Laser spectroscopy improves bomb-peak dating

19 Feb 2025

Zhejiang Normal University and ppqSense develop alternative to mass spectrometry.

A project at China's Zhejiang Normal University (ZJNU) has applied laser spectroscopy to bomb-peak dating, potentially assisting a number of carbon-dating and forensic applications.

Bomb-peak dating is an aspect of ¹⁴C radiocarbon measurements, exploiting the way that commencement of nuclear tests in the 1950s and subsequent cessation in the 1960s has influenced world-wide distribution of the isotope.

This phenomenon can provide a precise temporal reference point when measuring the ages of samples originating after 1950, often allowing the age to be calculated with better than one-year resolution.

However, the techniques used to carry out the necessary radiocarbon analysis tend to be complex and expensive, with accelerator mass spectroscopy the most advanced method currently in normal use.

The ZJNU project has developed an alternative approach based on saturated absorption cavity ring-down (SCAR) spectroscopy, and published the results in Optics Express.

Ring-down methods, based on multiple reflections of laser light to create an extended path length and an enhanced absorption signal, have been used for general carbon dating operations before, including a 2016 project using two quantum cascade lasers in a SCAR platform intended for both dating and climate studies.

The new ZJNU platform also employs a dual quantum cascade laser architecture, with one laser acting as the main source for detection and the other as a reference light source. This platform is the first test of SCAR's capability for bomb-peak dating applications, according to the ZJNU project team.

Cost-effective SCAR for commercial applications

"Unlike accelerator mass spectrometry, SCAR spectroscopy directly measures the concentration of radiocarbon by analyzing the absorption spectrum of ¹⁴CO₂," commented the project. This eliminates the need for complex graphitization during the sample preparation procedure, and reduces the costs of the overall dating operation.

Trials were carried out on a range of samples, including sediment from the Chinese Academy of Geological Sciences, Italian wine of 1979 vintage, old wood, and samples of paper from printed works dated between 1968 and the 2000s. This last material is a significant test, since the dating of paper is an important step in the identification of works of art, but carbon dating of the materials involved can be difficult.

The ¹⁴C concentrations in the different specimens measured by the new platform correlated with the bomb-peak datum and correctly indicated the production year of the wine, said the team, and placed the age of the paper samples 10 to 20 years older than the printing dates.

Italian developer ppqSense, a spin-out from the country's National Research Council and partner in the ZJNU project, is commercializing the SCAR technique. The company markets C14-SCAR, described as a "high precision laser-based table-top ¹⁴CO₂ analyzer." The company indicates that its platform carries a price tag of under €600k, as opposed to the million-Euro cost of an accelerator mass spectroscopy unit.