At 09:55 17/01/02 +0100, Julien Courtois wrote: >Short answer: YES, meteorites are radioactive, BUT not dangerous to humans. > >for a longer answer, please take your copy of "meteorites and their parent >bodies" by Harry Y. McSween, and look in the index for "spalliation" >(sp???).
For those who don't have McSween's "Meteorites and Their Parent Planets" on the shelf, here is what you would find on p. 211: "When cosmic rays strike the nuclei of atoms in orbiting pieces of rock or metal, they tend to dislodge protons and neutrons, a process known as spallation. The reactions change the identities of the target atoms; for example, the removal of one proton and two neutrons from 56Fe (an isotope of iron) produces 53Mn (an isotope of manganese). In some cases the newly created isotopes are sufficiently different from what already composes the object that they can be recognized and analyzed. Spallation-produced isotopes can be either stable or radioactive, but the radioactive ones are much easier to measure." [end of quote] Those who want to dig deeper into the details can enter "radioactivity meteorite" as search terms in the ADS query form: http://adsabs.harvard.edu/abstract_service.html The ADS database contains the full text of several articles describing laboratory analysis to measure radioactivity of specific meteorites, including one (Kobe) which was studied less than 24 hours after it fell. The reality is that this induced radioactivity caused by cosmic ray exposure is very, very weak, requiring bulky and sophisticated laboratory instruments to measure it at all. I cannot imagine that a hand held geiger counter held next to any meteorite would give an indication above background, even for a freshly fallen meteorite. In the articles which I looked at, none of the radioactive isotopes measured indicated an intensity of more than 100 dpm/kg (disintegrations per minute per kilogram of sample), and very low values of less than 10 dpm/kg were more typical of short-lived isotopes such as 28Mg and 57Ni. By comparison, the radioactivity of ordinary seawater is approximately 750 dpm/kg, attributable mainly to naturally occuring potassium-40. To give an idea how far these levels are from acutely dangerous levels: pure radium, which IS dangerously radioactive even for a brief exposure, has an activity of 2.22 million billion dpm/kg. Madame Curie would have undoubtedly lived longer if she had studied freshly fallen meteorites rather than radium. Since ALL natural objects are somewhat radioactive, the question "Is it radioactive?" is not very useful. Even the much better question "Is it dangerously radioactive?" is not always easy to answer with a simple yes or no without knowing details of the nature of exposure (non-contact, skin contact, ingestion, dust inhalation, etc.) and length of time exposed (seconds or decades?). For meteorites, it seems that one can safely answer "No more danger than common household objects." Best wishes to all, Piper ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
