Ever since the Big Bang, neutrinos (invisible elementary particles) from the cosmos have been bombarding the Earth. By harnessing TNO’s expertise to detect these particles – which are often billions of years old – we are learning more about the world’s origins.
The Earth is constantly being bombarded by countless neutrinos – tiny, elementary particles – that have been speeding through the cosmos since the Big Bang. These elusive and invisible particles barely interact with matter at all. They do not carry a charge and are not deflected from their course, but travel in a straight line from the moment they are created. Neutrinos were created in vast numbers during the Big Bang. They are also emitted by the sun and many stars. So if we can detect these neutrinos, we will be able to reconstruct their paths and find out which part of the universe they come from. In doing so, we may be able to find answers about our own existence.
A large international group of scientists and technicians is hoping to observe neutrinos. They are constructing two large sensor arrays on the bed of the Mediterranean Sea, at a depth of several kilometres. These sensors consist of numerous photosensitive glass spheres that are capable of detecting neutrinos. The data generated by this study (which is part of the KM3NeT project) offers opportunities both to the world of science and to the business community.
Expertise in acoustics
“TNO is involved in both of these worlds, which is exactly why it has an active role in the KM3NeT project”, says Dr Ernst-Jan Buis, a TNO physicist. “We are bringing science and industry together. TNO is also contributing its unique expertise in acoustics. Eventually, this may prove to be enormously valuable in terms of raising neutrino research to the next level. We are now using light to detect these undersea events, but sound detection can also improve our understanding of life under water. For example, we can use it to study marine mammals and to record earthquakes or seaquakes. It is also used in seismic research, which is important to offshore companies, in oil and gas production, for instance.”
“TNO is contributing its unique expertise in acoustics. Eventually, this may be prove to be enormously valuable in terms of raising neutrino research to the next level”
The only thing that can stop a neutrino is a frontal collision with the nucleus of a hydrogen atom. That happens very seldom. To improve the chances of observing this, the instrumented volume of water must be as large as possible. The seabed is a very suitable place to build the sensor array for a gigantic neutrino telescope. As they pass through water, some neutrinos may generate a miniscule flash of light, which can then be detected by the highly sensitive spherical modules. “Which is why we chose these two undersea sites. Down there, at depths of 2.5 to 3.5 kilometres, the water is still relatively warm and there is relatively little light. This means that there is little scattered light to interfere with the detection of these flashes from neutrino interactions. Taken together, these conditions greatly increase the chances of successfully detecting neutrinos. Indeed, the first observations using this ‘neutrino telescope’ are very promising”, says Dr Buis. The two telescopes, one near France and the other close to Italy, are both one cubic kilometre in size. They will eventually have a total of around six thousand modules, each containing photosensitive sensors. The spheres are fixed to lines, hundreds of metres in length, suspended in the water. The data they generate is monitored onshore.
Detecting using sound
But TNO wants to go a step further. In early 2017, Ernst-Jan Buis presented a revolutionary plan to a group of scientists at CERN, in Geneva (where he had previously carried out his PhD research). He proposed the construction of a third neutrino array just off the Greek coast, but this time using hydrophones to detect neutrinos. The basic idea is that, if they lose enough energy in the seawater, neutrinos can generate sound waves in addition to the tiny flash of light. TNO has developed its expertise in underwater acoustics over many years, in projects for clients such as the Dutch Ministry of Defence. TNO operates a unique acoustic basin in The Hague, where it can perform preliminary tests and experiments using underwater sound.
“The benefit of using sound to detect neutrinos is that these detectors can monitor a much larger volume of sea at a much lower cost”
“The benefit of using sound to detect neutrinos is that these detectors can monitor a much larger volume of sea at a much lower cost. We feel that one cubic kilometre is too limited. The new concept involves using around one thousand hydrophones to monitor not one cubic kilometre of sea but one hundred cubic kilometres, close to the Greek coastal town of Pylos. TNO is helping to identify the most suitable site for this array. It also supplied two deep-sea sound recorders, which were installed on the seabed last December. This equipment enables us to detect neutrinos over much larger distances, greatly expanding the detection volume. The system is based on fibre optics, so no electricity is required. Detection events can be monitored in real-time, on land, via an optical fibre several kilometres in length on which the hydrophones are mounted. TNO has developed the technology to detect high-energy neutrinos, something that is not possible using light. We are cooperating with the University of Amsterdam on this technology.”
One second after the Big Bang
Rasa Muller’s graduation thesis at the University of Amsterdam involved close cooperation with Ernst-Jan Buis’s team. She is testing TNO’s hydrophones, to see whether they are sensitive enough to detect neutrinos. She also wants to demonstrate the existence of cosmic neutrino radiation, which was created one second after the Big Bang, and derive a value for the numbers of high energy neutrinos involved. The detectors in the existing KM3NeT array are not suited to this purpose, but the hydrophones developed by TNO would probably suffice. “A massive marine hydrophone array can do much more than detect neutrinos. It can also be effectively used for a range of applications in other domains. Naturally, I hope that this fundamental research in cooperation with TNO will contribute to science, but it would nice if it ultimately helped to advance applications for society as well”, says Rasa Muller.
Opportunities for the business community
Dr Buis explains that “We are at the start of a process whose results are far from certain. Nevertheless, there are already some excellent opportunities for the business community in terms of cooperating with TNO in the further development, production and installation of hydrophones based on optical fibre. In the past, we have developed optical fibre sensors for the aerospace industry and, in line with this, the present work appears to hold out great prospects for our manufacturing industry. The Dutch are already providing significant input to KM3NeT, in the form of acoustic expertise, but it would be great if our business community could also do their bit.”
Credits images: KM3NeT
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