Twenty pure elemental metal samples have been studied with a coincidence Doppler broadening system （CDB）. The results show the relationship between the CDB spectra and the electronic structure of these samples. The ...Twenty pure elemental metal samples have been studied with a coincidence Doppler broadening system （CDB）. The results show the relationship between the CDB spectra and the electronic structure of these samples. The experimental results are compared to simple theoretical predictions, which show that the high-momentum part of the Doppler-broadening spectra can be used to distinguish different elements.展开更多
Coincidence Doppler broadening measurements of positron annihilation for multi- walled carbon nanotubes, double-walled carbon nanotubes, single-walled carbon nanotubes and graphite were performed. The ratio curves of ...Coincidence Doppler broadening measurements of positron annihilation for multi- walled carbon nanotubes, double-walled carbon nanotubes, single-walled carbon nanotubes and graphite were performed. The ratio curves of the Doppler broadening for these samples to silicon were obtained. It is shown that there are distinct peaks at the position of 10xl0-arn0c for both carbon nanotubes and graphite, however the amplitudes of the peaks are not the same. We have the opinion that these peaks arise from the annihilation of positron with the 2s and 2p electron of carbon element.展开更多
The interstitial solution carbon concentration and defects in continuously annealed Ti＋Nb bearing ULC- BH （ultra-low carbon bake hardening） steel samples are investigated by multi-functional internal friction appar...The interstitial solution carbon concentration and defects in continuously annealed Ti＋Nb bearing ULC- BH （ultra-low carbon bake hardening） steel samples are investigated by multi-functional internal friction apparatus, positron annihilation lifetime spectroscopy （PALS） and coincidence Doppler broadening spectroscopy （CDBS）. The relationship of internal friction peaks, interstitial solution carbon concentrations and movable dislocations in the sam- ples under different conditions is analyzed. A correlation of lifetime component v~ values with interstitial solution car- bon concentrations in the samples for different continuous annealing processes is established, while a correlation of li- fetime component r2 values with multi-vacancies, vacancy clusters, microvoids and other types of defects for various continuous annealing processes is also demonstrated. Furthermore, the average lifetime results illustrate the overall defect densities for various continuous annealing processes. The CDBS analysis reflects the chemical surroundings of the defects at the annihilation sites and reveals that the peak heights of the ratio curves relate to the total number of defects such as interstitial carbon atoms, dislocations, vacancies and other types of defects. The results show that in- ternal friction, PALS and CDBS are effective techniques to identify and characterize the interstitial solution carbon concentration, multi-vacancies, vacancy clusters, microvoids and other types of microscopic defects in annealed Ti＋ Nb bearing ULC-BH steel.展开更多
基金ACKN0WLEDGEMENT This work is supported by the Foundation of Chinese Academy of Sciences （CAS） for Back Abroad the Foundation of the president of CAS and the Foundation of the CAS knowledge Innovation Project the National Natural Science Foundation of China （No.10175061）.
文摘Twenty pure elemental metal samples have been studied with a coincidence Doppler broadening system （CDB）. The results show the relationship between the CDB spectra and the electronic structure of these samples. The experimental results are compared to simple theoretical predictions, which show that the high-momentum part of the Doppler-broadening spectra can be used to distinguish different elements.
基金supported by National Natural Science Foundation of China (No.10835006)
文摘Coincidence Doppler broadening measurements of positron annihilation for multi- walled carbon nanotubes, double-walled carbon nanotubes, single-walled carbon nanotubes and graphite were performed. The ratio curves of the Doppler broadening for these samples to silicon were obtained. It is shown that there are distinct peaks at the position of 10xl0-arn0c for both carbon nanotubes and graphite, however the amplitudes of the peaks are not the same. We have the opinion that these peaks arise from the annihilation of positron with the 2s and 2p electron of carbon element.
基金Item Sponsored by National Key Technology Research and Development Program in 11th Five-Year Plan of China(2006BAE03A13)
文摘The interstitial solution carbon concentration and defects in continuously annealed Ti＋Nb bearing ULC- BH （ultra-low carbon bake hardening） steel samples are investigated by multi-functional internal friction apparatus, positron annihilation lifetime spectroscopy （PALS） and coincidence Doppler broadening spectroscopy （CDBS）. The relationship of internal friction peaks, interstitial solution carbon concentrations and movable dislocations in the sam- ples under different conditions is analyzed. A correlation of lifetime component v~ values with interstitial solution car- bon concentrations in the samples for different continuous annealing processes is established, while a correlation of li- fetime component r2 values with multi-vacancies, vacancy clusters, microvoids and other types of defects for various continuous annealing processes is also demonstrated. Furthermore, the average lifetime results illustrate the overall defect densities for various continuous annealing processes. The CDBS analysis reflects the chemical surroundings of the defects at the annihilation sites and reveals that the peak heights of the ratio curves relate to the total number of defects such as interstitial carbon atoms, dislocations, vacancies and other types of defects. The results show that in- ternal friction, PALS and CDBS are effective techniques to identify and characterize the interstitial solution carbon concentration, multi-vacancies, vacancy clusters, microvoids and other types of microscopic defects in annealed Ti＋ Nb bearing ULC-BH steel.
