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New Neutron Detector has been Created
before March 9, 2006


RAS Nuclear Research Institute scientists have come out with an original technique for separating fast neutrons from gamma rays and measuring their energy. The technique is very simple and safe. The scientists have created the first supersensitive fast neutron detector. Of course, one can ask why do we need it.

First, such detector is necessary for our Sun fundamental research. Today all information is available through photons emitted from the Sun’s surface. But it seems much more interesting to look inside the Sun, where nuclear processes, which provide energy for every living being, take place. One can do so only by measuring neutrino flows, which are emitted from the centre of the Sun and are able to transpierce the Sun and the Earth. That is why scientists from all over the world are trying to measure these flows in order to understand why did the Sun appear and how long will it live. But neutrinos are very hard to study because they almost do not interact with any matter. Moreover, fast neutrons behave in similar ways and can be easily confused with neutrino. V.E. Yantz, the inventor of the unit, says that there are few fast neutrons in background radiation, so we need a supersensitive detector able to measure neutron share in neutrino imitation accurately.

Another reason why we need this unit is quite unpoetic - radiation control, for example. Devices that measure background radiation, hardly distinct its main components affecting living beings – gamma rays, protons and neutrons. In this case radiation neutron control gives general data on some total radiation dose. These data are somehow indicative, but problems arise when we think about protection against radiation. The problem is that lead is a good protection for gamma-quanta, but not for fast neutrons. Water and paraffin can be a safe screen against neutrons, but these substances can’t protect you from gamma-quanta. So protection level depends on radiation compounds – lead, paraffin or both.

Different radiation particles are usually detected by means of scintillators – substances, which give a short light flash when hit by a particle. Particle energy, neutron, for example, is estimated according to the flash intensity. This technique has one main difficulty – when background radiation reaches the scintillator, many flashes appear, and one neutron flash is quenched by a million gamma-quanta flashes. A thick lead box, which is transparent for neutrons, but resists gamma-quanta, can be a solution. But this technique requires too much lead, and the unit becomes heavy and inconvenient. The scientists from NRI suggested using scintillator together with decelerated neutron counter, which are insensitive to gamma rays. If flash generating particle is a neutron, the counter detects it immediately after the flash. If it is a gamma-quantum, neutron counter remains inactive thus showing the absence of neutrons near the scintillator. So, this is the method for separating neutrons from gamma-quanta and at the same time measuring their energy.

New detector pilot unit is a stainless steel tank, 50 cm in height, 35 cm in diameter and weighs 50 kilos. It hosts 30 liters of liquid scintillator and 19 thermal neutron counters (3 cm diameter tubes, filled with helium-3 and argon mixture under 4 atm pressure). The upper side of the tank is equipped with a lightproof hood, covering three photoelectric multipliers, registering every flash in the scintillator. The scientists place detector in the room, where background radiation should be measured, plug it to the data collecting system (computer), calibrate it, set the neutron spectrum receiving mode and leave for some time (a day or a week). The unit doesn’t have any special gates for neutrons. They come from all directions together with other background radiation particles and easily penetrate 5 mm thick tank walls – not a barrier for fast neutrons.

This model can be used for production of cheap and simple detectors, which will serve for radiation control on nuclear power engineering objects, for background neutron fields’ research in human natural environment, for nuclear physics and space research and for many other purposes.

As for solar neutrino studies, here new detector also showed his best. Detector tests have been carried out in famous Baksan Neutrino Observatory (BNO), located on the Caucasus near Mt. Elbrus. Here, in this observatory, the scientists explore neutrino (do not confuse with neutrons!) particle radiation form the centre of the Sun for last ten years. Fast neutron background measurements, which were performed by means of new detector, allowed accurate estimation of neutrino data distortion ratio, Mr. Yantz thinks.

In BNO NRI physicists have tested a new fast neutron detector (spectrometer) and got first ever data on fast neutron background in the chamber of gallium (Ga) - germanium (Ge) neutrino telescope, which was designed to study neutrino flows. The detector turned out to be so sensitive that measured the flow equivalent to ten fast neutrons per 1 square meter in 24 hours. Meanwhile, the gamma-quanta flow is hundreds thousand times more intensive. So scientists have come up with an encouraging conclusion – new Russian detector is hundreds of times more sensitive than any detector ever used in neutron measurements worldwide.

Tags: Russian Scientists     

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