========================================================================= Date: Thu, 2 Aug 2001 05:48:44 -0700 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Moss McCarthy Subject: uniformitarianism MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Dear C14-L members, Please forgive this intrusion as I do not really belong here but am looking for assistance. My particular interest is epistemology and my knowledge of radiocarbon dating is rudimentary. I recently chanced across David Rohl's book on the proposed New Chronology of ancient societies. This revived memories of a BBC tv documentary, in the 'Chronicle' series, which I watched as a young man in the early seventies. Cosmic radiation is found to be quite uniform but our measurements only have a history of 100 years. Someone like myself has to ask how do we know that this has always been uniform. I believe that it was Lyle's Geology which first articulated the proposal that the laws of matter were invariant for all time. It was a necessary assumption for 19th century geology, and presumably remains so for modern cosmology, but was felt to be self-evident. What niggles me is that if beyond 2,500 BP there is a significant divergence of the predicted C14 count and that observed in saturated oak and bristle-cone pine. Is the uniformitarianist assumption empirically legitimate, especially in a cosmic setting? My apologies once again if this is merely the fanciful flight of ignorance. If anyone is able to direct my studies to where this question may be addressed, I would be most grateful. As yet I have found no one tackle it. Best Wishes Maurice McCarthy __________________________________________________ Do You Yahoo!? Make international calls for as low as $.04/minute with Yahoo! Messenger http://phonecard.yahoo.com/ =========================================================================== To unsubscribe from this list, send the command SIGNOFF C14-L to LISTSERV@LISTSERV.ARIZONA.EDU, or send a request to C14-L-request@LISTSERV.ARIZONA.EDU. ========================================================================= Date: Wed, 29 Aug 2001 13:19:51 -0600 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Bill Doleman Subject: Post-atomic contamination of C-14 samples Comments: cc: Janette Elyea MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Dear list: No doubt this question has been asked before in one context or another, but I think we might have a special case. In 2000, our office excavated a site in central New Mexico, ca. 30 east of Socorro, along US 380 where it crosses Chupadera Arroyo. Testing in 1999 revealed a lithic assemblage with apparent Archaic and PaleoIndian affiliations (e.g., 2000 BP and earlier) -- not surprising, given the site's proximity to both the Mockingbird Gap Clovis site, as well as an unreported Folsom site. Excavations confirmed the assemblage's pre-Formative characteristics, but the radiocarbon dates from the site (analyzed by Beta) are all Formative (post AD 500). Here's my question. The site also lies but 40-50 km almost due north of the Trinity site, where the first atomic bomb was exploded in 1945, and is at least partly downwind. Is it possible that the archeological charcoal was contaminated by bomb-generated C14, thus making them appear younger? The dated materials were recoverd from relatively porous, stabilized sheet sand deposits. Cheers, Bill Doleman +============================================+ | William Doleman, PhD | | Principal Investigator | | University of New Mexico | | Office of Contract Archeology | | 1717 Lomas NE | | Albuquerque, NM 87131 | | Voice: (505) 277-5853 || wdoleman@unm.edu | | Fax: (505) 277-6726 || | +============================================+ =========================================================================== To unsubscribe from this list, send the command SIGNOFF C14-L to LISTSERV@LISTSERV.ARIZONA.EDU, or send a request to C14-L-request@LISTSERV.ARIZONA.EDU. ========================================================================= Date: Thu, 30 Aug 2001 10:22:28 +1200 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Rodger Sparks Subject: Re: Post-atomic contamination of C-14 samples Mime-Version: 1.0 Content-type: text/plain; charset="us-ascii" This sort of question has cropped up from time to time, and the replies you receive no doubt will cover the full spectrum from "definitely" to "no way!". My contribution, made from a great distance and with no knowledge whatever of the detailed circumstances, is a qualified "maybe". We can safely assume that a significant amount of 14C was generated by the Trinity test. This will have been formed primarily in the atmosphere by the absorption of thermalised neutrons by nitrogen. The atmospheric 14C, initially in the form of CO, oxidising after some time to CO2, would have quickly dispersed, but some would have drifted over the archaeological site if the wind was in the right direction. However, it is a little difficult to see how this gaseous 14C could have become incorporated in charcoal buried at the site. Was there rainfall straight after the test, that could have brought some of the 14C down? If so, we still have the matter of binding it to the charcoal. The other possibility is the activation of nitrogenous solid material which was then dispersed as dust, coming down as particulate fallout. I suppose the possibility of some of this material mixing with the charcoal under the action of rainfall, wind movement etc. should be considered. However, even this contamination will be extraneous material that is unlikely to have bonded to