符合多普勒展宽测量系统的性能研究  

Performance of a positron annihilation coincidence Doppler broadening spectrometer

作　　者：王丹妮[1,2] 王宝义[1] 张兰芝[1,2] 钟玉荣[1,2,3] 章志明[1] 李道武[1] 魏龙[1] 张天保[1] 

机构地区：[1]中国科学院高能物理研究所核分析技术重点实验室,北京100049 [2]中国科学院研究生院,北京100049 [3]烟台大学光电信息学院,山东264005

出　　处：《核技术》2008年第8期577-582,共6页Nuclear Techniques

基　　金：国家自然科学基金(10575112,60606011,10705031)资助

摘　　要：研制了一套具有外触发和内触发两种工作模式的高性能符合多普勒展宽测量系统（Coincident Doppler Broadening，CDB），其中外触发模式具有更好的时间分辨（FWHM〈7ns）和更高的峰谷比（〉10^6），适于强源高计数率测量（符合计数率〉200／s）；数字化的内触发模式，由于不需要复杂的外围电路，造价便宜、稳定性好因而更为实用，但时间分辨率（94ns）和峰谷比（〉10^5）明显逊于外触发模式。通过软件算法进行滤堆积处理后，在低符合计数率（～100／s）测量时峰谷比也能达到外触发水平（10^6）。本文系统介绍了谱仪的基本性能，测试了高纯金属标样Cu、Ni、W和A1的多普勒展宽谱，同时通过飞行正电子湮没（Positron Annihilation in Flight）实验验证了相对论动能公式E^2tatal=p^2c^2＋m^2ec^4，结果表明谱仪在时间分辨和去本底（峰谷比优于10^6）方面都具有较高的性能；作为应用例，表征了偏离正常化学比NiA1合金正电子湮没位置的化学环境，结果表明，CDB系统对开空间缺陷周围的化学环境变化具有较高的灵敏性，在材料微结构研究领域具有广泛的应用前景。A positron annihilation CDB （coincident Doppler broadening ） spectrometer of high-performance has been developed with modes of external and internal triggers. The external trigger mode, with time resolution of 〈 7 ns （FWHM） and peak/background ratio of better than 10^6, is applicable to measurements at high coincident count rate over 200/s. The internal trigger mode has a time resolution of 94 ns and peak/background ratio of 〉10^5. It, is not as good as the external trigger mode, but the peak/background ratio can be increased to10^6 after pileup signals are rejected by an arithmetic code, so as to be applicable to measurements at 100/s or lower coincident count rates. The internal trigger mode is simple and convenient to use, unlike the external mode. In addition to performance determination of the CDB spectrometer, CDB spectra of pure Cu, Ni, W and A1 were measured and relativistic kinetic energy formula E2total =p^2c^2 ＋ m^2ec^4 was validated by observing positron annihilation in flight. The results show that performance of this spectrometer is favorable in time resolution and background restraint. As an application example, chemical surroundings around the intrinsic vacancy-type defects in NiA1 alloys at deviations from the stoichiometric compositions were investigated. The results indicate that the spectrometer is highly sensitive to element variations around open-volume defects and has wide application prospect in the field of microstructure investigation of materials

关 键 词：正电子湮没 符合多普勒展宽 性能研究 

分 类 号：O571.23[理学—粒子物理与原子核物理] O483[理学—物理]