The Cretaceous–Tertiary (K–T) mass extinction ~66 million years ago is believed to be the result of a massive impact.
Alvarez et al.  found strong evidence for the hypothesis that an extraterrestrial cause was responsible for this event. More recently, additional work points to an asteroid impact. Other possibilities would be a comet but also, as already discussed in their original publication by Alvarez et al., a supernova-explosion could be a possibility. These authors searched for a specific long-lived radionuclide, 244Pu, which has a half-life of 81 million years. Under the assumption that this nuclide is only produced in supernova explosions, its presence would be a clear indicator of a nearby supernova explosion. No 244Pu was detected at that time thus the authors concluded that a solar object was the most probable cause.
We have organised a sample from exactly the same region in Italy that was analysed by the authors and where they found for the first time enhanced iridium concentrations in a sedimentary layer. Within an international collaboration we have access to more material. Since the original work, 244Pu detection-sensitivity, however, has improved by more than a factor of a million. We will apply Accelerator Mass Spectrometry (AMS) for 244Pu measurements. AMS is the most sensitive technique for Pu analysis.
Within this project we will analyse a sample from this time period to exclude a supernova cause providing a much more stringent limit on extraterrestrial 244Pu influx.
 L.W. Alvarez et al., Extraterrestrial Cause for the Cretaceous-Tertiary Extinction, Science 208 (1980) 1095.