Positron Annihilation in Nitric Oxide and Nitrogen Dioxide

Abstract

Positron-annihilation lifetimes in nitrogen dioxide and nitric oxide gases are carefully determined. Nitrogen is used as a dilutant. The free-positron-annihilation rate in units of the effective number of electrons per molecule Z,f& for nitrogen dioxide as a mixture of dimers and monomers is determined to be 720 to 1090 and the free-positron-annihilation rate for nitric oxide is Z,&f =34. The positronium quenching rate in nitrogen dioxide gas is very high and the conversion reaction by NO2 is found to be mainly responsible for the quenching. The quenching rate is determined to be 460D nsec ' amagat ', where D is the partial density. The positronium quenching rate in nitric oxide is determined to be only about 0.1GD nsec ' amagat, and it changes with the concentration of nitrogen.

The quenching of ortho ‐positronium

“…5 Attachment (chemical) quenching The gases NO 2 , Br 2 , and I 2 are known to have extremely high Ps quenching rate [5,6]. If we normalize the rate into 1 Z eff , the values are higher than 10 4 , as seen in Fig.…”

“…The values listed there are plotted in Fig. 1, together with the values calculated from the reported chemical and spin exchange quenching rates [5][6][7].…”

“…[3]. The values for NO, NO 2 , Br 2 and I 2 are calculated from the reported values of the annihilation rate [5][6][7]. …”