A single photon decay is only possible if another body (e.g. an electron) is in the vicinity of the annihilating positronium to which some of the energy from the annihilation event may be transferred.

The need to see if it really has the properties our theories suggest it should have, and also to learn how it can interact with normal matter-it need not always result in an annihilation event.

Every annihilation event produced a minute gravity pulse, and the additive effect of large numbers of these pulses occurring every second gave the apparently steady field that was perceived macroscopically.

Every annihilation event produced a microscopic, transient gravity pulse, and it was the additive effect of millions of these pulses occurring every second which, when perceived at the macroscopic level, produced the illusion of a steady field.

These algorithms compute an estimate of the likely distribution of annihilation events that led to the measured data, based on statistical principles.

Other low-level annihilation events will also take place, albeit very slowly.

Unlike PET, the radioisotopes used in SPECT (such as technetium-99m) emit γ-rays directly, instead of from annihilation events of a positron and electron.

These TGFs have included gamma rays with an energy of 511 keV-the energy signature of an electron-positron annihilation event.

NASA is trying to determine if such galaxies exist by looking for X-ray and gamma-ray signatures of annihilation events in colliding superclusters.

Data from PAMELA indicated that these annihilation events occurred a thousand times more often than would be expected in the absence of antimatter.