Radiochemical detector for registering neutrons.

Radiochemical gas neutron detector for non-destructive testing of fissile materials

Non-destructive testing detectors for fissile materials can be divided into two main classes. The first are based on the registration of gamma radiation produced during the decay of radioactive materials, the second - on the registration of decay neutrons. The last class is divided into two main subclasses: passive and active methods of detecting neutrons. The active method involves the initial irradiation of the material under study with a flux of neutrons created by an autonomous neutron source, which creates induced activity in the irradiated material, and then the neutrons emitted from the region of induced activity are recorded by a detector.

The main problem that exists when solving problems of non-destructive analysis of materials by the active method is the very high load on the secondary radiation paths, caused by the interaction of neutrons with the structural elements of the neutron source itself, the object under study, as well as with the matter of the entire space surrounding the source and the object under study. Until recently, the high level of background load did not allow us to talk about any significant practical application of active methods for the actual search for small quantities of substances located, for example, inside passenger luggage or cargo containers filled with various cargoes.

Другой немаловажной проблемой указанного способа регистрации является радиационное загрязнение исследуемого материала и окружающей среды. Пассивный метод регистрации не требует первичного облучения исследуемого объекта и основан на регистрации излучения, образующегося непосредственно при распаде делящихся и радиоактивных материалов. В частности, уран и все трансурановые элементы распадаются с испусканием альфа-частиц, которые имеют очень короткий пробег и взаимодействуют с легкими ядрами конструкционных материалов и окружающей атмосферы с образованием быстрых нейтронов. Вот эти то быстрые нейтроны и позволяет эффективно регистрировать предлагаемый нами метод.

Another important problem with this registration method is radiation contamination of the material being studied and the environment. The passive registration method does not require primary irradiation of the object under study and is based on the registration of radiation generated directly during the decay of fissile and radioactive materials. In particular, uranium and all transuranium elements decay by emitting alpha particles, which have a very short range and interact with light nuclei of structural materials and the surrounding atmosphere to produce fast neutrons. It is these fast neutrons that our proposed method allows us to effectively register.

The PGRM was used to monitor the neutron flux of a pulsed neutron target "RADEX" with illumination from the linear proton accelerator of the Moscow Meson Factory of the INR RAS, as well as neutrons from a Pu-Be isotope source. The counting rate was ~10 pulses/sec with a mass of active substance of 30 g. The minimum flow on the ampoule was ~3-5x103 N/cm2sec. The sensitivity of the PGRM detector is such that the mass of the active substance in the detector frame is 10 kg. at a distance of 0.5 m from the container, 1 g of U-235, 0.04 g of Th-230, 0.02 g of Pu-239, 0.002 g of Pu-240, 0.0002 g of Am-241 can be registered , 0.000004 g Cf-250 for 1 minute of exposure. The project is based on the research results published in the article:

S.G.Lebedev, S.V.Akulinichev, A.S.Iljinov, V.E.Yants, A Gaseous Radiochemical Method for Registration of Ionizing Radiation and Its Possible Applications in Science and Economy, Nuclear Instruments and Methods in Physics Research, v. A561(2006)90-99. The development received RF patent No. 2286586 with priority dated April 19, 2005.

Based on the original author's methodology, which has no analogues in the world, a laboratory prototype of a detector for non-destructive testing of fissile materials was created for use at airports, checkpoints and customs terminals, at traffic police posts, at turnstiles in the METRO, in crowded places, as well as in traffic railway, motor sea transport.

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