M. Skalsey, DISCUSSION ON THE LOWEST ENERGY POSITRON DECAY, Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment, 408(2-3), 1998, pp. 486-490
Positrons (e(+)) from Ni-59 decay have a maximum energy of 51 keV, the
lowest known energy for a e(+) transition. The identifying signal is
e(+)e(-) annihilation into two 511 keV gamma-rays that can be readily
observed. Modern Ge detector arrays offer the opportunity to accuratel
y check the Ni-59 result (to resolve an apparent error in the intensit
y) and, further, to search for even lower energy e(+) decays. The extr
emely small e(+) branching ratios associated with such decays: (1) req
uire efficient detection and suppression of backgrounds and (2) limit
the practical utility of low energy e(+) transitions. Branching ratio
results for allowed low energy e(+) decays could be compared to atomic
theory calculations and, at high precision, test weak interaction the
ory. (C) 1998 Elsevier Science B.V. All rights reserved.