Chemical Quenching and Inhibition of Positronium in Cr_2O_3/Al_2O_3 Catalysts  

作　　者：HUANG Shunhong DAI Yiqun ZHANG Hongjun CHEN Zhiquan 

机构地区：[1]Hubei Nuclear Solid Physics Key Laboratory/School of Physics and Technology, Wuhan University, Wuhan 430072, Hubei, China

出　　处：《Wuhan University Journal of Natural Sciences》2011年第4期308-312,共5页武汉大学学报（自然科学英文版）

基　　金：Supported by the National Natural Science Foundation of China (10875088, 11075120)

摘　　要：The pore structure of Cr2O3/Al2O3 catalysts and the surface chemical properties of these pores were characterized by positron lifetime and coincidence Doppler broadening （CDB） measurements. Four lifetime components could be resolved from the positron lifetime spectrum, with two long lifetime components and two short lifetime components. The two long lifetimes τ4 and τ3 are attributed to ortho-positronium （o-Ps） annihilation in large pores and microvoids, respectively. With increasing Cr2O3 content, both τ4 and its intensity I4 show sharp decrease, while τ3 and its intensity I3 keep nearly unchanged. The Doppler broadening S parameters also show sharp decrease with increasing Cr2O3 content. Detailed analysis of the CDB spectrum reveals that the parapositronium （p-Ps） intensity also decreases with increasing Cr2O3 content. This indicates that the change of o-Ps lifetime τ4 is due to the chemical quenching by Cr2O3 but not spin-conversion of positronium. The decrease of o-Ps intensity I4 indicates that Cr2O3 also inhibits positronium formation.The pore structure of Cr2O3/Al2O3 catalysts and the surface chemical properties of these pores were characterized by positron lifetime and coincidence Doppler broadening （CDB） measurements. Four lifetime components could be resolved from the positron lifetime spectrum, with two long lifetime components and two short lifetime components. The two long lifetimes τ4 and τ3 are attributed to ortho-positronium （o-Ps） annihilation in large pores and microvoids, respectively. With increasing Cr2O3 content, both τ4 and its intensity I4 show sharp decrease, while τ3 and its intensity I3 keep nearly unchanged. The Doppler broadening S parameters also show sharp decrease with increasing Cr2O3 content. Detailed analysis of the CDB spectrum reveals that the parapositronium （p-Ps） intensity also decreases with increasing Cr2O3 content. This indicates that the change of o-Ps lifetime τ4 is due to the chemical quenching by Cr2O3 but not spin-conversion of positronium. The decrease of o-Ps intensity I4 indicates that Cr2O3 also inhibits positronium formation.

关 键 词：Cr2O3/Al2O3 catalyst POSITRONIUM chemical quenching pore structure 

分 类 号：O572.322[理学—粒子物理与原子核物理] O643.36[理学—物理]