Our experience in radiocarbon dating has shown that dates obtained from samples of corn cob and kernels are usually too young compared with dates from wood samples. Since other laboratories have also commented on the same problem, a study of C13/C12 ratios in corn and other plant materials has been undertaken.

The radiocarbon dates obtained since August, 1967 are included in this report. The procedures followed have been described previously (Wisconsin II).

The reported dates have been calculated using 5568 as the half-life of C14, 1950 as the reference year. Samples are run at least once in each of two counters at 3 atm pressure for a minimum of 15,000 counts. The standard deviation quoted includes only the 1σ of the counting statistics of background, sample, and standard counts.

The College of Engineering Research Division radiocarbon dating laboratory began operating in November 1962 employing a Sharp Laboratories, Inc., CDL-14 system based upon the methane method of Fairhall, Shell, and Takashima (1961).

Dates reported herein are calculated using a 5568 yr C14 half-life. The modern standard is taken as 95% of the NBS oxalic acid C14 standard which is converted to CO2 followed by conversion to CH4 in the manner of Fairhall et al. The errors quoted are the 1 σ statistical errors.