Positron state Doppler broadening

AMOC allows time-dependent observations of the occupations and transitions of different positron states tagged by their characteristic Doppler broadening. Chemical reactions of positronium have been studied by beam-based AMOC as well as bound states between positrons (e+) and halide ions (cf. Sect. 2). 

In 1974, O.E. Mogensen and V.P. Shantarovich concluded from ACAR measurements on aqueous solutions of sodium chloride [15] that in this system a fourth positron state (in addition to p-Ps, free positrons and o-Ps) was formed, which they identified as an e+Cl bound state. The existence of such a bound state found support in several Doppler broadening and ACAR investigations on aqueous and non-aqueous solutions of halides and pseudohalides [16-20]. Since the commonly used expression bound state of positrons may lead to confusion with positrons bound in Ps, we refer to this fourth state as positron molecules and characterize it by the subscript M. 

The linewidth of annihilation from the free-positron state is Doppler-broadening measurements. In lifetime measurements the PsF component hides beneath the o-Ps component which has a similar lifetime. This is a case where the two-dimensional data analysis shows its great advantage As the Doppler broadening of each positron state is determined in its own time regime even positron states with similar features may be seperated from each other. Moreover, a tentative fitting procedure with only the three positron states as in pure water did not come to a satisfactory result with the AMOC histogram of the NaF solution. 

Hence, while the lifetime method yields information regarding the electron density in the region of electron-positron overlap through the determination of positron decay rates from various states in the metal, the method of angular correlation and Doppler broadening (the momentum technique) gives information regarding the... 

The positron lifetime experiments were carried out with a fast-slow coincidence ORTEC system with a time resolution of about 230 ps full width at half maximum. A 5mCi source of Na was sandwiched between two identical samples, and the total count was one million. The temperature-dependent Doppler broadening energy spectroscopic (DBES) spectra were measured using an HP Ge detector at a counting rate of approximately 800 cps. The energy resolution of the solid-state detector was 1.5 keV at 0.511 MeV (corresponding to positron 2y annihilation peak). The total... 

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