Nuclear Expert: Athol Rafter
Athol Rafter (1913-1996) was a groundbreaking New Zealand radiocarbon scientist whose work significantly advanced the accuracy and application of radiocarbon dating. His contributions were both technical and practical, addressing calibration of dates and the correction for the "radiocarbon age plateau."
Key Contributions
Radiocarbon Calibration
One of Rafter’s most important achievements was his early work on calibrating radiocarbon dates. When radiocarbon dating was first developed by Willard Libby, it was assumed that past atmospheric carbon-14 (¹⁴C) levels were constant. However, scientists noticed discrepancies between radiocarbon and calendar ages, especially for wood and charcoal samples with known age constraints (such as dendrochronological data or historical records).
Rafter and his colleague Bruce Grant recognized that atmospheric ¹⁴C content varied due to changes in cosmic ray flux, ocean mixing, and other factors. Their research showed that radiocarbon ages needed to be calibrated to yield accurate calendar dates. This led to the development of calibration curves, which are essential for converting radiocarbon ages into calendar years.
New Zealand’s Unique Shake-Up
Rafter demonstrated that the Southern Hemisphere—particularly New Zealand—had different atmospheric ¹⁴C levels than the Northern Hemisphere. This was due to local ocean circulation, the “Southern Ocean effect,” and the mixing of carbon reservoirs. His findings were critical for researchers in Australasia and the wider southern Pacific, ensuring localized calibration curves would be used for improved accuracy.
The “Rafter Radiocarbon Plateau”
Rafter also identified periods—most notably around 1000 CE—where radiocarbon data from different samples produced nearly identical radiocarbon ages, even though the true ages could differ by centuries. This “radiocarbon plateau” posed challenges for archaeological dating, and Rafter’s work helped scientists better understand and address this phenomenon.
International Collaboration and Leadership
Rafter was a founding member of the International Radiocarbon Dating Conference series and helped establish New Zealand’s Radiocarbon Dating Laboratory. His collaborations with leading scientists in the field facilitated the exchange of data and the improvement of calibration methods worldwide.
Legacy and Impact
Rafter’s work was foundational in moving radiocarbon dating from a tool with potentially large uncertainties to one of the most reliable and precise dating methods in archaeology, geology, and environmental science. His research directly contributed to:
- Improved accuracy by highlighting the need for calibration and local calibration curves.
- Increased confidence in radiocarbon dating results, especially in the Southern Hemisphere.
- Global scientific standards by promoting international data sharing and best practices.
- Educational outreach through publications and leadership, inspiring future generations of researchers.
Summary
Athol Rafter’s innovative research and leadership in radiocarbon dating corrected systematic errors, improved calibration, and helped establish the method as a cornerstone of scientific dating. His contributions remain essential to archaeologists, climatologists, and geologists seeking precise chronologies in their work.
In the 1950s, it was recognized that the proportion of C-14 in the atmosphere was not uniform over time or space. This was a turning point in Rafter’s research, as he began to focus on understanding the variations in ¹⁴C levels and their impact on radiocarbon dating accuracy.
In 1947, Willard Libby and Ernie Anderson made the first detection of C-14 in biological material. However, it was not until 1953 that Rafter and Gordon Fergusson obtained the first radiocarbon dates for moa bones and Taupo ash layers in New Zealand. Their findings were significant as they provided the first evidence of the "radiocarbon age plateau" and the need for improved calibration methods.
In the same year, 1953, C-14 measurements started by Rafter continue to this day, making it the longest such record in the world. This continuous record has been crucial for understanding the changes in atmospheric ¹⁴C levels over time and for validating new calibration methods.
In 1958, calibration curves allowed radiocarbon dates to be converted to calendar dates. This was a major breakthrough, as it enabled researchers to compare radiocarbon dates with historical records and other dating methods more accurately.
In 1968, Rafter was awarded an honorary doctorate in science by Victoria University of Wellington for his radiocarbon work and geothermal studies using oxygen isotopes.
The Department of Science and Industrial Research (DSIR) Institute of Nuclear Science was set up in Lower Hutt in 1959, with Rafter as the first director. This institution played a crucial role in the development and application of radiocarbon dating in New Zealand.
