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The U-Th-Pb method, properly corrected for neutron capture, gives recent dates (Talk.Origins)

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This article (The U-Th-Pb method, properly corrected for neutron capture, gives recent dates (Talk.Origins)) is a response to a rebuttal of a creationist claim published by Talk.Origins Archive under the title Index to Creationist Claims.


Claim CD016

Nobel prize nominee Melvin Cook discovered that lead-208 was found in ores in which it could not have come from decay of thorium-232 and could not have been "primordial" or "common" lead that was present when the ore solidified. The lead-208, therefore, must have been formed from lead-207 by neutron capture (Cook 1966). When neutron capture reactions are taken into account, the calculated age of the ores changes from approximately 600 million years to recent.

Source

  • Slusher, H. S. 1981. Critique of Radiometric Dating. Institute for Creation Research, Technical Monograph 2 (2nd ed.), 46 pp. (1st ed. 1973.)
  • Morris, H. M. 1985. Scientific Creationism. Green Forest, AR: Master Books, pp. 141-142.
  • Ham, K., Sarfati, J., Wieland, C. 2000. What about carbon dating? In: The Revised and Expanded Answers Book, ed. Don Batten. Green Forest, AR: Master Books. (1990), chap. 4.

(Note: Talk.Origins provides a link for the last source, but it now leads to a different article. A later version of the third source can be viewed here.)

CreationWiki Response

(Talk.Origins quotes in blue)

1. In one of his corrections for neutron capture, Cook (1966) calculated that an ore dated to 622 million years by conventional methods should be dated to 70 million years. This is still several orders of magnitude older than the Young-earth creationism time line. Creationists seldom (if ever) quote the reduced age derived by Cook; they call it "recent" (Ham et al. 1990) or "a few thousand years" (Slusher 1981, 54) or "essentially zero" (Morris 1985, 142).

Mentioning the "reduced age" is not particularly relevant. Creationists do not cite radiometric dates in support of their timescale, but instead point out that the radiometric dates can not be relied on, and showing that the date of 622 million years is wrong supports that claim.

3. Let us assume for the moment that the lead-208 is not common lead and was actually generated by neutron capture. Cook (1966) calculated his correction factor based on the (explicitly stated) assumption that the "cross-section" (a measurement of the probability of a nuclear reaction happening) for conversion of lead-206 to lead-207 by neutron capture is the same as the cross-section for conversion of lead-207 to lead-208 by neutron capture. This may have been a reasonable assumption in 1966, but it has not been a reasonable assumption since at least 1984. The two cross-sections differ by a factor of about 24 (e.g., Blackmon et al. 2002). When Cook's calculation is modified to account for the difference in cross-sections, the new calculated age is slightly older than the conventionally-calculated age; 644 million years versus 622 million years (Dalrymple 1984). If neutron capture is indeed a factor, our current best age for this ore is an underestimate.

Even with the neutron capture assumption removed, there are still several other assumptions that were not addressed.  If those assumptions are taken into account, then what Talk.Origins considers to be an underestimate could turn out to be a huge overestimate.