Let’s Go for Muons!

In 1936, when studying cosmic radiation, the physicists Carl D. Anderson and Seth Neddermeyer discovered a previously unknown elementary particle: the muon. In many ways, the muon is quite similar to the electron. However, the two particles differ significantly in two respects: unlike electrons, muons decay spontaneously within a few microseconds, and a muon is about 200 times heavier than an electron. Their weight gives muons an enormous kinetic energy, so that they can penetrate rock several kilometers thick before their energy supply is exhausted and they decay. Muon tomographytakes advantage of this property by analyzing the scattering and rate behavior of muons, as they pass through larger objects, which brings valuable insights into the material composition of the screened object. The trick is that the muon radiation required for the investigation does not have to be produced separately; much rather, the muons occurring in natural cosmic radiation can be used for this purpose!

The potential applications for muon tomography are enormously diverse. A few years ago, for example, researchers used muons to identify a 30-meter-long cavity in the famous Great Pyramid of Giza. Perhaps an ancient burial site? But muons don't just help decipher historical artifacts! The products of the Israeli start-up company Lingacom are a prime example of how muon radiation can be used for quite pragmatic issues such as soil analysis in the context of civil engineering projects, or the screening of shipping containers with regard to nuclear and radiological substances. For this purpose, Lingacom developers have come up with two different muon detectors, a flat detector (e.g., for area scans) and a tube detector (e.g., for boreholes). The research work has paid off in full: Lingacom has now grown to become a leading supplier of imaging systems based on cosmic muon radiation. Public bodies have also become aware of Lingacom's innovative ideas. For example, as part of the EU's prestigious Horizon 2020 program, the company is playing a leading role as the coordinator of the COSMIC project (www.cosmic-cbrne.eu) for automated scanning of shipping containers at seaports or border crossings. No matter what the application, the compelling argument in favor of Lingacom's detectors is always the same: they use only natural cosmic muon radiation, and therefore do not require any additional radiation source for their impressive measurement results.

Although the detectors are manufactured in a variety of form factors to support different spatial resolutions, they all follow the same operating principle: the incoming muons trigger ionization and electron multiplication in an inert special gas mixture located inside the detector. For this, it is essential that the detectors are first placed under vacuum, then filled with the special gas in a contamination-free manner, and finally hermetically sealed before they are put into operation. Three challenging process steps, to which Lingacom added three specific objectives when searching for the most reliable solution in terms of producing the detectors: 1) all three process steps should be merged into one; 2) the detectors should be capable of being opened and closed repeatedly; and 3) the solution should be easy to automate for future series production. Sounds pretty challenging, right? But: ISI, VAT's Israeli sales partner, came up with the perfect answer to this ambitious question! Enthusiastically, Lingacom and ISI agreed on a joint development, the basic idea of which Shlomi Sofer, the sales engineer responsible at ISI, describes as follows: "In close cooperation with our VAT colleagues in Switzerland, we adapted standard pump-out valves of the series 23 to Lingacom's special needs. In the case of the tube detector, where space is much more limited, we use DN25 valves. With the flat detectors, on the other hand, we can use DN40 valves." In both cases, the crucial difference to the standard solution is the plug: instead of conventional pump-out adapters, the VAT colleagues developed special plugs that are hooked onto the valve mechanism and serve as a vacuum-tight seal once the evacuation and the subsequent gas filling have been completed. Afterwards, the vacuum pump can be moved to evacuate/fill the next detector, while the plug remains in the already completed detector. But what if you do have to work inside the detector again? No problem! "In contrast to the traditional pinch-off technology, the plugs can be opened and closed as often as required. So our method is not only a viable alternative to the pinch-off approach, but it is also more sustainable because it can be reused," Shlomi Sofer proudly explains. "And unlike approaches where the valve remains on the detector, the plug cannot be harmed by sand, water and other environmental factors!" Since the plug provides a form-fitting seal, nothing protrudes from the detector that would require additional protection, as is the case with pinch-off solutions. Jürg Öhri, the responsible sales manager at VAT, also draws a very positive conclusion: "The plug method is a much safer, more reliable and more flexible sealing method than any other known approach."

In the Lingacom application, the vacuum level is in the range of 10^-5 to 10^-6 mbar; afterwards, the inert gas mixture (the exact composition of which is, of course, a well-guarded company secret) is filled to atmospheric pressure. Accordingly, it proved sufficient to provide the plugs with a standard elastomer seal. "But with an appropriate metal seal, the solution could easily be extended to UHV applications," Jürg Öhri points out. With metal seals, it is also easy to integrate a manufacturing-related "baking" of the products in question (while the elastomer seals reach their limit at a maximum temperature of 200°C). Thanks to their extensive know-how, VAT and its international sales partners are in the perfect position to respond specifically to each customer's needs, both in terms of plug geometry and sealing technology. "In this way, the plugs can be precisely adapted to the product," says Shlomi Sofer with a satisfied smile.

At Lingacom, everybody is also very satisfied with the solution. "Thanks to the innovative VAT technology, the production environment for the detectors has become enormously compact, " Lingacom’s CEO David Yaish explains. "Besides, the combination of a vacuum and a non-vacuum application makes the system much more reliable, since the valve does not have to be moved and foreign particles are thus much less likely to intrude." Shlomi Sofer aptly sums up the all-round successful collaboration: "There is just no other alternative to pinch-off technology on the market. At present, the production process is still manual, but thanks to the combination of the evacuation and gas filling into one single process step, we can easily automate the application of the valve plug." Of course, this great result quickly made the rounds in research circles; after all, clean, reliable and integrated vacuum-closing methods are urgently required in many other industries as well. "Just the other day, we took a group of interested entrepreneurs on a tour of our labs, and we explained the innovative VAT solution to them in detail," David Yaish concludes. "All the reactions were very, very positive!"