Mar 27 2008
Specialists from the Institute of Solid State Physics, Russian Academy of Sciences (town of Chernogolovka, Moscow Region), together with their colleagues from Joined Institute for Nuclear Research and the ASPECT Close Joint-Stock Company – Research and Production Center (town of Dubna, Moscow Region) are developing antiterrorist transmission device for express detection of explosives, toxic and narcotic substances. The future device operation is based on object translucence by a fast neutron flux and on subsequent recording of spectra of roentgen fluorescence induced by neutrons. Certainly, this is not the safest method for dangerous substances detection – people should be at the twenty to thirty meter distance during the inspection. But, on the other hand, the method is very efficient – nothing can be hidden from such control. It takes only five minutes to get complete information about the object – its 3D image, including all articles hidden inside the object and their chemical composition. So, one can quickly detect what is hidden inside a truck or a carriage, for example, where heroin or trinitrotoluene is concealed, and where there are simply sugar bags without any dangerous ‘enclosure’.
The device under design has several peculiarities, two of which are most important. One of them is the original neutron scanner construction of a new type based on thin-walled sapphire tubes, and the second is the original construction of X-radiation detectors that are made in the form of 3D matrices of reciprocally intersecting scintillation fibers. These peculiarities enable to perform the inspection quicker, more conveniently and precisely than similar-purpose devices existing so far. Besides, the device dimensions and its power consumption will also decrease significantly.
The device will operate approximately as follows. In the neutron scanner, the flux of deuterons (accelerated in a specially grown sapphire tube) hits the tritium target set at the tube butt-end. At that, each reaction (one hit) forms a fast neutron and an alpha particle (helium nucleus) flying directly in the opposite direction. It is difficult to directly characterize these neutrons (to measure the direction, velocity and energy of each neutron), but it is easy to do than indirectly – with the help of alpha particles paired to them. If a fast neutron flies through the tube walls and further through the object, alpha particles are held back by a thin film of a substance that glows upon interaction with an alpha particle. As a result, it can be determined how many neutrons were formed and in what direction and at what time they ‘flew out’. This is the first step – to detemine characteristics of scanning irradiation.
When a fast neutron collides with an atom, it ‘induces’ the atom for a short while. Coming back to the initial condition, the induced atom nucleus generates (emits) a gamma-quantum with certain energy, this energy being the value typical of atoms of each element. Consequently, recording of such secondary gamma-quantums can determine what elements the object under investigation is made of. Certainly, the ‘gross’ analysis is of no interest – a 3D image is needed to detect where materials of the target composition are located. The detector based on multiple piled thin scintillation fibers (a row is placed lengthwise, another row is placed across like a pile of logs, thus making ten rows altogether) enables to record the source of specified gamma radiation with precise indication to disposition of its thin scintillation fibers, which researchers from the Institute of Solid State Physics (Russian Academy of Sciences) have learnt to grow from melt.
As a result, knowing parameters of the ‘hitting’ neutron flux and precise characteristics of each of neutrons, as well as parameters of induced gamma radiation, one can in principle reveal the genuine contents of the object (of course with the help of a PC and proper software) and to find dangerous articles where no other devices or specially trained keen-nosed dog can detect it. “To be more precise, adds one of the authors, Nikolai Klassen, Ph. D. (Physics&Mathematics), devices based on fast neutrons do exist in principle. But our device is more compact (therefore, it can be produced in a portable version, which is very important for antiterrorist and drug controlling that becomes possible in any location where a suspicious automobile is stopped) and it provides information quicker, to a fuller extent and in a less expensive way.” In fact, the device per se does not exist yet. Its design has been developed, individual elements are ready, developed and tested. However, some components of the future device exist only ‘on paper’ for the time being – the researchers know how to produce them but the implementation requires funding. Since the work is extremely important not only for scientists but for everybody in general, the funds will hopefully be raised.