A Sharp Gamma-Ray Hologram

A sharp gamma-ray hologram, with atomic-scale resolution, has been achieved for the first time by physicists in Krakow at the University of Mining and Metallurgy. It is useful to compare x-ray with gamma holograms. In an x-ray hologram (Update 262) a beam of x rays strikes atoms and promotes electrons into excited states. The atoms return to their ground states by emitting fluorescence x rays some of which reach a detector unscattered and some of which scatter from surrounding atoms. The interference of the scattered ("object") and unscattered ("reference") x rays forms a hologram which provides an atomic-scale image of the atoms in their crystalline matrix.

In the gamma approach the incoming gamma rays excite not atoms (iron-57 atoms) but their nuclei. Any particular nucleus in the sample can be excited by either an unscattered gamma (acting as the "reference wave") or a previously scattered gamma (acting as the"object wave "). The excited nucleus de-excites by emitting electrons (conversion electrons) which are then detected. One problem plaguing previous attempts at gamma holography, that of "twin images," a sort of double vision suffered by the image reconstruction process, has now been overcome, resulting in 3D images of the local crystal structure to be rendered with half-angstrom spatial resolution (see figure at Physics News Graphics).

Pawel Korecki, now at the DESY lab in Hamburg (49-408-908-2602, pawel.korecki@desy.de), and his colleagues believe that soon gamma holography will map not only structure but also the local magnetic environment as well. (Korecki et al., Physical Review Letters, 19 February 2001; text at Physics News Select)