the charcoal. Provided the charcoal was rigorously cleaned you would expect any contamination to be removed. If it was present, it could be expected to show up as enhanced activity in the washings, although I imagine you would not have checked that. A clue might be found in the dates themselves. How many samples from this site were dated? If there are several, do the dates cluster together or do they show a wide scatter? Bomb-14C that could shift an age from 2000 BP to post-500 BP could just as well make some samples modern. Was there any sign of this? If the dates tend to cluster I would think that this makes the contamination explanation less likely. The interesting thing about all this is that possibly a systematic study of this case could provide a reasonably definitive answer as to whether 14C-bearing fallout can contaminate material on the ground in such a way as to perturb the 14C age. Or has someone done this already? Rodger Sparks //////////////////////////////////////////////////////////////////////////////////////////// Rafter Radiocarbon Laboratory, Institute of Geological and Nuclear Sciences, 30 Gracefield Road, PO Box 31-312, Lower Hutt, New Zealand. Email: r.sparks@gns.cri.nz Fax: +64 4 570 4657 http://www.RafterRadiocarbon.co.nz ///////////////////////////////////////////////////////////////////////////////////////////// Dear list: No doubt this question has been asked before in one context or another, but I think we might have a special case. In 2000, our office excavated a site in central New Mexico, ca. 30 east of Socorro, along US 380 where it crosses Chupadera Arroyo. Testing in 1999 revealed a lithic assemblage with apparent Archaic and PaleoIndian affiliations (e.g., 2000 BP and earlier) -- not surprising, given the site's proximity to both the Mockingbird Gap Clovis site, as well as an unreported Folsom site. Excavations confirmed the assemblage's pre-Formative characteristics, but the radiocarbon dates from the site (analyzed by Beta) are all Formative (post AD 500). Here's my question. The site also lies but 40-50 km almost due north of the Trinity site, where the first atomic bomb was exploded in 1945, and is at least partly downwind. Is it possible that the archeological charcoal was contaminated by bomb-generated C14, thus making them appear younger? The dated materials were recoverd from relatively porous, stabilized sheet sand deposits. Cheers, Bill Doleman +============================================+ | William Doleman, PhD | | Principal Investigator | | University of New Mexico | | Office of Contract Archeology | | 1717 Lomas NE | | Albuquerque, NM 87131 | | Voice: (505) 277-5853 || wdoleman@unm.edu | | Fax: (505) 277-6726 || | +============================================+ =========================================================================== To unsubscribe from this list, send the command SIGNOFF C14-L to LISTSERV@LISTSERV.ARIZONA.EDU, or send a request to C14-L-request@LISTSERV.ARIZONA.EDU. ========================================================================= Date: Wed, 29 Aug 2001 15:43:44 -0700 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Ken Cole Subject: Re: Post-atomic contamination of C-14 samples In-Reply-To: MIME-version: 1.0 Content-type: text/plain; charset=us-ascii; format=flowed C14 List: I have long wondered about a similar hyper-radioactive date on a packrat midden collected from under an overhang in the Salt Creek member of the Morrison Formation in southern Utah at Capital Reef National Park. Packrat fecal pellets from the midden dated to 141.8% Percent Modern Carbon (A-5206) while an AMS date on pine needles from the same midden yielded a more reasonable date of 3615 +/- 70 yr B. P. (AA-6447). The midden appeared several thousand years old, am I am not sure that it is even possible to get C14 as high as 141% naturally, and certainly not if they were intermixed with 3000 year old pellets. Could something in the midden been contaminated by fallout from atomic testing? Or, more likely, some physiologist in the distant past contaminated my lab or equipment with a C14 tracer study. If the later is true, could traces of this laboratory contamination follow me around as specs on equipment and just alter later samples enough to only slightly screw them up, say from 10,000 years to 7,000 years? Ken Cole At 01:19 PM 8/29/01 -0600, you wrote: >Dear list: > No doubt this question has been asked before in one context or >another, but I think we might have a special case. > In 2000, our office excavated a site in central New Mexico, ca. 30 >east of Socorro, along US 380 where it crosses Chupadera Arroyo. Testing >in 1999 revealed a lithic assemblage with apparent Archaic and PaleoIndian >affiliations (e.g., 2000 BP and earlier) -- not surprising, given the >site's proximity to both the Mockingbird Gap Clovis site, as well as an >unreported Folsom site. Excavations confirmed the assemblage's >pre-Formative characteristics, but the radiocarbon dates from the site >(analyzed by Beta) are all Formative (post AD 500). > Here's my question. The site also lies but 40-50 km almost due >north of the Trinity site, where the first atomic bomb was exploded in >1945, and is at least partly downwind. Is it possible that the >archeological charcoal was contaminated by bomb-generated C14, thus making >them appear younger? The dated materials were recoverd from relatively >porous, stabilized sheet sand deposits. > >Cheers, > Bill Doleman > > >+============================================+ >| William Doleman, PhD | >| Principal Investigator | >| University of New Mexico | >| Office of