The LHC goes in for an X-ray

For the past two years, a radiography laboratory has been operating in a "bunker" where it can X-ray materials in complete safety. The primary function of the radiography laboratory, run by Jean-Michel Dalin and Aline Piguiet, is to inspect welds and LHC components.


Technicians Jean-Michel Dalin and Aline Piguiet, from the EN department,  with the scanner used for digital radiography.

In the basement of Building 112 lies a bunker heavily protected against radiation leaks and housing a laboratory that employs high-tech apparatus capable of detecting the slightest fault in materials without destroying or damaging them. "It's the principle of Non-Destructive Testing (NDT). In our laboratory we essentially use two methods, tomography and digital radiography," explains Jean-Michel Dalin, who is a NDT radiography technician in the EN Department's MM Section. It was he who designed the laboratory in collaboration with CERN's radiation protection service, which ensured full compliance with the standards.

Tomography is a technique where 180 to 1200 images are taken in rotation around an object. The resulting section images are then used to make a 3D reconstruction of the object on the computer screen and to locate any faults that may lie within. To closely examine components located inside closed connections, in particular, magnet interconnections, Jean-Michel Dalin and his colleague Aline Piguiet have specially configured a tomograph built by an outside firm which can be transported into the LHC tunnel. "The idea of using a tomograph to examine the LHC interconnections came from Fritz Caspers of the BE Department and Lloyd Williams of the TE Department. It's very efficient because it enables us to identify possible problems without having to warm up the LHC or open the interconnections," the two experts confirm.

During the January 2011 technical stop, tomography was used on the LHC for the first time.

In their Building 112 laboratory, Jean-Michel and Aline also use digital radiography to inspect various materials and assembly methods and to detect any imperfections. "Since the beginning of the year, we have been using a phosphorous support for this kind of inspection, as it can be reused about 800 times. The images are then read by a special scanner and displayed directly on-screen," Aline explains. Digital radiography is far more environment-friendly than conventional X-ray techniques, which require a non-reusable photographic film (containing silver) and a dark room and chemicals for development (like normal photographs). Digital radiography is also faster as results can be viewed within three minutes and in high definition. Aline adds: "We use digital radiography in 80% of cases but sometimes we do have to resort back to photographic films, which are thinner and thus give better precision."

The tomograph was used at the LHC for the first time during the latest technical stop in January and February 2011 and the radiography experts hope to extend its use to other accelerator or experiment components.


by Anaïs Vernède