Investigation of positron annihilation-in-flight using a digital coincidence Doppler broadening spectrometer

Abstract

This work reports on precise measurements of two-quantum positron annihilation-in-flight using a digital coincidence Doppler broadening spectrometer. Annihilation-in-flight was measured for positrons emitted by 68 Ge/ 68 Ga and 22 Na radioisotopes and for various targets. Experimental data were compared with theoretical prediction by quantum electrodynamics. It was found that two-quantum positron annihilation-in-flight can be clearly recognized in two-dimensional coincidence Doppler broadening spectra as a hyperbolic curve with shape described well by the relativistic theory. The contribution of annihilation-in-flight is determined predominantly by the energy of incident positrons and is only weakly dependent on the target material. The profile of the positron annihilation-in-flight contribution for positron kinetic energies above 100 keV is well described by theory.

Cage‐Like B41+ and B422+: New Chiral Members of the Borospherene Family

“…Low‐lying structures were then fully optimized and their relative energies evaluated at both the hybrid density functional theory (DFT) levels PBE033 and CAM‐B3LYP34 with the 6‐311+G* basis set35 implemented in Gaussian 09 suite 36. The relative stability of the two lowest‐lying isomers are further calculated with the more accurate coupled cluster method with triple excitations (CCSD(T))37–39 implemented in MOLPRO40 using the 6‐31G(d) basis set at the PBE0 geometries. Chemical bonding analyses were performed using the adaptive natural density partitioning (AdNDP) method41 and visualized using the Molekel program 50.…”

“…CAM‐B3LYP includes long‐range corrections using the Coulomb attenuating method. The relative stabilities of the three lowest‐lying isomers were further refined using the more accurate coupled cluster method with triple excitations (CCSD(T))37–39 implemented in MOLPRO40 using the 6‐31G(d) basis set at the PBE0 geometries. The optimized structures of the chiral borospherene cations C 1 B 41 + ( 1 ) and C 2 B 42 2+ ( 2 ) and their degenerate enantiomers C 1 B 41 + ( 1′ ) and C 2 B 42 2+ ( 2′ ) are depicted in Figure 1.…”

Positronium Formation in Nanostructured Metals

“…(v) A bowl-like feature above the annihilation photo-peak is a contribution of positron annihilations in flight, i.e. 2 − γ annihilations of non-thermalized positrons [12,20,21]. Because of energy conservation E 1 +E 2 −2m 0 c 2 cannot be higher than the energy of incident positrons which is 30 keV in the present case.…”

“…Moreover, digital shape filters which are applied during analysis of sampled waveforms reject pulses with shape distorted by pile-up effects or ballistic deficit during charge collection in the detector [9]. As a consequence spectra with a high clarity and very low background were obtained using the digital CDB spectrometer [12].…”

Software for analysis of waveforms acquired by digital Doppler broadening spectrometer

“…Recent advances in this technique include development of a high-resolution digital spectrometer [1]. Excellent performance of this spectrometer was demonstrated by precise measurement of positron annihilation-in-flight [2]. Digital spectrometer exhibit not only superior energy resolution and signal-to-noise ratio over traditional analogue spectrometers but represent also more economical alternative.…”