Program - Brookhaven National Laboratory

R. Hirschi, A. Hungerford, G. Magkotsios, M. Pignatari, G. Rockefeller, F. X. Timmes, and P. Young,
“Nucleosynthesis simulations for a wide range of nuclear production sites from NuGrid” in Proc. of the
10th Symp. on Nuclei in the Cosmos (NIC X), 23 (2008). http://www.astro.keele.ac.uk/nugrid.
PR 3
Are Meteorite Impacts Nuclear Events?
Richard B. Firestone, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Global radiocarbon abundance has long been presumed to be in equilibrium between its production by
cosmic rays and its β − -decay with a half-life of 5730 years. This formed the basis of radiocarbon dating, first
developed by Libby 1 in 1949. Soon after it was discovered, by comparison with tree ring data, that there
was substantially more radiocarbon in the past than today. This led to the measurement and evaluation
of the IntCal 2 radiocarbon calibration curves, based on tree ring and marine sediment data for the past
50 kyr, for the correction of radiocarbon dates to calendar dates. I have shown 3 that the large increases
global radiocarbon are mainly attributed to the explosions of four supernovae, ¡250 pc from earth, 44-,
37-, 32-, and 22-kyr ago. Another large increase is observed in the global radiocarbon record about 13 kyr
ago, but this increase lacks the unique temporal signature of the earlier supernovae. This event coincides
with the Younger Dryas (YD) extraterrestrial impact that is postulated to have caused the extinction
of the mammoths and other megafauna and the sudden onset of a 1300 year period of global cooling 4 .
Radiocarbon dating of numerous carbon samples taken from the YD impact layer gave anomalously young
dates, sometimes hundreds of years into the future, despite indisputable stratigraphic evidence that they
are about 13 kyr old. Similar, albeit smaller, increases in radiocarbon are also observed in the radiocarbon
record coincident with the Tunguska (1908 AD), Japan (775 AD), Dark Ages (536 AD), and Great Flood
(2807 BC) impacts. Meteors and comets travel at velocities 10-70 km/s impacting with sufficient energy to
initially raise temperatures to ¿10 7 K at the impact site, well above the temperature necessary to sustain
nuclear fusion. If the impact site were sufficiently hydrogenous, neutrons produced by D+D fusion could
induce 14 N(n,p) 14 C, enriching the radiocarbon abundance in the impact plume. In this talk I will compare
the amount of 14 C that was produced globally at the time of the YD impact with calculated production
rate if the impact occurred in water. This work was performed under the auspices of the U.S. Department
of Energy under Contract No. DE-AC02-05CH11231.
[1] W. F. Libby, E. C. Anderson, and J. R. Arnold, Science 109, 227-228 (1949). [2] P.J. Reimer et al.,
Radiocarbon 51, 1111-1150 (2009). [3] R.B. Firestone, Evidence of four prehistoric supernovae