Chapter 12 of the Handy Dandy Evolution Refuter by Robert E. Kofahl makes some rather lame attempts to attack the decay constants used in radiometric dating including:
Furthermore, there is still disagreement of 15 percent between the two preferred values for the U-238 decay constant.
Scroll down to the bottom of the page and you will discover that this edition is copyrighted 1998. It might come to as a surprise to anyone unfamiliar with creationist deceit that when one checks Kofahl’s endnote one finds that his documentation for this is dated 1974. Kofahl is using a nearly three-decades old reference to support the statement what is current status of this question. This is a good example of creationist deceit. They know that the vast majority of ordinary people do not read the endnotes and thus will not notice how utterly inadequate the reference really is.
I dare say that a high school student using such an old reference to support what the current status of a field was should be penalized in his grade. And undergraduate could very well get an F for this. An upper division undergraduate or a graduate student not be looked on with approval used a reference more than a few years old for this. Kofahl is supposed to be a Ph.D. scientist. He either knows better than to do this or he should have never have been graduated. Looking at the rest of his endnotes I find only three from the 1990s and they are not from the scientific literature but references to other creationists. He most recent endnote is dated 1994 with most being from the 1970s or earlier. This is a very convenient way to be dishonest.
Let me quote from a work that was published in 1991, well before Kofahl wrote the edition of his work that is quoted above. It is G. Brent Dalrymple’s The Age of the Earth. It is the only book available that is written to tell laymen how the Earth is radiometrically dated and the most detailed explanation one can get without going textbooks or the scientific literature. It will demonstrate what was known well before the Kofahl wrote the work I cited. Dalrymple wrote on page 122:
First, of all the decay constants given on Table 3.1 have been determined by direct laboratory counting experiments and, with the exception of 187Re, are known to within an accuracy of about 2% or better. The activities, i.e. the number of decays per unit time, of the parent isotopes with the longest half-lives are low, and the measurements are difficult to make. Nevertheless, the decay constant of 87Rb, 147Sm, 176Lu, and 187Re are known to within about 2%. The decay constants of 40K, 232Th, 235U, and 238U are known to an accuracy of better than 1%. Thus, although the uncertainties in some of the decay constants are still significant soures of error when we attempt to distinguish between the ages of early events in the Solar System as measured by different methods, these uncertainties do not significantly affect the values for the ages of the Earth, Moon, or meteorites.
Thus the decay constant of uranium-238 is known to better than 1%, not the 15% which Kofahl claimed. If Kofahl had bothered to find a more recent source he would have disproven his own claim. Furthermore this small uncertainty does not significantly affect the measurement of the age of the Earth.
(For those who are interested, Dalrymple gives the value of the decay constant of uranium-238 as 1.55125x10-10 year -1. In one year, 1.55125x10-10 is the fraction of uranium-238 atoms which will decay.)