Contract Archeology | >| 1717 Lomas NE | >| Albuquerque, NM 87131 | >| Voice: (505) 277-5853 || wdoleman@unm.edu | >| Fax: (505) 277-6726 || | >+============================================+ > >============================================================================ >To unsubscribe from this list, send the command SIGNOFF C14-L to >LISTSERV@LISTSERV.ARIZONA.EDU, or send a request to >C14-L-request@LISTSERV.ARIZONA.EDU. ****************************************** Dr. Kenneth L. Cole U.S. Geological Survey Colorado Plateau Field Station P.O. Box 5614, Bldg. 24 Northern Arizona University Flagstaff, AZ 86011-5614 Phone:(928) 556-7466 ext. 230 FAX:(928) 556-7500 E-mail: Kenneth.Cole@nau.edu Personal Web Pages: http://www.usgs.nau.edu/staff/kcole.html Office Web Pages: http://www.usgs.nau.edu/ ****************************************** =========================================================================== To unsubscribe from this list, send the command SIGNOFF C14-L to LISTSERV@LISTSERV.ARIZONA.EDU, or send a request to C14-L-request@LISTSERV.ARIZONA.EDU. ========================================================================= Date: Thu, 30 Aug 2001 08:10:51 -0500 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Chuck Blatchley Organization: Pittsburg State University Subject: Re: Post-atomic contamination of C-14 samples MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit A minor footnote, please: Rodger Sparks wrote: > > ... We can safely assume that a significant amount of 14C was generated > by the Trinity test. This will have been formed primarily in the > atmosphere by the absorption of thermalised neutrons by nitrogen. ... C-14 would be formed by fast neutrons in a 15N (n, p) 14C reaction. Thermal neutron absorption by N-15 produces N-16, which beta decays to O-16. However, as stated, the real issue is how and if the radiogenic carbon could get into the samples. Chuck Blatchley =========================================================================== To unsubscribe from this list, send the command SIGNOFF C14-L to LISTSERV@LISTSERV.ARIZONA.EDU, or send a request to C14-L-request@LISTSERV.ARIZONA.EDU. ========================================================================= Date: Fri, 31 Aug 2001 08:33:04 +1200 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Rodger Sparks Subject: Re: Post-atomic contamination of C-14 samples Mime-Version: 1.0 Content-type: text/plain; charset="us-ascii" A footnote to a footnote, please. 14C is formed by thermal neutrons on 14N, not 15N, via 14N(n,p)14C. Cross-section is about 1.8 barns. Coupled with the abundance of 14N, this is the dominant 14C-forming reaction in most instances. Rodger Sparks A minor footnote, please: Rodger Sparks wrote: > > ... We can safely assume that a significant amount of 14C was generated > by the Trinity test. This will have been formed primarily in the > atmosphere by the absorption of thermalised neutrons by nitrogen. ... C-14 would be formed by fast neutrons in a 15N (n, p) 14C reaction. Thermal neutron absorption by N-15 produces N-16, which beta decays to O-16. However, as stated, the real issue is how and if the radiogenic carbon could get into the samples. Chuck Blatchley =========================================================================== To unsubscribe from this list, send the command SIGNOFF C14-L to LISTSERV@LISTSERV.ARIZONA.EDU, or send a request to C14-L-request@LISTSERV.ARIZONA.EDU. ========================================================================= Date: Fri, 31 Aug 2001 09:45:07 -0500 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Chuck Blatchley Organization: Pittsburg State University Subject: Re: Post-atomic contamination of C-14 samples MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Rodger Sparks wrote: > > A footnote to a footnote, please. ... Mea culpa. I wrote the target mass number incorrectly while trying to think of a way to make C-14 from nitrogen by neutron capture. As you stated, the target for the (n,p) reaction that produces C-14 should be N-14. My intended point was more about the energy of the neutrons that cause the reaction and the meaning of "thermal" in describing the energy of the neutrons. The mass defect between the N and C nuclides corresponds to a threshold energy of 149 keV. Completely thermalized neutrons have an average energy that is only a small fraction of an eV, not enough to make the reaction possible. However, the fine print on a table that confirms your cross section of 1.83 barns, says that for practical purposes they include as "thermal" neutrons, any that have an energy up to 500 keV, more than enough to make the reaction go. So it depends on which "practical" considerations are behind the terminology. Below the threshold energy, N-14 can only capture neutrons, which does not produce any carbon. However, C-13 in existing middens would also capture thermalized neutrons to directly produce C-14. Both the isotopic abundance (1.1%) and the reaction cross section are low (1.4 mbarns), so the midden would have to be fairly close to ground zero to cause an effect. If this were the case, the other discussion on the possibility of contamination by fallout would be moot, since C-14 would be produced directly inside all the samples within range. The argument for non-uniformity of dating results would especially be neutralized. Chuck Blatchley =========================================================================== To unsubscribe from this list, send the command SIGNOFF C14-L to LISTSERV@LISTSERV.ARIZONA.EDU, or send a request to C14-L-request@LISTSERV.ARIZONA.EDU.