A COMPARISON OF NATURAL AND LABORATORY-INDUCED RADIATION DAMAGE IN GEM DIAMOND

For over a century, radiation has been used as a tool to change the color of gem diamonds. The earliest treatments used radium salts and left the diamonds radioactive while current treatments are typically done using electron beams of various intensities with no residual radioactivity. Irradiation treatments (like natural processes) mainly serve to displace carbon atoms from their lattice positions to create vacancies and produce green or blue diamond colors. This process also creates a number of interstitial-related centers as well as more complex defect structures depending on what other impurity defects are present. Post-irradiation annealing creates additional color centers that can produce yellow or pink coloration. Strongly colored, naturally irradiated gem diamonds are highly coveted in the jewelry industry due to their rarity. However, similarities between the natural irradiation processes and those performed in a laboratory present considerable difficulty in identification.

In order to better understand the differences between radiation damage introduced in nature and that produced by bombarding a gem with subatomic particles in a lab, we have conducted irradiation experiments under carefully controlled conditions and characterized the results for 47 gem diamond samples. For comparison, over 250 naturally irradiated diamonds from eastern Zimbabwe were also characterized. Clear changes in appearance as well as absorption and luminescence spectroscopy (IR, UV-VIS, PL) are seen in diamonds before and after laboratory irradiation. Many of the spectroscopic features introduced by irradiation treatment are not observed in the naturally irradiated samples from Zimbabwe, offering the potential for use in gem identification.