Spheres are ideal objects to house measuring devices and detectors for deep-sea research. They have been well tried and tested in many thousands of diving operations.
The Neutrino Hunters
How was outer space created? What processes occur in suns and supernovae? What happens in black holes? Many of these fundamental questions that have long been the subject of research have close ties with the universe.
Most of our knowledge about the universe has been gained by observing photons. These light quanta are produced in large quantities, are stable and are easily traced in a wide range of energy. Their spectrum also supplies detailed information about the chemical and physical composition of the source. Unfortunately, the extremely hot, dense areas that form the center of stars, active galactic centers and other astrophysical energy sources are completely impermeable to photons. There is only one type of particle capable of helping scientists obtain more information about these highly interesting objects: the neutrino.
Neutrinos are electrically neutral elementary particles that belong to the lepton family. For every electrically charged lepton (electron, myon and tau), there is a neutrino counterpart (electron neutrino, myon neutrino and tau neutrino). These family members can tell us a lot about the universe, which is why their observation is so important to astronomers. Since they can cover enormous distances in matter without reciprocal action, they are helpful in investigating energy-generating processes, for example in suns, where they form during the fusion of hydrogen atoms. Veritable neutrino outbreaks occur when a neutron star develops in the heart of a supernova, a celestial phenomenon that also interests astrophysicists.
Deep-sea glass spheres help detect neutrinos
In the search for neutrinos, hundreds of borosilicate glass spheres are used as housings for instruments such as Cerenkov detectors.
Take, for example, the French project ANTARES, which after years of preparatory work is now entering its decisive phase. Some 900 of these glass instrument housings are in operation off the coast of Toulon. They are positioned at a depth of 2.5 kilometers in ten lines each 300 meters long to detect neutrinos from distant outer space.
The spheres consist of two half shells that are produced from “Duran” borosilicate glass in a 40-metric ton press mold at SCHOTT in Mainz. This process results in the fewest differences in wall thickness – a major prerequisite to ensure that the hollow object can withstand the extreme pressure of 900 bar – or 360 times the pressure of a car tire – at depths of 9,000 meters. The high optical quality of the glass is also important. Even when the glass wall of the spheres is 18 millimeters thick, the exceptional optical quality enables cameras inside the sphere to take excellent photographs, for instance, of the sea floor.
The unfinished glass shells are further processed at SCHOTT Medica in Wertheim, where the edges are cut and rough-ground with a milling machine. The exclusive customer is Nautilus Marine Service GmbH in Bremen, which sells an average of 2,000 glass spheres per year throughout the world. “We perform the final processing steps according to customer specifications. This work includes precision grinding of the sealing surfaces, in addition to coating, drilling for the cabling of instruments and assembling vacuum valves to produce a partial vacuum inside the spheres,” explains Gerald Abich, Managing Director of Nautilus. The absolutely perfect fit of the half shells ensures a uniform load transmission – a decisive factor for the stability of the fully assembled sphere, which is closed with a sealant band.
Another area of application: seismology
Äußerste Präzision schon bei der Herstellung der Kugeln sind die Voraussetzung für eine gleichmäßige Wandstärke, die das Geheimnis ihrer Stabilität selbst in 9.000 Metern Meerestiefe ist. Hier herrscht ein Wasserdruck von 900 bar.
GEO PRO GmbH in Hamburg works in this field. “The glass modules are extremely versatile, can be used at depths between two and several thousand meters and are compact and light,” says Jannis Makris, retired professor of geophysics at the University of Hamburg and Managing Director of GEO PRO. The company not only sells spheres equipped with measuring systems, but also uses them to collect their own data. “From this information, we are able to develop geological models of, for instance, tectonic disturbances for our customers,” explains Makris.
There is also considerable interest in such results in Japan, which is frequently struck by earthquakes and seaquakes. For this reason, scientists regularly compile seismic profiles. More than 100 measuring instruments in glass housings are used for the campaigns that are organized and conducted by the Japan Marine Science and Technology Center (JAMSTEC). As a technical service provider, JAMSTEC then furnishes complete sets of data for evaluation by the participating Japanese universities. JAMSTEC obtains its deep-sea spheres from the city of Bremen in distant Germany.
There are good reasons for this choice of supplier. “The spheres from SCHOTT may have their price, but they are also top quality,” stresses Abich. Generally speaking, glass offers the best ratio between buoyancy and price. Possible alternatives such as titanium or plastic foams are more expensive by a factor of 50 and 10, respectively, while steel is too heavy. Due to the high quality of the glass, it is also possible to save costs. “Each operation with a ship results in considerable costs of up to 20,000 euros per day, which is why it is so important that the instruments and their protective shells function without fail. That is the key to the success of every measuring campaign,” says the Managing Director of Nautilus. For this reason, oceanographers and marine biologists also use versatile buoyancy floats to measure pressure, temperture and conductivity or to determine the turbidity or flow rate. In addition, they bring so-called landing systems back to the surface. These devices are used to observe sediments, marine life on the ocean floor and fish populations.
A dive into the Mariana Trench
In oceanographic applications, the deep- sea spheres are used as buoyancy floats or as housings for electronic instruments and batteries.
With great expectations the specialists at Nautilus are also waiting for the NEMO project to be realized. Off the coast of Sicily the biggest neutrino experiment of all times is scheduled to take place under this name. A gigantic neutrino array could be set up over an area of ten square kilometers. Some 10,000 glass spheres would be required to hunt down the elusive particles from outer space over such an area – a commission that CEO Abich would be more than pleased to secure for Nautilus.