Serge Mathot, applied physicist at CERN, and Tessa Charles, accelerator physicist from ANSTO University, performing the first experiment with the mini accelerator ELISA which is now being used for real heritage research in Science Gateway's "Discover CERN" exhibition. (Image: CERN)
A particle accelerator on display in a museum exhibition is rare. But a functioning particle accelerator conducting real scientific research in a museum exhibition? That's unprecedented. After years of development, the proton accelerator ELISA (Experimental Linac for Surface Analysis) is now being used for archaeological research at Science Gateway, CERN's education and outreach centre. This marks the first time a proton accelerator of this kind has been used for research as a part of a museum exhibition.
ELISA has a lesser-known mission for a particle accelerator: to analyse the composition of objects, such as art, geological or cultural heritage objects, without causing any damage. With an accelerating cavity just one metre long, it works by accelerating a beam of protons to 2 MeV (for comparison, the Large Hadron Collider accelerates protons to over three million times that figure), focusing it towards a small point on a sample, such as archaeological paint used for ancient cave art. This interaction excites electrons in the sample's atoms, causing them to emit photons with wavelengths unique to specific elements. By analysing these photons, researchers can construct a detailed profile of the sample's composition.
"The paint samples we're using for ELISA's first test have been created by scientists to mimic the paints used in ancient cave art from across the world," says Tessa Charles, an accelerator physicist from ANSTO working on the project. For this first experiment, researchers are assessing the damage to each sample inflicted by the proton beam, and what conditions (exposure time and current) are ideal for each material to avoid damage. "The aim of this is to see how ELISA can be used to analyse samples while avoiding damage, which is essential when working with material cultural heritage," she adds. "The idea is to work towards a fully portable accelerator that can be taken to different regions of the world that don't have local access to an accelerator facility, into the field or other museums."
The idea of including a working accelerator in an exhibition arose during brainstorms that CERN's exhibitions team organised with scientists from across CERN at the beginning of the Science Gateway project. The accelerator itself was the brainchild of Serge Mathot, an applied physicist at CERN, who was part of the team that developed the Linac 4 RFQ (Radio Frequency Quadrupole), the first accelerating cavity in a proton beam's journey through CERN's accelerator chain to the LHC. ELISA is a smaller version of the first component of Linac 4. Mathot, who initially worked on small linear accelerators for medical applications, realised that this technology could be used for research in cultural heritage, too. "The proton beam technique is very effective in comparison to other techniques for analysis because it has high sensitivity and the background is very low," Mathot says. "You can also perform the analysis in the ambient air, instead of in a vacuum, making it more flexible and better suited to fragile objects." Mathot has previously worked on MACHINA, a similar accelerator created in collaboration with INFN and other CERN specialists. MACHINA is the first transportable accelerator and will soon be operational at Florence's Opificio delle Pietre Dure (OPD) to study artworks.
Courtney Nimura, archaeologist working with Professor Jamie Hampson at the University of Exeter on the project, is involved as part of the non-destructive mobile analysis and imaging device project (NoMAD), funded by UK Research and Innovation. "There is still much we don't know about what was used to create rock art pigments thousands of years ago," she says. "We are limited in the analysis techniques we can use during archaeological fieldwork, as samples usually have to be taken to a facility. We have high hopes that compact accelerators like ELISA are the first step towards creating a portable accelerator that can be used in the field."
Using the accelerator for experiments live on the exhibition floor is just one of the uses planned for ELISA. A series of demonstrations for visitors, presented by exhibition guides, are also in the pipeline. Everyone will soon be able to see ELISA in action during CERN Science Gateway opening hours.
