceous protective layer was formed on the ternary composites than the EVA/OS composite. It was obtained from SDT that CB in the material could retard the smoke production with the application of the pilot flame. The EVA/OS/CB composites assumed a higher thermal stability than the EVA/OS composites and pure EVA.