A few of our colleagues, upon receiving a radiocarbon date younger than they expected, have wondered if X-rays in airport security devices might have increased their 14C content. Unfortunately for them, our colleagues have been forced to find alternate explanations for the uncooperative dates. Airport X-rays simply cannot produce 14C. However, a new security technology is almost ready for installation at Kennedy Airport for some international flights, and, according to the Wall Street Journal, 100 additional units are planned for other high-risk airports. The new device will detect high concentrations of nitrogen (a component in explosives) by thermal neutron activation (TNA). Since TNA on a global scale is the process by which nature produces virtually all 14C in the atmosphere, some 14C must be produced in high-nitrogen materials, such as bones, as they pass through a neutron activation airport security device. The question important to the radiocarbon dating community is how much effect can the 14C thus produced have on the 14C date?

Timothy Weiler Linick died on June 4th, 1989. He was a dedicated researcher, and an important part of the NSF Accelerator Facility for Radioisotope Analysis at the University of Arizona. He will be remembered for his care and attention to details, especially in the calculation and reporting of radiocarbon dates. He made important contributions to the fields of oceanography and tree-ring calibration of the 14C time scale.

Radiocarbon dating (Libby, 1955) has been an important tool in the marine sciences since the early 1950s (eg, Arrhenius, Kjellberg & Libby, 1951; Ericson et al, 1956; Broecker, Ewing & Heezen, 1960; Emery & Bray, 1962) and the basic principles and analytic procedures of the method have changed little. In the late 1970s, the Accelerator Mass Spectrometer (AMS) method of 14C dating was developed (Bennett et al, 1977, 1978), the major advantages being that samples several thousand times smaller than needed for beta-decay counting can be dated, and analysis time is reduced to ca 1 hr from the 1–6 days needed for beta-decay methods.

Many 14C dating laboratories have established that coal samples exhibit a finite 14C age, apparently caused by contamination of the specimens before any laboratory preparation is undertaken. In this work, the possibility that the contamination is due to microbial and fungal activity in the coal substrate is considered and some suggestions are made for alternative sources of background test materials for 14C dating laboratories. Initial results indicate that geologically formed graphites contain little 14C and are likely to be good background test materials, especially in 14C AMS laboratories.

The importance of chronometric dating in archaeology cannot be overemphasized. Indeed, most chronologies developed throughout the world during the past three decades have depended on radiocarbon age determinations to provide a temporal framework for examining change over time in cultural sequences during the late Pleistocene and Holocene. With the advent of legislation in the mid-1960s designed to protect archaeological sites in the United States threatened by increased urban development or government sponsored projects, archaeological surveys and excavations were mandated as a means for preserving information otherwise destroyed. As a result, thousands of projects have contributed to a growing body of “gray literature,” ie, unpublished proprietary or manuscript reports with very limited circulation. Within these reports are hundreds, if not thousands, of 14C age determinations, most of which are not accessible in published form. One objective of this paper is to present all the 14C age determinations for the island of Moloka'i, Hawai'i as of December 1988, including 41 dates never before published with stratigraphic details.

The accuracy of AMS radiocarbon determinations on very small samples has been tested by measuring a suite of microgram-sized samples of a known-age material. The total measurement precision for the smallest sample (50μg) was found to be ± 3% and the precision improved with larger sample size. The accuracies of the measurements were found to be within the measurement precisions.

The occurrence of atmospheric 14C variations complicates calibration, ie, the translation of 14C ages into real calendar ages. The procedure of wiggle matching, however, allows very precise calibration, by matching known 14C variations with wiggles in the floating chronology. In principle, wiggle matching can also be applied to a series of 14C dates from organic (peat) deposits. Where, in general, 14C ages are required at short distances and on small samples, dating by 14C accelerator mass spectrometry (AMS) is required.

Radiocarbon ages on handpicked foraminifera from deep-sea cores are revealing that areas of rapid sediment accumulation are in some cases subject to hiatuses, reworking and perhaps secondary calcite deposition. We present here an extreme example of the impacts of such disturbances. The message is that if precise chronologies or meaningful benthic planktic age differences are to be obtained, then it is essential to document the reliability of radiocarbon ages by making both comparisons between coexisting species of planktonic foraminifera and detailed down-core sequences of measurements.

Temporal variations of cosmogenic radionuclide atmospheric concentrations can be caused by such global phenomena as solar activity and geomagnetic field changes as well as atmospheric circulation processes. These causes can be distinguished by the comparison of several isotope records corresponding to the same time period. We discuss a possibility for reconstructing the geomagnetic moment during the last 30,000 years from the comparison of 10Be and 14C concentrations in terrestrial archives. The results agree with conventional paleomagnetic data and promise to enrich our knowledge of geomagnetic field variations and reversals.

Large numbers of 14C dates of the base and top of Holocene peat layers may be plotted in 14C histograms in order to establish statistically a chronology of periods of essentially clastic sedimentation and peat formation. Due to the non-linearity of the 14C time scale in terms of calendar years, clustering of 14C dates on random peat growth may occur. This seriously hampers the interpretation of histograms. A quantitative method and computer program were developed to correct the histograms for this effect. The correction factor that has to be applied depends on the calibration curve and the interval width of the correction parameter dy. For peat samples, an interval width of 100 14C yr and a calibration curve based on a 100-yr moving average seems to be a reasonable choice.

Twenty-eight 14C analyses are reported for carbonized roots and other plant material collected from beneath 15 prehistoric lava flows erupted from the northeast rift zone (NERZ) of Mauna Loa Volcano (ML) utilizing the recovery techniques of Lockwood and Lipman (1980). Most samples were collected from the Hilo 7 1/2’ quadrangle during field work for a geologic map of that quadrangle (Buchanan-Banks, unpub data); a few sample sites are located in adjacent quadrangles: Piihonua to the west and Mountain View to the south. Altitudes are given in English units as well as metric to facilitate locating sites on USGS topographic maps.

This list contains the results of 14C determinations obtained at the laboratory in 1986 and 1987. δ13C was measured by the British Museum Research Laboratory or the Free University of Brussels: *δ13C is estimated (Stuiver & Polach, 1977).

Since our publication of the high-precision calibration curve for the larger part of the 4th millennium BC (de Jong, Becker & Mook, 1986), we found that the dendrochronologic scale (cal bc) needs a correction of 26 years. Instead of using the zero-point of the Niederwill chronology (4039 bc) which was floating at the time, our dendrochronologic scale was erroneously based on the zero-point of the Hohenheim master chronology, which, in its 1986 stage, extended to 4065 bc.

During the International Radiocarbon Conference in Dubrovnik in June 1988, several laboratories expressed the need for quality assurance. Furthermore, on several occasions 14C laboratories have shown an interest in reference materials of known 14C activity, apart from the recent activity of the NBS oxalic acid.

Groningen, April 3, 1989 W G Mook

I recently had the privilege of attending the Conference on Technology-Based Confidence Building: Energy & Environment, hosted by Los Alamos National Laboratory and The University of California, in Santa Fe, New Mexico, July 9–14, 1989.