Abstract
A precise measurement of the angular correlation of two gamma-rays emitted from copper single crystals by the annihilation of positrons has been carried out. The crystals were irradiated by neutrons to produce 1∼2 C of 64Cu so that the positrons were confined in the crystals. This containment of the strong positron sources in the crystals allowed us to use two pairs of slits perpendicular to each other rather than the ordinary one pair of slits. With this geometry inaccuracies in determining the shape of the Fermi surface due to poor resolutions were considerably eliminated.
The necks of the Fermi surface of copper were found on the curves of the angular correlation. The observed value of the radius of these necks, 2.7×10−20 gr·cm/sec, agrees with those obtained by the magnetoacoustic effect etc.. The maximum momentum of electrons in the ⟨111⟩-directions was found to be 1.60×10−19 gr·cm/sec, which agrees well within the experimental error with the distance of the {111}-Brillouin zone boundaries from the origin of the momentum space, 1.587×10−19 gr·cm/sec.. The latter fact gives a new evidence to the current conclusion that the annihilating electron pair moves freely from the other electrons in metals.
The present method of containment of the strong positron sources in specimens themselves will be useful for the investigation of the Fermi surfaces of various copper alloys which have never been studied by other experimental methods.