In 1972, the 8th International Radiocarbon Conference was held in Lower Hutt, a sign of the important role played by Rafter and colleagues in the radiocarbon dating community.
In 1974, the Waikato Radiocarbon Dating Laboratory was set up at the University of Waikato. This laboratory, along with the Rafter Radiocarbon Laboratory, continues to provide radiocarbon dating services to researchers in New Zealand and beyond.
In 1977, Accelerator Mass Spectrometry (AMS) made radiocarbon dating more accurate and using much smaller samples. This was a significant improvement, as it allowed for the dating of smaller and more delicate samples, such as human remains and ancient textiles.
In 1987, an accelerator mass spectrometer at the Institute of Nuclear Science, Lower Hutt, was the first for radiocarbon dating in the southern hemisphere. This advancement marked a new era in radiocarbon dating, as it provided researchers with even more precise and accurate results.
In 1991, the Institute of Geological and Nuclear Sciences (GNS), a new Crown Research Institute, was formed in New Zealand. The Rafter Radiocarbon Laboratory became a part of this institution, ensuring its continued role in radiocarbon dating research and application.
In 1993, the Institute of Geological and Nuclear Sciences named their dating facility the Rafter Radiocarbon Laboratory to mark Rafter’s 80th birthday. This recognition of Rafter’s contributions to radiocarbon dating was fitting, as his work had a lasting impact on the field.
In 2010, a new accelerator mass spectrometer opened at the Rafter Radiocarbon Laboratory, making it the only facility of its kind in the southern hemisphere. This advancement further cemented New Zealand’s role as a leader in radiocarbon dating research and application.
In 2014, Professor Thomas Higham lead a team who re-tested a number of Upper Palaeolithic bone samples from across Europe, providing new insights into Neanderthal distribution and extinction. These new findings were made possible by the continued advancements in radiocarbon dating technology and the high-quality data provided by the Rafter Radiocarbon Laboratory.
In 2012, cores from Lake Suigetsu in Japan were expected to provide more precise terrestrial data for radiocarbon dating. This was significant, as it would help to further improve the accuracy of radiocarbon dating and provide a better understanding of past climate changes.
In 2006, the Bayesian statistical method was introduced in radiocarbon dating, making it even more accurate. This statistical method allows for the incorporation of prior knowledge about the data and improves the accuracy of the dating results.
In the late 1960s, it was discovered that Libby’s original estimate of the half-life of C-14 - 5,568 years - was out by 162 years. Improved estimates set it at 5,730 years. This discovery was significant, as it allowed for more accurate radiocarbon dating results and a better understanding of the rates of carbon decay.
Between 1955 and 1963, the use of atomic bombs doubled the amount of C-14 in our atmosphere. This was a significant event, as it caused a spike in radiocarbon levels that could be detected in archaeological samples. Rafter and Fergusson link a measured increase in radiocarbon in the atmosphere with nuclear weapons testing.
Willard Libby received the Nobel Prize in chemistry for his radiocarbon dating work in 1960. This recognition of Libby’s work was significant, as it brought attention to the importance of radiocarbon dating and its potential applications.
Rafter retired in 1978 but continued to be active on science committees. His wife, Val, died in 1992 after being married for 53 years. Rafter died in 1996 at the age of 83.
In conclusion, Athol Rafter’s contributions to radiocarbon dating were significant and far-reaching. His work on calibration, the "radiocarbon age plateau," and the Southern Hemisphere’s unique ¹⁴C levels have had a lasting impact on the field. His leadership and collaborations with other scientists have helped to establish radiocarbon dating as a cornerstone of scientific dating. His work continues to be relevant today, as radiocarbon dating remains an essential tool for archaeologists, climatologists, and geologists seeking precise chronologies in their work.
- The advancements in radiocarbon dating by Athol Rafter have not only revolutionized the field of archaeology but also extended to medical-conditions, health-and-wellness, and environmental-science, as precise chronologies are instrumental for understanding the history of various diseases, pollutant levels, and climate changes.
- As the development of technology has progressed, scientific methods such as Accelerator Mass Spectrometry (AMS) have been introduced, allowing for more accurate radiocarbon dating and shedding light on topics as diverse as medical-conditions in ancient populations, the history of specific compounds in the environment, and the timing of critical events in technological advancements.
