A diamond that has been treated by one of several modern scientific processes (e.g. exposure to radium bromide or bombardment with atomic particles, electrons or neutrons) whichresults in changing the colour to green or in some cases to blue or pink (on the surface or throughout, temporarily or permanently) and sometimes further changing to yellow or brown by applying heat.
Some such processes leave the stones radioactive for varying periods of time. The early experiments of exposure to radiation were performed in 1904 by Sir William Crookes, and some stones so treated by him are still radioactive, with the induced green colour unchanged. Few diamonds have been so treated, and they can be distinguished by various laboratory tests. Such diamonds are variously termed 'irradiated' (or 'radium-treated'), 'cyclotroned', 'electroned', 'neutron-treated', or 'pile treated'.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson